Omni wheels

[kajeevan]

I m cadding an omni directional base and would like to know which of andymarks omni wheels work best the newer molded plastic 6in or the older Al omni wheels.
Also im new at the omni directional thing and just experimenting and would like to know aout your experiences with this type of base and what works best 45 degree wheels or being 90 degree to each other.

Also if its the newer omni i would like to know were i can find a cadded version with it firstcadlibrary seems to only have the older version.

[Joe G.]

I assume you are referring to this wheel and this one, or the eight inch equivalents. We have only ever used the plastic ones, which have worked fine for us. The main advantage of the plastic wheels is that they have space for two bearings, which is nice for stability in dead axle applications. If you are using live axles, this feature is not as necessary, as you would probably have some type of hub providing further stability as well as mating to the axle. The aluminum omniwheels, on the other hand, have the advantage of being more repairable, as if they are hit on the side and bent, they can simply be bent back into place, where if the plastic wheels break, they will likely snap, and require a replacement wheel. So it really depends on which is more important to your design. If there is absolutely no way anything will ever hit your wheels, the plastic wheels are a good choice, but if they are out in the open, you may want to look into ways to get more stability out of the aluminum omniwheels, such as doubling them up.

I'm a bit confused on what you mean by your question about wheel angles. Do you mean which of these two overhead views would work better?



Our team has never done this type of drive, but I believe that if you work the vectors, you get more power out of four wheels pushing against eachother at angles, as seen in the top drawing, compared to 2 wheels with full power, as driving forward with the bottom drawing would do. You would probably want your maximum power to occur in common directions like forward and sideways, rather than 45 degree angles.

Don't know if any CAD models exist of the Plastic omniwheels.

[AndyB]

Andymark has CAD files of all of there products available on their website. Just right click on the filename.stp and Save Link As.

[vivek16]

From experience, the 6" aluminum AM omnis are great. Made SURE all wheels touch the ground or have some sort of suspension. I think the xbots used racquet balls and tennis balls for a suspension. I'm not sure how it went but I thought it was really creative.

-Vivek

[fuzzy1718]

The bottom right drawing is a bad idea, we tried somthing similiar, 6wd instead of 4, but you will never get the 2nd direction wheels to get traction, unless you use a suspension system. Due to the rollers on the wheels the frame never stays level long enough to gain traction with the 2nd direction wheels.
Go with the plastics ones, we tried the aluminium ones and once they are bent they are hard to get back straight, and make driveing in a straight line a nightmare, even with a gyro.

[vivek16]

Originally Posted by fuzzy1718

The bottom right drawing is a bad idea, we tried somthing similiar, 6wd instead of 4, but you will never get the 2nd direction wheels to get traction, unless you use a suspension system. Due to the rollers on the wheels the frame never stays level long enough to gain traction with the 2nd direction wheels.
Go with the plastics ones, we tried the aluminium ones and once they are bent they are hard to get back straight, and make driveing in a straight line a nightmare, even with a gyro.

Well, we did double up the aluminum omniwheels so that would have prevented any bending. AM sells a spacer to double up the wheels like that.

-Vivek

[AdamHeard]

Originally Posted by fuzzy1718

The bottom right drawing is a bad idea, we tried somthing similiar, 6wd instead of 4, but you will never get the 2nd direction wheels to get traction, unless you use a suspension system. Due to the rollers on the wheels the frame never stays level long enough to gain traction with the 2nd direction wheels.
Go with the plastics ones, we tried the aluminium ones and once they are bent they are hard to get back straight, and make driveing in a straight line a nightmare, even with a gyro.

Both frames have 4 wheels offset 90 degrees from each other. I'd imagine both have the same problems without a suspension.