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Unread 26-04-2014, 02:40
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asid61 asid61 is offline
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AKA: Anand Rajamani
FRC #1072 (MVRT)
Team Role: Mechanical
 
Join Date: Jan 2014
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Re: The Perfect swerve

It's a hobby of mine to design gearboxes and strange drivetrains, because those are things that we can count on being applicable each year mechanically.
Through extensive research into swerve drives, I have seen two swerve drives which in my opinion are supreme:
-Team 221's Revolution Swerve
-Team 2451's Cim-in-wheel swerve
I like the Revoltution because it is the most compact solution to a coaxial swerve I have ever seen. It's pretty much optimized for its design. For that reason alone I basically gave up on coaxial swerves because I decided if I wanted to make a coaxial swerve, I would just copy Team 221's CAD and modify it for smaller wheels (this is the route I think 368 took this year, or maybe they're just very similar) or just buy some from them. If we needed to have a lower gear or didn't care about COG, I would go coaxial swerve and turn the modules using 4 different motors with two centralized gearboxes like 3-cim ball shifters. Plus, because they are available from 221, it's extremely easy to implement one in a FRC robot in a short time (although still not during build). For example, 368 was able to get their swerve off the ground in one year according to their mentors.

Team 2451's Cim-in-wheel swerve (I forget the actual name) is based off of the "swerve god" Aren Hill's Cim-in-wheel swerve. The only reason I put 2451 as the team is because they released their CAD so it's easy to look at and modify. It is the best all-in-one module I've seen including all those shifting ones because of its compactness. It is the most space-efficient design I have seen, and there is even room for improvement to boot. If you don't need the shifting and care a lot about COG, this is a very good solution.
Team 221 has a picture of a Cim-in-wheel swerve (hollow pivot wild swerve), but the CAD for that product is just the regular Wild Swerve witha hollow pivot- the cim is mounted above the wheel.

Shifting all-in-one modules are pretty pointless IMO unless you have a lot of resources. This is because unless you really care about COG, a coaxial swerve makes shifting half as hard. Plus, in order to really make good use of these modules you need to lighten them as much as possible by boring out gears and plates and wheels... for most teams I think a coaxial swerve is the best solution.

I talked with an old mentor of ours who has done a lot of engineering, machining, and FIRST for a looooooong time (~25 years for the first two, 12 for the last). According to him, the hardest part of a swerve drive is the programming. It's for that reason that he heavily advises against our team doing a swerve drive, because he thinks that we would need professionals to program it for us. His opinion is based off of our team's sad efforts to build a swerve drive years ago.
I don't agree with that completely, because many teams have graciously released swerve code and whitepapers on the subject, so you don't really need an engineer to do it anymore because the hardest calculations are already written down. I think any team with interested and smart programmers can implement even a rudimentary swerve drive at this point.
However, we have a completely assembled crab drive (mistake #1 was to crab) sitting in our shed that weighs something like 80lbs from several years ago. We took it into our room in September to show the rookies, and I remember having trouble with the think because it was like a rock- solid, hard to hold and extremely heavy. It never drove because it was too hard to program. Nowadays there is a lot more info out there plus far lighter swerves that I want to use someday.

I remember Aren once had an idea in a paper of his about using a swerve drive that implemented a wheel tilted at a 45* angle to the ground. I don't think it was ever produced though.