4" Heavy Duty Mecanum Wheels

[Ether]

Originally Posted by compwiztobe

four 4" omnis at 90º to each other offers the exact same functionality with approximately the same footprint

Just to be clear: given the same wheel radius and same motors and gearing, omnis have a theoretical advantage of 41% in speed, and disadvantage of 29% in force (compared to mecanum)

[Ether]

Originally Posted by Brandon Holley

You are definitely going to want the outer rubber to adhere to whatever is on the inside. Otherwise the roller is just going to shred itself off.

For a dual pour, I agree that adherence between the outer "skin" and the inner "core" is critical, for the reason you stated.

However, adherence is not necessary between the core and the Teflon sleeve.

[Alan Anderson]

Originally Posted by Brandon Holley

I too was considering a dual pour, but it does get tricky. You are definitely going to want the outer rubber to adhere to whatever is on the inside. Otherwise the roller is just going to shred itself off. I also believe you are going to want your outer rubber to have a pretty uniform thickness along the entire roller to get the best performance (this way its actually like a "tread" on a standard wheel).

So why not treat the outer rubber as an actual tread? Make the roller out of a hard material, and create the equivalent of a rubber slipcover that gets pulled over the roller core. Keeping the "tread" in place is a matter of appropriate engineering; I can think of several options.


Or you could form the roller core to have some overhang around small pits or slots, then pour the softer material around it. Even if it isn't adhering the same way a dual pour between highly compatible materials would, it is still mechanically secured.

[Brandon Holley]

Originally Posted by Alan Anderson

So why not treat the outer rubber as an actual tread? Make the roller out of a hard material, and create the equivalent of a rubber slipcover that gets pulled over the roller core. Keeping the "tread" in place is a matter of appropriate engineering; I can think of several options.


Or you could form the roller core to have some overhang around small pits or slots, then pour the softer material around it. Even if it isn't adhering the same way a dual pour between highly compatible materials would, it is still mechanically secured.

Absolutely there is a way to make a design like that work. In my experience on some molds I have done, even with features like that, the tread has come off (this is particularly true when dealing with skid steered drive wheels where they scrub along the surface, or even getting pushed sideways from an opponent). Again, I'm not saying its not possible, it is actually quite do-able. Just in my experience, I would do everything I could to make sure those two layers were bonded. Whether its a direct "insert mold", a spray on adhesive, a roughened surface, grooves or slots, or some combination of all of them...

-Brando

[craigboez]

Alright, thanks to everyone for your input. It looks like I've got some R&D to do. It might take me all summer, but I'll post some updates along the way.

[techedguy]

Late reply I know:

The core of our rollers were teflon tubing. I came up with buying push nuts what would grip into the teflon and pushing them on in opposing directions so that in order for the core to come out it would have to pull both push nuts off (also those push nuts had holes between all of the teeth biting into the teflon tube, resulting in even more of a mechanical bond.

I can tell you from the experience that it takes razors, a vise, vise-grips, and some sweat to take one of those rollers apart (we had a few duds and wanted to recover the teflon cores for re-dos).

Did you continue this project?

[craigboez]

The project lost steam, mostly because I got busy doing some other projects. After the 2012 FRC season finishes up I'm hoping to dedicate some time to it.