If you are reading this FAQ in hardcopy, or on a newsgroup, you should know that the FAQ lives at http://www.oocities.org/MotorCity/2314/rc-faq.html; you may find more up-to-date information there. I've written two other pieces on R/C electric off-road racing:
This memo is full of my personal opinions, based on experiences racing since 1989. Your opinions may differ. My employer doesn't have any opinions about R/C racing; I don't work in the R/C hobby industry and I am not sponsored by any hobby shop or manufacturer of R/C racing equipment.
Mark R. Brown
R/C electric off-road racing is a scaled-down version of the Mickey Thompson off-road "stadium races" that many people have seen televised on ESPN. Racing takes place on a closed dirt course featuring a variety of turns, jumps, bumps, and straightaways. Because the races are run on dirt the racers brake- and power-slide through turns, and a certain amount of bumping goes on among the cars. The two most prevalent classes in R/C electric off-road racing in the USA correspond directly to two Mickey Thompson classes: R/C buggies are scaled-down Super 1600 open-wheel racers, and R/C trucks are scaled-down Grand National trucks.
Although R/C electric off-road racing resembles Mickey Thompson racing, R/C electric off-road racing actually came first. R/C electric off-road racing was born when Tamiya, a Japanese model manufacturer, created its radio-controlled model dune buggies, the Rough Rider and Sand Scorcher. These models were not designed for racing, but "mini-Baja" competitions soon developed in Southern California. Mickey Thompson's idea of bringing Baja-like competition to a stadium came years later.
R/C electric off-road racing really came into its own with the introduction of the Associated RC-10, the first buggy engineered well enough to survive the rigors of competition. Improvements to racing technology have continued year after year, making it easier for newcomers to come up to speed.
R/C electric off-road racing is less expensive and safer than full-scale automobile racing, but just as real. Winning requires a combination of skills: building, set up, and driving. Nearly any tuning parameter available for setting up a full-size racer is also available in R/C electric off-road racing. Organized R/C electric off-road racing events now take place at the local, regional, national, and world levels.
An R/C electric off-road racing car bears some resemblance to an R/C toy that you can buy at Radio Shack. Both are radio-controlled, are powered by an electric motor, and use a rechargeable battery.
At a deeper level there are big differences. The racing car has a four-wheel independent suspension, oil-filled shock absorbers, and fully proportional steering, throttle, and brake. The racing car goes much faster and is built to survive high-speed collisions. When the racing car breaks, replacement parts are available so you can always fix it without replacing the whole thing.
If a type of auto racing is done with full-size autos, it is probably done in a scaled-down version via R/C. Paved oval, dirt oval, road course, drag race, truck pulls, monster truck car-crushing, ice racing, ... you name it, people do it.
This memo deals specifically with R/C electric off-road racing in the USA. You may find that some of the information here applies to other forms of R/C electric racing, to gas powered (really fuel powered) off-road racing, and to R/C electric off-road racing in other countries.
Pluses:
Minuses:
Electric power is both reliable and easy to use, and electric racing is much more prevalent than gas racing. For these reasons alone, electric power is the only way to go if you are a beginner interested in racing.
As you get experience in racing you will form your own opinion about gas power. By all means attend some races and drive some cars if you get the chance. In my opinion gas power is well matched to outdoor road racing. Gas powered road racing cars travel at 70 MPH (actual), and major races last an hour with short refueling stops. Clubs exist all over the USA to race 1/8 and 1/10 scale gas road racers. I believe that fuel is less well matched to off-road, largely because of the high maintenance created by mixing oil and dirt. Manufacturers are trying to generate interest in 1/8 and 1/10 gas off-road racers, but with only modest success (as measured by actual racing activity) so far in the USA.
In the USA, off-road races are currently four minutes long. In the rest of the world (and in international competitions held in the USA), the standard is five minutes. Even five minutes is not a long time, so bad luck or bad driving early in the race can put you in a seemingly hopeless position. But anything can happen in racing. At the really big races they run the main event (top ten drivers) two or three times and combine the results to determine the overall winner.
Generally there are more entries in a given class than can run together on the track, so there is a qualifying phase followed by the main events. Qualifying is done by dividing the entries into qualifying groups, then having each group run some number (often two or three) of races. A driver gets some score for his performance in each race; drivers are then sorted into main events according to their best qualifying race score. The "A" main contains the ten (or eight, or whatever the track will bear) top qualifiers, the "B" the ten next, etc. Everybody runs a main event.
The most common system is to run each race to the time limit, then it is "finish the lap you're on." The score is a number of laps and an elapsed time. For instance, ten laps in four minutes, four and three-tenths seconds -- written 10/4:04.3. You want the most laps and then the shortest time.
The technology used in timing off-road races varies a lot. For small races you can do it by hand with a sheet of paper, using a watch for timing the last lap to the nearest second. These days it is more common is to use a program running on a PC, with an operator to punch in the car number each time a car goes by. The most common system uses radio transponders to count the cars automatically. Transponders give more accurate timing and reduce the race organizer's labor, but they aren't an unmixed blessing since fussing with transponders always slows down the racing program.
Another system is sometimes used when no timing computer is available. In this system the track is divided into some number of sections, say ten. The race runs four minutes; during the four minutes somebody counts laps by hand. When the four minutes are up, you stop your car and count the number number of sections. The score is the number of laps and the number of sections. You can run a fine race using this low-tech method. The main drawback of this method is that it doesn't produce lap-by-lap results at the end of a race, so it doesn't help you understand why you finished where you did (were you slow every lap, or did you have a couple of very slow laps due to crashes?) and it doesn't permit easy correction of lap counting mistakes.
When there's only going to be one main in a class, it may seem silly to run all the qualifiers just to determine the starting grid for the main, but that's how it is done. Even when there's only one main, the qualifiers give people a chance to work out their set-ups and generally have fun. And being on the pole can be a big advantage in the main.
Some tracks run the mains on a bump-up system. Rather than filling the mains strictly according to qualifying scores, the race director leaves one or two spots open in each main except the lowest. Then the top one or two finishers in the lowest main start at the back of the next higher main, and so on up through the "A" main. This system slows down the program because of the extra time it takes for the bumped-up cars to get ready.
At some tracks the heats are not packed as tightly as the mains - say 8 per heat and 10 per main. Really small heats are bad because the drivers from one heat are the turn marshalls for the next heat. A small heat means poor turn marshalling or delays in trying to scrape up volunteers.
If the track has narrow lanes or is very short then it will usually run fewer drivers per heat and also in the mains.
Prizes vary a lot. Some places give hobby shop certificates as prizes -- you can buy a new set of tires (or make a down payment on a set) if you win. Other places give plaques or trophies. Sometimes the only prize is bragging rights until the next race.
A typical entry fee these days is around $10. Often there is a discount for the second class you enter, so it might cost $18 to run both a buggy and a truck, or to run one buggy or truck with both stock and modified power.
There are two national sanctioning bodies for electric off-road racing: ROAR and NORRCA.
ROAR is the original, largest, and most powerful sanctioning body. ROAR's power derives from its membership in IFMAR, the international sanctioning body for R/C racing. Because ROAR is a member of IFMAR, ROAR has a voice in setting international rules, and ROAR controls US entries in international championship events. Internal political struggles and mismanagement reduced ROAR's effectiveness through most of the 1990s; ROAR is functioning pretty well at the moment, though.
NORRCA is run by Mr. J.R. Sitman of California. He casts NORRCA as the organization that cares about racers, in contrast to ROAR which (in this view) cares more about equipment manufacturers and their financial well-being. Certainly NORRCA has been more innovative than ROAR over the past several years. NORRCA has created racing classes that separate pro drivers from the average guy, and recently has experimented with tire limits at major events to hold down costs. NORRCA's national championship events are considered less important that ROAR's national championships, but the major teams contest them both.
The stock class is meant to give all cars limited and approximately equal power at low cost and low technical sophistication. When these goals are met, the result is an interesting class of racing that's more accessible to beginners. The cars are easier to drive because of the limited power, and with equal power the focus becomes setting up the car and driving clean lines.
In the early days of racing, the Mabuchi 540 was the stock motor. If you ran a six-cell battery pack and a Mabuchi 540, you were legal for stock class. The Mabuchi 540 had limited power and was very easy to use -- it did not allow much if any "tuning". You would just bolt it in and run.
Today's stock class is not so simple. There are many stock motors to choose from, and these motors allow tuning through the replacement of brushes and springs. The motors are much more powerful than a Mabuchi 540 but have a correspondingly shorter life. And because of advancing technology driven by the economic competition between motor manufacturers, a stock motor can become obsolete overnight.
Evidently, today's stock class is inferior to the original in many ways. Yet stock is still the best class for beginning racers, so you need to understand it.
To run in stock class, you must use a ROAR stock motor and a six-cell battery pack. A ROAR stock motor
(These are the main points; the actual rules are considerably more detailed.) A ROAR stock motor has "ROAR 91" or "ROAR 95" or whatever stamped on the can near the mounting holes; the number represents the year in which the motor type was first manufactured.
A key restriction on stock motors is the non-removable endbell. This feature means that the armature cannot be removed from the can for servicing when the commutator goes out of round, as it will after four or five runs in competitive racing. A stock comm lathe will true a stock motor's comm while it is still in the can, but the quality of the cut is inferior to what can be achieved by a modified motor lathe, which trues the bare armature.
