Major Gearbox Problem Found

Our robot was experiencing major drive issues. At full speed, it would veer significantly off to the side when both sides were driven at full power. At other times one side would seemingly stall.

I found a major problem was the low speed gear in the shifter gearbox. The bearing seat is approximately 20 thousands off center. This causes the gearbox to bind up. At full power, the motors can overcome this binding, resulting in one side going a bit slower- causing the veer. At low speeds, the motors wouldn’t have enough momentum to overcome the binding, causing one side of the robot to lock up.

Here you can see it visibly off center.

If you are having drive problems and nothing else seems like its wrong, check the gears. In our case, the offending gear is visibly off center. I hope this helps someone.

What gear box is this from?

Or maybe I should ask, what is the source of this gear?

Seems like an AndyMark 35T Dog used in the Shifters. EDIT 28T!

It’s an Andymark gear. 28 tooth.

Why am I not surprised you can identify this???

OK, next question.
Have you contacted AndyMark about this? I’m CERTAIN they will want to know and may go out of their way to get it resolved.

Yep, we contacted Andymark this afternoon and they are sending a replacement gear and bearing out to us. You’re totally right about Andymark, they were awesome to work with on the phone and will be sending us a replacement part.

I’ve been in the game for 15 years now and can’t believe the amount of support companies like Andymark provide. They’ve really done a great job making high quality, machined products accessible to teams.

We have AM Sonic Shifters on our robot this year and have also noticed significant differences side-to-side in gearbox friction causing the robot to veer in one direction. I have not looked for the bearing seats to be off-center but I found that one of the bearings in the same dog gear was not fully pressed in. This caused a binding due to lack of clearance between gears on the output shaft. Fully pressing the bearing in all the way fixed the problem.

We had similar problems with our transmission during the competition, I’ll make sure to check for this at our next meeting, thanks for letting us know!

Do you have a picture? Do you mean there wasn’t enough lateral room for everything along a shaft?

Sorry, I don’t have a picture. But yes, there was not enough lateral space along the shaft causing the gears to bind against each other. It was very obvious when we tried to turn the output shaft of the pre-assembled gearboxes that one of them was not right. One was very easy to turn, while the other one was basically locked. When we loosened the screws on the housing the shaft immediately became easy to turn like the other one. When we disassembled it you could see a slight gap between the underside of the bearing flange and the gear. The gap was very small (paper thin) but enough to cause binding on the shaft.