Let's Make Robots!

Wild Thumper Motor Issue

Continuing my fun with my Wild Thumper (yay!) I've been tracking down an issue where to get the right set of motors turning I need to issue much higher PWM values than the left side. For example on a charged 7.2v battery a PWM of 80 will turn the left side motors (unloaded, up on a block) but 100 or more is requred for the right side motors to turn. 

I disconnected each of the right side motors and have found that one of the motors seems to be the culprit. That motor needs a higher PWM before it gets out of stall and the current drops to only slightly higher than expected levels. 

Questions! 

1. Is this a normal problem people see with these motors?

 

2. Are there hardward or software workarounds? 

 

Bonus Question:

Anyone have a picture of how to properly mount the Controller in one of the lower chassis slots? Just having it sit there seems a bit hacky.

 

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The Wild Thumper controller comes with brass spacers for mounting it. Here is a quick photo I took of my EnviroBot. Basically you screw a hex spacer onto each corner of the controller.

*slaps forehead* Of course. I was reluctant to mess with those screws at all. A very helpful picture. My thanks!

This is perfectly normal operation. First, no two motors are truly identical. More importantly, motors tend to run better in one direction than the other. Because one of your motors is running in "reverse" on the "other side" of the robot, it could be running less efficiently than the other. Point is, that is why we use PWM to control our speed.

Work around --Yeah, play with your robot until you find the numbers that make it go straight. You can also add encoders to allow your brain to actually know how fast the motors are going and adjust speed as needed.

Ok, I was surprised because 5 out of 6 motors are within 5% of each other in both directions, but one is 20-30% off. 

 

I would totally buy a version of the chassis that had encoders built into the motors, but I'm still working on finding optimal wheels so I can't go optical encoder to the wheel quite yet.

Thanks again!