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Too often those who have not seen or have ignored the truth, will preach their favorite gospels on repowering locos. The mysteries, miracles and wonders of can motors, flywheels, "humpers" and DCC are praised by evangelists on every pulpit, but on what basis. There are no secrets in simple physics, only facts and dubious conclusions drawn from them. Before digging in, throw away any preconceived ideas derived from magazine reviews or other sources, unless they clearly state the methods used to derive and evaluate the parameters presented and they can be deemed valid by duplicate testing. MR references an average steam locomotive with ridiculous graphs, based on similar locos they have tested recently. What is an average steam locomotive? Comparing it to data I have collected over 40 years, including many locos which they have reviewed, it does not represent anything close to an "average". In statistics average is a dirty cover-up word. What range does similar cover? How far back does recently go? How do they measure drawbar pull (starting tractive effort) and speeds accurately? They claim to use a "professional" strain gauge, but how? How does one duplicate the test? What methods are used to measure speeds. In a recent review, a $500 loco had a starting voltage of 9V and a control range of 3V without reprogramming. Why didn't the "experts" reprogram it to the lowest possible point to provide more useful data? The only fair way to evaluate locos is with a well filtered DC power supply to reveal its true characteristics and not those of a particular decoder board and supply. Apples and oranges? Or is everyone required to use DCC because it is heavily advertised. Possibly a comparison could be made with and without a DCC module to reveal the truth. For the type of loco in question, you can develop more believable data yourself, by simple testing of the important parameters for your mode of operation of it. A knowledge of the prototypes characteristics is helpful during this process. Before any analysis, the loco must be thoroughly TESTED, LUBED AND RUN-IN . The performance may change drastically from before to after. The data collected and recorded will serve as reference for later analysis, comparisons and decisions. To get some feel for the locomotive's performance and for comparison, some basic tests should be made. First measure the no load or deadhead SPEED and current at 12 v with good METERS. Then determine the starting and the lowest smooth operation voltage and speed. Next load it with the heaviest train you plan to run and repeat measurements. If possible, add enough cars to simulate your maximum grade and repeat. Or better, test on the grade itself. As discussed in the main article, the maximum deadhead speed should be at as close to 12v as practical to utilize maximum range of throttle. Although not quite as critical, except for bragging purposes, the low end speeds should be at the lowest voltages practical to increase throttle range. As opposed to the inconsequential motor startup voltage, locomotive and train values depend on the torque delivered to the drivers. Higher gear ratios increase driver torque at all levels thus lowering startup voltage and slowest smooth operating speed. At lower speeds, motor RPM is higher, reducing cogging effects and the need for skewing, plus improving flywheel momentum. Only a good match between the motor and gearing can optimize this. To determine the effectiveness of weight; at 12 V, measure the current at which the drivers just start to slip, by keeping the loco immobile while avoiding any downward force on the drivers. If possible find the DRAWBAR PULL . Traction, OE's and GE's usually do not require drawbar attention unless pulling trailers. For optimum performance, current should approximate but not exceed motor's rated continuous current. Unfortunately, at present, no usable dynamometer car is marketed to measure drawbar pull, while running at speed. A few years ago, the "great" Walthers promised a digital readout for their offering. But after suckering in many, they quietly reneged. The dial indicator track fairly well, but is almost impossible to read, while in operation on track. This beautiful, but almost useless, car has been "retired". Evaluate the characteristics. Probably the most important factor for road locos is the ability to pull trains at correct speeds on the line. Slow speed is only important in starting and stopping smoothly. While for switchers, slow speed is all important, throughout operation. Controlling the speed easily is just as important, if you plan to operate prototypically. Often the power supply is at