Let's Make Robots!

Motor driver

Well.. Ever since I found this page (through ing.dk) I've been dying to build my first robot.

I have bough all the parts I need, and i've been trying to modify an RC toy car, but i have blown up the motor driver in it :D. I tried with the 293D, but it couldn't take the current. So right now i'm just stuck...

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

It's really close.  600 mA continuous for the L293D and 1A for the L293.  The sn754410 is pin for pin compatible for the L293D, just a bit better at 1A.  Yeah, you can do the same thing with them.

Just a quick thought... (and I know you are pretty far already going in the relay direction, but...)


When I started playing with pics and toy cars, I found it a lot easier to hack into the remote and add a brain there. All the electronics stayed the same on the car and the remote/ brain just tagged along riding on top. This arangement is quite bulky, but it worked great for me and solved a lot of problems -like coil steering.


Again, just a thought --Good luck my man. 

www.rocketbrandcustom.com baby!!


4 relays: http://picasaweb.google.com/fritslyneborg/WallRacers

2 for on/off, 2 for reverting current. Only question is how much pover you can put into your coil before frying it. But start with a lot of resistors, and take them out / reduce till it reacts the way it used to do - that would be my aproach :) 

I totally agree with you Fritz! We would miss out a lot of god robot knowledge if we were jabbing along in danish.

 Now to the moto driver:

I found 2 Omron relays laying around, so I tried to make something out of them. I have now got I functional relay-H-bridge:


I'm very excited! But then again... It's not much fun with a robot that only is able to drive back and forth.... I've taken a look at the electronics that originally was in the car, but i can't really get the transistors to work as a H-bridge. I think the only way to get the steering coil going is using an H-bridge, is that correct? What did you use for your Wallracers?

It would probably be a bad idea to hook it up directly to my Arduino board :b


Dennis L

Thanks for your inputs! :D


When I first tested my brand new L293D, I just hooked it up on the smaller one of my two old toy cars (didn't give it much thought about stall-current etc. :D) and in my eager to get the darn thing to move I blew up the chip (no loud bang or any smoke, so it wasn't worth the effort).


Relays sounds like a good idea. Isn't there a catch (are they expensive/slow?). 

I also considered making something like this with the L298 chip:

Techno Bot motor driver



My two RC cars

After I burned the L293D, I did some readings on my RC cars. It turns out that the small one on the picture uses around 2.12 A when stalled and the big one used around 6 A. What would u suggest I should use to drive the small one (or the big one,just thought to start in small scale).?


Dennis L

A sn754410 should work.  Normally it is used as two separate full h-bridges but you can wire them together into one that handles 2A. For something bigger you might try a VNH2SP30, but for 5+ amps it is usually a lot easier to use a pre-built motor controller.  Good ones should do current limiting so you can safely drive motors with higher stall currents than what the motor controller can output.

That's teh same as the 293 mentioned above, is it not? You can parallel the two channels to get 4A, or something....

Relays, relays, relays!

Current goes straight from battery to motor - the way we want it!

Expensive? No!

Slow? Well - you cannot do PWM (slow down the motor by sending pulses instead of a floating current).. But then again; Yes, you can. Robo-builders are used to PWM being high frequency to simulate analouge voltage-regulation, and not get jerky moves on light stuff with no inertia etc.

You can not make such a vehicle do jerky moves, and so the speed with which you can turn on/off/revert current with a relay is PLENTY fast for this.

I only would whish somebody told me this before I used about a year on trying motor drivers and all other sorts of strange stuff for the quite simple task of having a microcontroller to control an RC.

Relays just work!!

Try something like this for your small car:

http://www.maplin.co.uk/Module.aspx?TabID=1&ModuleNo=37522&doy=10m6 (N18AW)

(you will need 4)


I will definitely consider using relays instead of MOSFET! I will atleast try it out on my first bot, to se how good it works. Then I might try to experiement with a more exotic design of motor driver later.

It's been pretty annoying, that the only thing I really need to make a robot, is to get those darn motors to spin (for more than 10 seconds before blowing something up ^^).

I wonder if these will do the trick?

I think it would be cheaper to buy it locally. Unless I find something interesting and make an order abroad anyway.


Dennis L

This bot uses a FET / relay combo with which I'm really happpy. The FET just supplies juice to the motor and the DPDT relay reverses motor direction. This means I can have speed control by PWM with only one FET (rather than the 4 you need for H-bridge) AND reversable motors.

You just gotta remember to set the drive speed to zero BEFORE reversing the motor direction...!