Octocanum Drive/ Mecanum Suspension Designs?

[Darkseer54]

Originally Posted by dougwilliams

Agreed on the point of spending most of our time on mecanum. I guess the trade off you made on your chassis was that suspension for the mecanum was not worth as much as the possibility of losing pressure and having the system fall back to the traction wheels?

Yes, especially as it would turn the robot into a 4 wheel long bot(which can't turn well.) The biggest issue that an octocanum has is it can't turn well in octomode unless you have your traction wheels position inward far enough for it to be a wide base. Defaulting to mecanums fixes this issue.

[Dale]

Here's a closeup of how 1540's Octocanum drive works. It pivots on the traction wheel and uses 1" pancake cylinders to switch back and forth and to provide suspension. There's a custom single speed transmission built into the 2x1 frame but you need not do that. There is no chain tensioning, we just CADed it to be the right distance and it's been fine.

We started out with a variable air pressure system for the cylinder so that we could change how stiff the suspension was depending on how many toes we were carrying. We ended up dropping that feature because we needed the weight elsewhere. In the end, while we found Mecanum performance was better (more consistent strafing) with the suspension, our software with a heading sensor could do what we needed for this game. We actually don't strafe as often as we thought we would.

For St. Louis we ended up dropping the cylinders to get the weight for a can-grabber. We still have the traction wheels but they are just used to go over the scoring platforms and are just fixed a quarter inch above the ground.

[MStump]

3309 used an octacanum drive in 2014 with suspended mecanum. We had the mecanum geared for 17 ft/sec and the traction for 4 ft/sec. It worked well but we had to make sure to conserve our air so as not to run out and drive on eight wheels going at two different speeds (yikes). Although we did well and that never happened in a match. Also looking back on it we probably would have used a 6 wheel west coast drive last year to maintain traction when doing turning maneuvers quickly (it depends on the game obviously). I will look for some photos and post it here if I find them.

[GeeTwo]

Perhaps a crazy idea, but what if you did a "duodecanum" with the default being traction wheels?

This would have eight traction wheels, two on the same drive train as each mecanum wheel. The traction wheels are all at the same gear ratio as each other, and the mecanum all at the same gear ratio as each other.
Four of the wheels, one on each drive train, are located at the center front-to-back, and share the same axis of rotation. The other four are "outboard" of their respective mecanum wheels. The eight traction wheels form a standard 6-wheel drop-center drive chassis, with an extra pair of wheels. The four mecanum are off the carpet normally, but lift the chassis high enough that the drop-center wheel is off the carpet when the pistons are actuated.

What I'm thinking is that the center-axle wheels' interactions with the carpet will serve to clutch the front and rear half drive trains together when in traction mode, but these drive trains will operate independently in mecanum mode. I'm thinking that the corner and mecanum wheels would be in a traditional octanum butterfly configuration rotating about the traction wheels, with the center wheels being driven from the corner wheels.

It would look sort of like this from overhead, with a-d indicating which drive train each wheel is on. [L] is a traction wheel, /L/ or \L\ is a mecanum wheel.

     [a]                             [b]

     \a\                             /b/


    [c][a]                          [d][b]


     /c/                             \d\

     [c]                             [d]

Another edit: Another possibility would be to have ten wheels (decanum?), and a clutch on the center axle that engaged/disengaged the two drive trains on that side. Either of these systems would be programmed exactly like octanum, presuming that you're already constraining the outputs so that the two left axes and the two right axes match each other when in traction mode.