Re: Mecanum Differential Drive
 

Your calculations are totally dependent on weight. Acceleration on a 90lb robot is fine. Just look at 254 to see very sucessful drivetrains that have been geared fast(16-18 fps).

While you can't run a 6 CIM mecanum, you are ignoring the fact that at this weight and complexity you might as well make an octocanum or swerve.


Teams do it all the time on butterfly. Mecanum is no different.

Honestly I have no idea what will be available in 8 years, so it isn't worth speculating about.

Re: Mecanum Differential Drive
 

I'm not ignoring that, I even stated it as a problem in the OP.

Re: Mecanum Differential Drive
 

Actually, thinking along these lines, has any team tried a 4-shifter mecanum with locking rollers? Seems to me it might be a nice alternative to octanum; it'd offer pretty much identical functionality with comparable complexity/weight.

Re: Mecanum Differential Drive
 

Complexity and weight isn't comparable whatsoever. Look at 3928 butterfly and 973's offseason butterfly. Substitute in mecanums and you have a octocanum. Their drives are significantly less resources than a WCD even and almost as light.

Re: Mecanum Differential Drive
 

Shifters aren't that much heavier than normal toughbox nanos (~3-4lbs extra, total), and a locking mecanum system doesn't add much weight either if you build it intelligently.

In terms of moving parts, you've got four extra cylinders on a locking mecanum system, yes, but you remove the need for an extra belt, axle, and pulleys.

With the probable advent of 4'' mecanums from VexPro (which one could run straight from a CIM with direct-mounted gears and no gearbox), octanum does get quite a bit lighter, admittedly.

Re: Mecanum Differential Drive
 

What about a swerve drive with mecanum wheels? haha nevermind...

Re: Mecanum Differential Drive
 

Nah, that's not good enough, you've gotta put octanum modules on the swerve modules.

With locking plates on the mecanums, of course.

Re: Mecanum Differential Drive
 

Re: Mecanum Differential Drive
 

Care to expand?

Re: Mecanum Differential Drive
 

They both use the same basic design:

https://scontent-b-lax.xx.fbcdn.net/...29116488_n.jpg
https://scontent-a-lax.xx.fbcdn.net/...54889069_n.jpg

Essentially they have gotten butterfly down to the bare minimum causing it to be extremely easy to make(easier than a WCD) and just a bit heavier.

Re: Mecanum Differential Drive
 

With current COTS hardware, it's very hard to just swap out those omni-wheels with mecanum wheels without any changes; the 12t pinion on the 72t gear direct-mounted to the wheel relies on a 4'' wheel to work.

Incidentally, 4464 is making a slightly-modified version (we've made some material/layout changes to accommodate our specific machining capabilities) of that second type of module (actually, we cribbed most of our design choices from RoboWranglers - they had one of their modules on display at Worlds this year) as an offseason project.

Re: Mecanum Differential Drive
 

Our variant of this was trivially different (biggest difference was using 2" tall tube versus 3") and I can confirm it was easier to manufacture than our WCDs. There just aren't a lot of parts.

Re: Mecanum Differential Drive
 

The omni wheel is 6" dia and the traction 4" dia. I don't see the problem

Re: Mecanum Differential Drive
 

I am quite sure that omni wheel is 4'', with a 72-tooth VexPro gear on it; vexpro does not sell gears that are that size proportional to a 6'' omni.

Re: Mecanum Differential Drive
 

VexPro doesn't sell a traction wheel smaller than 4" either