Omni Wheels

[savagecreature]

Since Kresty posted a link to those files, I did another wheel in a similar vein.  I have uploaded the files to make this omni wheel. They can be found here.

Omni wheel no. 2 (4 in omni wheel)


This is along the lines of the design that Kresty linked to, but there were things about that design that I thought could be improved so this is my version. I made the hub solid instead of a frame for strength, I made the two hubs identical instead of having two unique pieces and I designed it to use nuts to hold the axle bolts in place instead of simply threading into the plastic. 

Here's what the computer version looks like:

The first step was to print the pieces.  When printing things that will be bolted together I increase the number of shell layers to add strength and to provide enough plastic in case I need to drill the holes out at all.  I printed these much like the first wheel, which is to say using whatever filament I happened to have on hand. I like to have the rollers a contrasting color, so I went with yellow and black for the hubs.

Two hubs (they're identical) and six rollers. The rollers should be printed on end (obviously ) and with supports turned on.  The hubs don't require supports.  The first step is to press fit the bearings into the rollers, two bearings for each, one on each end.  I designed them to use 623zz bearings which are both common place and inexpensive.

I also happen to have a lot of them lying around so it was a logical choice for me .  Oops, but wait. Not the first step. The first step is to remove the supports from the hole in the end of the roller. To do this I used my angled needle-nose pliers and simply pinched them together and twisted and they came right out.

No further clean-up was necessary.

To press fit the bearings into the holes just put the bearing on your work surface, place the roller on top, and press as evenly as possible downward. The bearing should just pop in.  The bearings are countersunk to leave room for an M3 nut, so once the bearing is flush with the end, place a nut on the table, center the bearing on the nut and press again, driving the bearing the rest of the way home

Once pressed in the bearings should be about half a bearing width from being flush with the end.

Now here comes the fiddly part. Getting the bolts through the forks and into the rollers is a little difficult. Only a little, but still.
I started by putting one 10mm M3 bolt through one of the forks and putting a nut on the end. I didn't tighten the nut down, I just put it on enough threads to keep the bolt from falling out of the fork.

Next I rocked a roller on top of the nut and slipped the other side into the fork. It's a tight fit, but it'll go. If the bolt is sticking too far through the nut it won't work.  Once the roller was roughly in place I slipped a nut between the fork and the bearing and stuck a bolt through the other side of the fork.

Then I just wiggled the bold around until it lined up with the nut, held the nut with my fingers and threaded the bolt into it with the other hand. As far as tightening them down, firstly, they don't have to be too tight. Just enough to stay put. I was able to press the roller bearing against the nut with enough friction to tighten down the bolts. After doing it a few times I actually got fairly good at it and it only took a moment to put each roller on. If that doesn't work for you, let us know what you come up with. Alternate methods are welcome, for sure.

Do that for all three rollers on the wheel half and you get something that looks like this

The two halves are going to have to go together in such a way that the rollers are opposite of each other. They only go together one way and there are only three possible options, so I'm not going to spend a lot of time suggesting intricate methods for their alignment. I'm sure you can figure it out.

That last part is to simply bolt the two halves together with four 20mm M3s and four nuts.  I always alternate the direction I insert the bolt, unless there's a good reason not to like access to the nuts or that sort of thing. You can do that or do them them all from the same side. It'll work either way.

I really like these omni wheels. They're very rolly and offer very little resistance in directions of movement other than the drive vector.  I'll have to upload some video of them in use sometime soon.