GoPiGo veers to the right going forward


#1

Our GoPiGo always turns sharply to the right when going forward. It also gets stuck going left (and doesn’t do a bang up job of going right). It appears that the right wheel doesn’t grip as well, perhaps? I’ve tried tightening the motor mounts and checking for anything obviously out of alignment but nothing I’ve done so far works.

Once the GoPiGo veers right it does tend to go more or less straight after that. Though, on our old wood floors it will sometimes hit an uneven spot and veer sharply right again.

Oddly, it goes backwards completely straight. Any ideas on what to try to fix this? It’s going make the obstacle course mission a bit frustrating for my son, I fear.


#2

Hey Rex,
Sorry to hear about this. With some surfaces the GoPiGo motors can be tricky and slip. One might grip better than the other. You might consider two tactics:
1). Wrap both wheels with rubber bands. This should help grip the floor.
2). Place the battery pack on top of the canopy (rather than on the back of the GoPiGo). This should put more weight over the wheels and again, help it grip.


#3

Thank you! These tips did the trick!


#4

Ah… I spoke too soon. The rubber bands and battery placement change do make it better but trying to do Mission 2 today we realized that it still veers to the right going forward. Fine, we thought, we’ll just program some quick lefts to correct for that. But then we realized that sometimes it doesn’t veer at all, other times it veers a tiny bit, and other times it veer a LOT. It’s completely unpredictable. Turns are fine now and backwards there is no still no veering at all.

And the wheels do fall off from time to time, which is also frustrating. Any other ideas?


#5

So the GoPiGo is only veering when it goes forward. That’s a bit odd. Did you check if the motors are tightly screwed to the chassis and the wheels are not very loos and face straight when they are turning. We haven’t heard of the wheels falling off a lot. The friction between the motor shaft and the wheel is usually enough to leep the whole thing together. Are the wheels held very loosely to the motors?


#6

Hi RexMagoo, if the wheels are falling off, we can try to replace those and the motors. However, just to double check, are the wheels falling off or are the encoders falling off? The encoders look like little wagon wheels and they sit in between the motors.


#7

Yes, it’s the wheels. The encoders haven’t been a problem.

As for the veering, we tried again later and noticed that the veering was less severe at full speed and more pronounced at slower speeds, which seemed counter-intuitive. In any event, we realized that we had set the speed a bit slower when playing with the Basic Control example the night before and it carried through to the obstacle course. We added a step at the beginning to set the speed to 255, made our obstacle course a bit wider and more forgiving and managed to get a few successful runs which was great.

Still, every run was slightly different due to the varying amounts of veering on the forward portions of the course.

I should mention that I have a separate thread that I started earlier solely about the wheels falling off. karan recommended wrapping the motor shaft with Teflon tape and I’ll try that tonight to see if that does the trick. I was also asked to send a photo of the robot’s wheels and shaft. I forgot to get the shaft photo, but here’s the pic of the wheels and motors in case that will be helpful.

Thanks again for the help.


#8

OK - so, Karan’s suggestion to wrap the motor post with Teflon tape solved the wheel falling off problem. Upon further investigation, it is veering go backwards as well, but not as pronounced as it is going forward.

Attaching a video, hope that’s helpful in diagnosing the problem.


#9

That much veering can be fixed by trimming one of the motors. Can you follow this tutorial: http://www.dexterindustries.com/GoPiGo/programming/python-programming-for-the-raspberry-pi-gopigo/add-trim-to-the-motors/ and see if it gets fixed.