Some tracks allow "outlaw" stock motors in their stock class racing. These are typically motors that resemble ROAR stock motors in having bushings and a non-removable endbell, but violate ROAR rules in some other way -- usually by having more timing advance. Outlaw stock motors became popular when ROAR's timing restrictions first went into effect, because the first crop of 24 degree motors gave lower performance than the stock motors they replaced. Also, NORRCA still doesn't embrace the ROAR 24 degree timing restriction, except in "Sportsman Stock" classes. But today's ROAR stock motors are much higher in performance than any of the old stock motors, so there is little excuse for the continued use of outlaw stock motors.
NORRCA has recently floated a proposal that would in effect change the stock class to a stock armature class. Motors would have removable endbells and special armatures that are identifiably stock. This system is now in use elsewhere in the world. Perhaps it will catch on here.
R/C car races generally have a fun, relaxed atmosphere. Even at big events most people don't take themselves too seriously. The racing is competitive, yet most racers are not secretive -- if you ask, they will tell you exactly how they've got their rides set up. (Often they will tell you even when you haven't asked.)
Most race venues have strict rules against the consumption of alcohol and illegal drugs on the premises, and against any sort of abusive behavior.
If you can read directions and use a screwdriver you can successfully assemble an R/C racing car. If you buy your equipment from a knowledgeable dealer, the dealer will help you through any rough spots.
Building and maintenance will definitely improve your mechanical skills. R/C racing is not a good hobby for you if you dislike working with mechanical things.
The driving part of R/C electric off-road racing is definitely suitable for young children. The building and maintenance part of racing is not so suitable, due to the limited attention spans of youngsters. If somebody older can be the pit crew, the child can be the driver. At the age of eleven or twelve the child can start taking on more of the pit jobs.
Organized racing is competitive in nature. Many kids would rather play than compete. The Tamiya 1/14 scale QD (quick drive) series of cars and trucks are a good choice if the goal is recreation rather than competition -- good performance, rugged, long run times. They are a step up from what you'll find at Radio Shack, for about $100 (includes everything needed except batteries and charger.) If you are getting into racing but your child isn't ready, think about getting the child a Tamiya QD. A race car would be overkill.
To find a place to race, try calling local hobby shops. Even if they don't run races themselves, they may know other local shops or clubs that do.
Another way to find a track is to consult the track listing printed every other month in Radio Control Car Action magazine.
A third way to find a track is to post a message to rec.models.rc.land, the Internet newsgroup for land-based R/C modeling. These days it is pretty likely that some racer near you is reading this newsgroup.
By far the best way to learn more about R/C racing is to find a race track and show up on a race day. Wander around, look at what's going on, and ask questions. Most racers are happy to share what they know.
Other sources of general information on the hobby include books, magazines, and the Internet. I'm not aware of any really good books. Radio Control Car Action magazine is excellent for staying current with new product introductions. rec.models.rc.land contains some useful information, some misinformation, and a fair bit of noise. You can use Alta Vista to find specific information on the Web, or go browsing from Tony van Roon's RC Webdirectory index. But none of these sources is an adequate substitute for talking to local racers.
How much you spend on R/C car racing depends entirely upon your attitude. If you approach racing as an enjoyable diversion from your normal responsibilities, and focus on setting up your car, driving it, and having fun, your cost will be quite moderate. If you insist on having every on-track advantage that money can buy, your cost will be much greater.
If you are a beginner and want to advance to the point where you are competitive within your class, the most effective way to get there is to spend a lot of time driving. This will have a much bigger payoff than installing super batteries or titanium chassis parts. And it is more fun, too.
If you take this approach, you'll spend about $10 per race on entry fees and perhaps another $15 on replacement parts (tires are often the single most expensive item.) It will cost you about $150 to get started if you can find suitable used equipment, otherwise it will cost $275 or so. This is for a bare-bones setup that you'll want to upgrade as you get more experience. Expect to pay about $575 for a setup that won't require upgrades. If you want to start with top-of-the-line equipment figure more like $875.
For some people, half the fun of racing is in selecting and installing upgrades. You can certainly express your ingenuity, mechanical skill, and good taste in this way, and if the modification doesn't work out, you can always undo it. The costs associated with this activity are up to you; they aren't closely related to the number of races you run or to race results.
It is cheaper to race at one track than at several. No two tracks are alike, so you'll find that the chassis setup and motor that rule one track can be middling at another. It can be lots of fun to race at different tracks, but come prepared either to compromise on performance or to spend more money. At a minimum you should be prepared to buy a new set of tires when you go to a new track; there is nothing more miserable than being way off the pace because your tires aren't hooking up with the dirt.
At the highest levels of racing there are a lot of drivers who can drive consistently fast, lap after lap near the limit of what's possible. At this elite level, small differences in equipment can make a difference in race results, so competitive racing becomes very expensive. Don't worry; you probably don't have the time or the talent to compete with Brian Kinwald, and you can have a lot of fun racing at your own level at a modest cost.
You should probably start with a truck. Here are some factors to think about:
Truck is the most popular class in the USA, and more and more newcomers are starting with trucks.
If you are making this choice in early 1997 here's another factor to complicate your decision: The popularity of four-wheel-drive buggies is expected to increase explosively in 1997 (see the answer to the next question.) If four-wheel-drive takes off, some other class is bound to decline in popularity; I expect that class to be two-wheel drive buggies, not trucks.
Four-wheel-drive buggies are fast and fun, but they aren't raced much in the USA.
Some will say that no four-wheel-drive buggy is as well engineered as the two-wheel-drive buggies, but the current four-wheel-drives by Kyosho, Schumacher, Tenth Technology, and Yokomo are quite good. Engineering quality is not the problem.
Four-wheel-drive buggies were fairly popular here until trucks came along and displaced them. Trucks have several advantages that caused them to take over:
Things are changing, however. Team Losi released the XX-4 four-wheel-drive buggy in April 1997. The XX-4 contains significant innovations including a fully sealed drivetrain to reduce maintenance and a forward-mounted motor to make the buggy more stable. The XX-4 should trigger a revival of the four-wheel-drive buggy class in the USA.
Stay tuned for further developments. Four-wheel-drive sedan racing on pavement is very popular, and Losi could adapt the XX-4 drivetrain to the pavement, just as Tamiya and Yokomo did with their four-wheel-drive off-roaders.
Absolutely! You can use an entry-level vehicle to get your first racing experience. As a beginner your main objectives are to stay on the track, finish the race, and have fun. You can do this with an entry-level buggy or truck.
But don't get caught in the trap of adding expensive upgrades to an entry-level vehicle. No amount of upgrading can overcome the design limitations in the chassis, suspension, and transmission of such a vehicle. You will spend a lot of money and end up with something that is unreliable and uncompetitive.
Race your entry-level vehicle as is, except for a tire upgrade if needed for your track. After awhile, if you decide you want to continue racing, get yourself a kit that's race-bred.
The only entry-level vehicles worth upgrading are the ones derived from today's competitive racers. Entry-level trucks in this class include the bushing XXT kits from Team Losi and the bushing RC10T2 kits from Team Associated. It is not worth upgrading older designs such as the Team Losi Jr-T and Team Associcated bushing RC10T.
You can save a lot of money on major pieces of equipment by buying them used, either from someone getting out of the hobby or from someone upgrading his equipment. You can generally get good used equipment for half the price you would pay for new equipment.
Buying used is risky if you are inexperienced. If you've got an experienced friend, that's a big help. Generally you should insist on trying before buying, especially when it comes to electronic equipment. In buying a used car or truck, pay special attention to the condition of the ball bearings, especially the big expensive ones on the output shafts of the transmission ("outdrives").
The best place to look for used racing equipment is at the track, since that's where the racers are. Some tracks have bulletin boards of for-sale notices; if there is a hobby shop at the track, the shop may sell used equipment on consignment. You can also just walk around the pits and ask people if they have equipment for sale. Be warned that some tracks don't allow used equipment sales on the premises, because they feel that sales of used equipment will reduce their business. If the track is associated with a shop, ask to be sure.
After exhausting whatever used equipment opportunities you decide to explore, make a list of everything else you need. (The answer to the next question will help you in drafting your list.)
If your local shop
then you have a vital interest in seeing that shop succeed. Take your list to the shop and negotiate the best package deal you can. By all means use mail order prices for comparison, but don't expect your hobby dealer to match them to the dollar.
If you don't have a local shop, or your local shop doesn't deserve your business, then go with phone/mail order. I think you should bias your purchases toward shops that support racing in their vicinity and have knowledgeable staff to help you. My favorite shop in the Boston area is Hi-Tech Hobbies and Raceway (508-880-5373) because they run races at their on-site track, they stock parts and charge fair prices for them, and they are nice people.
First, the list; then the details.
low mid high
kit (low: Losi XX w/bushings; others: Losi XX-CR) 124 186
tire upgrade ..................................... - 19?
turnbuckle upgrade ............................... - 21
transmitter, receiver, servo
(low: JR Python, mid: Air XL2P, high: Air CS2P) . 65 83 159
transmitter ni-cd, trickle charger
(low: alkaline batteries) ....................... 8 25
spare set of crystals ............................ - 20
servo upgrade (mid: LDM bearing, high: Air 94157) - 7 90
servo saver ...................................... 5?
electronic speed control (low: mechanical,
mid Tekin F10, high: Tekin G12c) ............... - 53 106
batteries (low: 1, others: 3) .................... 29 87
connectors ....................................... - 15
battery charger
(low, mid: timed, high: Tekin BC 5A) ............ 33 33 93
stock motor (low: included in kit) ............... 20
pinion gears (low: included in kit, others: 3) ... 12
thin CA glue ..................................... 4
paint ............................................ 10
RTV adhesive ..................................... 5
motor oiler ...................................... 3
motor spray ...................................... 5
comm drops ....................................... - - 4
hardened wrench (pinion set screw) ............... - - 8
ball driver (motor screws) ....................... - - 8
shock wrench set ................................. - - 5
tooth brush ...................................... 0
box .............................................. 0
totals 286 589 886
These prices are November 1996 mail order prices for the big items, and my best guesses for the smaller items. Prices for the kit and the tire upgrade are for a buggy; truck tires are about $5 per pair higher so truck kits are about $10 higher.
