rotation of body of crab drive robots

[Al Skierkiewicz]

Originally posted by michael_obrien
I'm confused as to how a crab style robot rotates itself entirely (not just wheel modules), I see on the wildstang video page that they have a little foot that comes down to pivot on,
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Basically what I'm asking is how crabs turn and how well it works.

Michael,
A crab drive system does not need to steer to drive. You just point the wheels in the direction you want to go and apply power. Wildstang used the foot this year so as to provide an easy way to reorient the robot to pick up bins or to align with the ramp. There are actually two feet, used one at a time, to achieve the desired effect. The foot raised two wheels off the ground while driving the remaining two in opposite directions. This is not an efficient method but it works when needed. We have used steering in past years that allowed for a different turning radius on one side of the robot than the other. This would give an arc to the robot motion and hence a turn. Max power is still when all the wheels meet the road.