Single Sided Hubmotor Mount Design, Integrated Torque Transfer

[amberwolf]

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:



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).

 

[haulincolin]

Amberwolf- sorry you asked me about this a while ago and I didn't get around to reading it thoroughly until now. I think I understand all the features, and I would say it's technically possible, but pretty difficult to do well, especially DIY-style. There are a few major tripping points.

One is that your inboard bearing needs to have a larger ID than your new stator interface, which means finding a really big bearing which will probably be really heavy and/or prohibitively expensive. In fact, the whole birthday cake is going to add quite a bit of weight without extensive relieving of the layers (essentially recreating the thinned out sections and/or spokes that your stator body and side plate originally had).

Another is that it's a total crapshoot to find a bolt that will work as an axle. Most bolts are at least a few thousandths undersize which is enough to ruin their fit in the outboard bearing. The other parts require a lathe, so it's probably best to just make that part from scratch on a lathe, too.

Third is that making mating splines is not trivial, even on CNC equipment. I have no idea how you'd pull it off with hand tools, besides incredibly tedious trial-and-error hand filing.

Your design requires that the inboard bearing and stator adapter splines be pressed into place with the birthday cake already installed on your trike, rather than on the workbench or in a press.

Here's my counter-suggestion that I think covers all your criteria in a simpler-to-build and simpler-to-use way:

1. Remake the inboard side cover for a larger bearing, but not gigantic, something like 1.5" or 2" ID depending on how strong you want your axle to be.
2. Turn a new axle that is hollow on the inboard side for your wires to run through and has milled flats for clamping into your frame (like my custom axle, but bigger to handle the fact that this is a single-side setup). No need for any threads on this axle. It can terminate after the outboard side cover bearing seat.
3. If part of the point of this exercise is to use a motor with broken stator spokes, then make an intermediate piece that keys to the axle the same way the original stator body did, and then connects to what's left of the stator body using bolts, pins, and/or a press fit with square key(s) to lock against rotation.

This should give you a strong single-side axle motor which does not require any really complex machining, or particularly expensive parts, adds less weight, and is easily installed or removed from the trike without partial disassembly.

Let me know if I missed any important points.

Colin

 

[fechter]

I missed this one earlier also.

I've thought about a one sided design before, mainly as a way to effectively cool the stator. Mechanically, it could be just like an old drum style brake. One side plate rotates, one is stationary. The rotating side has both bearings and needs a very strong hub area and also has all the spoke holes. The stationary side holds the stator, which can now be directly air cooled or easily water cooled. This also gives a really good anchor for the torque arm.

One tricky part is to keep junk out of the gap between the moving part and the stationary part. At least if stuff got in there, this design should be very easy to take apart.

 

[amberwolf]

There are a few major tripping points.

Only a few? :lol:

I appreciate all of your thoughts very much, because I've seen what you've built and can see your experience in it--and that's the kind of thing I need to sort out my fantasies from actual possibilities.

One is that your inboard bearing needs to have a larger ID than your new stator interface, which means finding a really big bearing which will probably be really heavy and/or prohibitively expensive.

Which is why I figured I"d probably have to use a number of small bearings as "rollers" instead. I've seen something like that done, somewhere, on something, but I can't for the life of me remember where.

It should actually only need support on the lower half, if I understand the dynamics of this structure correctly, so a "smiley face" of small bearings (like rollerskate bearings, or even smaller) might work, as long as they are capable of carrying the load.

In fact, the whole birthday cake is going to add quite a bit of weight without extensive relieving of the layers (essentially recreating the thinned out sections and/or spokes that your stator body and side plate originally had).

I figured it could potentially double the stator weight, which sucks, but if it lets me use a "huge" axle and lets me just bolt the thing on like a typical car wheel, more or less, it would simplify so much stuff that it would be worth it.

It would save some weight (tiny amount) on the outboard frame area, because the three tube sections presently used there would go away (so the wheel could come straight out), although I suspect the more-rigid inboard frame required to support a one-sided axle design with the kind of weight I need to carry (with no suspension, at least at present) would more than balance that out.

Another is that it's a total crapshoot to find a bolt that will work as an axle. Most bolts are at least a few thousandths undersize which is enough to ruin their fit in the outboard bearing. The other parts require a lathe, so it's probably best to just make that part from scratch on a lathe, too.

Yeah. I'm not really used to thinking in that kind of precision--most of the stuff I have or work with or make is very sloppy--when I get things within a millimeter of where I intended them I'm pretty proud of it. :lol: A machinist I iz not.

