rotation of body of crab drive robots

[Bill Gold]

Michael,
First off, I don't think I've seen a crab system where every wheel is driven by the same gearbox. That type of setup would only allow for translational steering. The crabs powered by a coaxial system that I've seen have had one gearbox per side of the robot. This allows the robots to reverse the wheels in either gearbox to employ tank steering.

Wildstang's robot, like The Sea Dawgs' this past year, doesn't utilize a coaxially driven crab system. There are four drive motors, one mounted inside each crab module. This setup enables the robot to use tank steering by driving the 2 motors on one side of the robot in one direction, and the other 2 drive motors from the opposite side of the robot the reverse direction.

A robot like Wildstang's and The Sea Dawgs' can also use complimentary steering where, for example, one set of the modules points a certain degree to the right and the other set of modules points a certain degree to the left. This is just another way of turning. The Sea Dawgs used this method in their autonomous mode at the California Robot Games back in September.

If you want to see a crab robot in real life feel free to check out The Sea Dawgs' 2003 robot. You, and anyone else, are welcome to drop by during one of our meetings. If you can't do that then our robot will be on display at the November and December WRRF Motors/Drivetrain classes. Members of 258, including myself, will be there to answer and questions you might have about the drive system.

I'd say that crab steering is great, but it's definitely not a huge advantage. I think 2000 was the last game where having a swerve made a huge difference in the success of a robot. Although, now that I think about it, I can remember 5-7 times (over my team’s 2 event season) where we made it on top of the plateau with 1-2 seconds left in matches where we wouldn’t have been able to without our crab drive system. It all depends on how the game is laid out, and what strategy you want your robot to be designed for.