If a column is blank, use the figure to the left. If a column contains a minus sign (-) omit that item from that setup. If the price is followed by question-mark the item may not be required, and its price is not included in the total.
The "low" column is the lowest-price setup that actually gets you started. You get a bushing-equipped kit with motor, pinion, and mechanical speed control, a simple radio system with two servos, throwaway alkaline batteries for your transmitter, a timed charger, and one battery pack. You live with the flimsy turnbuckles packaged with your kit and the junky connectors supplied with your battery and speed control. If you stay with the hobby for any length of time these choices will cause you frustration and cost you money. They are perfectly valid choices if you aren't sure of your interest or if you are on a very tight initial budget.
The "mid" column is a much better setup. You get a ball-bearing equipped kit, turnbuckles that won't bend, a transmitter with full adjustments, crystals for an alternate channel, a high-frequency speed control, a bearing so your servo won't add a lot of slop to your steering, the same timed charger, three battery packs, good connectors, and three pinions. The only significant compromises here are the charger, the AM radio, and the not very fast or powerful servo.
The "high" column is a no-compromise setup. You get an FM radio, a fast, strong, rugged servo, a better high-frequency speed control, an adjustable-current AC/DC peak charger, and some fine tools. Not many people start with a setup like this one, but quite a few get there after a few years of racing.
As a beginner you should pick a car that allows you to get the maximum support from local racers. Select something that other people are running -- people you think will help you. Hang around your track, observing and asking questions, and you'll quickly draw conclusions about who will be helpful.
At many tracks in the US you will find strong Associated and Losi camps. Associated Electrics and Team Losi are the US manufacturers of R/C electric off-road racing cars and trucks. They both make fine products and many shops stock parts for their cars and trucks.
I find Losi's competition-level kits (the XX 'CR' and XX-T 'CR') somewhat more beginner-friendly than Associated's kits. Here is why:
Based on all these factors I recommend that you get a Losi XX 'CR' buggy or XX-T 'CR' truck. The XX buggy was introduced in October 1993, after top qualifying and finishing second at the 1993 2WD off-road world championship, and has become extremely popular for its speed and easy maintenance. Losi updated the XX buggy with the XX 'CR' kit in July 1996. The Losi XX-T truck became available in October 1994 and was by far the most popular truck everywhere I raced in 1995 and 1996; the XX-T 'CR' kit appeared in September 1996.
In spite of all the positive things I've said about Losi, you should go with Associated if your track has a lot of helpful Associated racers and not very many helpful Losi racers. Associated makes fine products. The RC-10T2 truck is competitive in performance with the XX-T 'CR' and contains many design and manufacturing improvements over Associated's earlier kits. The Associated RC-10B2 buggy shares many design features with the XX 'CR' (plastic chassis, long suspension arms, modular rear end, etc.) and improves on the XX in some areas (stiffer standard chassis, more room for speed control and receiver mounting). The Associated and Losi buggies are very similar in performance.
Team Associated has been extremely successful in the off-road world championships. They won the first off-road world's in 1985 with the original RC-10. They took the 1989 and 1991 races with their "Stealth" cars, which used some RC-10 components. Brian Kinwald won the 1993 race using a buggy that closely resembles the RC-10 World's Car that's still available. Matt Francis won the 1995 race using a prototype RC-10B2.
For those on a very tight initial budget I recommend the bushing-equipped Losi XX and XX-T kits. These entry-level kits have a great deal in common with Losi's full-race kits. They differ in using metal or plastic bushings in place of most ball bearings, in not being Hydra Drive equipped, in using plastic rear drive shafts, in using shocks that aren't hard-coated, and in not incorporating the recent 'CR' updates (e.g. rear suspension geometry, steering geometry, battery hold-down.) You can upgrade these kits to full-race specs piece by piece as the original parts wear out.
The entry level kits include a stock motor and mechanical (resistor) speed control. The motor is underpowered compared with modern stock motors, and the speed control won't work as well as an electronic unit. But the whole point of an entry-level package is to get started with the minimum initial outlay. If you have the money and are convinced that you'll keep racing then you are better off starting with a better kit. All the money you've saved by buying an entry level package you will spend when you upgrade to ball bearings and hard-coated shocks. Entry level kits are a short term savings strategy that costs more if you keep racing.
I used to recommend a cheap frame-rate electronic speed control as part of the entry level package, avoiding the mechanical speed control. But a cheap frame rate control is still pretty expensive, won't handle most modified motors, and is vastly harder to drive than a high-frequency speed control. (The terms "frame-rate" and "high-frequency" are explained in the speed control item below.) The mechanical speed controls supplied in Associated and Losi kits work well if you run stock motors and maintain the speed controls according to directions. When you are ready to step up from these speed controls, get a high-frequency electronic control.
If you've decided to go with Associated and want to start with an entry-level kit, you are in luck: In late 1996 Associated introduced entry-level versions of their RC-10B2 buggy and RC-10T2 truck.
What about the other manufacturers? The other off-road manufacturers with a major presence in the USA are (in alphabetical order) Kyosho, MRC, Schumacher, Tamiya, and Traxxas. All of them produce good quality kits:
If one of these manufacturers is popular with racers where you live, and your local shop stocks parts, then by all means consider them for your first car.
Tires are the biggest factor in how your car or truck handles. If the kit you buy does not include tires that are good for your track, don't waste your time with the kit tires. Install some tires that will work. Watch what the locals use and follow their lead. On many tracks the best tire will use a soft rubber compound, either the Losi Silver or ProLine XTR-M2.
As suspension arms on kits like the Losi XX-T 'CR' have grown longer, the kits' steel turnbuckles used as the upper suspension link have not grown beefier. As a result, the stock turnbuckles bend in the sorts of crashes that occur to a novice driver every race or two. The stock turnbuckles should be replaced with Lunsford 'Punisher' turnbuckles, which are very strong and come with a "no bend, no break" guarantee.
Be careful when buying turnbuckles in sets -- be sure you are getting turnbuckles that are the correct length for your application.
The most popular brands of radio gear for off-road racing in the USA are Futaba and Airtronics. Both Futaba and Airtronics make entry-level radios that cost $80 and better radios for around $150.
You can buy radio equipment piece by piece, but most people buy a package that includes a transmitter (with crystal), a receiver (with crystal), a steering servo, and either a throttle servo (for use with a mechanical speed control) or an electronic speed control. The packages with speed controls are more expensive and the speed controls aren't very good, so it often makes sense to buy the package with two servos even though you only need one.
The radio I quote for the low-priced setup is the JR Python. This is the lowest-priced transmitter that includes a steering rate control. Steering rate control (also called "dual rate") allows you to set how far the front wheels steer when you turn the steering wheel from lock to lock. This allows you to get full steering without performing tedious mechanical adjustments.
The JR Python comes with two basic servos, one for a mechanical speed control and one for steering. It also includes a receiver that incorporates JR's proprietary ABC&W circuitry for increased noise immunity.
I've specified the Airtronics XL2P in the mid-priced setup. This is a popular, high quality AM radio with a full range of adjustments.
The most important property a radio can have is freedom from glitches. Higher grade radios with FM transmission have more noise immunity than entry level radios with AM; the difference is real in competition, with ten radios turned on at one time. The Airtronics CS2P is the lowest priced FM radio available. It is clearly a competition-quality unit based on the number of top racers who use it. For this reason, I recommend the CS2P as a worthwhile improvement over the XL2P and quote it for the high-priced setup.
KO and Futaba also make fine radios. Masami Hirosaka, many-time world champion in off-road and on-road, uses KO. Futaba's entry level radios, bundled with electronic speed controls, are very popular. If one of these brands is popular at your track you might decide to go with it.
Some receivers come with antennas that are much longer than a normal antenna straw. If you buy such a receiver you'll need to build an antenna loom to to hold all of the antenna wire in excess of what goes up the antenna straw. If you don't build a loom you are likely to experience glitches in competition.
There are two radio bands to choose from: 27 mHz and 75 mHz. The 27 mHz band has only six channels. The 75 mHz band has narrower channels, but thirty of them. Because there are so many more channels, racers on 75 mHz tend to have fewer frequency conflicts when practicing and racing. If seven racers on 27 mHz all qualify for the same main event, the slowest qualifier will not get to run. I have seen this happen. It doesn't happen on 75mHz. A modern radio receiver copes quite nicely with the narrower channels on 75mHz. I recommend that you buy 75mHz equipment. Some tracks restrict the use of odd-numbered channels on 75mHz, so ask about this before you buy.
You will hear people talk about PCM. PCM is a digital encoding technique for communicating control information from the transmitter to the receiver. The primary advantage of PCM is that a PCM receiver can detect errors introduced in the radio transmission; thus a car being controlled with PCM is much less likely to go completely out of control. PCM is primarily intended for powerful gas cars, which benefit significantly from the extra safety margin. PCM receivers introduce some extra delay in transmitting your commands to the speed control and steering servo, and they aren't compatible between different manufacturers (for instance you can't use a Futaba PCM receiver with an Airtronics PCM transmitter.) Overall I recommend against investing in PCM for electric-powered racing.
You can run a transmitter on alkaline cells, but in doing so you will quickly spend enough to have bought eight rechargeable Sanyo AA cells and a trickle charger.