fault. The output voltage of inexpensive rheostat throttles is very sensitive to load current. As train load increases, more motor torque is required, which in turn requires more current. This lowers the voltage and slows the train, sometimes very unrealistically. Even some solid state throttles have internal resistances, which produce similar results. The performance of throttles, including DCC, should not be overlooked. At this point you may decide that no modifications are necessary. But if some factor should be changed, more data will be needed. Insufficient draw bar pull is one of the most common faults. As suggested in the main page, check the easier corrections, such as balance and truck springing. To be on the safe side, before adding weight, find the maximum continuous running current of the motor. The maximum weight added should permit driver slippage at this value. To test, partially fill a small, sealed plastic bag with B-B's or shot and drape it over the shell near the driver center point. Adjust to the proper weight, then weigh. Check the drawbar pull with the added weight to determine if it is sufficient. If train slows excessively or stalls on up grades, you may want to use a motor with more TORQUE , or power, a higher gear ratio or both, in order to use additional weight. Before deciding, examine and measure the cavities for possible insertion of weights, considering balance on the drivers. Several smaller pieces may be distributed throughout. They may be fitted in smoke boxes, in or under cabs, under cover plates and under or over motors. Lead is about 1.5 times the density of steel, brass or zamac and easily sand cast or shaped to fit cavities. Patterns can be made from wood or molding clays. BEARMETAL, from Bear Locomotive Co., an alloy that melts at 158 F., can be poured in with care. Remember to test the balance. To adjust speeds, torque or mousepower more data is needed. First measure driver diameter with good calipers or micrometer. Stated or expected values may not be correct. Next find the gear ratio. Count teeth, if necessary. Then, using measured on-track speeds, CALCULATE MOTOR RPM using the equation given and the program, if possible. Examine the GEAR FUNCTIONS including torque, RPM and power. You now have all the parameters to analyse the situation. Compare what you have to what you want, speculating on possible changes and search for solutions. View the problems and solutions as a whole, including motor, gear train, and power supply limitations. Base your new MOTOR EVALUATION on true data and not hype or hearsay. Especially in remagneted motors with neodymium (NdFeB), there are many surprises in motor comparisons. Recognize your limitations and the market's. Parts may not be available. Installation may be beyond your ability or tools. Compromises may have to be made, but any improvement is better than none. An Athearn S-12 with an old motor hits 160 SMPH and the desired speed is about 40. Installing a new version motor would bring it down to, a still too fast, 110 SMPH. With drivers close to 42" and a gear ratio of 11/1 the motors turn at about 14000 and 9700. The required motor should turn at about 3500. No reasonable motor replacement exists. An Ernst regear kit yields a 3/1 reduction to produce about 53 or 36 SMPH respectively. Either might be acceptable and require only standard hobby tools. An MDC old timer consolidation had a speed of about 65 SMPH, a gear ratio of 66:1 and a motor RPM of about 29000. Using a NWSL regear kit with 72:1 ratio the speed was lowered to about 60. Just replacing the motor with a NWSL Sagami 10153 at about 14000, produces a more believable speed of about 31.5 and 28.9 with the gear change. The motor fits nicely and can be applied to the HOn3 versions. A Bowser L-1, with a DC-71, 62" drivers good power and 29:1 ratio, runs at 90 SMPH has a motor RPM about 14000, while the desired speed is about 62 . A motor of 7800 RPM would be required. Can motors of the same mousepower do not fit in the cavity or over the drivers very well. A NWSL 40:1 gear change with remounting of the motor at new angle yields 65.2, This is closer than you can eyeball. Using a DC-71 with an NdFeB magnet, the RPM drops to about 10500 RPM to yield a speed of 67 SMPH without regearing plus more torque and power. SEE SELECTING GEARS A Bowser I-1 with the same parameters and a desired speed of less than 45 would indicate a ratio of 58:1 requiring double reduction. Since the axle is 1/8" diameter the worm wheel must clear it, possibly limiting the selection of upper gears. SEE OTHER EXAMPLES BACK TO METHODS BACK TO REGEARING BACK TO REMOTORING BACK TO REPOWER |
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