Quote:
Originally Posted by GeeTwo
We miscalculated on the amount of defense last year, and went mecanum. Our programmers got mecanum working from the libraries in about two weeks from a cold start. We're going omni H-drive this year - we're doing a "bottom stacker", and feel that a bit of strafing is going to be essential to quickly and precisely line up on the totes. We decided to pass on mecanum this year because of the issues with a moving center of gravity.
|
Quote:
Originally Posted by Ether
When you experimented with H drive in the off-season, did you find that it was less affected by variations in center of gravity than mecanum is?
|
Did I say we experimented with H drive in the off season? Actually, we built a tank drive for a prototype chassis because we recognized that it was the best chassis for 90% of the games for teams without massive funding or the ability to crank out a swerve drive in the shop (like us).
Anyway, we do not expect a major variation due to (front-to-back) variation in the COG on an H-drive. We're going to put the COG at the transverse wheel when we have about a 75% load. The short moment arm to this wheel should keep the torque about the COG small when we have 3-6 totes. We'll have to learn to adjust at lighter loads, when it's less critical. I also can't think of a reason why, in a tank-mode spin, an H-drive wouldn't rotate around its COG - lateral forces balance about the new COG, leaving only torque.
Actually, when I later thought about the forces on a mecanum with a COG that moves forward and in reverse, I became a little less concerned, but still glad that we switched. Moving forward and back would be largely unaffected by moving the COG forward or back. Strafing or translation with a strafing component introduces a torque so that the robot will rotate towards the strafe direction. On an attempt to simply rotate, the robot will tend to strafe in the direction of rotation on the side to which the COG moved. Also, the axis of rotation seems to move to in the opposite direction of the COG, which sounds likely to cause the robot to fall on its face eventually. I did not think about combination maneuvers involving both translation and rotation. Disclosure: this is all based on pictures in my head, not on paper or even a whiteboard, and certainly not experience.