Chief Delphi - Banebots 42mm gearbox: Recommendations for use

Quote:

Originally Posted by gburlison (Post 608684)

I would like to give a big THANK YOU to Shane Colton from team 97. We had the carrier plates you made for the 42mm banebot transmission hardened and they performed extremely well. As expected, the harder plate just moved the failure to a different part of the transmission. After 7 matches at the Colorado Regional, our 256:1, 42mm tranny seized. Upon disassembly, it was hard to determine what failed first, but the brass gears in the final stage were missing teeth, the pins in the carrier plate had sheared, and the ring gear had some damaged teeth from the damaged brass planet gears. We had an extra carrier plate with pins (thanks Shane) and extra planet gears. The ring gear was our biggest concern. We turned the barrel over so that the damaged portion was at the first stage of the transmission where it would see less torque and we were pleasantly surprised to find that due to the spacing of the stages, the damaged portion was almost entirely between the stages. We had to play one match without an arm, but had the whole thing back together and made it through 5 elimination matches before losing in the semi-finals. I would recommend that you pay close attention to the entire output stage, replace or rearrange the brass planet gears, and flip the barrel to keep the transmission in good shape.

Let me state that I would use this transmission in the future, I would just be more careful in my design and increase the safety factor to avoid this type of failure.

Glad I could help. I think the advice you give is valuable: keep a close eye on the transmission. All it takes is one snag and the FP motor will gladly tear the last stage apart. Add it to your pre-flight checklist to make sure the gearbox isn't binding, the backlash isn't unreasonably large, and the housing isn't rotated out of place (see earlier posts). It may also be a good idea to tear the gearbox down and inspect it carefully whenever you have a long break.

I wonder...what ever happened to the motor current sensors from '04? I would love to have one of those on the FP so that if it sees abnormal currents it will shut down and minimize damage to the gears. Or better yet...a Victor with built-in current feedback!

Edit: I know I've been the one saying the whole time that the load isn't determined by the motor, but by the arm, and that the double-D failure is more preventable by limiting the output load via springs/counterweights/extra reduction, so I should probably clarify a bit at this point. I still think that is the way to prevent long-term, cyclic failure modes, like the double-D widening out. But for the catastrophic failures that occur when the gears bind or the housing goes out of alignment, limiting the motor current so that it cannot provide anywhere near stall torque would be extremely helpful.