To race, or just to play around with a friend whose radio uses the same frequency as yours, you need to have at least one alternative to the frequency your radio came with. If you don't have a second frequency you may be unable to race at all, or you may qualify but be unable to run your main.
Crystals are not interchangeable between AM and FM and are sometimes not interchangeable between different brands of radios. So buy the same brand of crystals as your radio unless you can return crystals that don't work for you.
Buy a set of crystals for a frequency that's near your original frequency; that way your radio won't need to be sent to the factory for re-tuning when you swap crystals. Changing two channels up or down should work fine. A set of crystals is a matched pair in which the two crystals have distinct roles: The one marked "Tx" is for the transmitter and the one marked "Rx" is for the receiver. If you get the two mixed up your transmitter will not be able to control your vehicle. Crystals plug into sockets so they are easy to change. Store your extra crystals carefully so they'll still be in good shape when you need them.
You will probably need to pry a cover off of your transmitter in order to expose its crystal. That's because it is a violation of FCC regulations to change transmitter crystals without re-tuning your transmitter. But racing is not practical without crystal swapping, so everyone ignores the FCC regulations.
Just about any standard-size servo will steer a buggy. Your truck will work OK with a standard servo, but won't turn as well as it could. A truck works best with a steering servo the produces at least 50 ounce/inches of torque. The KO PS703 servo has good price/performance at $50.
Servos have a lot of tiny gears inside. These gears are made of either plastic or metal. Metal gears cost more, weigh more, and require lubrication, but they survive crashes much better than plastic. The Airtronics 94157 is a top-of-the-line metal-gear servo with 95 ounce/inches of torque and very high speed (0.06 seconds per 60 degrees) and costs about $90.
Most standard servos, including the Airtronics 94102 and Futaba S-148, don't have a ball bearing on the output shaft. When the bushing on this shaft wears, it creates extra slop in your steering. A ball bearing upgrade from LDM for an Airtronics or Futaba servo costs $7; well worth the investment if you go with the standard servo.
The steering servo is designed to turn the steering linkage of your car. When you crash, the front wheels of your car try to turn your steering servo. If you crash really hard the force can be enough to break teeth from the gears inside your servo. This puts you out of action until you can lay your hands on a new set of gears and replace the old stripped gears.
A servo saver is anything that absorbs shocks before they get get to your servo. You want a servo saver for the big shocks, not the little ones, so the best designs pass small forces right through but absorb the larger forces.
Some cars come with built-in servo savers: XX, XX-T, RC-10B2, RC-10T2. For those that don't (older Associated and Losi designs), Kimbrough Products makes the industry-standard servo saver. For off-road use you want Kimbrough's large servo saver; the small one is way too flexible and thus gives up too much steering.
For racing you want a high-frequency, forward-only electronic speed control. In the USA this means a Novak or a Tekin.
A good speed control lasts for a very long time. What tends to happen is that new models come out that offer new features to entice you to buy while your old speed control is working perfectly well.
The last really significant innovation in speed controls was "high-frequency" operation. What does "high-frequency" mean? A speed control works by chopping the voltage delivered to the motor. At half throttle, the speed control delivers full voltage to the motor half the time, and no voltage to the motor the other half. The faster the voltage is switched on and off the smoother the motor runs. High-frequency speed controls give you better control, are more efficient at partial throttle (give longer running times), and help the motor last longer. That's why you want one. Tekin and Novak don't make anything else.
Some speed controls offer an adjustable current limiter, sometimes called "torque control." When your car is standing still or moving slowly and you mash on the throttle, the motor draws a huge spike of current. The surge of current generates a lot of torque at the wheels, but the torque may go into wheelspin and be wasted. The current also heats up your motor and drains your battery. On a track with challenging jumps it may not be possible to make the jumps when using a current limiter, so current limiters are not used much by top off-road drivers. But if your skills aren't that well developed, a current limiter might help you reduce wheelspin, decrease motor temperature, and increase run time. A moderately useful feature.
What about reversing speed controls? Reverse is a great feature to have when you are practicing: When you turn in too soon and run into an obstacle, you can back out and try again. Reverse is also great for just playing around. But there are some downsides to adding reverse to a speed control. First, reverse adds resistance to a speed control. The added resistance of a reversing control will slow you down a little bit, and means that the speed control may overheat if you try to run a low-turn modified motor. (Due to the marvelous FETs and high-speed switching incorporasted in modern ESCs, this is less true than it used to be; all of Tekin's reversing controls now handle hot modified motors.) Second, reverse adds a small amount of weight to the speed control. Third, some reversing speed controls lack brakes. Finally, it is illegal to use reverse while racing. If you want reverse and also want to race, be sure to get a reversing speed control that handles modified motors, that has brakes, and that allows you to disable reverse entirely for racing.
All of today's Novak speed controls and most of Tekin's feature an on-off switch that allows you to plug in the battery without turning on the car; you flip the switch to turn on the car, flip it back to stop. This is extremely convenient. Beware the inexpensive low-frequency speed controls that are bundled with some radios -- they may lack an on-off switch, making them awkward to use.
You adjust older-design speed controls using two potentiometers (little things you stick a tiny screwdriver into and turn) and an LED indicator. You adjust newer-design speed controls using a single button: push the button, then move the trigger from neutral to full throttle to full brake and back to neutral; the speed control stores the settings electronically. The older system was more prone to drift and needed occasional readjustment; the new system is more prone to forgetting the adjustment entirely, making the speed control act dead. Since all new speed control designs have the one-button adjustment (advancing technology makes it both cheaper to produce and, in principle, more reliable), you don't really have much of a choice here.
The Tekin Formula 10 is the least expensive high-frequency speed control I've seen; it is a new model and I have no word-of-mouth on it. An alternative for $12 more is the Novak Duster, a one-button setup model that's been around for over a year. Both of these lack a current limiter.
The Tekin G12c is a no-holds-barred racing speed control. It has very low resistance, an adjustable current limiter, externally replaceable wires, and strong brakes. I love my G12c.
Will upgrading from an inexpensive high-frequency speed control to a more expensive one make you go faster? Possibly, but not because of the slightly lower on-resistance of the more expensive speed control -- the difference is not significant. Consider buying a more expensive speed control if that speed control gives you better control of the throttle, allowing you to drive better.
High-capacity Ni-Cd cells make our hobby possible. Today's cells are technological marvels and provide great racing.
The main technical things you need to understand about cells are the concepts of cell capacity, voltage, and internal resistance:
The Sanyo RC2000 cell was introduced at the 1996 Chicago Hobby Show and became legal for ROAR-sanctioned competition in 1997. These cells have high (2000 mAH) capacity, fairly high voltage, low internal resistance, and are rugged enough to survive being charged more than once per day with no ill effect. They are amazing.
The predecessor of the RC2000 was the Sanyo 1700 SCRC (black label) cell. This was the only cell used in top-level off-road racing from 1993 to 1996. These cells have a slightly lower capacity (1700 mAH) and are more variable in quality than the RC2000, but the good ones are very good. As of early 1997, some SCRCs are still available but the supply will dry up soon.
What should you buy? If you are buying new batteries you should buy RC2000s, not 1700 SCRCs; the most recently produced 1700 SCRCs had quality problems. If you want to save some money you should buy used SCRCs from drivers who take good care of their equipment. As a beginner, it will be a year or two before the difference between 1700 and 2000 mAh becomes meaningful to you, unless you race for more than four minutes with modified motors on a high-bite track. Buy three packs so you can be running one, charging one, and resting one (preferably with a fan cooling it). If you take care of your three packs, they will last for years.
Stay away from packs that are not built with Sanyo RC2000 or SCRC cells. The other cells don't perform or last like these Sanyos. This advice holds even for other types of Sanyo cells, including the Sanyo SCE cell that once dominated modified off-road racing. (The one exception is the red Sanyo 1400 SCR cell, which is even more rugged than today's cells but whose lower capacity is a handicap in competition with modern cells.)
The only RC2000 cells that are legal for racing in the USA are cells carrying the RBRC logo on the shrink-wrap. This logo simply means that the US distributor of the cell has paid money into a fund that covers the cost of eventually recycling the cell. You may see RC2000 cells without the RBRC logo; these were probably purchased in Europe or Japan and then brought into the USA. These cells have no performance advantages or disadvantages over cells carrying the RBRC logo, but they are illegal for racing in the USA.
You will hear people talk about matched cells. Cell matching is the process of evaluating a large batch of cells and grouping the most similar ones into packs. Most commonly, cells are grouped according to the number of seconds they take to discharge from fully charged to 0.9 volts under a 20 amp load. A matched pack does not necessarily run longer or make you go faster than an unmatched pack; I watched Cliff Lett win the 1990 ROAR National Championship for 2WD buggies using inexpensive unmatched stick packs while most of his competition was using matched packs. The advantage of a matched pack is that it takes the abuse of full discharging better than an unmatched pack and therefore has a longer lifetime.
Most matched cells are sold loose rather than assembled into packs, but some of the larger matchers sell matched packs as well as cells. If you do decide to buy matched packs or cells, don't spend a lot of money to get top ratings; they are overkill for off-road racing. And don't think about cell ratings in absolute terms; cell matchers have an obvious incentive to inflate their numbers, so the only way to compare the quality of cells from different matchers is by experimentation.
You may hear people talk about voltage-increased cells. Most cell matchers now pre-process all of their cells by applying a high voltage to each cell for a short period of time. They claim this 'zapping' permanently increases the output voltage of some of the cells. I'm not aware of any scientific experiments that substantiate this claim. At any rate, the matchers select the cells with the best output voltage and sell them for a premium price. These ultra-expensive cells won't help you unless you are an excellent driver racing with stock motors against tough competition. Leave them for the oval racers.
