pic: Crab Drive


This is a potential crab drive module that I’m developing. Cut me a little slack since I used Alibre Design and had it about 2 hours when I made this. I’m using 3" wheels and the ratio is 10.29:1. I think that is about 12 fps or so. If you go to http://www.chiefdelphi.com/forums/showthread.php?t=46652&highlight=crab , I have a parts list up. Send comments ect. If you want more pictures pm and I’ll send them to you.

judging from the picture it looks like the middle of your wheel and the center of rotation of your module (the vertical rod, i’m assuming) are offset from each other. depending on the wheel traction and strength of your drive and rotation motors, this could cause it to behave oddly. also, if you were to get into a pushing match with this set-up, your modules could get pushed out of alignment as well. this is not really a major problem; all you need to do is shift the module’s center of rotation so that its centered over the wheel.

Yeh I realized that. Then I thought that would help when turning the wheels because the wheel would roll a little and we wouldnt try to be turning on wedgetop treading.(I tried ot make up a reason it might be good instead of changing it, and be a bit unique) Also, I plan on haveing a 5" Aluminum circular plate at the bottom of the plate to help spread weight evenly. I also plan on putting a lazy susan or something on it to mount the robot to. The focal point of this Module is that its very easy to make/put together. Minimal welding and machining, lots of standoffs and screws making it very easy to fix and maintaing.

Looking at this makes me think that it would be easy to make a ball-bearing shifter and build that into a swerve module. Now, that’d be awesome. I agree with RogerR on the rod placement, and I’ll add that you might want to consider moving the wheel down some, it looks like it brings the module too close to the ground. You have to remember that the wheel material will compress a bit with the robot’s weight on it and wear down a bit.