pic: 971 Friction Clutch Transmission Insides

[Travis Schuh]

Originally Posted by Answer42

On another note I was wondering what ratios you guys geared this box for? Also what material were the clutch pads made of?

Low was geared at 14.3:1 and high 4.9:1 with a 3.5" wheel. (5.8 and 17 free speeds). In hindsight, we would have made our low a bit higher. It took 0.5 seconds to get to top speed in low, which made the shift point a little too early. One of the things we learned from this gearbox is that the optimal speeds for accelerating to high gear assuming shifting are different than speeds chosen for pushing. We have a student who is currently doing the simulation effort to see what the best speed pairings are for an auto shifting robot. That and how fast we can make our low gear before we start blowing breakers in low gear also.

The clutch pads are made of a machinable brass. The drums are something like a 4140 steel. We really didn't know what the best friction pairing to use would be, so we ended up settling for brass and steel because it has a decent coefficient of friction and because we have seen this pairing used in other friction applications. We ended up designing the clutch based on a friction factor assuming that it was greased brass on steel because we figured we couldn't garuntee that we wouldn't have grease get in there, and we figured that it might help with wear if we preemptively greased it. So far we have been pleased with the clutch material chosen, however we have in no means run it through the paces of an entire FRC competition season. If anyone knows of a better clutch material pairining, please let us know!

Part of why we built the transmissions was because the theory behind the design was solid, but there were enough uncertain factors like this that we really couldn't tell for certain if it would work without building it.