Low Buck ESC’s

 I’m always on the lookout for inexpensive, low and moderate current ESC’s with a simple reverse function for my scale model boats. I’ve even built some of my own, but I have a hard time justifying the cost of the components, much less my time, given the current crop of reliable low cost commercial units. 

Here are four units that I’ve worked with. All have their pros and cons, and some may not be suitable for certain applications. For example, 12v systems are common in model boats, in which a 7.2 or 8.4v ESC might not live. 

 Features

Input Voltage & BEC: Most ESC’s get their power from a direct connection to the battery. An internal 5v  regulator supplies power to the microcomputer, and is often used to feed the same 5v power directly to the receiver, eliminating the need for a separate receiver battery pack (battery eliminator circuit, BEC). The microcomputer controls the FET’s, which are special transistors acting as switches between the battery and motor.

PWM Frequency: Unlike a rheostat or old train transformer which supply variable voltage to the motor, ESC’s supply the full battery voltage to the motor. Speed is controlled by pulsing the voltage. The pulses come at a fixed frequency, and are allowed to vary in length from nothing (off) to 100% (full on), and everything in between (PWM, pulse width modulation). The PWM frequency is of interest, because at light load, you’ll hear the motor switching on and off. The Actionkit’s 50 Hz produces a noticeable growl, while the EZX-R’s 1000 Hz makes a whining sound. 

Current Capacity: The FET’s can handle just so much current before burning up. You’re interested in the continuous current rating. “Momentary” or “peak” current rating recognizes that micro- and milli-second length spikes don’t last long enough to generate a lot of heat- but this isn’t an “emergency power” setting that you can run at for any length of time. Better ESC’s have thermal protection circuits that will shut down the unit when temps get out of hand. Heatsinks and cooling air help keep the ESC within operating limits.

  Power Switch: It’s better to use a small switch on the logic (computer) side of an ESC, rather than using a massive switch appropriate for high motor currents to disconnect the battery from everything else. Some ESC’s include such a switch; those that don’t are for systems where you are expected to unplug the batteries after every run.

  Programmable Set Points: A nice feature for tuning the ESC to your radio. You push a button and go through a quick setup routine to set neutral, full forward and full reverse. Once set, the ESC remembers the setup even after power-off.

  Reverse Function: Many low cost ESC’s are designed for car racing, and may have reverse functions that don’t work well in boats. Many allow you to lock out reverse altogether. Some have time-outs on reverse to avoid burning up racing motors, which don’t like going backwards due to their timing advance. Others require a reverse stab to operate a brake, then neutral, and only then allow reverse to engage. Some have fewer/smaller FET’s in the reverse circuit, and have a lower reverse current limit. This may be ok for your boat, but big tugs may want a lot of current both ways.

Scale model boaters want a simple reverse function- hit reverse, go backwards. All of the ESC’s here do just that.

	Msonic4 15   This unit comes from Mtroniks in the UK and is available through Hobbypeople.net. It has a moderate current rating of 15A, and has the nice feature of being waterproof. BEC, 6-12v, programmable, no switch; $39.99
	EZX-R From Hitec, great price at Tower and plenty of current capacity for most scale boats. BEC, 7.2-8.4v, programmable, switch; $34.99
	Condor 10 & Condor 20   A cottage-shop product from ActionKit in the UK, available for 20A, and for a little less, 10A; both as kits, or a bit more preassembled. Uses a small relay for reversing instead of a full complement of FET’s. I’ve been using a 20 in my tug Sanguine for a few years now. 2-12v, no BEC, no switch, autoprogrammable for neutral point only. £20/24
	Airtronics ES-01  The tiny ES-01 is designed for small r/c cars. It’s low rating of 3.6A is suitable for small boats using 280 or smaller motors. I’m using it in a 1:350 plastic battleship with no issues. 6.0-7.2v, BEC, switch; $25.99
	New! Proboat Sold by Horizon as a spare to the Riptide personal watercraft. This looks like a winner! Inexpensive, big capacity, wide voltage range, autoprogrammed setpoints, waterproof. Weighs in at 89g (about 3 oz), so not a good candidate for miniature models.  I haven't used one of these, but I keep hearing good things about it. 6-12v, switch, waterproof, $39.99

 Pat Matthews, updated 12/2004

Pat's Pages- more r/c stuff!