Let's Make Robots!

Difference in motor speed

I have build a robot out of old LEGO bricks, since my gearbox and tank tracks haven't arrived yet. I have used the standard one-motor-per-wheel-in-the-front-and-one-small-wheel-in-the-back-design. My problem is, that the two motors aren't running with the same speed, so my 'bot is turning to the right all the time. I have considered putting a resistor on the fast motor to make it slower, but would like to ask, if any of you have any other solution to this problem? The best solution would be some sort of sensor on the motor to tell the speed and let the CPU adjust the speed.

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Strange I can't seem to attach files to this comment... anyway you can get it from here:


- Jimmy

(We are getting into the file attachement-issue in comments etc)

/ Frits 

This allways happens to robots with that design.

My approach is never to rely on the robot drive in a straight line.

Even if you do manage to make them equal, next thing is a bump on the road, and you are back to square one.

You could also begin counting how many spins pr wheel, but then again you are knocked out if one wheel is spinning a little for one reason or another.


So this is typical to the approach I prefer; Say your purpose is to track another object. Well, then focus on tracking that. Nomatter if your wheels are uneven, if the object moves, if one wheel is stuck etc etc, the bastard will try to follow that object no matter what.

Think of it as Terminator one, the movie; One goal, no matter what else happens. Don´t think of it as a train where you plan the next station before departure. 

Constant focus on the goal, constant ajustments. Then you should be able to deliberatly hinder one wheel, and the darn thing still just wants to go the right direction.

See the Line Follower - film here: http://letsmakerobots.com/node/37 (Better videos are on the way for this site) At one point I stick out my foot to stop the one side of the robot, that does not make the thing turn. When I remove my foot, it godes same direction. I am sure that if I just "turned on both weels, that robot would go in circles, just like yours.

/ Frits