Thanks for the suggestions.
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Originally Posted by cbale2000
A few suggestions...
1. Consider direct driving the center wheel from the gearbox. There's really no reason not to and it virtually guarantees that regardless of what might break elsewhere on the drive system (short of the gearbox itself) you'll always have one working wheel. It's also a good way to help balance the robots weight. Team 703 has done this for several years and its worked great.
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This setup allows us to get all the reduction we need without adding another gear before the drive shaft. If we direct drove we would have to do something similar to the VEX 3 stage ball shifter and it would push our gearboxes further into the chassis. This system should be nearly as reliable as a direct drive. This also requires less machining, since we don't ever need a bearing on the far plate.
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2. Consider vertically offsetting the outer wheels from the center one. Doing this greatly improved the robots ability to turn. In the past when we used large numbers of wheels in our drive, we would position the wheels on an arc of something like ~30ft, it worked well because it could turn on a dime, but in a pushing match you'd always have at least 4 wheels on the floor.
3. Without knowing your teams experience with them, I might advise against using the VersaWheels, I've talked to several teams that have used them and complained that they wear down quite quickly, and unlike Traction Wheels, must be completely replaced, instead of replacing just the tread. That said, this is just what I've heard, your experience (if any) may very well be different.
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The two outer wheels in each set of 5 are raised 3/16" (which is a lot but it's on purpose). The middle six shouldn't have much of a problem turning, since it's like a normal 8 wheel with the added benefit of part of the load on the two center wheels that don't scrub.
We ran an 8 wheel VersaWheel setup this year and loved them when they were new. (Ask the Hawaiian Kids about trying to push us at IRI on Saturday afternoon.) However they do wear down. We have swapped them three times this season. They cost about a 1/4 of a comparable wheel, so that's still a bargain but it does take up time. That is why we have them only in the corners and raised more than normal. Our 4 outer wheels didn't wear nearly as badly as the others since they are only engaged in pushing matches. We also learned that you basically can use them twice if you just swap them front to back when the edge that is pushing starts to go away.