Re: Pic: Easy to make mecanums..
 

Do you have some cad files? If so, you should share them with us; I'm sure a lot of people would love to make their own.

Re: Pic: Easy to make mecanums..
 

we'll whitepapre and upload it once we get all the problems worked out.. we've found a few, we're in the process of fixing them.

Re: Pic: Easy to make mecanums..
 

Sweet! Very nice process.

What, if any, bearings are used on the shafts that hold the lab stoppers?

I'd also be interested in hearing more about the durability of the stoppers.

Don

Re: Pic: Easy to make mecanums..
 

As of now the lab stops are on bolts. This was just for the picture :P
We are in the process of ordering a bunch of .250 ID 1" length bushings to put in all the rollers. They will then run on a ground steel shaft that is pressed into the wheel housing, with E-rings on the edges to keep the rollers from sliding off. We know that the wheels are slightly fragile with the rollers outside the wheel like that, and the steel roller shafts would be prone to bending. But like most robots, we plan to have our wheels well protected from all sides. The wheels can take huge forces radially, because if pushed hard enough the rollers will compress and the wheel bottoms out against the aluminum housing. This takes about 150-200 lbs per wheel to do.

A side note, efficiency is not reduced by weight on the wheel (other than more friction in the bushigns) because there is enough clearance on the sides of the rollers to allow for expansion due to weight compression. Also, these wheels get very good traction because the rollers are made of gum rubber. This means that all the rollers will have to be replaced every regional, but at 25 cents a piece from mcmaster, I dont think that will be a problem.

Our goal from this is basically to have an agile mecanum robot with lots of traction and pushing power, something not common with omni-directional robots. Look forward to designs for ball shifting transmission for each wheel...

Re: Pic: Easy to make mecanums..
 

For some reason I'm contradicting myself, I've designed a set of these before, but I think I might have done them wrong; what angle are the rollers supposed to be offset to the hubs?

Re: Pic: Easy to make mecanums..
 

Nearly any offset will work in theory, but 45* is most efficient.

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Its not that 45* is most efficient. It is that 45* results in the max speed to the side is equally to the max speed forward. They are actually less efficient than say 30* because the rollers need to turn faster when moving in a direction other than forward. Of course 30* also means that the max side speed is lower than the max forward speed and the pushing power is greater.

Re: Pic: Easy to make mecanums..
 

A little birdy told me that free mecanums are always the easiest, but if you don't win them these are pretty darn cool!

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By 'most efficient,' I meant simply that a 45* offset allows for the fastest perpendicular drive speed. It's true that you can optimize the offset angle to better suit the conditions under which the drive will operate.

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Question:

Most mecanum wheels have the rollers at a 45* angle on 2 axes (I think you all know what I mean, at least, I hope it's clear: the rollers are at a 45* angle to the wheel and then angled upwards, correct?)

Is this necessary, is it simply for increased traction, or could one theoretically design a mecanum wheel more in the style of an omni wheel, simply rotating the rollers to a 45* angle instead of a 90* angle?

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Yeah, take a look at this report (where i got most of my Mecanum information from) specifically the image on the first page titled the conventional Mecanum wheel. I think that is what you are talking about and although not as cool looking as the others, probably the easiest Mecanum to build if you don't have a CNC mill or, mill master and don't want each wheel to be a multi piece wheel.

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Is the oblong roller necessary as well, or could one do something more along the lines of an AM trick wheel with the roller at a 45* angle?

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The shape of the angled roller is intended to make the overall profile of the wheel a smooth circle. If that's not done, the wheel will be somewhat "bouncy" in operation, and it won't have consistent traction as it turns. If the inconsistency is severe enough, it will be difficult to maintain a desired direction of travel.

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The finished mecanum! (Sorry about the glare)


A comparison with the spares.


Much lighter now :D

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Excellent job 1072 very nice machining process. I also love what you have done on being able to lighten the wheels. I like the fact that 1072 makes most of the stuff they design and has some great initiative about things like that. Finally, amazing pictures.

-Drew