Third is that making mating splines is not trivial, even on CNC equipment. I have no idea how you'd pull it off with hand tools, besides incredibly tedious trial-and-error hand filing.

Most likely I'd use the Dremel (or the similar but larger B&D unit I have) mounted to something that lets me run it in and out as I turn the objects and lock them in place. Probably mount the stuff on the lathe chuck, with a clamp to lock the chuck in place, and use the toolmount as the slide, clamping the dremel/etc onto the mount. (how, I don't know yet).

There was another member that made splines to hook up a motor shaft to a gearbox (IIRC) pretty much by hand, not even with the "precision" I'm talking about above. Supposedly worked for him.

https://endless-sphere.com/forums/viewtopic.php?f=10&t=93865&p=1374207#p1374207


Dunno if any of the above would work for me. I don't know how precise a fit it would all have to be. But we're talking pretty gigantic splines, so should be relatively easy to carve out even if I did it by hand. (this I say without ever having tried it...of course).

Your design requires that the inboard bearing and stator adapter splines be pressed into place with the birthday cake already installed on your trike, rather than on the workbench or in a press.

I hadn't worked out order of build yet. Why would it ahve to be done while already on the trike?

Here's my counter-suggestion that I think covers all your criteria in a simpler-to-build and simpler-to-use way:

Well, it certainly sounds more practical to make with my skills and tools. and it is probably undo-able to go back to the original if I had to. I just don't know if it's sufficient.

1. Remake the inboard side cover for a larger bearing, but not gigantic, something like 1.5" or 2" ID depending on how strong you want your axle to be.

The axle has to be strong enough to support whatever the weight is on that wheel even under the stress of deep sharp-edged pothole impacts sufficent to destroy the actual rim/etc., without damaging the motor or axle itself, or bending under that load (and allowing the wheel to rub on the frame).

The actual load varies, but the whole trike with me on it probably weighs as much as my dogs, around a quarter ton at present. (I'd like to weight it but I need one more scale to do that, to have one under each wheel, then figure out how to add those weights together--dunno if it is straightforward addition). Then there can be up to at least a couple hundred pounds of cargo on it. Potentially more than that. Some of it wiggly, complicating the dynamic loading.

2. Turn a new axle that is hollow on the inboard side for your wires to run through and has milled flats for clamping into your frame (like my custom axle, but bigger to handle the fact that this is a single-side setup). No need for any threads on this axle. It can terminate after the outboard side cover bearing seat.

I would rather not use flats to clamp to; they create stress risers at the transitions to round that break; tha'ts part of the problem with my existing axles. Plus if it's hollow in the middle of that flat area (as it would have to be for the wires to go thru it) it's probably even more prone to breakage there.

If I kept a round tube and clamped *that* securely, perhaps with a pin or bolt thru it and the mounts, that might work.

But I don't know how large a diameter I'd need to support the weight I have, or what kind of metal it would have to be.

Or how I'd fix it to the stator supports where the existing axle goes (it's a pretty small space, so I would have to narrow the tubing somehow as it reaches that point to make it fit, and I expect that would make it weaker too, and prone to break at the stress riser points which would be at the most outboard loading point of the axle, IIUC).

3. If part of the point of this exercise is to use a motor with broken stator spokes, then make an intermediate piece that keys to the axle the same way the original stator body did, and then connects to what's left of the stator body using bolts, pins, and/or a press fit with square key(s) to lock against rotation.

No(t yet, at least); the only present reasons to do it are:
--small axles just don't handle the hundreds of pounds jouncing on potholes very well, nor do they handle the hard sudden regen/EABS braking and then hard sudden full-torque acceleration of those same hundreds of pounds, dozens of times within a couple of miles, twice a day almost every day.

--make it easier to take the wheel off for any kind of maintenance, tire/tube work, etc. Or to swap out the whole rotor/wheel if necessary. (for this, ideally, I'd have the magnet rotor still attached to the trike, like brushless powerchair wheels do, and then just have a spoke flange that bolts to that...but I don't presently have a way to do that sort of thing, while I could at least in theory do some version of what's proposed in this thread).

--Eliminate the stuff outboard of the axle so I can put the contact patches a bit farther apart for stability in turns while actually decreasing the trike width a bit.

--was something else, but I can't remember right now.


But it would require removing the existing stator supports, to do it the way I originally proposed (removing the ability to go back to the original axle/etc, unless I were able to remove the supports/axle as a whole unit out of the existing wound stator).

