Mecanum Differential Drive

[MichaelBick]

Originally Posted by efoote868

In FRC, 16fps for a single speed has no advantages to 12fps for a single speed. By the time you accelerate to the top speed, you're already clear across the field.

You can't use 6 cims in present mecanum drives.

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.

Controlling a robot through 4 independent shifts on a mecanum drive would be difficult.

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

8 years ago if I told you that in the future, mecanum wheels would be available for purchase to every team at a reasonable cost, you would have called me crazy.

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

[efoote868]

Originally Posted by MichaelBick

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.

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

[Oblarg]

Originally Posted by MichaelBick

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

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.

[MichaelBick]

Originally Posted by Oblarg

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.

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.

[Oblarg]

Originally Posted by MichaelBick

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.

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.

[BBray_T1296]

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

[Oblarg]

Originally Posted by BBray_T1296

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

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

With locking plates on the mecanums, of course.

[BBray_T1296]

Originally Posted by Oblarg

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

[Gregor]

Originally Posted by MichaelBick

Their drives are significantly less resources than a WCD even and almost as light.

Care to expand?

[MichaelBick]

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.

[Oblarg]

Originally Posted by MichaelBick

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.

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.

[AdamHeard]

Originally Posted by MichaelBick

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.

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.

[MichaelBick]

Originally Posted by Oblarg

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.

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

[Oblarg]

Originally Posted by MichaelBick

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

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.

[MichaelBick]

Originally Posted by Oblarg

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.

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