Mid drive with a proper Q factor + spacing - does it exist?

neptronix

neptronix

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My first experience with a mid drive was with a BBS02, where the pedaling stance is both wide ( not biomechanically efficient ), plus has the right pedal half an inch out.

I have multiple twists in my bones that makes walking difficult but bicycling very easy and natural. Using the bbs02 for a few weeks hurt me so intensely that i ended up in physical therapy when i was sidelined with extreme knee pain.

At this point i'd be willing to fork out 4 digits for a mid drive that quiet, reliable, and has good biomechanics. I ordered the 'lightest bike' drive early this year and delay after delay keeps it out of my hands. What's out there?
 
I haven't measured my specific Q factor lately.

What i am looking for is a mid drive that retains the original 110-120mm spacing on most bikes.
That is the most biomechanically efficient spacing. And i am particularly biomechanically inefficient, so i need that to efficiency to soak up my disadvantage.

The 'lightest bike' mid drive pulls off the hat trick i'm looking for. haven't seen anything else that does - maybe a cyclone, but.. :roll:
 
Hi,I quess you are talking about conversion kit.If not the new Yamaha pw-x3 motor have 128 mm
https://global.yamaha-motor.com/business/e-bike-systems/products/pw-x3/
 
Yeah i'm talking about a conversion kit that sits in an ordinary ol' bottom bracket.
 
As I have always understood Q factor it is the distance between the pedal attachment points on the crank arms, when measured parallel to the bottom bracket axle. So the offset, if any, and thickness of the cranks is a part of the equation and in general in the 170mm range is considered narrow, at least on a mtn. type bike.

PaulD, above, had a kit for awhile that had a narrow Q factor using the same type of mount/gear reduction, the housing of which is the reason all the others are wider, as the Light system you have on order. However I am not sure how much extra width the spider the hold the two chain rings with enough room so that the chains don't rub add to the equation.
 
neptronix said:
What i am looking for is a mid drive that retains the original 110-120mm spacing on most bikes.
Click to expand...

I don't know what spacing you're talking about, but modern pedal bikes generally don't have anywhere near that narrow a Q measurement.

As for the offset problem, there's no reason not to use an old fashioned "square" crank arm on the right and a typical flared crank on the left.

Because I use large flat pedals without clips, I know my feet will naturally make up the difference if there's a bothersome amount of crank offset. When I had a BBS02, I used unicycle cranks to minimize the tread width.
 
With left side middrive you can have as narrow Q as you possibly want (I, for instance, do NOT want narrow Q and in fact would welcome more space on the right - I need a pedal extender there anyway :))
DIY RC crank drives also can have as narrow a Q as you want, but unless you go two-stage assist torque will be limited.
 
I used the wrong term 'q factor'.
q factor is relative to the rider and relative to the bike.

I just want a mid drive that doesn't add extra width to the pedaling stance and lets me use a regular width BB. Using a lower offset pedal on either side to mitigate the extra width is not an option due to the type of bike i ride.
 
neptronix said:
I used the wrong term 'q factor'.
q factor is relative to the rider and relative to the bike.

I just want a mid drive that doesn't add extra width to the pedaling stance and lets me use a regular width BB. Using a lower offset pedal on either side to mitigate the extra width is not an option due to the type of bike i ride.
Click to expand...

Q-factor is an absolute and means distance between outsides of the crank arms, but yea, if a bike has 'shifted stance' simply knowing Q-factor is not going to help (but will not hurt).

If your physiology is different from other people, going custom is sometimes the only reasonable alternative (I know that all too well).
 
Paul's "first" kit used a "normal" BB with a torque sensor. Probably that is the Holy Grail. There's an individual on MTBR who wants (wanted) to sell his, and if you're interested PM me. Too bad Paul hasn't kept manufacturing his great system.
 
BalorNG said:
Q-factor is an absolute and means distance between outsides of the crank arms, but yea, if a bike has 'shifted stance' simply knowing Q-factor is not going to help (but will not hurt).
Click to expand...

See, i understand the term not from the bicycle realm but the orthopedics realm.
In fact, the orthopedics term is 'q angle' and is relative to how the bones are aligned.
i used the wrong term but you get the idea..

