A month ago, I received 12 skatemotor-sized motor cans that I had commissioned through mfg.com by a semirandom Chinese machine shop. It was mostly an excercise of curiosity, but with 12 motor cans and no other motor parts, I decided to keep going with it – I went back to the semirandom Chinese machine shop and had them fabricate 12 sets of skatemotor parts: both endcaps, the center shaft, and the big ring nut thing that mounts the wheel.
That’s alot of little aluminum bits. What I have now learned is that someone else will actually hold the tolerances I indicate on my drawings, whereas I usually would just ignore them. The result is that the endcaps fit very tightly in the can (one is supposed to be looser) and the shaft-bearing fit is also a little tight, but it’s within sandpapering reach, not second lathe operations. The next time I do this, I have to specify a different tolerance band… though for now I do not mind making a single lathe pass and freeing up said endcap, or heating up the bearing and freezing the shaft for a real bearing fit.
Before I sent the dimensioned drawings off for quoting, I did a little re-engineering of the motor in the interest of easier assembly.
The shaft was remade as a straight pass-through, single-diameter part with key slot to clear wires. I actually designed it to mimic a 15mm metric keyed shaft such that it can form the starting stock, and the only operations done to it would be drilling and grooving.
Otherwise, the method of axial alignment has now switched to retaining rings. Yes, I know – snap rings are terrible, and I hated them the most when I was younger and eagerly disassembling appliances which always seemed to use them and I had no retaining ring pliers to cleanly remove them with and and… well, normal circular snap rings didn’t fit in this design anyway. I designed in two “low clearance” retaining rings (e.g. McMaster 97414A670) on each side of the stator. The inner ones keep the stator aligned, and the outer ones both space the bearings out and act as a restraint to prevent wire insulation from grinding on the bearings. I think this is a nice and simple system that is easy to assemble.
The stator is still a 50mm copier stator mounted on a custom 3d printed adapter hub – there is no more “stator bore” shoulder on the shaft. I did try getting quotes for fully custom punched and stacked laminations designed to a slightly different geometry with thicker teeth to maximize torque production, but it would have cost way more than I wanted to spend (or had) – $1200 for tooling alone. While the stators would be cheaper per unit afterwards, I think my best bet is still to find a supplier of completed (and epoxy coated) stators. The problem is that most places want minimum orders of 1000 or 10000 – small quantities for this kind of value added item is always difficult, and even if they cost a dollar each after that I still can’t dump that much.
The endcaps also got a little fatter. To fit the extra width of the retaining ring and wire-clearing gap and to give myself more room to put windings, I pushed out the interior width by 6 millimeters, necessitating protruding the endcaps out on each side. This makes the motors 42mm wide – while that’s just as wide as the old version 3 RazEr wheelmotor upon which this design is based, it does make them incompatible with the existing RazErBlades frame.
Gee, my stuff is always so much shinier when someone else makes it. Here, I’ve arbor pressed the static endcap into the can and pressed bearings into both. The bearing bore is actually a somewhat tight slip fit – again, another fiddle factor to adjust – so I dropped them in with a dose of 609 Loctite.
I have 2 sets of custom curved magnets remaining from the ‘blades project which didn’t see use in the final vehicle because I ran against a deadline. This set installed perfectly – the final one was a not-too-tight press fit into the bore, so this set doesn’t even need any glue to hold it in. However, it IS a little close for my comfort – there’s no guarantee this diameter will be the same across all the cans; so again, a dimension to change very slightly (on the order of 0.03-0.05mm or less).
I only have 1 50mm stator (the one shown), so either I’m gonna need to buy some more copier motors, ravage some more recycled office equipment, or find a source for them Yo Real Quick. I’m not keen on selling them to strangers over the internet just yet due to these sourcing issues, but it’s either that or build infinite hub motor powered vehicles…