You will get lots of advice about the need to discharge your cells after use. Most of this advice originates, directly or indirectly, from people who sell battery discharging devices. If you have a peak charger you don't need one of those devices. See the battery charging section for more information.
Seven cell packs are no longer legal for modified off-road racing in ROAR sanctioned events. Use six cells.
You will find more information about ni-cad batteries on Red Scholefield's home page, http://gnv.fdt.net/~redscho/. Not all of the information applies to R/C cars -- the site is more oriented toward the use of ni-cads to power receivers and servos in model airplanes -- but the information that's there is very very good.
To avoid frequent use of a soldering iron, you need two connectors on your speed control: one leading to the battery and one to the motor. You need one connector on each battery and one on each motor.
The battery and the speed control motor connectors should be female; the speed control battery and the motor connectors should be male. So to start with you need four female and two male connectors, plus one extra of each wired up to help with battery charging, motor break-in, etc.
The "Tamiya-style" connectors that come with batteries are terrible. They have high resistance and are unreliable. Replace them with Dean's Ultra Plugs, the best connector available.
You may see some racers "hard wiring", which means soldering connections to their batteries and motors on each run. A good connector introduces very little resistance, is reliable, and is convenient. Get the best connectors and you'll be at no disadvantage.
A low-end battery charger is a timer-controlled current source. If you know that your battery is fully discharged, and you know how long it normally takes to fully charge from the discharged state, you can set the timer and charge the battery. If you miscalculate, you can destroy the battery you wanted to charge. The battery will vent its chemicals, melt its wrapper, possibly even catch fire. You can get a timed charger for about $33 from several companies.
A peak charger operates by sensing the voltage the battery puts out as it is being charged. As the battery reaches full charge, it heats up and its voltage drops. A peak charger is fully automatic; if it makes a mistake, it will stop charging too soon rather than too late. Most people start with a timed charger but get a peak charger later when they get serious about racing. A basic peak charger pays for itself pretty quickly by saving battery packs and by saving your time.
The Astro-Flight 114D at $52 is an AC/DC peak charger with a non-adjustable charge rate. The drawback of a non-adjustable charge rate is that when a new type of cell comes out, like the Sanyo 2000 cell, it may not like the rate your charger uses.
The least expensive competition quality AC/DC peak charger with an adjustable charge rate is the Tekin BC 5A at $93.
I haven't mentioned DC-only peak chargers. That's because most people don't have a convenient source of 12 volts DC where they race. If you always race outdoors and pit next to your car (which has a large 12 volt battery), or if you already have a 12 volt regulated power supply that puts out at least 5 amps, then you can consider buying a DC-only peak charger to save money. Some people use an automobile battery charger as a power source for a DC-only charger, but this combination will false peak when the AC line voltage varies due to variations in load.
A useful feature in a peak charger is the ability to charge 8 cells, for transmitter packs. You get a fuller charge with a trickle charger, but the trickle charger won't help you if your transmitter pack is dead and your next race starts in 20 minutes.
The Trinity/Speedworks Midnight is a very popular ROAR stock motor. As stock motors go it is a good one -- it is powerful and efficient, giving a long life if used properly. It comes with good quality brushes and springs already installed. The Trinity/Speedworks X-Star, introduced in October 1996, is a higher RPM stock motor designed to complement the Midnight. The Race Prep stock motors, the only stock motors assembled in the USA, are also strong performers, as are the Reedy Firehawk motors. The stock motor business is more competitive than ever.
There are many other stock motors on the market. Most of them are simply one of the motors mentioned above with exotic racing brushes installed. As a beginner you are better off with standard brushes, which produce a bit less power but are far easier on the commutator and allow the motor to last much longer.
You will get longer motor life from a mild modified motor. You may want to practice with a modified and save the stock motor for races. You'll need a wider range of pinion gears to run different motors (see next topic.)
The longer you race the more pinions you will accumulate until you have a full set (ranging from 14 to 25 teeth or so). Start out with one pinion at the recommended gear ratio for your stock motor, and with the pinions with one and two fewer teeth. (For a Losi XX buggy and Green Machine II motor you would buy 23, 22, and 21 tooth pinions; for a Losi XX-T truck and Green Machine II you would buy 22, 21 and 20 tooth pinions.) Start with the smallest pinion gear. After a complete run, press your thumb on the motor. If you can hold it there for five seconds with no discomfort, then it is OK to try the next larger pinion. A larger pinion will give you more speed on long straights but may give less acceleration out of the corners.
If you only buy one pinion, buy one that's two teeth smaller than the recommended one. As a beginning driver you will be carrying less speed through the turns than a more experienced driver, so you will need to run a smaller pinion than the more experienced drivers do.
I like Team Losi pinions because they use a 5-40 set screw. The drawback of the 4-40 set screws used in other US brands is that they are more prone to stripping. It can be hard to remove a pinion whose set screw has stripped!
A convenient feature to look for when choosing a pinion gear is a visible indication of the number of teeth. There are few things so tedious as counting the tiny teeth on a gear.
All the pinion gears I've been talking about are 48 pitch gears, which match the spur gears supplied in competition-level Losi and Associated kits. 64 pitch gears are too easily damaged in off-road use, while 32 pitch gears give away too much efficiency. 48 pitch gears are the right compromise.
You need a small bottle of thin cyanoacrylate ("super") glue for gluing tires to wheels.
Since different brands of hobby-quality CA glue seem about the same, I buy based on the quality of the packaging. The glue is pretty useless if it has leaked out, or if the package has become glued shut. My favorite CA glue package is Pacer's, which has a double cap. It travels well.
Resist the temptation to buy the large economy size; you won't be using glue that quickly. A 1 ounce bottle will last you a long time, and even a 1/2 ounce bottle will mount quite a few tires. CA glue can solidify in the bottle, in which case you have to throw the bottle away and get a new one. (The shelf life of CA can be increased by storing it in the refrigerator, but doing that is often inconvenient.)
Be sure to read and follow the label directions when using CA glues. CA will bond skin to skin, so be careful; you *really* don't want to get any into your eyes. Wear safety glasses. Some individuals display allergic reactions to CA glues. Avoid getting it on your skin (disposable latex gloves ensure this) and avoid breathing the vapors.
You will need a couple of spray cans of Pactra R/C Finish for painting the clear polycarbonate body of your racer. (You will hear people talk about Lexan bodies -- Lexan is GE's brand of polycarbonate, the original.) This sort of special paint sticks best. Another reputable brand is Coverite; I have no experience with Coverite paint.
The solvents in paints for R/C car bodies attack the polycarbonate material, giving the paint a better grip. They also attack your nervous system. Be sure to read and follow the label directions when using these paints. Wear glasses and a respirator and do your painting outside if you possibly can.
RTV (room temperature vulcanizing) adhesive is a sticky rubbery glue. It is sold under the Shoe Goo brand name for repairing the soles of tennis shoes; the Goop brand is also widely-distributed. RTV adhesive is perfect for reinforcing the high stress areas of polycarbonate bodies, gear covers, etc. (CA glue attacks polycarbonate, making the material cloudy and brittle.) As a beginner you will be doing a lot of crashing, so reinforce before you begin.
Buy the smallest tube of RTV adhesive you can find; it goes stale in the tube. When the adhesive loses that ultra-sticky consistency coming from the tube, it is time for a new tube.
Be sure to read and follow the label directions when using RTV adhesives. The solvents are really bad for you, so keep the stuff off your hands and use RTV in well-ventilated places only.
Bushing motors need a drop of oil on each bushing before each run. The Trinity oiler has a needle tip that's perfect for the job. It is available filled with either bushing or bearing oil; for a stock motor you want the bushing oil.
Depending upon the track conditions, you should clean your motor every few runs. Buy a motor spray for this purpose. Brake cleaner is cheaper and has a similar list of ingredients but has a different formulation; don't use it.
Motor spray is also good for spraying out wheel bearings as they get gritty; re-oil with one drop of light oil after spraying.
The components of motor spray that are bad for you are absorbed readily through the skin; always wear safety glasses and rubber gloves when using motor spray.
Comm drops used to be a "speed secret" for stock motors, but they caused accelerated wear of the commutator and were not suitable for modified motors. The current crop of comm drops is different; they should be used in all motors. Comm drops reduce arcing, brush glaze, and comm wear. That they make your motor faster is just a bonus.
Trinity's Revtech drops work, are not horribly expensive, and are widely available. Lab tests reported in R/C Car Action showed that the more expensive Race Prep and Extreme drops produce more power than the Revtech drops.
You want to get that pinion on tight, but you don't want to strip the set screw. To achieve both at once you need an Allen wrench that's a lot harder than the screw, so the edges of the hex end won't round off with use. Many folks make these wrenches. RPM makes wrenches with nicer grips than the others. The Associated and Trinity wrenches have a replaceable tip, an potential advantage if you drop your tools a lot, but replacement tips cost nearly as much as a whole RPM wrench. Losi pinions use a 1/16 inch wrench; most others (e.g. Robinson, Trinity) use the 0.050 size.
You can live without this wrench for awhile, but once you've had one you'll never go back.
You need an Allen wrench for tightening the 3mm screws that hold your motor to the chassis. For about $3 you can buy a Bondhus ball driver that makes the job easy by allowing you to drive the screw from an angle. For about $8 you can buy a hardened ball driver from RPM.
Again, you can make do with a plain Allen wrench. But you will become very familiar with the motor screws as you adjust gear mesh each time the motor goes on after cleaning. You'll be happier with a quality wrench.
