Motor recommendations for mid-mount

[fourbanger]

Thought I'd try something different here and ask for a bit of advice... HA!

Basically I'd like to keep both the battery and motor, maybe controller (as much stuff as I can, really) INSIDE the triangle. To accommodate this (and because I like the way they look) I'll be using an old school diamond frame MTB. I want to stick with a single stage reduction ratio for the sake of simplicity and cost, and I'm keen on driving the left side of the wheel. What else....? I'd like to keep the cost of the entire drive train (incl. motor) to under $400 CAD which is about 320 USD or so. Yeah, I know, but this is just a commuter. Speaking of which I really can't see the need for more than about 1750 peak watts, though more is always nice, less than 1200 would be a bit on the puny side for my taste. Oh yeah, regen. Love regen. Oh and one more thing; I really really don't want to piss around with finding wider BBs to accommodate all this, which basically means around 120mm OLD if it's a hub motor, or something like 5 1/2 inches wide all in.



Ok, so what am I looking at again?

- motor mounted low and inside the triangle w/ enough room for battery
- single stage reduction (preferably driving LHS)
- not less than 1200W peak power
- fit between standard MTB crank arms
- regen
- no more than $320 US for motor + drivetrain

Is this all asking for a lot? Maybe. Too much? I don't really think so. Some options I've been looking at so far have been:

• GNG type motor with #25 chain to the rear wheel.
  - They make something similar with a foot tacked on for easy(er) mounting, which would be nice.
  - Not so sure about how to mount a #25 sprocket to the wheel (esp. LHS) but I'm pretty sure I can figure something out

• Bafang BPM or similar front wheel motor with 1:1 ratio using 16t disc mount cogs
  - Requires disc hub wheel not found on the type of bicycle I'm using
  - Requires welding the clutch
  - Using this option it'd be really nice if I could get the wiring to exit the side of the axle... somehow

• Mini Conhis front hub motor w/ 1.75:1 reduction to LHS
  - re-terminate motor winding to delta for 48v OR run at 72v (not really a huge fan of either option, really)
  - 16t disc cog to 28t rag-joint sprocket
  - will need venting/ferro fluid and even then I might be pushing my luck a bit far...

• Scooter hub motor w/ 16t disc cog to 44(ish?) rag joint sprocket
  - most of these motors have 15 pole pairs which (according to someone somewhere) means peak eff. at 1000 or so RPM
  - ummm. I think that's about it for this option. Again with wiring out the side of axle. Again with the maybe...

Soooo, yeah. That's pretty much what I've been looking at so far. One freaky alternative is that I've got an eZee front hub motor here (MAC/BMC as far as I can tell) with mushed planetaries to play with. If I were to dispense with the gears entirely and somehow affix the magnet bowl to the motor case I could get her to spin up nice and fast, then give it some (maybe) appropriate reduction ration from the outside. An even FREAKIER option would be to Crossbreak this motor in such a way that the axle spins at the full RPM of the magnet bowl and, again, do the gearing externally.

What else can I say? Grin tech. sells 16t disc mount cogs down the street for $5 CAD so that's a handy resource to exploit. Pretty sure two 3/32 cogs side by each work out to 3/16 which is what the width between internal plates of #415 chain is which, in turn, are what motorized bicycles sprockets are made at and those are cheap like borscht. Hell, maybe I could even splooge on one of those Manic Mechanic hub clamp adapter thingies to avoid the whole pineapple/rag joint thing for just that added touch of class.

Right now I'm leaning towards the scooter hub motor concept, if nothing else because of the wide variety of options out there, but I could probably be swayed in pretty much any direction. I don't know guys, that's why I'm asking. Looking forward to any questions, comments, concerns, ridicule, lore, sexual innuendos, WHATEVER YOU'VE GOT I'll take it.

Many gracious thanks, as always.

P.S.
I'll try to keep the double/triple posting to a minimum on this one, but I promise nothing.

 

[amberwolf]

I'm keen on driving the left side of the wheel.
<snip>
Oh yeah, regen. Love regen.

You seem to already be aware of it, but just to point it out in case, you wont' be able to have any freewheels between the wheel and the motor to do regen, so the wheel will always be backdriving the motor when the motor is not driving the wheel. Meaning, if you lose power to the motor / controller for whatever reason, it'll be like a DD hubmotor in that it will be harder to pedal than if you did have a freewheel. If you have a high reduction ratio between the wheel and the motor (meaning the motor is backdriven at a high speed by the wheel), then it may have a lot of drag and be harder to pedal than a typical DD hubmotor...depending on the specific drag the motor you use has at that RPM.

