Wild Thumper, progress but help/advice requested

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motorbyte.c (1971Bytes)
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Hi all,

I had a lot of trouble with motor driver boards and my Wild Thumper 4WD chassis - in the end I bought a more expensive motor controller said to handle 60A. I am controlling the paired (left/right side) motors by PWM signal and  it now drives forward/backwards/left/right etc.

The issueI am facing now is that the robot moves in a curve... and I don't meant the usual gentle drift off course - this happens immediately and dramatically. Both motor sides are receiving exactly the same PWM signal. I am aware that some correction is needed in certain circumstances but I feel this Thumper has something wrong with it.

The suspension does not appear to be even and the wheels are very angled in compared to the front.

Video and pictures attached.


I'd really appreciate some advice. This is not my first robot - the other ones I have built have a tiny bit of drift over a long distance (10m) but nothing like this. 

Your rover looks awesome

Hello Alex,

Your project looks awesome and I do see the slight bend in the frame that you are describing. I have the wild thumper six wheel drive and without the frame twist that you have my rover also pulls to the right (maybe not quite as much as yours). I am currently using RC control with the T’Rex motor controller and I notice that after a long bit of driving the pull becomes gradually less significant. 

I am currently working on adding encoders to my project to correct the drift. 


Drift correction

I would not expect the brushed motors to supply the same power for a given PWM value. You need some form of feedback such as encoders or compass reading. Compare the sensor with the feedback and adjust the PWM. A common algorithm is called PID.

My RC car based robot in a

My RC car based robot in a perfect straight line with no corrections:


My Dagu Rover 5 with no corrections


If the wild thumper is badly calibrated and this is all that is wrong then PID control and encoders is my only way forward - however the suspension does not look even and the wheels do not appear to have the same angle when stationary. I think this is causing the dramatic drift and I’d like to address that first before going into the PID controller and encoder interrupt code. 

Hopefully the chap that makes these will comment soon and offer some advice. As far as I can see the suspension is in the same connecting holes (central ones) on the front and back four motors.