Shock wrenches are a wonderful invention of RPM. They are for tightening the cartridge on a Losi shock or the cap on an Associated shock (two versions of the same tool.) They are made of plastic to do the job without scratching. They are perfectly adapted to the job. You can do without them but don't mangle your shocks using inferior tools; a shock wrench set costs less than one new shock.
After each run you should clean the bottom of the shocks, where the seals are. Dirt that accumulates in this area causes accelerated wear of the seals and slows down the shock action. An old tooth brush is the perfect tool.
Get a good-sized cardboard box to hold your stuff. Get some smaller cardboard boxes to keep the smaller parts organized. As you accumulate spare parts you will need to get some divided plastic boxes, such as the ones designed for fishing lures.
You don't need a modified motor right away. But as your driving improves you will get the itch to experiment with more power.
Your first motor for modified racing should be mild, not wild. You want something that's faster than stock, but still easy to drive. Most beginners in modified go slower in modified than in stock, but if you pick the right motor you can go faster right away.
Modified motors are rated by turns and strands. A 14-turn triple has three strands wrapped fourteen times around each pole of the armature.
Other things being equal a motor with fewer turns draws more current, has more no-load RPMs, and produces more power. (This explains why a stock motor is specified to have at least, not at most, 27 turns.) A motor with fewer strands has more "snap" -- it accelerates more quickly from low speeds. A motor with the same number of turns and more strands has more power at the top end.
If you buy a 14-turn triple from Reedy, it won't necessarily perform the same as a 14-turn triple from Peak Performance or Trinity. The variables include the quality of laminations in the armature stack, the strength of the magnets, the wire size and winding pattern used, the diameter of the commutator, and the choice of brushes and springs. But if you stick to one line of motors, you can predict the relative performance of two motors by knowing their winds.
As a beginner in modified you want a motor with a lot of turns and a lot of strands. Especially a lot of strands -- at least four for a buggy, three for a truck. Otherwise you will spend all your time spinning out while you try to develop the sensitive throttle control needed with a big motor.
A mild modified motor that I liked a lot was the Reedy Mr. K 17-turn quad. This was the only motor I used in my first year of modified racing. These days I usually run a 12-turn triple in my buggy, but I keep an old Mr. K handy for running on very tight tracks and tracks with bad traction. I've worn out a couple of Mr. Ks through hours of use.
The "big two" in off-road racing motors are Reedy and Trinity. Both offer a huge selection of winds; that's an advantage because if you want to go a little hotter or a little milder, the motor you want is nearly always available. Reedy offers a series of motors specifically for off-road, the Sonic-II large commutator motors; these motors sacrifice some peak RPM and efficiency to gain a wider power band, and require less maintenance than conventional motors. Both Trinity and Reedy sell armatures as well as whole motors; if you want to try a lot of winds it is cheaper to buy armatures than whole motors. But beware: often, before an armature wears out the magnets have lost their peak strength and the bearings are gone so the motor is nearing retirement.
Building an R/C racer from a kit is mostly a matter of carefully following instructions. Here are a few notes on issues that are often not described well in the instructions provided with kits.
If your kit involves any screws that thread into metal parts, you'll need to use a thread lock compound to keep the screws from loosening. (On the Losi XX and XXT the three screws that tie the transmission to the motor plate need thread lock.) The standard thread lock compound is blue Loctite 242.
You must glue your tires to their wheels. Without gluing, you will lose speed as the drive wheels slip within the tires, and you will lose control as the tires come off the wheels due to forces generated in hard cornering.
It pays to do a careful job of the gluing. You want the tire/wheel assembly to run true and you want the job to be strong. The fussy-sounding procedures below are designed to meet these goals.
First, examine the mounting surfaces of the tires and trim away any excess rubber with sharp scissors. This permits the tires to sit down straight and true on the wheels. Examine the tire bead mounting areas of your wheels for gluing holes (provided on Losi wheels); if not present, drill four holes evenly spaced around the rim from the tire bead mounting area through to the other side of the wheel. Next, clean the mounting surfaces of the tires and the wheels with rubbing alcohol. This removes any mold release agents from these surfaces and allows the glue to work its best. Then mount the tires on the wheels, and get them true. One way to get them true is to hold a mounted tire between your hands, press in slightly, and spin the tire back and forth with a rubbing motion. Do this a couple of times, shift the tire 1/4 turn, and repeat four or five times. You can check the trueness by mounting the wheel on your car and giving it a spin.
Use a thin CA glue (e.g. thin Pacer Zap, Hot Stuff, blue Goldberg Jet). A narrow tip applicator makes the job easier. Apply the glue to the mounting holes for one tire bead and rotate the wheel to work the glue around the wheel. Let the assembly sit and dry before doing the other bead.
It may not be strictly necessary, but I like to glue the tire to the inner and outer rims of the wheel also; this bond prevents dirt from lodging between tire and rim. A thicker CA, with accelerator, works best for this, but thin CA does the job also.
Now your wheels and tires are ready for use. At some point this set of tires will wear out and you will want to replace it. You can remove the tires from the wheels by boiling the tire/wheel assembly for a minute or so. The easiest and safest procedure is to cut the tread surface from the worn out tire before boiling; this prevents scalding hot water from collecting inside the tire, where it might squirt out and hurt you. After boiling, you should be able to pull the sides of the tire from the wheel without leaving any rubber behind. You will leave some glue behind; clean this off completely with a small file before mounting the next set of tires.
As a beginner, if you aren't skilled in soldering, you can get someone who is to help you. But even better is to get someone to teach you, and spend some time practicing. You'll be soldering whenver you install new motor brushes or buy a new motor or battery (assuming that you follow my advice and junk the Tamiya battery connector.)
Here are a few basic tips on soldering:
Heat-shrink tubing can be applied over solder joints for insulation and finished appearance. Use heat-shrink in preference to electrical tape - it is more permanent. To shrink the tubing, hold a hot soldering iron close below it or a match farther below it.
You will see advertisements for nifty temperature-controlled soldering irons. Unlike regular soldering irons, you can leave a temperature-controlled iron hot all the time while you are racing, so it is ready the moment you need it. (Leaving a regular iron on without using it for long periods of time will greatly shorten its life.) The drawback of the temperature-controlled soldering iron is cost -- roughly $100. And soldering irons don't last forever, especially when you are carting them back and forth to the race track. You will be better off spending the money on something else -- like high-quality connectors that reduce the need for using a soldering iron.
The capacitors you use on your motor depend upon your speed control, not upon your motor. The packaging on your motor may say that it is "ready to go" but that's nonsense because different speed controls require different capacitors. The instructions to your speed control will explain what types of capacitors to use on your motor. In most cases you need three capacitors: one from the positive terminal to the can, one from the negative terminal to the can, and one between the positive and negative terminals. In general the higher the frequency of your speed control, the smaller capacity you need between the positive and negative terminals.
It is conventional to orient the motor so that the positive terminal (marked on the endbell) is at the rear of the car. (I have no idea why this is, but it is.) Mount the capacitors on top of the motor in this orientation so they are less likely to be scraped off in a collision. Keep the leads short and neat.
Some stock motor cans are finished with a powder coating or with paint. You need to remove this finish in two spots in order to solder the capacitor leads to the can. A small file is the best tool for the job, but a hobby knife will do if you are persistent. You need to expose clean bare metal for the solder to stick.
There is a standard three-wire interface between receivers and servos (also receivers and speed controls): +5 volt power, ground, and signal. This receiver wiring harness originates in the servo (or speed control) and plugs into the receiver. But there is no standard for the colors of the three wires, their arrangement in the plastic connector body that plugs into the receiver, or the shape of the plastic connector body.
Novak and Tekin have dealt with this situation by providing the necessary plastic parts and instructions for converting the receiver wiring harnesses of their speed controls to work with all common receivers (Futaba, Airtronics, JR, and KO). The conversion is simple and takes only a couple of minutes. Similarly, while Novak and Tekin receivers are designed for Futaba connectors, they include plastic parts and instructions for converting the wiring harnesses that plug into the receivers. You can buy these plastic connector shells separately, e.g. Tekin "Universal Servo Plug Connector Set," part #UNV005.
The servo manufacturers (all of whom make receivers) aren't so helpful. If you buy a servo from one manufacturer and a receiver from another (other than Novak and Tekin), you'll need help doing the wiring harness conversion.
Here is a key to the wiring of various servos:
Futaba: Black (-), Red (+), White (signal)
Airtronics: Red (+), Black (-), White (signal)
JR: Brown (-), Red (+) Orange (signal)
KO: Red (+), Black (-), Blue (signal)
(JR wins the non-conformist prize for choosing Brown for the ground wire!) Thus you can plug a JR servo directly into a Futaba receiver, but you must reverse the power and ground wires on Airtronics and KO servos before plugging them into a Futaba receiver or you will fry the servo.
Some servos are called "standard" but there is in fact no standard for the size of servos or for the locations of their mounting ears. (Just for fun, servos also differ in the number of splines on their output shafts!)
The Losi XX and XX-T have a beautifully-engineered servo mount; its only drawback is that to use it you must first grind off the lower mounting ears of your servo. No matter; two mounting ears are plenty.
The older Associated cars and trucks come with servo mounting posts. These posts work fine, but you are responsible for drilling holes in the posts to suit your servo. In some cases you'll need to drill holes in the chassis as well.
When using the large Kimbrough servo saver you will have to either slot the chassis or space the servo up off of the chassis to prevent the servo saver from rubbing on the chassis.
