pic: FRC488's Octocanum Ver 2.0

[Jonathan Norris]

Any thought into making the Mecanum wheels the pivoting ones?? Our team last year developed some CAD prototypes for this combination, and eventually didn't implement it due to the added complexity. However, we did use mecanum last year, and didn't have a great experience with it. I think one of the biggest problems we saw (other then malfunctioning Jaguars...), was that when all four wheels were not on the ground (due to an un-even playing field, and seams in the carpet) the controllability of the system declined, and even worse the power of the drive system declined. Some of this we could correct with programing, but loss in power and acceleration was really noticeable. The loss in acceleration is I believe the biggest downside of using mecanum, the reality I saw was that our robot was just far slower in accelerating, changing direction, and stopping (decelleration) then high traction based drive systems.

I was wondering if you pivoted around the traction wheels instead of the Mecanum wheels in the octocanum, if you would see any advantages because the pistons could act as a suspension system. I've been told that mecanum drive systems perform better with a suspension system, I would be interested in hearing from teams that have used suspension in their mecanum drives. But for me I would need to see a big improvement in acceleration/deceleration to advocate for using mecanum again.

[Ether]

Originally Posted by Jonathan Norris

The loss in acceleration is I believe the biggest downside of using mecanum, the reality I saw was that our robot was just far slower in accelerating, changing direction, and stopping (decelleration) then high traction based drive systems.

What do you think would cause a mecanum to stop unacceptably slowly?

Are you saying it slides across the carpet when you try to stop quickly?

Do you have any video showing this?

[Dad1279]

Originally Posted by Jonathan Norris

....
I was wondering if you pivoted around the traction wheels instead of the Mecanum wheels in the octocanum, if you would see any advantages because the pistons could act as a suspension system. I've been told that mecanum drive systems perform better with a suspension system, I would be interested in hearing from teams that have used suspension in their mecanum drives. But for me I would need to see a big improvement in acceleration/deceleration to advocate for using mecanum again.

That is what we did. Not necessarily for the suspension, but we wanted the traction wheels to be the most outward wheels for stability, and on the the fixed axles for strength. Also, if there was an pneumatic failure, we wanted the default wheels to be the traction wheels.

Not shown in the sketch below, the pistons were vertical, one on each side, and they pushed down where the front and rear pivot arms met in the center of the robot. We used the 8" Andymark wheels, not by preference, but budget. We had a new, unused set on the shelf as spares from the prior year. Also not shown below, the transmissions and outer axle bearing were rigidly mounted to chassis.

Yes, 8 motors on drivetrain, 1 CIM and 1 CIM-U-LATOR/775 per wheel.



While I personally preferred the field-orientated driving, unfortunately (for me) mentors don't drive. Our driver preferred traditional controls, so that his orientation didn't change when swapping between traction and mecanums.

[Joe Ross]

Originally Posted by Dad1279

While I personally preferred the field-orientated driving, unfortunately (for me) mentors don't drive. Our driver preferred traditional controls, so that his orientation didn't change when swapping between traction and mecanums.

You could do something like 451's SOAD - Semi Omni Arcade Drive.