This should give you a strong single-side axle motor which does not require any really complex machining, or particularly expensive parts, adds less weight, and is easily installed or removed from the trike without partial disassembly.

It sounds like a good idea, but I don't know if it would work for the weight/conditions, and I don't know materials well enough to know what would be needed. I'm pretty sure I wouldn't have anything laying around that could handle that loading, in 2" or less OD. I have bigger diameter, around 3" I'd guess, maybe 4", in some large thickwall steel pipe originally used as a light pole. I think all my smaller diameter stuff is pretty thinwall steel of unknown origins, except for some of the bicycle frame tubing that I doubt would work.

I'd guess that the tubing axle would work if I kept it as a double-ended axle, just not sure if it wouldn't just fold up as a single-ended.

But it is a starting point for further thought.

And any further thoughts you or anyone else with this kind of experience have, I appreciate as well.

 

[amberwolf]

One side plate rotates, one is stationary. The rotating side has both bearings and needs a very strong hub area and also has all the spoke holes. The stationary side holds the stator, which can now be directly air cooled or easily water cooled. This also gives a really good anchor for the torque arm.

One tricky part is to keep junk out of the gap between the moving part and the stationary part. At least if stuff got in there, this design should be very easy to take apart.

FWIW, this hubmotor off a powerchair is basically exactly like you describe (except it's not a spoked wheel, the rotor is the "rim"; I don't have the outer rim flange for it).

https://endless-sphere.com/forums/viewtopic.php?f=30&t=32838
Motor exterior

interior of mounting "box", including parking brake

stator

rotor

both

axle

It is pretty much my primary inspiration for this.

If I had two of them and knew they'd handle the power I need to throw at them, I'd work fairly hard to figure out a way to use them to hold the spoke flanges for my wheels, and be done with it, but I only have one and it's not tested under the kinds of loads I have, nor do I know what speed it would end up capable of at the battery voltage I have (about twice what the powerchair it came from operated at), in the wheelsize I use.

I strongly suspect it will do what I want...but I have to do a fair bit of work to find out. :/

I keep telling myself I'm going to make a mount for it on the trike, and then do up a wheel and adapter plate to bolt a small spoked wheel onto it equivalent to what I have on the trike, and just test it...but I never seem to be able to get around to it. (which is probably also true of the subject of this thread, but at some point I have to do *something* about the axle problem. Some point very soon would be best, so I can unleash the full potential of Incememed's SFOC5 on the trike and see what happens. :lol:

 

[amberwolf]

I had another thought about motor axle replacements, that would be much simpler than the "cake" idea above.

However, it has some gotchas I have to think of a way past.


Basically, just press out the original broken motor axle, then hand-file or dremel or whatever some deep "splines" into the hole in the stator the axle came out of.

Then use a long hard lag bolt, which has smooth sides most of it's length, and threads at the end, that fits exactly into that hole. Long enough to weld the head of the bolt to the inboard trike frame, and still have it's threaded end stick out past the outboard side of the outboard motor cover to allow a washer and nut to fit on it.

Weld tabs onto it to fit those splines, close fit but not a press fit, so the motor wheel can be pulled off the trike without special tools.


However...the main gotcha is that to get the splined bolt inot the motor, it'd have to have a much larger ID inboard bearing, or else the splines can't pass the bearing. (the bolt itself won't fit either, if using one large enough to fit the hole in the motor, but only a slightly larger ID would be needed to deal with that).

The other gotcha is that there's nowhere to get the wires in (without making channels in the bolt, whcih I don't want to do cuz it would weaken it).

Thankfully, I think the fix for both is the same: Use a large-ID inboard bearing, with also a larger OD, modifying the inbaord cover to accept it. Inside the ID of the bearing would be a ring, machined to fit it's OD to the ID of the bearing, and it's ID to the bolt surface--but wtih slots for the splines matching the ones in the motor stator support structure.

THe tabs on teh bolts would be made long enough to reach these splines, to ensure they both stay lined up to pull the motor on and off easily.

Then drill holes for the wires in the ring.


So my first step would be to measure the OD of the existing axle, and see if I can find bolts with that OD. Then measure the inboard side cover's "hump" that is meant to hold a freewheel or disc rotor (whichever cover I end up using) and find a bearing with an OD smaller than that, but an ID significantly bigger than the bolt's OD. Order those, then when they arrive, make and perfect a ring to fit between them.


I've crossposted this over on the SB Cruiser thread.