Making a vex compatible motor

I have a project i am working on and i am in desperate need of more power delivered to the drive chain. What i am planning on is using two drill motors which i already have, coupled with an after market PWM motor controller. My question is, would this PWM chip accept the signal from the vex microcontroller? If this doesn’t work, than what PWM chip could i get that would work. The new motors would be drawing in around 15 Amps so i can’t just reuse the original vex motor controller.

Motor Controller

Motor (12 volt model)

Also, i am trying to build this robot on the cheep so this is out of the question

Thanks, Riley

You will not be able to use either VEX microcontrollers as they have self-resetting breaker that limit the output of ports 1-5 to 4 amps, and ports 6-10 to 4 amps. So in other words, if you were to use a 15 amp motor, you will trip the breakers very quickly.

I forgot to add that i won’t be using the vex microcontroller as the power source, just to create the PWM signal. I am planning on using an external 12 volt battery.

Basically this without linking it back to the Microcontroller

wow, now that you mention it, was that before the vex power expander came out? :wink:

I don’t think that motor controller will work “out of the box” for you because it does not appear to be controllable by an RC signal.

The output from the vex controller/cortex is an RC signal which is a pulse that varies from 1ms to 2ms with 1.5ms being “center” or no movement and the two extremes being full speed reverse and full speed forward. Many motor controllers (such as the Victor 833) are designed to use this “protocol” for controlling the motor. They actually have a microcontroller within them that measures the input pulse length and then generates a pulse-width-modulation signal which actually turns the motor on and off at the right proportion to give the speed you’re requesting.

This controller looks like it needs you to directly supply the pulse-width-modulation signal rather than an RC “servo pulse”. Pololu is run by very nice people; I bet if you asked for help on their forum they might have a solution for you (I haven’t looked through all of their motor controllers).

Thanks! That makes alot of sense. So i am looking for a board that runs off of a RC imput? Would one like this make sense?

Thanks for the very helpful post, Riley

Yes, that one should work as long as its voltage and current specs can handle the motors you selected.