pic: Easy to make mecanum wheels

[mechanicalbrain]

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[mechanicalbrain]

I was wondering when this would pop up. OK the idea is basically to bolt mecanum wheels to tread instead of making a wheel (some people only have wood shops ). I'm pretty sure that if you have two sets of tread on each side you can get the necessary sideways motion. My only concern is the side stress on the tread. I don't think rubber will work. It is going to need to be plated tread which Ive been searching for. If anyone with knowledge on either tread or mecanum wheels could help me it would be very welcomed.

[BrianBSL]

Interesting idea, but I can tell you that the octagonal hub that 190's wheels bolted to was one of the easier parts of making the wheel. Just take a 3" square piece of aluminum and mill off the corners until you have 8 equal sides. You say only with a wood shop, but I don't know how you are going to make a roller support with only a wood shop. Casting the rollers and making the supports was the most difficult part.

I don't know how well non curved rollers would work either.

[mechanicalbrain]

Originally Posted by BrianBSL

Interesting idea, but I can tell you that the octagonal hub that 190's wheels bolted to was one of the easier parts of making the wheel. Just take a 3" square piece of aluminum and mill off the corners until you have 8 equal sides. You say only with a wood shop, but I don't know how you are going to make a roller support with only a wood shop. Casting the rollers and making the supports was the most difficult part.

I don't know how well non curved rollers would work either.

Well i can make them curved but as you can tell from this picture that this is hardy a schematic. Actually i was thinking of taking a material (not sure what exactly but ive got a top five list) and using a belt sander. Ive actually seen teams make wheels just by sanding raw material! So yeah im hoping i can do this with a minimum on complexity.

[phrontist]

wouldn't those metal plates need to be bent? How would you keep it on the wheel? Wouldn't any force stretch the strip of fabric?

[BrianBSL]

Originally Posted by mechanicalbrain

Well i can make them curved but as you can tell from this picture that this is hardy a schematic. Actually i was thinking of taking a material (not sure what exactly but ive got a top five list) and using a belt sander. Ive actually seen teams make wheels just by sanding raw material! So yeah im hoping i can do this with a minimum on complexity.

We tried that, but it wasnt too sucessful. We also tried taking urethane round stock and turning it on the lathe, but that didn't work too well either, atleast at the hardness we wanted. (We ended up with custom molds and pouring the rollers). If you went with a harder material, it might be possible.

It just seems like you are simplifying one of the easier parts of building them, and would require tons more rollers as well. I definitally see the same problem you do, with the strength of whatever you use as a tread actually holding it up.

[mechanicalbrain]

We can bend plates of metal. Also I'm not looking at rubber, I'm looking at plastic or thin metal tread. Even if it doesn't terribly simplify the process I think a tread has certain other benefits when it comes to stability and climbing stairs.

[BrianBSL]

Originally Posted by mechanicalbrain

We can bend plates of metal. Also I'm not looking at rubber, I'm looking at plastic or thin metal tread. Even if it doesn't terribly simplify the process I think a tread has certain other benefits when it comes to stability and climbing stairs.

I'm no ME, but I doubt you can bend the size metal that you need to make those plates out of (and not have them bend) with a regular manual break. I'd guess theres some pretty big loads, as you are supporting a roller that is supporting a significant amount of the robot's weight on it.

[sanddrag]

Well, I am becoming an ME so I'll take a shot at this one. We don't have a manual brake but I've bent 1/8" aluminum (and steel for that matter) quite nicely and fairly easily with a good mini-sledge and a vice. I think 1/8" would absolutely be sufficient for this, and you could probably get away with .090"

[mechanicalbrain]

Originally Posted by BrianBSL

I'm no ME, but I doubt you can bend the size metal that you need to make those plates out of (and not have them bend) with a regular manual break. I'd guess theres some pretty big loads, as you are supporting a roller that is supporting a significant amount of the robot's weight on it.

well the weight is distributed evenly along the length of all the touching rollers on both treads on each side, but yeah they would be adequately thick.

[ahecht]

Again, 190's wheels were slightly different than your treads, but our original aluminum supports bent with normal use (I don't remember the thickness, but they were at least 1/8") and we had to upgrade to steel.

Oh, and be careful bending metal on a vice. If you form a sharp corner, you will be losing a significant amount of strength.

[mechanicalbrain]

Originally Posted by ahecht

Again, 190's wheels were slightly different than your treads, but our original aluminum supports bent with normal use (I don't remember the thickness, but they were at least 1/8") and we had to upgrade to steel.

Oh, and be careful bending metal on a vice. If you form a sharp corner, you will be losing a significant amount of strength.

So I take two pieces bent toward each other to make a tent type shape... Yeah you always protect whatever you stick in a vice! I use scrap Balsa wood (1/4") as a buffer of choice!

[EricH]

I have three questions.
One, how are you going to keep from bouncing? You're driving along, and the roller edges hit the carpet coming around a 90 degree or so turn. Either you bounce, or you shatter the roller. Or maybe you shatter something else...

Two, how are you going to keep the rollers on? I mean, you can't just stick an axle through and say "stay" and have them stay on the axle. You need something hard on the outside, but how do you do that and not have to replace the whole tread?

Three, how much weight will this have? If it's too heavy, you might consider just wrapping the whole thing around a wheel for less weight.

[mechanicalbrain]

Originally Posted by EricH

I have three questions.
One, how are you going to keep from bouncing? You're driving along, and the roller edges hit the carpet coming around a 90 degree or so turn. Either you bounce, or you shatter the roller. Or maybe you shatter something else...

Two, how are you going to keep the rollers on? I mean, you can't just stick an axle through and say "stay" and have them stay on the axle. You need something hard on the outside, but how do you do that and not have to replace the whole tread?

Three, how much weight will this have? If it's too heavy, you might consider just wrapping the whole thing around a wheel for less weight.

I dont think this would bounce more then a tread and i don't think it would necisarily break. Look at most robots, none have suspension yet they arent (always) falling apart. Since i haven't tested it I can't speak to the reality of this answer.

I was thinking of using faerie dust. Agian this is me using AutoCAD agian after two years. No i intend a central shaft or even two triangle mounting plates on either side with a central core.

Well.... this idea hasn't been built yet, but... take an average tread design and add 2-3 pounds.

[EricH]

Originally Posted by mechanicalbrain

I dont think this would bounce more then a tread

When you consider that normal treads don't really bounce, but mecanum wheels might in a spin, and you'd get full mecanum effect... but we'll see once you get a set built and tested. You've got 3 months...after which point they need to be in testing or you won't be able to convince your team to do it this year.

Oh, and for mounting the rollers, you may want to twist the supports so the tread will actually move over tread-suppporting rollers without tearing something. And for roller axles, just make sure you can get the rollers off when you want to but not when you don't want to.