Quote:
Originally Posted by JesseK
Perhaps my idea of crab drive is a bit skewed, but with Crab drive and 4 traction wheels touching the ground, couldn't you program it to be semi-holonomic, like Team 118?
My prelim. parts list make the cost & weight pretty high compared to others (~$2k including motors, chassis $@#$@#$@#'y, and the # of victors you'll need for its control). The weight is around 50lbs depending on your machining skills (crab modules are tough to do accurately w/o machining).
For comparison, 6-wheel tank drive with 2 AM super shifters is roughly the same cost (victors included) but ~8lbs less.
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Swerve (crab) systems have limitations on motion that holonomic systems do not have (but they gain full torque from their drive motors as opposed to a vector quantity, as obtained in holonomic systems). A swerve system cannot, for example, achieve accurate "frisbee motion" (spinning and translating at the same time). Additionally swerve systems cannot "instantaneously" change direction, as the wheels have to re-position alignment.
There are a great deal of different ways to build a swerve drive. The way 118 did it in 2007 didn't allow for them to change the orientation of their frame, thus requiring them to build a rotating turret for their manipulator. Contrary to this, 111's swerve allowed for traditional "tank drive" motion as well as swerve motion, but they wouldn't have been able to couple 6 drive motors together or have a multi-speed transmission nearly as easily as 118 did.
Most swerve drives do require a fair bit more machining and machine expertise than holonomic systems, as well as a fair bit more weight and money dedicated to it. But there have been lighter, cheaper, and less-complex swerve systems in the past (
1261 in 2006.)