Just wondering if I could get an inventor drawing of a swerve drive. I’m designing one now and would like to get some input on sizing stuff.
I’d be glad to send you a CAD of one of my crab designs, but they’re on my hard drive back home and I’m at competition. I’ll get back to you once I get home, and shoot it to you.
-Craig
Craig, could you send me one of these also? [email protected]
Hmm… You should post it as an attachment (or provide a link…)
I think A LOT of people will ask, including me 
Yea I’ll post an image of what I have currently. Also What type of wheels should be used in a crab drive? Right now I’m basing it off of this year’s wheels but I doubt next year will have wheel restrictions.
well of course, you’ll want to be able to turn the wheels with relative ease, but you wouldn’t want to use something like this year’s wheels because the coefficient of friction is a little too low.
You’re right to take that into consideration. In 2002 traction was everything and my team built a crab drive with 2 wheels in each corner. What’s worse, we had a coefficient of friction around 1.6!. That thing could pull, but we were burning out our motors and stripping gears trying to turn. Taking off one of the wheels on each housing we were able to turn more effectively, still with a 1.6 uf. The wheels were off the turning center of the housings, though, and I’m sure that helped. We also restricted our major turning to when the robot was in motion, which does take away some of the advantage of crab.
The following year a similar design worked with the wheels in line with the turning center although we eventually moved away from the high traction material because it wasn’t as necessary.
It’s actually probably a misconception that you need low traction wheels in general for crab. If anything, crab allows you to have high traction on all wheels because the wheels don’t have to slip sideways like they do in tank drive. You just have to keep in mind the force required for stationary turning, just like turning the wheels on your car when the car isn’t moving.
I thought there needs to be just enough traction to allow the turning of the wheels. High traction wheels would just rip to shreds with that kind of turning.
This argument has been beaten to death. Check out other crab threads for more info on this idea…
In crab you don’t turn the wheels much more harsly than you do with car steering, and you definitely don’t drag them sideways. With tank steer the wheels actually have to skid horizontally in order for the bot to turn. With crab, you rotate the wheels in place, so where the friction gets you is torsion on the tread in contact with the ground. This is no different than front wheel steering and it’s not a ton if you have regular wheels. If you go to high-traction wheels you just have to make sure you’re moving at least a tiny bit when you turn large angles or you could run the rist of tearing tread just like you can tear your car tires if you turn the steering wheel too much when the car isn’t moving.
There really is no reason to shy away from high traction tires. The robot I mentioned in my prior post had 4 wheel crab and could out pull any robot at the championship that year, I’m betting even the Beaty walker.
http://hamosad1657.net/inventor/Chassis.html
Viewed via Freewheel, I can give you the DWF or answer questions if you’d like, just tell me.
Wow, that is a very cool website, and great CAD.