Re: Mecanum Wheels
 

http://www.fingertechrobotics.com/pr...mecanum-set-hg

what if instead of using 4 6 inch mechs, you used 8 or even 12 of those. that would greatly decrease the amount of rotational inertia in the wheels, those little wheels are also higher quality.

Re: Mecanum Wheels
 

I suppose it would get pretty heavy and costly to have four shifting gearboxes, but it would be possible I guess.


Doing a little back-of-the envelope math...

assuming constant deceleration

a = (V*V)/(2*x) = (18*18)/(2*5) ~ 32 f/s/s ~ 1g

... so you'd need an effective CoF of 1.

To get that with mec, you'd need about 1.4 CoF between the tread material and the carpet. So you'd have to make your own custom rollers with high-traction tread.

Re: Mecanum Wheels
 

The software would get interesting, unless you plan to mount 3 coaxially at each of 4 locations and drive all three 3 wheels within each coaxial set at the same speed (which would be approximately correct but not quite, resulting in friction).

Re: Mecanum Wheels
 

i was actualy thinking of mounting all 3 right next to each other on a standard frame setup. i would probably use #25 chain directly driven from a cim ( no gearbox)

Re: Mecanum Wheels
 

By "right next to each other" I assume you mean "in the same plane" and not "coaxially".

Such being the case, a correct inverse kinematic translation would require that each of the 3 wheels in a set be driven at slightly different speeds.

If you just chain them together and drive all 3 at the same speed, you'll get some scrubbing of the contact patch which means additional loss of power and traction.

Re: Mecanum Wheels
 

i think that the same thing would happen if the were mounted co-axially. while it is true that while using all 3 degrees of freedom there would be some scrub, during normal translation there would be none, conceptually it is 3 entirely separate mechanum bases, driving in the same space, at the same speed.

Re: Mecanum Wheels
 

I believe that is correct.

Re: Mecanum Wheels
 

Looking through the links on this thread, I see that the number of rollers per wheel seems to vary based on who is designing them. Is there an optimum number?

Re: Mecanum Wheels
 

It depends on what you are trying to optimize.

Re: Mecanum Wheels
 

Ether is right. If you want to optimize a smooth ride, lots of rollers are better (less "flat" distance between crowns of rollers). If you want to optimize manufacturability, fewer rollers are better (to a point--4 rollers to a wheel will most likely really, really make life miserable for the drivers). And it will depend on your design.

The center-hub designs typically carry about 6-8 rollers per wheel from what I've seen; the AM outer-hub design carries something like 32. I've seen an outer-hub design carry 8, and a combination of outer and inner carry something like 20. It varies depending on design and wheel designer.

Re: Mecanum Wheels
 

Fewer rollers also means fatter/wider wheels, assuming diameter and angle stay constant. The rollers have to be longer to cover a sector of the wheel, and since they're at a 45 deg angle, that means they'll stick out farther to the sides as well.

Also, can everyone in the thread agree that the Mecanum vs. 6WD discussions were already done this season in numerous other threads? If someone thinks that horse isn't dead enough, I implore them to revive one of those threads or at least give us a break until next season.