COTS parts are used pretty extensively, we’d only have to fabricate three plates, four standoffs, and two shaft per gearbox. The first stage of reduction is 12:100 32 DP, then 16:60 / 32:44 20 DP reductions for the shifting stages. Weight with fittings and bolts (but we forgot spacers…) is 5.016 lb.
The gearbox is geared for 7 / 20 FPS adjusted speeds with a 3.5" wheel, we plan to test with voltage ramping, current limiting, and auto shifting. If 20 FPS is too fast for our driver or we have electrical issues we can lower the high gear to 14.5 FPS by swapping in a 26:50 instead of the 32:44.
The current design has the gearbox mounted using 4x 6-32 screws attaching into the shifter pistons threaded holes. The gearbox back plate does have a 1/8" lip so that the gearbox sits on a 2x1 rail instead of directly on the screws, and the gearbox is pretty light compared to traditional FRC gearboxes, but I’m still not entirely sure if such small fasteners will be sufficient.
We’re planning to use a steel 16t gear for the low gear input, and may switch to a steel 100t 32 DP gear if needed.
Looks great, the only thing I would change is using 1 shifting pancake piston instead of 2. You are going to use alot of air, and take up alot of slots on the block, and you dont really need 2. I know its for them to be on the outside but maybe making the other side a linear bearing or moving it in the middle?
The way you setup the drivetrain in the pictures you have to use chain in tube. Is this gearboxes designed with that in mind?
The 6-32 screws are not just the only screws holding the gearbox to the drivetrain, they’re also the only screws holding the gearbox together. Those screws are only on the bottom, so the top of your gearbox will flex. Whether that’s actually significant or not, I don’t know, but it’s just a bit sketchy and it’ll be nice to have a bolt holding the gearbox together at the top part, and more bolts holding the gearbox to the drivetrain.
I really like this design, especially the way you flipped the shifters. It’s a bit risky though, which is fine to play with in the offseason, but build more robustly in build season!
Can I ask why and where WCP says that? Is that not what Pwnage used this year with theirs? Haven’t heard of them having any issues regarding the gears.
Can you please suggest an alternative to using 32dp gears with using 775pros?
The problem isn’t that it’s 32dp, the problem is the material.The smaller wcp 32dp gears are steel but the larger ones are not. Aluminum gears may work but have a much higher likelihood of failure in this use case. Andy mark does sell a steel 85t 32DP gear(am-3533) but you may struggle to package this gearbox with a smaller cluster gear.
We were going to source steel 100t 32DP gears from SDPSI if the 7075 gear does have issues. It would just be nice to not having to do any machining since the WCP one is already lightened and 3/8" hex.
Pretty much this. 2451 used a carbon steel cluster gear at first and wore it out in one regional (iirc). They switched to a custom 4140 cluster gear and haven’t had issues since.
YMMV though. 2451’s cluster gear is much thinner than the WCP 7075 gears so there’ll likely be less stress on the gear teeth. Only way to tell for sure is through testing (or waiting for someone else to do the testing).
