Quote:
Originally Posted by Alex.Norton
To clarify what I said earlier (why I don't like mecanums), each wheel creates a vector of force in the direction that it moves but regardless of what direction the robot moves in it also creates a vector perpendicular to the wheel....
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This is true (gee... funny how those basic physical concepts like vectors tend to be, eh?) and something we briefly worried about during the design stage this year, but it turned out to be only a minor issue with our mecanum drive. We machined our own hubs to do a direct drive of the AM mecanum off a BB tranny. We ended up putting set screws into each side of the hub, and actually mounted a small allen key right on the robot so that we didn't have to look for one when it was time to adjust the wheels and/or tighten up the set screws that had wiggled loose due, in part, to the changing lateral forces. This only needed to be done a few times each regional. If we were really concerned about it we could have simply pinned or loc-tited the hubs to the shaft and they would have stayed put permanently.
During build we did have to manufacture a couple of spacers to go between the bearings of two of the the BB trannies due to some issues with the location of the shoulder on the drive shaft... the drive shaft actually had about 1/16" of end play... but that would have been necessary with tank drive wheels, as well. After all, although mecanums put lateral forces onto the drive shaft, so do traction wheels when you are pushed from the side.
So yes, mecanums generate lateral forces on the drive axle, but it isn't really that big of a deal. Regular bearings can handle it, and if your axle mounts/drive system can handle the lateral forces imposed by traction wheels being pushed sideways, then your mecanums should not present a real challenge based on our experience.
Jason
P.S. It has just occured to me that traction wheels may actually generate higher peak lateral forces on the drive train (although I know your concern focuses mostly on the cycling of lateral forces whenever the mecanum changes speed as opposed to peak). When the robot is hit... hard... from the side the mecanums will translate some of that impact force into rotational force... or, at the very least... slide and skid... while the traction wheels will direct 100% of the impact as a lateral force (okay... with a bit of it coming in as torque, too).