- Not so sure about how to mount a #25 sprocket to the wheel (esp. LHS) but I'm pretty sure I can figure something out

If it has a disc brake rotor mount on the hub, it should be easy enough, either directly or using an adapter (which you could make if you can't find one for the sprocket you want to use).

If it doesn't, then there have been mounts for gasser bikes made to clamp a sprocket to the spokes themselves.

If that's not an option, you may have to build a wheel using a hub that has mounting points either for your sprocket, or by the disc rotor/adapter method, and a rim that fits your needs/tire/etc. (the actual rim off the original wheel if you have to, but you should be able to buy a new one instead), and new spokes that allow lacing the new hub to the rim.

- Using this option it'd be really nice if I could get the wiring to exit the side of the axle... somehow

Do you mean exiting the axle before the end of the axle, like just past the cover bearing / axle shoulder? If so, then that is relatively easy to fix, but requires pulling the wiring back thru the axle from inside the motor, most of the way, before doing the mod to the axle.

One freaky alternative is that I've got an eZee front hub motor here (MAC/BMC as far as I can tell) with mushed planetaries to play with. If I were to dispense with the gears entirely and somehow affix the magnet bowl to the motor case I could get her to spin up nice and fast, then give it some (maybe) appropriate reduction ration from the outside. An even FREAKIER option would be to Crossbreak this motor in such a way that the axle spins at the full RPM of the magnet bowl and, again, do the gearing externally.

You could also "Crossbreak the motor" and replace the gears (if they're available, I havent' checked--it's not quite the same as the MAC/BMC AFAICR but they might still work--Grin might even have some laying around). It'd be more compact to do that internal reduction than to do it externally, so if you're trying to save space and keep it neater, that's a more elegant solution. If it's built to fix the main casing in place like Crossbreak did, then force-cooling it is easier to get higher power out of it if you need it.

 

[fourbanger]

Mmm hmmm. Food for thought as always, AW, thank you. What stands out most to me is the point you raise about the possibility of increased drag (cogging effect) of a DD hub hardlinked to the rear wheel with a high ratio. This is something I'd been thinking about for some time without ever REALLY figuring out. The same issue arises when I think of using something like the GNG motor or anything designed to spin much faster than the rear wheel. I hadn't really considered how this would affect freewheeling so much (but I am now) as how regen braking would be affected. I'm pretty sure what I came up with in the end was that the added torque of driving what is now in essence a generator with the relatively huge diameter of the bike's wheel would balance out any mechanical inequities. Basically I figured it'd all come out in the wash and promptly (and arrogantly) went along my merry way, choosing not to give it any more thought. Seems like a pretty solid design philosophy to me.

In all seriousness, the same principle comes up for folks who weld the clutches in their geared hubs. Yes you now have regenerative braking, but now there is all this extra drag as soon as you take your foot off the gas. Your brake pads will love you long time, just hope the motor keeps running otherwise it's gonna be a looooooong ride home. The GMAC motor at Grintech comes with a clutchless planetary gear assembly and overcomes this by turning in the idle screw in the base/phaserunner programming to give the motor *just* enough juice that it "freewheels" without a fuss. One thing I haven't found a definitive answer to is whether fetcher's elegantly simple solution of adding a variable resistor inline with the ground wire to the throttle in order to "pull up the idle" can achieve the same thing, though I see no reason why it wouldn't.

Yes, I could replace the gears in the eZee AND do the standard crossbreak conversion, and while I'm a fan of the entire principle of the conversion I do feel at this point that the greatest benefit is that it is easier to keep these little geared numbers cool. Having said that, people seem to be having good luck with oil cooling as well. By omitting the internal gears, however, there would be no real reason not to simply vent the side plates to air cool the motor. This also gives me the option to play around with LOWER gear ratios that the standard 5:1 that these things tend to come with, if it turns out that's a thing I'd want to do.

One thing I hadn't mentioned originally is that whatever I end up going with, it would be nice to be able to replicate *fairly* easily. Reason being that if this turns out OK I'd like to build a couple more for my friends. If THAT goes ok then maybe I can think of putting something together for the public at large. A kind of "ebike for the everyman" that looks cool, has some balls and doesn't break the bank. A bit fanciful maybe, but everyone is entitled to a dream now aren't they?

