Fully up-to-date. Weight per module is somewhere between 4.8 to 5.2 lb. With a frame weight of 7 lb as before, whole thing weighs between 26.2 and 27.8 lb, so it is under our 30 lb limit. There is a thrust bearing and a hex bearing inside the turning pulley, and the caster and turning pulley is meant to be 3D printed in Kevlar.
How are you supporting the module? Is all the support coming from the top plate, or is there something I can’t see? If so, you might consider adding another support to keep the module from bending out under the weight of the robot.
Looks like a modern take on the classic 118/Team221 LLC design. That being said, using a 775pro for your drive motor means that you’ll need to gear much lower than if you used MiniCIMs or CIMs. What free speed are you geared for right now?
Second thing: the use of what seems to be a single 1/8" plate for taking all thrust and side loads is probably going to be inadequate. Using 2 plates instead with 2 ball bearings will probably get you better results than what you’re doing now.
Last thing: Your module sideplates look a little thin. I don’t know if that will be a problem or not, but make sure you pay attention to it if this gets built.
It is boxed in with the frame, so it is supported all the way around. That plate (mounting plate) is 3/16, and we had no problems with that thickness all season. The module plates are 1/4, and again, we had no problems with that this year.
I may consider adding a second plate to the mounting plate as the single 3/8 inch shaft worries me a bit.
It is geared for 13 adjusted. I don’t care about pushing matches and it is traction limited.
[strike]It’s not just about pushing power. If you only have 2.7 CIMs of power in your drivetrain and you’re geared for 13 ft/s, you’re not going to have much acceleration. It doesn’t matter if you can get up to 13 ft/s if it takes a whole field to reach that speed, or if you don’t have enough torque to start up at all. You’ve done more calculations on this than I have (I haven’t done any, so I’m assuming), but I’d just be wary of using so little power in your drivetrain.[/strike]
I think you are underestimating the power of 775 pros. That said, I will run some more calcs.
I’m sorry, that’s my bad. I mixed up your swerve with the other one posted today, which only used a miniCIM in each module. I know a few teams ran one 775pro per module this year with success. Just make sure you have good current limiting and such so you don’t burn them out. You may want to talk to 16 Bomb Squad to see how they did it.
Sam,
I believe you’re familiar with our swerve. Here is some performance trivia.
We ran 4, 775 Pros geared for 15 fps @ 85% motor full speed.
It got to full speed in about 10 ft.
It was in current limit (50 amps) for about the first 3 ft.
The robot was 119.6 lbs.
50 amps seems to be the max current you should be operating at to save the motors AND keep the main breaker from tripping. Even at 50 amps we could trip a breaker. The Talons are capable of doing the current limit. DO NOT limit the drive motors by limiting max voltage. For a shameless plug here is our highlight reel.
More worrisome than traction limiting is how quickly the 775s will burn out. Even 80A for just a few seconds will kill a 775. That being said 13fps is fairly conservative, so you should be fine.
What kind of thrust bearing setup are you using?
Just saw some matches from you this year - very impressive! What free fps were you running at?
We do have very good current limiting software. We ran 8 775s in our swerve this year, 21 fps free speed, 18 adjusted. It was a tad faster than this one, as we had to limit the top speed only to full field crossings, where our driver could use “turbo mode.” We ended up generally going 10-13 fps.
The thrust bearing setup is a needler 3/8 VXB bearing and is, in my opinion, the weakest point of this design. We used a turntable from VXB (150 mm on an 84 tooth gear) on our competition robot this year and want to use belts now. Inside the pulley is both a regular 3/8 hex bearing and a needle bearing on the other side.
Sam,
Some performance trivia on our swerve if you want to compare notes:
15 fps at 85% motor max RPM.
0 to 15 fps in 10 ft.
50 amp current limit using the Talon’s current limit.
Against the current limit for the first 3 ft.
Robot weighed 119.6 lbs.
We found 50 amps was about right to keep the 775s from being destroyed AND to stop from tripping the main breaker AND keep our driver from complaining. Even at 50 amps we could still trip the main breaker if not careful.
Hope you find this informative.
That looks great! One of our students did something similar for FTC:
https://drive.google.com/folderview?id=0B9kDX0yqs8NTT1dyLVBnRDFxYVE