Sometimes it’d help to carefully read the numbers of the parts you use to design a prototype…
Today, the 624-type ball bearings, I’ve ordered earlier, arrived. When unpacking, I was somehow surprised how small these ball bearing are. Definitely smaller than the two 624 bearings I used for my Mecanum wheel prototype 2 days ago.
Well, after checking again, I saw that the ID of the old bearing is indeed 4mm, but the number on the side isn’t 624, but 80034. Sigh! Obviously I grabbed the wrong bearings out of my “bearing box” when creating the original Mecanum wheel design, and I didn’t bother to check the numbers on them…
That means, that my Mecanum wheel design I published on thingiverse 2 days ago doesn’t work, at least without buying additional 80034 bearings. However, this doesn’t make any sense since I now have a bunch of “real” 624 ball bearings lying around and the smaller size of them might be a big advantage.
So I try to make the best out of it: I re-designed the Mechanum wheel for the real 624 ball bearings.
The smaller bearing size allowed me to make the whole Mecanum wheel smaller. The center wheel diameter is now 59mm (instead of 73mm in the old design). I also simplified the design of the slots and the bearing holders. The (kind of) key & slot joint connection didn’t work very well on my prototype, so I got rid of it and designed straight slots to directly glue the holder into. I also slimmed the whole center wheel and cut off the ends of the holders:
After looking on the new wheel design for a while, it eventually struck me: The smaller center wheel, including the bearing holders had now a diameter smaller than 100mm (90,1mm to be exact) and thus would fit on a standard MakerBot build platform. Since the holders are attached in a 45° angle, I figured that it should be possible to print them without support material.
So I changed the model again,
exported it to STL,
and sliced the whole thing:
The sliced layers look definitely printable.
I had no chance yet to print the new design (it’s in the middle of the night and my neighbors probably wouldn’t be as exited about a printed Mecanum wheel right now as I). But it’s on the list for tomorrow.
Since the problems with the last design, I rather first print the complete new design and check if it’s working before publishing the STL files on Thingiverse again. So please give me a day or two to try the whole thing…
Finally, here are two renderings of the new design. The first is a normal “pack shot” of the assembled Mecanum wheel. The second image was rendered in parallel perspective. It’s a nice image where you can see why the Mecanum wheel indeed is round :)