Single Sided Hubmotor Mount Design, Integrated Torque Transfer

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Single Sided Hubmotor Mount Design, Integrated Torque Transfer

Post by amberwolf » Sep 13 2018 8:45pm

This isn't a typical single-ended axle kind of thing, nor can it be used with any hubmotor until the motor is highly modified (but which modification is actually pretty simple). It requires a DD hubmotor to do it; I don't know a way to do it with a geared hub yet.

But...if you have a motor laying around whose axle-to-stator supports have broken, it's a perfect candidate for this type of reuse. I know some of you out there have one or more old Crystalte X530x and similar powerful motors taht you can't use because of that.

I haven't built this yet, so it's still just an idea; figured I'd post it before I forget it, and see if anyone has reasons it won't work that I haven't thought of. The present idea is to make hubmotor wheels that easily mount to my trike's rear end, without the side frame in the way, so I can take them on and off for whatever reason easily enough, without either laying the trike on it's side or jacking one side up far enough to lean it against something. It would also create a torque-"arm" solution that doesn't deal with axles, flats, etc, and would easily stand up to about anything I could throw at it, torque-wise, that wouldn't fold up the trike frame it's attached to. ;)

On to the explanation, with a picture of the new bike-side mount for the motor:
trike hub mount 1.png
trike hub mount 1.png (8.19 KiB) Viewed 280 times
Yeah, it looks like a birthday cake, doesn't it? ;)

Red is the new axle, which is a high-grade bolt at least 1" (bigger the better) in diameter, and the fixing nut for the outboard end. The bolt itself would be fed from teh back of the white/blue "cake", thru it's entire solid mass, and then a nut and washer would secure it to the white face of that disc. This bolt will be the new axle that feeds thru only the outboard cover of the motor--the inboard cover will be entirely removed and replaced.

A spacer tube would fit between that nut and the motor's outboard side-cover's bearing's inner face. The fixing nut then goes on the outboard side of the motor cover bearing, with washers as needed.

The green holes are for bolting this assembly to the trike frame (or bike).

The yellow rectangle is a mounted connector, so the motor can be taken on and off without dealing with wires of any kind. I'd probably use PP75s or a couple of SB50s (with only one contact in the second one), as they are large enough to carry a lot of current, and easy to plug/unplug and can panel mount, etc. The mating connector would be attached to the stator. A similar smaller connector of some panel-mount type could be used for hall signals, thermal or other sensors, etc.

If you'd rather have wires, you can leave the connector out of the hole, and run whatever size wires you like thru there, because it would be able to handle just about any size you like, if you make the holes big enough. You could also use liquid cooling if you like, or forced air, etc, since this cake-disc is the same diameter as the stator core, which on most DD hubmotors is pretty big.

The gray square areas are splines, to torque-lock the core to the stator's inner circumference. If they are machined at an incline from outboard to inboard, they will also key the stator to stop at a specific point as it's installed, helping to stabilize everything relative to each other, but I will probably only be able to make them straight and level with the tools I have here.

The blue ring is a plate (or section of the cake if it's a single block) on the back that gives the inboard motor cover bearing(s) something to ride on. Note the motor cover must be completely replaced with a custom-made one, or else machined to leave only a small part of it's outer circumference. I'll probably have to make mine as a separate plate.


Ok, now seeing that, which replaces the motor's axle and stator support core, the descriptions below may be clearer. If they're not, I'll try to redescribe it differently.

Remove the inboard side cover of the motor, and set it aside. You won't be reinstalling it. Instead, you'll make a new thicker plate that can house a large diameter bearing that will fit it's ID over the blue plate above. *or*, as I will probably have to do, attach a number of much smaller (skate?) bearings to it's inner circumference in a way that they roll over that blue plate's OD. (kind of like planet gears around a sun gear).

Optionally, the bearings (either type) can be mounted on the cake-hub itself, and a surface for them to ride on could be made as part of or attached to the new (or remainder of the) inboard cover.

If you think the cover you have will support it you could just cut out a large hole in it for the bearings, but I doubt it'd work for a lot of the thin covers.


Remove (almost) the entire core of the stator that connects the stator laminations to the axle. You won't need any part of this, though you could reuse the axle if you like, I'd recommend not, as most of those are crappy anyway.

Depending on the way you do the splines (see diagram below) you might need to leave the outermost ring of the core attached to the laminations, so you can make splines out of it. Otherwise, you can either make your own ring and attach it to the inner circumference of the laminations, or you can notch the splines into the inner circumference of the laminations themselves. Probably depends on what materials were used for the motor's core to start with, for which is easier.

The red bolt in the cake hub can just go thru the existing outboard axle bearing, if it's a large enough ID, or you can get a new bearing that has a larger ID (either with the same OD to fit in the unmodified outboard cover, or with a larger OD that requires machining the outboard cover (or making a new cover). I'll probably just use the biggest bolt that fits my existing bearing. It still has to be better than the existing axles. ;)

Run the phase (and other) wires to appropriate mating connectors to what you have in the cake hub, and mount those connectors so they are lined up, and will mate as the motor is mounted to the hub.


Not many people will ever need anything like this, but if they do, it is possible to DIY this. A lathe would be useful for doing it, but I suspect much of teh work could be done using the motor itself, attaching the plates and parts to teh motor's side cover one way or another, once a hole is made to pass the hubmotor axle thru.

I have a lathe, but I don't think it's big enough diameter to do some of the stuff I need, so I may have to modify it to raise it higher over it's bed, and figure out a clamp to put in the chuck to hold larger diameter parts. We'll see if that's necessary or not.


I also have a powerchair hubmotor that is sort of the inspiration for this idea, which has the entire motor as the hub, with a box on one side to bolt to the chair, and a wheel bolts to the hub pretty much like a car wheel does. If I had two of those, I'd just design something to allow me to bolt wheels to them. Since I only have one, I'm looking at the above method to modify two hubmotors (probably my MXUS 4503 and 4504 motors).

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