It is quite common to mount the servo using servo tape, a thin foam double-stick tape. Servo tape is not quite strong enough to keep the servo from squirming around while it is in use. This squirming makes steering slower and less precise; in time, the servo will come loose. Therefore it is common to augment the servo tape with a small bead of shoe goo, joining the servo case firmly to the chassis. To remove the servo you cut, chip, or peel off the dried shoe goo. (Not a fun job.) This style of servo mount is used on many Associated cars and trucks.
Receivers and speed controls mount easily to the chassis or shock tower using servo tape. Your kit instructions should give tips on the best mounting locations. Some recommended locations may rely on being able to run the speed control's receiver wiring harness under the battery to reach the receiver. If you are using stick type battery packs (cells oriented with the long axis of the pack instead of running across the pack) then to run wires underneath you will have to raise the pack. One way to do this is with a layer of servo tape, cut out where the wire passes through, and all covered with a layer of duct tape. To avoid this mess you may decide to mount the speed control on the shock tower (recommended on Losi) or the receiver and antenna tube on the shock tower (recommended on Associated). The receiver and speed control are light enough that mounting them on the shock tower doesn't raise the car's center of gravity very much. Never extend the speed control's or servo's receiver wiring harness in order to solve a mounting problem.
Tekin and Novak speed controls have an on-off switch. The standard mounting location for the on-off switch is on the rear bulkhead or transmission case right behind the rear shock tower. This is a good location because the switch is unlikely to be bumped or covered in dirt. If you can't reach this location with your switch, improvise. Tekin switches have ears for mounting with tiny screws; you mount Novak switches with servo tape and shoe goo or with a small cable tie.
Painting can be more time consuming than all the rest of the assembly. If you want a durable, distinctive, and attractive paint job, it probably will be. Set your expectations accordingly.
Trim the body completely before you paint it. This includes cutting any mounting holes and the hole for the antenna straw. Place the body on the chassis to ensure that you've provided clearance for the shocks, suspension, and steering. If you try to trim after painting you are likely to mess up your paint job.
You can trim the edges of the body most easily with a pair of short, stout scissors. Failing this, use a sharp Xacto knife, but go slowly. Start holes by rotating the point of a sharp Xacto knife, using slight pressure. The best tool for enlarging holes to their final size is a Dremel tool with a tapered steel or abrasive cutter, or a tapered hand reamer. Lacking these, use a set of graduated drill bits, rotating them by hand to keep them from grabbing and tearing the plastic, or use the sharp Xacto knife with great patience.
After trimming, clean the inside of the body thoroughly. Though it seems barbaric, I prefer to clean the inside of the body using extra fine (400 grit) wet-or-dry sandpaper, used wet. The scratches produced by the sandpaper are invisible once the body is painted and they help the paint bond to the plastic. Don't sand areas that are to remain clear, e.g. windshields and windows.
Next step is masking. The body may include masks for the windows; apply them first. Then, for a two-color paint job, mask to completely cover the area that will be painted the lighter color. Use a high quality masking tape, such as 3M, and press the edges of the tape down firmly with the back of a fingernail to make it more difficult for paint to seep under the tape.
You can paint with an air brush, a spray can, or a bristle brush. Brushing (air or bristle) gives the widest choice of colors -- you can mix your own. A bristle brush gives a heavier job, which is not an advantage. Most people go with the spray cans.
Some keys to spraying success are:
As noted earlier, the solvents used in paints that stick to polycarbonate are quite bad for you; follow directions by spraying outside or in some other well-ventilated area.
When you are done painting, and the paint has dried thoroughly, reinforce the high-stress areas of the body from the inside with RTV adhesive. High-stress areas include the body mounting holes, slots where the shock towers come through the body on a buggy, and sharp corners such as the bottom rear of a truck's cab. A little RTV adhesive applied where the body rubs on the chassis can keep the paint from wearing through in these places.
People have some truly amazing ideas about breaking in motors. Fortunately, breaking in motors for off-road is very simple:
All that motor break-in needs to accomplish is to remove any burrs or rough edges on the brushes before you run the motor under load. Break-in does not need to achieve full contact between the brush and comm. The first time you run the motor under load, the intense heat at the brush-comm interface will quickly give full contact.
Some specialized break-in techniques are marginally useful in some special competition situations, but the procedure above is all that an off-road beginner needs to think about. Spend your time driving!
If you've bought a peak charger, congratulations! Just follow the directions.
If you've bought a timed charger, you will need to be very systematic about charging and discharging your batteries, or you will ruin them in short order. Here's what to do:
Now you appreciate why peak chargers are worth the extra money.
Don't charge a battery when it is hot from being used. Wait for it to cool, using a fan if you want it to cool faster.
If your R/C car is turned on but no transmitter is turned on to tell it what to do, it will go wild (unless it has a PCM receiver with fail-safe turned on.)
Thus to run your car, turn on the transmitter first. Then turn on your car (with the on-off switch or by plugging in the battery.)
To finish a run, turn off the car first (with the on-off switch or by unplugging in the battery.) Then turn off the transmitter.
Don't run your R/C car until the batteries are completely dead and the car stops. This isn't good for the batteries, and you risk losing control toward the end and having the thing run off the track and get run over, or whatever.
When you feel the car lose its punch, it is time to bring it in and shut it off. On that final lap, just nurse it along, don't yank the throttle.
R/C transmitters operate at low power (one watt or less) on assigned frequencies. The range of a transmitter is a few hundred meters at most. Of course, your 1/10 scale car is pretty much invisible at a distance of a hundred meters so this range is ample.
When two transmitters operate in the same vicinity on the same frequency, they interfere with each other. A receiver can't untangle the signal coming from its transmitter from the signal coming from the other transmitter. Result: the car goes wild (unless it has a PCM receiver with fail-safe turned on.)
If you are out running in the street with friends, you prevent this by talking to your friends and making sure that you don't have any frequencies in common. (Actually, it is best to sort this out before your friends buy their radios, so you can all run at once.)
If you are running at an organized track, you use whatever form of frequency control that track employs.
The most common form of frequency control involves clothespins (not very high tech.) The track has one clothespin for each frequency: 1-6 on 27 mHz and 61-90 on 75 mHz. Before running you go to the board with all the clothespins clipped to it, find the pin with your frequency number, attach the pin to your transmitter, and go run. If the pin is gone you go find who has it, wait for this person to finish, and get the pin from him or her. When you are done running you return the pin to the board.
People will get justfiably mad at you if you break the rules, turn on, and wreck somebody else's car. So find out what the rules are and follow them.
This isn't the place for a treatise on R/C race-car driving. But here are a few notes on getting started:
After each run you should clean the dirt off of the bottom of each shock, where the shaft enters, using an old toothbrush. This will make the shock seals last a lot longer between rebuilds.
If you are running a stock or other bushing motor, put a drop of oil on each bushing before running. If the endbell bushing has accumulated dirt then brush the dirt off before oiling. Let the motor cool down between runs. Put comm drops on the brushes just before the next run.
How clean you keep the car is up to you. If you keep the various suspension hinges clean they will last longer, but if you'd rather spend time driving than cleaning that's your decision. At some point the suspension will start squeaking and feeling sticky, and this will make the car handle worse.
Every so often you should just strip the car down, spray out the ball bearings with motor spray, clean everything else with soap and water, replace the parts that are badly worn, and put the car back together again. This will make the car work like new.
Your motor has overheated if, after a four minute run, you can't hold your thumb on the motor can for five seconds. (Don't burn yourself!) An overheating motor will not last long -- the commutator will distort out of round, the brushes will wear quickly, and performance will take a quick nosedive. The motor may even fail completely due to an internal short.
Overheating is either caused by overgearing -- too large a pinion or too small a spur -- or excessive friction in the car's drive train.
Gearing is always relative to both the course and the driver.
A course with slow corners and short straights requires a smaller pinion than a course with sweeping turns and longer straights. If you are just playing around with your car, it is very easy to overheat the motor by making tight slow turns and then yanking the throttle. Set up a course that involves some sweeping turns and longer straights. Go easier on the throttle, or use the current limiter if you have one. If this doesn't do it then buy a smaller pinion.
On the same course a better driver can run a larger pinion than a poorer driver, because the better driver carries more speed through the corners and doesn't have to accelerate from such a low speed. The better driver also uses part throttle early in acceleration rather than yanking on the trigger instantly. If you have an adjustable current limiter on your speed control, you can turn the limit down to keep the motor cooler by simulating this driving technique.
Check the friction of your drive train by first holding one rear tire and spinning the other. If the pinion gear is mating too tightly with the spur gear, you'll be able to feel and hear it; loosen the mesh. No spur gear is perfectly round; rotate the gear and make sure there is a little free play even at the tightest point. Next, remove the motor and spin both rear tires. The spur gear should move freely and coast to a gradual stop. If not, it is time for transmission disassembly, cleaning, replacement of bad gears and bearings, and reassembly. Now that the motor is out of the car, remove the motor brush springs. Spin the motor's armature by spinning the attached pinion gear. The armature should spin freely, but not for long because of the magnets. If not you have some cleaning to do. If the motor bushings are badly worn you need a new motor.
Don't forget to check the front wheels for free-spinning operation as well.
The gear ratio of your buggy or truck is simply the number of times the motor shaft must turn in order to make the rear wheels turn once. The gear ratio affects the acceleration and top speed of your buggy or truck. The larger the gear ratio, the quicker the acceleration (assuming sufficient traction) and the slower the top speed.
One reason for understanding how to compute and use gear ratios is that some motors you buy come with gear ratio recommendations that are a good starting point when dialing-in. Another reason is that you may be new to a track and get a gear ratio recommendation from somebody who is experienced at that track and running a similar motor and similar diameter tires to the ones you are running; if that person is running another brand of car, you'll probably need to run a different size pinion to get the same gear ratio.
