pic: Jester Drive:Mecanum Wheel Drive Train

[Evan Austin]

Hey, I see it now!
Great job, this is an idea I would never have thought of. I like this design a lot. In this game, maneuverability is important and you should definitely have that under control. What is it like to drive? I have never driven an omni directional robot and I am curious. It looks excellent
Good Luck!

[pakrat]

did making those wheels take up a lot of your build season time?

[Alex357]

The one roller vs. two roller difference is indeed significant. Two rollers allow for more controlled motion because of better release of friction. One roller wheels have a 50% higher coefficient of friction causing for more draw and no extra pushing power for the cost.

To answer another question, building the wheels was a very long process. We prototyped throughout the summer in our SRP (Summer Robotics Project)... our team doesn't have an off-season really. Anyway, deciding to make and use these wheels during the six weeks isn't really feasible. There's a lot that goes into the process, from hubs to molding rollers. You cant go out and buy these wheels pre-made, so there's a lot of hardworking and trial-and-error stuff that goes into it. But it's a fun process, and when you finish, you feel like you've accomplished something awesome (cause you have).

[BrianBSL]

Originally Posted by Alex357

The one roller vs. two roller difference is indeed significant. Two rollers allow for more controlled motion because of better release of friction. One roller wheels have a 50% higher coefficient of friction causing for more draw and no extra pushing power for the cost.

We haven't done any tests on the two roller model, as we decided that the machining difficulty for the hub was be far too great and supporting the rollers from only the middle would be difficult. I highly doubt that it is a 50% higher coefficient of friction - the only way it would hurt you is if one roller was going to be spinning at a significantly different speeds. I'm no ME (I'm an EE), but doesn't the coefficient of friction deal with the actual force you apply to the ground, meaning you would actually have more pushing power? I agree that the two roller design is better, obviously Airtrax had a reason for using it, but I think you are blowing it out of proportion a bit. The single roller design is much easier to manufacture, although it is more parts. (The hub is simply a piece of square 3x3 aluminum stock with the corners cut off). We had absolutely no issues with pushing power.

[Alex357]

Originally Posted by BrianBSL

We haven't done any tests on the two roller model, as we decided that the machining difficulty for the hub was be far too great and supporting the rollers from only the middle would be difficult. I highly doubt that it is a 50% higher coefficient of friction - the only way it would hurt you is if one roller was going to be spinning at a significantly different speeds. I'm no ME (I'm an EE), but doesn't the coefficient of friction deal with the actual force you apply to the ground, meaning you would actually have more pushing power? I agree that the two roller design is better, obviously Airtrax had a reason for using it, but I think you are blowing it out of proportion a bit. The single roller design is much easier to manufacture, although it is more parts. (The hub is simply a piece of square 3x3 aluminum stock with the corners cut off). We had absolutely no issues with pushing power.

It's not coefficient of friction... sorry i hadn't had coffee yet. The 50% figure comes straight from the studies Airtrax performed. It's that the single roller model has 50% less release of friction. The two roller model has two independent rollers, meaning that either side can move either forward or backward, so one could be spinning in a different direction than the other allowing for more release of friction.
The one roller design does not limit pushing power, but it draws more juice to get the same pushing power as the two-wheeled design.

[techtiger1]

Thanks Alex. as the engineer from beach bots said think and have a back up plan before u get into doing this. Making these is extremely labor intensive and you have to make them from scratch I have seen prints for wheels like 357 and there a whole off season's worth of work as Alex stated.

[EricH]

Originally Posted by techtiger1

as the engineer from beach bots said think and have a back up plan before u get into doing this. Making these is extremely labor intensive and you have to make them from scratch I have seen prints for wheels like 357 and there a whole off season's worth of work as Alex stated.

I'm not an engineer, I'm a student. Thanks for the compliment.

Making the wheel we had at nationals (for display only) took about 2 years from initial concept through prototyping to the wheel. The first year: After seeing the ones used to remove containers from airplanes, my dad decided to try to make some. By the end of the summer, we had a set for the Robovation kit. We also had the programming to operate it. The second year: two experimental wheels were made, similar in design to the current ones. When we decided to try them this year and keep six wheels as a reserve, we had a set made. However, when we tested that set, we found that it did not have enough traction, and we could not get another set of rollers designed and built in time to test them before ship, so we went with six wheel drive. We had the textured rollers made before ship day, but have not tested to find out which roller tread is best. More testing to come at a later date.

One set of wheels can be made in about 3 days, from part production to assembly to mounting on a robot.