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Re: Mechanum Wheels?
My team has done quite a bit of experimentation with mecanum wheels this season, since we were initially doubtful of their effectiveness in certain critical areas, like traversing the barrier and climbing the bridge. Unfortunately, until we get some videos and pictures up (hopefully this weekend!) you'll have to trust me that our inadequately-described mechanisms actually work.
Surprisingly, the mecanum roller material grips better on plastic than on plywood. I suspect that fine sawdust is the culprit here, as our test of taping a sheet of plastic to one half of the bridge and then driving up resulted in the robot turning away from the side with the plastic, demonstrating higher traction on that side. We would be able to ascend while strafing, but our bridge has a significant lip that makes it very difficult to go from the ground to the bridge while sideways. No problems with turning sideways partway up and balancing that way, though!
We devised a system of raised powered traction wheels to pull the robot onto the barrier and provide a better point of contact to the mecanum wheels. Our prototype long chassis has no problems climbing over the barrier, even from a stop very close to the barrier without a high-speed run-up. The mecanum rollers function exactly as they should, in that the force vectors cancel due to the wheel orientation and no disadvantageous rolling occurs.
We use mecanum wheels because the extra range of motion is highly useful in offensive play. The ability to strafe has been particularly helpful when lining up on the bridge and will likely be very useful when the robot is sideways while trying to balance three robots. From a control perspective, we use flight simulator joysticks with a twist axis, a setup which has proved highly intuitive and easy to explain to 6th-graders during our school's open house.
In short, while mecanum wheels are certainly not perfect for everything, they have none of the negative traits frequently attributed to them, namely low traction, and we expect to use them to great advantage this season.
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