Thanks! Several students from my team attended (along with myself). We don’t yet have the fabrication capability to do a good swerve drive (and we realize it takes years of work to perfect it) but we would like to try it as an off-season project for the learning experience.
We are thinking of perhaps using a COTS swerve module such as one from AndyMark, or one of the 3D-printed solutions floating around on the web. Again, not for an FRC-ready robot, but as a prototype drive chassis for experimentation and maybe demo use.
So I read the powerpoint and most of it makes sense. But what do you mean by “Bevel gears need thrust washers or bearings”? Are “bearings” normal bearings or thrust bearings? And where do they go? Between the gear and a wall of the module?
Thrust (bearings or washer). Since the drive shaft here is vertical, you need something to support the vertical weight of the wheels and gears. Most “standard” bearings are only rated for radial loads, but when you have a vertical shaft you need to support that weight.
Another option (that are good for both radial and axial loads) are angular contact bearings, but you generally need to stack two of them together to hold your load, which might make for a pretty bulky setup.
We used copper bushings for our drive columns until this year (after some key failures stemming from our axial load in 2017), and for Power Up we went with two stacked tapered/angular roller bearings. In past games, we’ve usually had one or two failures in our drive trains that really came back to bite us, and I think this year was the first in which we experienced no real mechanical problems with our swerve (even with a change to 775pros as drive motors!). I chalk it up to luck, accumulated experience, and that design change.
Regarding bulk, the addition of two bearings required a 0.6" height and ~0.5 lb increase in each of our modules (in comparison to if we had stuck with copper bushings). We considered these pretty negligible adjustments for this year’s design, though many of the modules posted here tend to be relatively wide and tall, making the additional height/weight perhaps not worth the additional robustness.
I hope this helped, you can view CADs of our past swerve drives on our site!
What others have said above is great, just to add on, we used thrust washers this year, I believe something like these. There is a groove on the back of the vexpro bevel gears they can fit in (look at a picture of it). The thrust washer goes in-between the bevel gear and the bearing/wall.