pic: A mechanum wheel that shouldn't bump around at all.
 

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

Have you ran various mecanum wheels and encountered "bumping" problems? What improvement will eliminating this "bumping" give?

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

There are various nominal benefits, such as more reliable traction and an accelerometer with much less noise. No single benefit stands out, but it's always fun to ponder new designs that address even the small issues in order to perhaps come up with a much better design.

This is good work for creating a nice round profile. However, the hardest part is in the mounting of the rollers; a single plate that forms the middle of a "T" may or may not be enough to support the cantilevered stresses from the rollers. 357 may be able to give some insight there. Additionally, the mounting of the rollers will inevitably create some sort of gap when mounted in the center -- i.e. each roller as shown is not possible. In reality each roller is more like two roller halves, split in the center where the mount goes.

Combining the two dominant Mecanum designs into a hybrid design may be a better solution. A hybrid design has 3 rollers with 2 thin mount plates; the two rollers on the outside look like rounded cones and are cantilevered whereas the roller in the middle looks more like a bulging omni wheel roller (or a squished donut).

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

Do those elliptical things actually roll (how?), or are they fixed in relation to the wheel?

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

They would roll. That's the way a mecanum wheel works--the rollers (the elliptical things) roll to alter the vectors the wheel is putting out. There would be an axle down the middle to allow them to roll; I don't see it here yet.

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

Like the segway mecanum wheel??



-Brando

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

I have been thinking about how you did this, and I have to say, you have me stumped. How did you design the 3D wheel with that perfectly circular side profile?

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

in actuality the arm will go all the way out, and match the profile of the roller and be coated in delrin, that will slide and will make it perfect, the way i did it was to assume that each roller had to have an arc that would look exactly like a circle when viewed from 45 degrees, thus the line that defines the outer edge of that roller is an elipse with one dimension being 8, the diameter of the wheel, and the other dimension being 8/sin(45) or about 11.3, this makes the profile of the roller a perfect circle from a 45 degree angle. the rollers are just revolves with that line as the edge. the arms are .375 inch thick 7075 aluminum alloy, and according to solid works, this wheel should hold at least 200 LBS safely. the total weight of the wheel is 1.8 LBS, it is 2.6 inches wide from roller tip to roller tip, and is 8 in diameter, the axle hole will have have a hub or something to attach it to the motor. the method for manufacturing the rollers is to print off a mold on our 3d printer, then use urethane, coated in rubber. overall it should be pretty sweet.

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

These wheels remind me of Airtrax wheels, did you get the idea from them? I would like to see a nice set of mechanum wheels for FIRST.

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

Hi Brandon,

Could you provide a link that shows the rest of this picture? I am curious to see the rest of the platform.


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Re: pic: A mechanum wheel that shouldn't bump around at all.
 

That's the Segway RMP 400 Omni.

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

Thanks Alan.

Looks like the wheels in the picture Brandon linked to are mounted incorrectly.


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Re: pic: A mechanum wheel that shouldn't bump around at all.
 

hmmm... this wheel sure does look pretty, but does it run that way too? the side wheels (or whatever the technical term for them may be) look as if they are at a very harsh angle. now, i'm just a programmer, but isn't the ideal angle 45 degrees?

Re: pic: A mechanum wheel that shouldn't bump around at all.
 

There is no "ideal" angle.

Many mecanum wheels have rollers at 45 degrees. This makes the kinematic (and dynamic) analysis easier. The forward and inverse kinematic matrix transformations are simple, with no trig functions or square roots.

Making the angle smaller than 45 degrees (angle between roller axis and plane of the wheel) improves forward/reverse traction but reduces strafing traction, and vice versa.

So there is no one ideal angle. It depends on the application.


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Re: pic: A mechanum wheel that shouldn't bump around at all.
 

You can buy some from AndyMark.