Programming a Crab Drive System

[Tom Line]

My team is trying to prototype a crab drive over the summer so we have it in our arsenal. We've looked extensive at ways of setting it up, and ways of programming it, and have some questions to teams that have done this long-term.

We're looking at doing either a single chain rotates all 4 modules, or 2 chains rotate two modules.

I've been doing pro/con on both, but I need to clarify something regarding the programming.

When a crab-bot is translating sideways, can it also rotate 360 degrees? If you run a single chain on all 4 modules, the answer appears to be an obvious no unless you stop to do the rotation.

With two chains running two modules each, it appears with some clever programming that it would be possible to rotate the robot 360 degrees while translating.

However, after watching a ton of match video of teams who have done crab, I've seen almost none of this. Most teams can tank-steer, but once they go into translational motion they do not rotate without going back into tank-steer configuration.

Is this correct? Is this due to the difficulty of the programming to rotate while translating, or this something else I'm missing? It would seem that having to go to tank mode to rotate the bot would be losing part of the beauty of crab drive.

So clarify it for me, if you can. What is your crab robot programmed to do when driving?