Let's Make Robots!

Motor control




I'm building a robot based on my old RC-car and an arduino. The motor-control in my cars is "mechanical" where a servo switches the motor on/off etc. I would like an electronic motor-control instead...and i'm pretty lost.

Do you know a simple motor-control that will make the motor go forward,  just for a start? ;)

I think my motor draws a lot current so L293D is out of question..


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I am originally from Kansas... WFO means "Wide Fuckin' Open"

As in:

"Damn boi, we sure did run a gud race out 'dere... Damn right, we we're out 'dere runnin' WFO da hole race."

This is good profile material Chris! Should clear up a whole lotta questions in the newbies' minds!


If this is a bigboy RC, I would think twice before measuring the current draw with a multimeter. Many of them wouldn't handle this amount of current, check the meter spec first! Some are 10Amps max and I've seen some good for only 2Amps.

 Thats how I got my first multimeter :) Friend of mine tried to measure the current draw on his car headlights, >poof< magik smoke all gone :(  He had to buy a new meter. I got his old one and fixed it :)

Seriously, if you are looking for a bang-bang system (full-on, full off) you really just need a relay. One 15amp relay and a single NPN switching transistor to click the relay on and off. Again, we are talking about the motors WFO.

If this seems right, I'll draw you a diagram, it should be super simple

Tell me again, what is wrong with the servo throttle? --You arduino will run a servo, no problem. --If it ani't broke, don't fix it.

if a PWM is just a squrewave couldnt you use PWN with a relay and get the same effect, since the relay is just translating the PWM into a mechanical action which will produce a square wave on the other end, it works in my head but dont know if it will work
Relays have  a mechanical limit to their switch rate, guessing in the 100s of hertz. PWM rates for motor speed control is best when getting beyond the electrical time constant of the motor, and usually good to get out of the range of human hearing, so 20 kHz is a good start.

i think if you use the solid state relay (SSR) which you want the photo-coupled one ...which should handle higher frequency output

the only issue i see is they can get quite expensive

#rik: I don't have a multimeter. Anyway, The car runs about 30 km/t on a 9,6 battery pack?

#Chris: Lots of guesses. Heres a few answers :) The car was proably about 200 $. runs on a 9.6 batterypack. My new battery pack is ni-mh, dunno if the original one was ni-cd

100 bucks semms like a lot!? I don't need a speedcontrol, just a small circuit that will turn the motor on/off with HIGH/LOW pin voltage from arduino.

I have seen all the motor-driver designs at LMR, but i new to electronics and they are too advanced at the moment.




How about relays like the wall racers rather than PWM. That should be cheap.


Mike: thanks i think i'll try relays.

Chirs:Theres nothing wrong with the servo throtle, I just thinks it's odd that i need a servo to turn the motor on/off.

i'll try to make the diagram, When i'm stuck ill post again ;) What is WFO btw?


Thanks for the quick replies!