pic: Mecanum Musings

Originally Posted by M. Mellott

Very interesting design! It's so simple, enough so that almost anyone could make these in a small shop! I'll be really interested to see these in action.

What size wheel would this equate to? Maybe 4" or 4.5" mechanum?

The goal was definitely to have minimal impact on machining resources (gotta save all that complex stuff for the manipulator!), and keep cost down.

The effective diameter is about 4.375. It is a little rough ride, as the design goes, so I'll be doing some incremental changes to address the problem.

[MrForbes]

What would happen if you tried to use a smaller hex for the central hub?

[dtengineering]

Nice design! It is apparent that you took practical considerations into account as the primary design factor. There was a recent thread on CD, in contrast, discussing a mecanum wheel that the designer took aesthetic considerations into account as the primary factor... but as a result the wheel needed to be made on a 5 axis CNC mill in his opinion.

I can guess which one is more likely to show up on a robot!

As for the bumpy factor in the ride, you could always (at this cost) build 8 wheels, and attach them in tandem, with one rotated 30 degrees from it's partner... much the same way you can use two omnis to smooth out the ride.

Jason

[Andrew Schreiber]

Originally Posted by dtengineering

Nice design! It is apparent that you took practical considerations into account as the primary design factor. There was a recent thread on CD, in contrast, discussing a mecanum wheel that the designer took aesthetic considerations into account as the primary factor... but as a result the wheel needed to be made on a 5 axis CNC mill in his opinion.

I can guess which one is more likely to show up on a robot!

As for the bumpy factor in the ride, you could always (at this cost) build 8 wheels, and attach them in tandem, with one rotated 30 degrees from it's partner... much the same way you can use two omnis to smooth out the ride.

Jason

I remember that thread, IMHO this wheel looks almost as nice as it. Not as flashy but it has an elegance that certainly makes it beautiful.

Jason, would mounting two of them like that really work? I mean I suppose it would but has anyone ever done it with Mecanums?

[Alan Anderson]

Originally Posted by Andrew Schreiber

Jason, would mounting two of them like that really work? I mean I suppose it would but has anyone ever done it with Mecanums?

I've driven a platform with doubled AndyMark mecanums, and it works just fine. It almost looks like they were designed to be able to be mounted that way.

[Andrew Schreiber]

Originally Posted by Alan Anderson

I've driven a platform with doubled AndyMark mecanums, and it works just fine. It almost looks like they were designed to be able to be mounted that way.

Ok, thanks, Ive just never seen anyone do that.

[JesseK]

For even less necessary machining, you could not mill out the inside of the hex stock, and instead thread-tap the holes where the counter-sunk screws go in. This makes it a bit heavier, but you wouldn't need a mill to make the wheel.

Then, you could also drill the KOP hub bolt-circle pattern into the side, eliminating the necessity of having to make a key way.

To take this even further, instead of counter-sunk screws you could use half-head-height machine bolts, eliminating the need to create the extra dimple after the initial hole is drilled.

Originally Posted by squirrel

What would happen if you tried to use a smaller hex for the central hub?

Not sure. Next time I boot my Mac into windows to do some CAD, I'll throw together a different version with smaller hex. But to be honest, I'm not sure I'd feel comfortable making it any smaller. The team I'm mentoring has an affinity for Banebots transmissions, so I think the goal is to keep to wheels that can be direct driven off a BB tranny.

Originally Posted by JesseK

For even less necessary machining, you could not mill out the inside of the hex stock, and instead thread-tap the holes where the counter-sunk screws go in. This makes it a bit heavier, but you wouldn't need a mill to make the wheel.

Then, you could also drill the KOP hub bolt-circle pattern into the side, eliminating the necessity of having to make a key way.

To take this even further, instead of counter-sunk screws you could use half-head-height machine bolts, eliminating the need to create the extra dimple after the initial hole is drilled.

There are definitely many revisions that could be made to seriously reduce machining time, but this is really just a 1.0 wheel. I'm debating changing the milling operation on the hex to be entirely one sided, so the "dishing" of the wheel would be done in a single Mill op. I'll have to do some FEA tests to see how the strength would stack up.

Also, for the rough ride concerns: Once I make the wheel wider, and thus the rollers longer, the wheel actually smooths out a good bit.

[Akash Rastogi]

Woah, the assembly for these looks incredibly easy! Great design.

[M. Mellott]

Originally Posted by Speedfiend

There are definitely many revisions that could be made to seriously reduce machining time, but this is really just a 1.0 wheel. I'm debating changing the milling operation on the hex to be entirely one sided, so the "dishing" of the wheel would be done in a single Mill op. I'll have to do some FEA tests to see how the strength would stack up...

I think what you have here is just fine. If you're using a CNC mill, the same program would be used for both sides, so there could be time savings there. Another option would be to incorporate a spoke pattern something like our 4" tread wheel design. It might help if you plan on making the wheel wider.

[jwfoss]

that mecanum looks really good, reminds me alot of the WPI wheel from 2005 except a little smaller. Do you have a view directly from the side so we can see the complete arc of the rollers?

Originally Posted by jwfoss

that mecanum looks really good, reminds me alot of the WPI wheel from 2005 except a little smaller. Do you have a view directly from the side so we can see the complete arc of the rollers?

Sure, let me grab a render real quick. I'll edit this post in a minute with it.

There's two renders here: My 1.0 ultra-cheap design, which is with 6 rollers. It's outer diameter is around 4, 4-5 inches. Next is the 8 roller one, a bit smoother, and a little bit larger with a effective diameter of 6 inches.

[rutzman]

You're completely right. My apologies for getting off topic.

Originally Posted by Speedfiend

Also, for the rough ride concerns: Once I make the wheel wider, and thus the rollers longer, the wheel actually smooths out a good bit.

How wide do you think the wheel would have to be to give a smooth ride?

Originally Posted by rutzman

How wide do you think the wheel would have to be to give a smooth ride?

About 3 inches wide, then it's pretty much smooth.

Here's a render of the latest revision. It's little bigger (effective diameter of 8ish inches), and uses more machining resources. to shave weight off.

Once I hit a revision that i feel comfortable putting on a robot, I'll be hosting the CAD for anyone that wants it, with only one rule: if you make it or modify it, you also have to put the CAD up. It's time to bring Open Source to robotics, folks.

[MrForbes]

can you render it with a viewpoint that's much further away, so the view of the side of the wheel is "flat"?

also....open source is nice! we did some this past season, I know we inspired a few teams