Great thread.
I appreciate all the resources folks have posted. I have looked at swerve drives off an on over the years and never had the resources to build one. I think we might have enough interest from the kids to do a swerve as an off season project.
I apologize if the answer to this is in one of the documents (I didn't see it during my quick skim). I have wondered why teams would run one drive motor and one steering motor per module (like
http://www.chiefdelphi.com/media/photos/40299? or
http://www.team221.com/order.php?cat=3). This seems like a waste of weight to me. The concept shown briefly in
http://www.youtube.com/watch?v=CAJBC-DDL9w and commercialized as the Revolution Swerve (
http://www.team221.com/viewproduct.php?id=89) seems like a better idea. The reason it seems like a better idea to me is that you can have a single steering motor set and a single drive gearbox.
Why do teams use 4 total gear reductions instead of one central gearbox and a chain to transmit power to all 4 wheels? With a 72T or 80T 20 DP gear attaching to 4 CIMs you could make one big gearbox in the center, perhaps even add shifting for a second overall gear ratio.
Why do teams use 4 steering motors? This would seems to make it hard to steer straight forward (as mentioned in one paper previously linked). With 1 or 2 motors for steering and a worm gear based gearbox and a chain the wheels would be mechanically synced (minus any stretching of the chain). I realize that you would need two steering chains (i.e. 2 sets of 2 wheels chained together) to be able to rotate the bot around its center. By using less motors and therefore less controllers this would seems to save weight
I realize that belts can also be used for power transmission between wheels, but chain has a much higher overall load rating in tension and is easier to make very, very long.
These answers may be obvious to teams that have done swerve before, but are a mystery to us.
Thanks!
-matto-