OH! Before I forget, I'm glad to hear someone say that running the motor wires out the side of the axle (yes, you got what I was going for) would be a fairly simple modification. It is, however, not one I relish the thought of much. Of particular concern to me is the fact that the drilling would have to be done AT THE AXLE FLAT in order to get the whole thing through the side plate bearing. This isn't a problem just as long as there is enough shoulder protruding from the side plate to keep the wiring from rubbing up against the motor when it's bolted into the dropouts (or whatever). If there ISN'T enough shoulder to accommodate this, then it IS a problem, hence I've been pretty biased (prejudiced, really) in my search for a motor towards one that already has this taken care of for me, which pretty much puts all of the geared hub motors out of the running. That may be for the best anyway.

One geared motor that DOES have this little annoyance pre-dealt with for me is the Bafang SWX02, like the kind our friend over at batteryclearinghouse.com supposedly sells. Unfourtunately I too have been unable to do business the the man, and I fear that he may be dead, in a coma, in the throws of a crippling addiction of some sort, or maybe just an asshole.

: )

 

[amberwolf]

Basically I figured it'd all come out in the wash and promptly (and arrogantly) went along my merry way, choosing not to give it any more thought.

I think the Grin Tech motor simulator has a way to find out what happens backdriving a motor, but I can't remember how. It is probably in Justin_LE's posts, or something in the blog on the Grin site itself. Sorry I don't have more info.

 

[amberwolf]

By omitting the internal gears, however, there would be no real reason not to simply vent the side plates to air cool the motor.

You can vent even with the internal gears--but what I would do to minimize dust ingress into grease, etc is to force-cool it by putting filter paper (etc) on the inlet side of the casing, and suck the air out using a centrifugal (squirrelcage) fan, controlled from a thermal sensor inside the motor to monitor whatever the hottest thing you can physically wire something to will be. (preferably the windings on the stator). So the fan only runs when it's hot enough to require it--saves power and stays quieter.

Of particular concern to me is the fact that the drilling would have to be done AT THE AXLE FLAT in order to get the whole thing through the side plate bearing. This isn't a problem just as long as there is enough shoulder protruding from the side plate to keep the wiring from rubbing up against the motor when it's bolted into the dropouts (or whatever). If there ISN'T enough shoulder to accommodate this, then it IS a problem, hence I've been pretty biased (prejudiced, really) in my search for a motor towards one that already has this taken care of for me, which pretty much puts all of the geared hub motors out of the running.

If you were crossbreaking the motor anyway, you would be rebuilding most of the stuff that would be problematic for this process, and wouldn't need to exit the axle--you could bring the wires out the cover anywhere you like.

Were I to reroute axle wires for a DD motor, however, I would remake the covers (at least on that side) to use a larger ID cover bearing, and then use a spacer between that ID and the shoulder, then drill holes for individual phase wires in the spacer, and another for the hall bundle, and another for any other sensor wires (with their own separate grounds/etc). Then I would not use a hollow axle at all, so it would be stronger. If possible I would remake the axle itself so it *is* that spacer, so it's shoulder area is much larger, and then have mounting holes in the other end of it (other side of motor) for an integrated torque arm to bolt to (a bit like the GMAC, Heinzmann, coaster brakes, etc). No axle flats anymore, and much better torque transmission.

If not doing this, you may also find it easier to use a die grinder to create an angled groove into the axle instead of drilling a straight hole. (it's hard enough to feed axle wires thru as it is).


An entirely different way to do it is like APL is doing on his custom made axial-flux motor, designed specifically to be a middrive pancake motor. there are at least two versions at this point, latest one at end of thread: https://www.endless-sphere.com/forums/viewtopic.php?f=30&t=97860

One geared motor that DOES have this little annoyance pre-dealt with for me is the Bafang SWX02, like the kind our friend over at batteryclearinghouse.com supposedly sells. Unfourtunately I too have been unable to do business the the man, and I fear that he may be dead, in a coma, in the throws of a crippling addiction of some sort, or maybe just an asshole.

Thankfully you don't ahve to deal with him to get those:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=110408
https://jag35.com/collections/accessories-1/products/26-bafang-36v-dc-electric-bike-wheel-tire-w-tektro-disk-break
AFAICT it's the same motor (I have two of those and two of the IGH, and would like to get more but BCH hasn't responded to me since that order early last year, so Jag will get the new business when I get around to it).


