Quote:
Originally Posted by IKE
The prinicple Art was getting at is over-constraining a system. A good example is a 3 legged vs. 4 legged table. A three legged table does not rock. It may not be level, but it does not rock, even on an uneven surface. A four legged table is very tricky to not have it rock. This is because 3 points make a plane. 4 points overconstrain. With a stiff driveshaft, 2 bearings will constrain the shaft in all planes except for possibly concentric sliding (you need a collar or a lip of a clip). If you try to do 3 bearings, and they are not perfectly aligned, the 3rd bearing may fight with the other two and cause stress in the bearings which will cause them to fail early.
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This is slightly off topic, but I'm curious; has anybody had an actual problem with over constraining a hex shaft in an FRC application?
The versaplanetary gearboxes have two bearings on the output shaft, so anybody who supports the vp output shaft with an additional bearing is locating the shaft in three places. We ran setups with four bearings on the same shaft both this year and last year with no problems, including a bearing that was pressed into a welded sleeve that couldn't have been extremely accurate.
I'd guess we can get away with this because of the fit between hex shafts and bearings and the clearance holes for standoff bolts. A #10 is a slip fit in a .1875" hole, so it has almost .01" of slop in the recommended .196" clearance.
I'd also assume that the hex bearings which tend to come in a little oversize are also pretty forgiving.