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Wild Thumper Controller Left/Right speed way off


i'm using a Wild Thumper controller on a DFRobot 4wd chassis and motors.
I noticed if I set a certain speed, there's a lot of difference between the left and right wheels.

But it is not consistent. The speed tends to equal out after a few seconds.

And it is dependent on the direction. e.g.: going forward starts with left going faster than right, and with going backwards it starts with right going faster than left... weird....

 The effect is worse with higher speeds...

Any ideas?


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Encoders should allow you to assist in keeping the motors all moving near the commanded speed.

I think I should expand on my subject line. As all motors are not built the same they will move at differing speeds in different directions.

yah. i was just adding the encoders, even they weren't compatible with these motors and chassis (not enough room), but they work.... However since the motors Start with the biggest difference, it has turned already before i can even make a useful encoder measurement.... But i guess i just want to know: is this difference normal? could it be because i'm using 5 NiMH AA's? I do see quite a voltage drop running at higher speeds....

not all motors are created the same , small variations in the motor windings can create speed differences between one motor and another of the same make. and in your case the motors run better in one direction than the other ,witch may have some thing to do with the brush arrangement in the motor it's self   

the best fix is an odometer , speed detection for each motor and using that data you can adjust the speeds to mach , i have never had the hardware to do this but that's the the idea