Making an ESC... - RC-Monster Forums

BrianG · 12:37 AM

I've been reading up A LOT on how servos work for an electronic project I've been working on and realized a simple brushed ESC can be created with just a few dollars and an old servo that has broken gears or motor.

Generally speaking, the circuitry in a servo is simply a speed controller with feedback. The tiny servo motor moves according to the transmitter until the feedback potentiometer tells the circuitry that the motor is in the right position and stops powering the motor. If you remove the feedback, the output of the servo circuit (the motor) stays on until the transmitter is back to neutral - thus becoming a simple speed controller. The output is of the circuit is a varying PWM signal just like the big boys so the speed is variable.

The purchase of a couple inexpensive of MOSFETs and a little soldering on a PCB should work quite nicely. Just replace the feedback pot with a slightly different resistor/pot setup to fine-tune the "off" position. MOSFETs can be purchased for a dollar or two that can handle a LOT of current and voltage. Plus, being MOSFETs, they have high input impedance, therefore easy to use.

Specifically, the servo circuitry I've used is based on the M5166OL IC chip, which is commonly used in servos to translate the 1-2ms pulses from the receiver into something usable.

Anyway, if anyone is more interested on the subject, I can elaborate on the theory and electronics involved...

squeeforever · 01.15.2006, 12:49 AM

what about a brushless esc? and what kind of price, cell count, and motor limit on these homemade esc's?

BrianG · 01.15.2006, 12:56 AM

Well, a BL ESC is a different animal altogether since it is a three phase system. Some of the circuitry is the same (the part that takes in the channel pulses and converts to something usable), but the rest is different.

The current capacity is limited by the number of MOSFETs you use in parallel and wiring. Some MOSFETs handle more than 100A in one package. However, you still want to use several to reduce the internal resistance and to distribute the load. The number of cells is determined by the voltage rating of the MOSFETs used. 50v is a typical value. Since the controller part of the circuit is powered by the +/- wires from the receiver, that voltage will only go to the motors.

Serum · 05:40 AM

I've got a PCB layout for a BL esc.

It is not only about the current the mossfets can handle, it is about the speed they are able to put the signal on. It is a 90 degree pulsangle, so the faster it responds, the more efficient it will be.

this might be a usefull thing.

BrianG · 01.15.2006, 08:12 PM

The document is quite interesting - It makes you appreciate how much technology and work goes into a BL controller!

Yeah, rise-time (or slew rate) is a factor, especially for greater efficiency of the circuit.

My idea with the servo is really only useful if you have a broken one laying around, otherwise it would be simpler to just use a real controller. It was just the product of a little tinkering around...