Hi
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..
step 1
Put some numbers to your guesses. Can you measure how much current these motors draw? They will draw the most when they go all out while you hold (stall) them.
Knowing the max current will help you decide which motor control method to chose. And will help us advice you.
8ik
How fast is the RC car?
I would assume that this is a big-boy rc car (the kind that is like $200 or so) with a very big drive motor. I would also assume it is a big 7.2 or bigger ni-cd pack. Still more, I’m gunna guess you are probably in the 20 amp draw range. This is about the same as the motors I am using to drive my robot. I have to be honest with you, if indeed your motor is in the 20 amp range this is going to be a minimum of $100 bucks --If you can etch your own board. Off the shelf, you are looking at about $200. I would search big motor dirver here and there is a ton of info to go through. – good luck
RE
#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.
Cheers
How about relays like the
How about relays like the wall racers rather than PWM. That should be cheap.
Mike
Well this will be cheap then…
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 this is a bigboy RC, I
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
RE
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!
alert tha newbies
This is good profile material Chris! Should clear up a whole lotta questions in the newbies’ minds!
I think you may want to
I think you may want to start liking that "servo"-thingey. I think it may be quite an expensive motor-controller, PWM-controlling the speed. These are vey nice, much nicer than relays for something like this.
Yiou should post some pictures
I tried RC-car yesterday -
I tried RC-car yesterday - full speed is way too fast indoor! Maybe i’ll use the servo throttle anyway.
Otherwise i’ll get another motor, possibly the tamiya double gearbox (http://www.hobbytronik.se/product_info.php/cPath/41/products_id/159). Do you have any experience with hobbytronik? seems cheap
I will post some pics, when its done So far i have finished servo control and the sonar + a very simple navigation program.
if a PWM is just a squrewave
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
Not fast enough
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
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