To figure your gear ratio you need to know the number of teeth on your pinion gear, the number of teeth on your spur gear, and the reduction of your transmission. Here is a table giving reductions for a few common trannies:
Losi XX buggy (XX, XX buggy retro) 2.19
Losi XX truck (XX-T, XX truck retro) 2.61
Losi LRM (Jr-2, Jr-T) 2.18
Associated Stealth-2 buggy (RC-10B2) 2.40
Associated Stealth-2 truck (RC-10T2) 2.60
Associated Stealth-1 (RC-10, RC-10T) 2.25
Your gear ratio is
number of teeth on your spur
------------------------------ * reduction of your transmission
number of teeth on your pinion
For instance, a Losi XX comes with an 88 tooth spur gear. If you install a 22 tooth pinion you get a gear ratio of
88
-- * 2.19 = 4 * 2.19 = 8.76
22
For reference, here are gear ratio tables for the current Losi and Associated competition kits:
Losi XXT (2.61 tranny) Losi XX (2.19 tranny)
84 86 88 90 84 86 88 90
14 15.66 16.03 16.41 16.78 13.14 13.45 13.77 14.08 14
15 14.62 14.96 15.31 15.66 12.26 12.56 12.85 13.14 15
16 13.70 14.03 14.36 14.68 11.50 11.77 12.04 12.32 16
17 12.90 13.20 13.51 13.82 10.82 11.08 11.34 11.59 17
18 12.18 12.47 12.76 13.05 10.22 10.46 10.71 10.95 18
19 11.54 11.81 12.09 12.36 9.68 9.91 10.14 10.37 19
20 10.96 11.22 11.48 11.74 9.20 9.42 9.64 9.86 20
21 10.44 10.69 10.94 11.19 8.76 8.97 9.18 9.39 21
22 9.97 10.20 10.44 10.68 8.36 8.56 8.76 8.96 22
23 9.53 9.76 9.99 10.21 8.00 8.19 8.38 8.57 23
24 9.13 9.35 9.57 9.79 7.67 7.85 8.03 8.21 24
25 8.77 8.98 9.19 9.40 7.36 7.53 7.71 7.88 25
Associated RC10-T2 (2.60 tranny) Associated RC10-B2 (2.40 tranny)
81 84 87 90 81 84 87 90
14 15.04 15.60 16.16 16.71 13.89 14.40 14.91 15.43 14
15 14.04 14.56 15.08 15.60 12.96 13.44 13.92 14.40 15
16 13.16 13.65 14.14 14.62 12.15 12.60 13.05 13.50 16
17 12.39 12.85 13.31 13.76 11.44 11.86 12.28 12.71 17
18 11.70 12.13 12.57 13.00 10.80 11.20 11.60 12.00 18
19 11.08 11.49 11.91 12.32 10.23 10.61 10.99 11.37 19
20 10.53 10.92 11.31 11.70 9.72 10.08 10.44 10.80 20
21 10.03 10.40 10.77 11.14 9.26 9.60 9.94 10.29 21
22 9.57 9.93 10.28 10.64 8.84 9.16 9.49 9.82 22
23 9.16 9.50 9.83 10.17 8.45 8.77 9.08 9.39 23
24 8.78 9.10 9.43 9.75 8.10 8.40 8.70 9.00 24
25 8.42 8.74 9.05 9.36 7.78 8.06 8.35 8.64 25
You shouldn't use the same gear ratio on a truck and a buggy; the truck needs a larger ratio because the truck motor must turn a tire with a larger diameter and accelerate a heavier vehicle and a tire with a greater moment of inertia. A rule of thumb to convert between a buggy gear ratio and a truck gear ratio on the same track with the same motor is to multiply the buggy gear ratio by 1.3. So if you are running a 22 tooth pinion on a XX and want to compute the corresponding pinion size on an XX-T, you'd figure it like this:
8.76 * 1.3 = 11.38
88 88
-- * 2.61 = 11.38 so PP = ----- * 2.61 = 20.18
PP 11.38
So you might try a 20 tooth pinion on the XX-T. This is only a rule of thumb but it provides a reasonable starting point if you have no other information in hand.
One possible source of confusion about gear ratios: When somebody tells you to "gear up" they mean to use a smaller gear ratio, i.e. a larger pinion.
All competition buggies and trucks have transmissions equipped with a slipper clutch. On a transmission without a slipper, the spur gear is keyed directly to the top shaft of the transmission, which drives the rear axles through a gear train and ball differential. On a slipper-equipped transmission, the connection of the spur gear to the top shaft is made through an adjustable friction coupling that allows some slippage.
The slipper, used correctly, both improves performance and reduces wear and tear on the transmission:
The slipper is a fussy topic. It takes awhile to learn when to loosen the slipper and when to tighten it. Most beginners set the slipper too loose, which makes the car easier to drive but slower overall.
Before you start adjusting the slipper, you must double-check the diff adjustment. Remove the gear cover. Tighten the slipper all the way so it won't slip. Hold both the spur gear and the right rear tire with your right hand, and try to turn the left rear tire with your left hand. It should be quite hard to turn. If the left rear tire turns with moderate effort, with the transmission top shaft stationary as the left rear tire turns, tighten the diff and repeat.
Now loosen the slipper adjustment a few turns, hold both the spur gear and the right rear tire with your right hand, and turn the left rear tire with your left hand. It should not be extremely easy to turn the tire, but not be extremely hard to turn it, either. Fiddle the slipper adjustment to get it into the right ballpark.
Now put the car on the track pointing toward you. Press down on the car and punch the throttle on-off. Listen to that sound -- that's the slipper slipping. Feel how much forward drive the car has. If the forward drive is weak you need to tighten the slipper.
Keep the car on the track pointing toward you. Back away a couple of feet and punch the throttle on until you catch the car. The slipper sound should last only for about a foot -- it should stop before the car reaches you. (It takes practice to hear the slipper sound among all the other sounds, especially the sound of slipping tires.) If it slips more than this, tighten the slipper; if there is no slip at all, loosen it.
Go out and drive the car. If it is working well, bring it in and feel the adjustment again by turning the left tire. Learn how hard the tire is to turn. This will help you get closer to the right adjustment next time you have to adjust it from scratch.
The Team Losi Hydra Drive slipper incorporates a small torque converter (like the hydraulic clutch in an automatic transmission) in addition to the conventional friction slipper. The torque converter allows the friction slipper to be set very loose, yet maintain good acceleration. The benefit is even better handling on rough tracks and big jumps; the drawback is a slight loss of acceleration with stock motors on tracks with good traction. You can remove the Hydra Drive and use the friction slipper alone if that works best (not likely if you are a beginner.) Hydra Drive is very user-friendly in that the adjustment is less sensitive than a friction slipper. You make major adjustments by swapping the torque converter for another one with lighter or heavier fluid inside. The Team Losi instruction manuals contain a full description of how to adjust the Hydra Drive. Hydra Drive can be retrofitted to Associated cars and trucks; Brian Kinwald used one in his 1993 off-road world championship winning RC10.
The speed control performs braking by making the motor run as a generator. Some high-frequency speed controls actually charge your batteries during braking. You adjust the brakes when you are adjusting the transmitter and speed control.
On pistol-grip transmitters, you push forward with the trigger finger to apply brakes. This forward push is much less sensitive than the pulling motion used for throttle control. In effect, you have an on-off control for brakes unless you are very talented with the trigger finger. (Stick transmitters are better than pistol-grips in this regard.)
The other adjustment at your disposal is how much braking, if any, is applied when the trigger is at its neutral point (i.e. finger off the trigger.)
My advice is to adjust the transmitter and speed control for little or no neutral braking and moderate push braking.
The amount of braking you have at neutral affects the way your car enters turns and goes through them. More braking transfers more weight to the front tires and allows you to turn more, which sounds good at first. But too much braking causes the car to spin out unpredictably as it enters turns. Too much braking also slows the car down before it finishes the turn, so you have to get back on the throttle. When you get back on the throttle the weight transfers off the front and the car steers a wider arc. You will be faster with a smoother turn that carries more speed all the way through. So you see that a balance is needed in the neutral brake adjustment, and this balance may depend upon the course you are driving. Most top drivers today dial in no neutral braking at all on a typical off-road course.
Push brakes are useful in order to slow down before turning into a tight corner. You want to brake while going in a straight line, then let off the brakes and turn in. If you turn while braking the rear end will skid, which may get you turned around quickly but is difficult to control lap after lap. Adjust the push brakes to slow the car as fast as possible without locking up the rear wheels.
Brake adjustment depends on the motor you are using, because motors have different amounts of inherent braking. A stock motor may have a lot of inherent braking (due to its large timing advance, heavy springs, and bronze bushings) so you get significant braking without dialing in any brakes. With a modified motor you might have to dial in a some brakes to get the same effect. If you run the same car in stock and modified and forget to make this adjustment, you are likely to be disappointed at the results.
First of all, don't overheat the motor. See the comments above about overheating.
Secondly, make small changes when gearing up. If you make a big change you are likely to cook your motor. Add one tooth to the pinion, two only if the motor was *really* cool the last time. Don't change the spur gear unless you have maxed out the pinion (e.g. 26 teeth for 48 pitch gears).
Thirdly, get somebody to time your laps with a stopwatch. Change the gearing and do it again. Compare the typical laps from each run -- not the fastest laps. Choose the gearing that makes your typical lap the fastest, while not overheating.
What I've described here is a procedure for a perfectionist. Usually you pick a gear ratio that's easy on the motor and gives competitive performance, and spend most of your time working on other things, like tire or suspension tuning and getting enough practice time to master the course.