Gearing for mecanum
 

I have attempted to calculate the necessary gearing ratio for a mecanum drivetrain. The drivetrain will have 1 CIM per wheel (and no other wheels), and use 8-inch Andymark mecanums.

I calculated the gear ratio so as to be traction-limited under the following assumptions:

• 150 pounds max robot weight
• 0.7 max CoF for the wheels (reported by Andymark)
• 40 amps max continuous current per motor

I came up with a desired ratio of about 16.25:1. This results in a theoretical free speed of 10 ft/s.

Last year's robot used a kit frame. This had about an 8:1 gear ratio. Since this computes about double the required gear ratio for (theoretically) slicker wheels, I am skeptical of my results.

Does this seem correct?

Re: Gearing for mecanum
 

I don't know much about ratio however,

This excludes bumpers.

Re: Gearing for mecanum
 

Taken care of. Note that the ratio was calculated for 150 lbs (robot+bumpers+battery).

Re: Gearing for mecanum
 

... and batteries.

I used 150 pounds so I had a bit of a margin for error.

Re: Gearing for mecanum
 

I figured that was the case, but I wasn't sure.

Re: Gearing for mecanum
 

We used stock 12:1 banebots planetaries with CIMs and 8" AM Mecanums several years ago and were relatively pleased with their performance.

I don't remember having wheel slip aside from when one of the wheels was off the ground, and we did get in some pushing matches... so I can say that a 12:1 ratio does not exceed the ability of an AM mecanum to put torque to the ground.

Going to a slower, higher torque gearbox, like the 16:1 may have advantages in that a higher torque output can allow for greater acelleration and better low-speed handling.

But I think I'd stay away from the 8:1 ratio... that seems very "fast" to me. Although it is common to calculate for a a robot's top speed, if you watch the game closely teams spend very little time at top speed, and a lot of time maneuvering, acellerating and decellerating.

Jason

Re: Gearing for mecanum
 

Okay, that helps clear things up.

I think that in our case, we want to be traction-limited more than fast. Therefore, I'll let the team know that we need a 16.25:1 ratio.

Thank you.

Re: Gearing for mecanum
 

If you used 9:1 for 8" wheels, would you expect to see CIMs cut out at initial full acceleration? Not that I have any reason to ask :-)

Re: Gearing for mecanum
 

We've used 9:1 on Andymark 6" HD mecanum for several years and are very happy with the results... That is at least close to a 12:1 on 8" wheels.

I'm not sure I'd want 8:1 on 8" wheels!

Re: Gearing for mecanum
 

Last year we used the mecanum wheels directly out of AndyMark nanotube. The gearing on that was 12.75:1. We were pleased with the results.

Re: Gearing for mecanum
 

We use the AndyMark nano transmissions but swapped gears to get 10.67 for 6" wheels - it works great. We figured quickness was paramount for this years game since the hump and bridges won't allow for full court sprints.

HTH