We have two TB Mini’s running on the AM KOP chassis. One of them runs quiet as can be, the other one not so much. It makes a very loud whining sound when running. We’ve had it apart several times, made sure all gears are positioned correctly (we know they have the bosses on one side for spacing from the bearing). Everything is lubricated nicely too. Gears on the CIMs are not too tight (small amount of axial movement). Only thing I did notice is that the gear that’s driven by the CIMs seems to mesh a bit tighter than I would think is normal.
Are you sure the sound is internal to the gearbox? We had a similar experience this year, did all the troubleshooting you listed, and discovered the bolts on the pulleys were scraping the side of the frame.
We had the same issue and already corrected that by enlarging the spacer on the output shaft between the pulley and the chassis plate (and reducing the spacer on the opposite side of the wheel of course). No joy.
We also had a similar issue, and eventually an issue where one side of our drive train stopped functioning, only to discover that we had an issue with one of our CIM motors.
I had this happen back in 2011 with a TB nano. One of the larger aluminum gears seemed to be off-center, past the point of “needs broken in” (AM does have a listed break-in period). Swapping the gear for a steel one that we had sitting fixed the issue. Try removing parts from the gearbox (motors, etc.) to isolate the source of the noise.
Similar issue a year or two ago. One gearbox was noisy, the other quiet. What we found was that the bolt holes on the CIMs were not perfectly aligned. Crazy right? And the CIM gear was pressing too hard against the first gear in the ToughBox Mini. The pressure was causing a lot of whiny/screachy noise. And that gearbox was very hard to manual turn.
Our solution was to rotate the CIM 180degrees, and while tightening it down to pull it as far to the direction “away” from the first gear as possible. That reduced the noise considerably and made it easy to manual turn.
Last year we had an issue with toughbox mini where one of the gears (think it was input gear) was slightly oblong. If both cims were installed you couldn’t turn the output shaft. Check your gears to see if one is slightly out of round.
CIM rotation solved the problem - quiet as can be . Now I have to flip them back again and let the students figure it out - LOL. Thanks for all the feedback.
. Now I have to flip them back again and let the students figure it out - LOL. Thanks for all the feedback.