But these aren't going to give you anything like the power you're after.

 

[thepronghorn]

I'd say this thread would be better suited for the non hub motor drives subforum than the motor tech forum. Maybe take a look at my build for some inspiration.

https://endless-sphere.com/forums/viewtopic.php?f=28&t=110034

The hard part about doing a LHD from inside the front triangle is usually interference with the chain stay and maybe seat stay. It limits where you can position your motor and how large the rear sprocket can be. When you say drivetrain <$320USD, does that include controller or battery?

 

[fourbanger]

@amberwolf

I had thought about doing something similar with the ram air intake + paper filter - fan. I like the idea of having a fan pulling air through the motor, especially one wired up to a thermostat. That's pretty clever. It's starting to add to the complication of the build a bit, but I do find the ingenuity appealing.

I had also considered the concept of turning the one sideplate to accept a large dia. bearing and run the wires out through a spacer rather than the axle. It appears that Bafang used to do this at one time with their front wheel BPM motor. I can only guess that they dropped this design as a cost saving measure. Pitty, as something like that would have been more or less ideal for this application.



Bonus points for integrating the spacer as a part of the axle its self. In fact I've found myself thinking about that option with just a stock axle ever since you mentioned it, although the thought of doing away with axle flats in favour of something more practical is pretty sweet. Hmmm... Good call on the die grinder btw.

As for what APL is doing... I don't even know what to say. The amount and level of talent that can be found in this forum I don't think will ever cease to amaze me. I'm going to have to spend a rainy day just reading through that thread. Truly incredible.

Good old Jehu. Did he ever finish that VW bus? Unfourtunately he doesn't like Canadians and won't ship anything across the line. Yes, there are ways around this, it's still a pain in the nuts though. May his maple syrup attract many flies! You don't think I can squeeze 1200W out of that little Bafang? Really? That's sad and a little surprising. I actually had that specific motor in mind when I started playing around with this whole concept to begin with. Hmmm again... I may have to rethink what I can expect from some of the motors I've been considering using...

@thepronghorn

Yes! and that's exactly where I was going to post this until I noticed the little note underneath the link saying that that sub-forum was slated for demolition. I do agree though, that DOES seem to be where this thread belongs.

Ah, that was you! I was looking through that thread the other day as I was searching for something along those lines. 12:134 ratio? I love it! The world of RC motors is one that I find more and more intriguing as time goes on (so much power in such a tiny package *giggeddy*), but I just don't think I'm ready to go there yet. I have to admit (somewhat sheepishly) that I really just don't like RC motors aesthetically. I know, I know, but another design principle that's integral to this build is that it looks cool. Subjective? Yes. Possibly even silly but the fact is that I've never really appreciated the way mid-drive(mount) motors hang off underneath the bike's frame. To me they always look like too much of an after-thought rather than something that had been really integrated INTO the bicycle (so to speak). Also there's something vaguely tumorous... I don't know, they just bug me.

I see a lot of commercially built ebikes done up to look like the old board track racers of yore (my own, completely original idea which was STOLEN from me, years ago) and I always think what a missed opportunity it is NOT to have the motor mounted in the middle of the bike. I mean, it's a drop looped frame for a reason isn't it and it's RIGHT THERE PEOPLE, COME ON!! Anyways, I *DO* like the simplicity of your build and I actually agree with fetcher in that I think it really would make an excellent kit. I'm also impressed with your battery build and the amount of value you got for $160 worth of laser cutting. All in all the whole thing is pretty impressive. On another note, I am starting to notice RC motors of larger diameter and lower kv values that seem to be calling me somewhat. I'm really hoping to keep the sprocket options as "off the shelf" as possible, so sticking with 28-56t for 1/2" chain link sprockets or (I don't know) 60-90t for 1/4" chain a.k.a. #25 seems like where I need to be, and that puts the rpm/v range of appropriate motors below where most RC motors tend to hang out. Yet another reason I seem to be talking myself into the scooter motor option... yup.

$320 is for motor, mounting bracketry, sprockets and chain, fasteners etc. I'm cheap, and I'm probably at least a little eccentric, but I'm not delusional (yet). Controller will be on the cheap(er) end of the spectrum (probably a KT something) and the battery will in all likeliness be of my own pvc sewer pipe bomb design because, again, I think it looks cool.