pic: Why aren't omni wheels like this used?

[GeeTwo]

Originally Posted by Skywalkar

I'll take your current design, and raise you an improvement.

I definitely like this one better. At first, I was worried about the variable distance from the pin to the roller, but then I realized that this is also a problem with the DuraOmni, or any omni with fewer than a couple dozen rollers. I can easily imagine how to have the wheel be together, but how it comes together is certainly a challenge. Perhaps if you had some spacers that entered through the hub and held the two halves of the wheel frame apart equal to the pin diameter, laid it horizontal, then maneuvered each wheel/pin in, and finally removed the spacers and bolted the two halves together? To do this properly with minimal roller wobble, you'd probably have to have the top and bottom halves not be reflection images.


Ether, as to Duraomnis: We used them this year for what was originally an H/slide drive. They are shipped assembled, and dis-assembly was not something obvious. I'll try to remember to take a look at ours on Saturday to see how they go together and if I can confidently take one apart find out what they're made of. By "axial load", I take it that you mean load parallel the roller axis, or equivalently, thrust/braking along the wheel's canonical direction of travel. Please advise if this is incorrect.

[Ether]

Originally Posted by GeeTwo

Duraomnis: ...I'll try to remember to take a look at ours on Saturday to see how they go together and if I can confidently take one apart find out what they're made of.

Thank you.

By "axial load", I take it that you mean load parallel the roller axis

Yes. The load that causes the roller to slide on its axle (one way or the other) until it hits something that stops it. What is the thing that it hits made of, and what is the shape and dimensions of the contact patch?

[BJC]

Another primary reason these types of Omni Wheels will not see use in FRC is due to the roller thickness. Both the original and the "improved" wheels have parts of the rollers with near zero thickness. This comes with a number of problems including that the rubber rollers preferred for traction won't support a robot's weight on near zero thickness (bumpy ride) and as the wheels wear they will very quickly become non-round (very bumpy ride.)

[Ryan_Todd]

Originally Posted by BJC

Both the original and the "improved" wheels have parts of the rollers with near zero thickness. This comes with a number of problems including that the rubber rollers preferred for traction won't support a robot's weight on near zero thickness (bumpy ride) and as the wheels wear they will very quickly become non-round (very bumpy ride.)

That's for sure! Neither of these designs could be expected to produce a perfectly smooth ride in real life, even after they were tweaked for durability and manufacturability. Even dualies can only be perfectly smooth if the wheel axle is held perfectly parallel to the ground (flat ground AND infinitely stiff robot frame), but with a good enough roller design, they can indeed usually be expected to produce a smoother ride than these two wheel designs would.

Engineering is all about trade-offs, however, and a design like these two would seem to strike a potentially useful balance between a traditional single-omni design and a dual-omni design: smoother than a single-omni, and lighter/more compact than a dual-omni. It still remains to be determined whether they could be produced at a low enough price point to compete with the current market leaders, of course!

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EDIT:
Now there's an odd idea. I was considering refining my design and printing it in pieces just to evaluate the concept, but then I remembered that many "impossible-to-make" designs are trivial when additive manufacturing is employed. What if a multi-nozzle 3D printer were employed: nylon for the structure, TPE for the rollers, and a soluble support material to maintain clearance where necessary?

[Greg Needel]

you mean like this one?