pic: Mecanum Musings

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

Originally Posted by squirrel

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

I'm not understanding this, sorry.You're asking for a view that's in orthographic, not perspective, and from a "front" of the wheel view, or a "side" (front being looking at the narrow view, what I have in the middle there, "side" being the one on the left)?

[MrForbes]

side view, as in looking at the side of the robot. The view in the left of your picture above. Change the perspective to infinite, so you can see how "round" the wheel is.

[Brandon Holley]

Originally Posted by Speedfiend

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.

I've spent some time designing mecanums (on a smaller scale), and I have my own method, but I was wondering if you would share the method you used to create the curvature of the roller. Specifically in CAD terms (I'm very familiar with any CAD system), what you did to ensure your roller curve was as effective as possible.

Thanks in advance!
Brando

[D_Price]

The only question i would ask would be if they were to be bumped into would they break easier or would they still have enough strength.

Originally Posted by Brandon Holley

I've spent some time designing mecanums (on a smaller scale), and I have my own method, but I was wondering if you would share the method you used to create the curvature of the roller. Specifically in CAD terms (I'm very familiar with any CAD system), what you did to ensure your roller curve was as effective as possible.

Thanks in advance!
Brando

Sure thing. Start with a center line that will serve as an axis to revolve the roller around. Next, draw your edge lines on the left and right edges of the axis. Put a third in the center, higher than the first two. Draw two arcs connecting these outer lines to the center line. Let me know if this is confusing and I can upload a drawing for you.

Originally Posted by Hell918

The only question i would ask would be if they were to be bumped into would they break easier or would they still have enough strength.

They're quite solid as they stand, but I don't like leaving a wheel uncovered for any reason. For that reason I'll probably enclose the wheels, most likely in 1/8th aluminum sheet on which the bumpers will be mounted.

[Brandon Holley]

Originally Posted by Speedfiend

Sure thing. Start with a center line that will serve as an axis to revolve the roller around. Next, draw your edge lines on the left and right edges of the axis. Put a third in the center, higher than the first two. Draw two arcs connecting these outer lines to the center line. Let me know if this is confusing and I can upload a drawing for you.

I believe I understand what you are saying, it is similar to what I do as well, but a picture would not hurt... thanks!

Originally Posted by Brandon Holley

I believe I understand what you are saying, it is similar to what I do as well, but a picture would not hurt... thanks!

Well, here's a Paint version... I don't entirely feel like booting into windows right now, so I can swap this image out for a screencap of the sketch some other time.



Then you revolve it around that bottom line. After that you put a hole through the center for the bolt, then put recession into the roller for bushings.