BalorNG said:
If your physiology is different from other people, going custom is sometimes the only reasonable alternative (I know that all too well).
Click to expand...

My physiology is so different that only one orthopedist in my entire state understands the mechanics of human movement and how mine are at the heart of developing arthritis in my early 30's.

But, it's been shown again and again in clinical research that the optimal biomechanical position for an average human cyclist is quite narrow, and roadbikes use narrow pedals for just this reason. So, pretty much any bicyclist could benefit from the mid drive i'm describing, since they'd get some additional HP ( human power ) out of it. And most likely, less wear on the cartilage in their legs.

I would like to see that additional 20-40mm of pedal offset on most mid drives disappear, and i'm wondering who, other than 'lightest bike', is shooting for that.
 
neptronix said:
I would like to see that additional 20-40mm of pedal offset on most mid drives disappear, and i'm wondering who, other than 'lightest bike', is shooting for that.
Click to expand...

Based on how much wider the Q/tread of non-electric bikes has gotten in the last 30 years, I'd guess... nobody. If people keep buying duck bikes, they'll keep making them.

There are some purists out there, but they aren't doing e-bikes.
 
My recommendation: drop your mid-drive requirement, put a torque sensor BB in a road frame and use a good rear hub. Problems solved.

Mid drives are never going to be narrow as a road bike, the biggest reason is compatibility with modern mtb frames (wider tires, wider hubs, those wider stays need more heel clearance).
 
The mid drive requirement is not so easily dropped.

With a semi recumbent bike, i have a very light front end, and could use a mid drive as ballast to prevent power wheelies. Ideal place to put a motor is up front, ideal traction wheel is in the back because >80% of the rider weight sits on the back. A mid drive is a good idea here.
 
neptronix said:
The mid drive requirement is not so easily dropped.

With a semi recumbent bike, i have a very light front end, and could use a mid drive as ballast to prevent power wheelies. Ideal place to put a motor is up front, ideal traction wheel is in the back because >80% of the rider weight sits on the back. A mid drive is a good idea here.
Click to expand...

Now wait a second.
You have a recumbent with built-in multiplication middrive and a ES poster?! Why do you even consider a stock middrive than?!

6384 140kv aliexpress flipsky motor for 100$, left handed freewheel (southpaw 16T) replacing input cog on your middrive (you'll need have a square taper adapter machined but that's certainly not a 4 figure job), VESC with FOC with with bluetooth for ~120$, a 3d printed ~120T HDT5 cog replacing large output cog on your middrive from the right side (or go with gates for higher efficiency), a set of clamps/laser cut adapters like on my bent to install the motor and voila! Low power (or high power if you are willing to forgo pedalling), lightweight assist with front weight bias. In fact it is so lightweight that weight shift is going to be pretty negligible and, in fact, you want a heavier battery for that purpose (ok, maybe a 40 pound one like I have is a bit of an overkill :))

By coupling the VESC to an arduino your options are absolutely endless, but a simple throttle/PAS will also do I guess. You WANT a throttle on a recument, starting on those are usually awkward, throttle fixed that.
 
Yeah well i don't happen to have a good CAD/machinist guy laying around, and usually those types aren't interested in small jobs around here.

I could probably DIY a hub motor holder though.. when i get my space back next spring.
 
neptronix said:
Yeah well i don't happen to have a good CAD/machinist guy laying around, and usually those types aren't interested in small jobs around here.

I could probably DIY a hub motor holder though.. when i get my space back next spring.
Click to expand...

I can do it for a recumbent bro free of charge if you do me some measurements and willing to wait a little - I sometimes have free time at work with nothing to do buy play in CAD and browse forums, ehehe.

I can 3d print you the bits and mail them as well, though that would not be free but certainly not expencive either (cause they are light and not that large, even from Russia). I can even do the laser cutting/machining bits for you I presume, I have that part figured out and will be needing to order some more in a few weeks... I guess my bike is a good indication of that :)
r4k5ubch.jpg


That you would be more expenicve, postage included (cause metal).
You'll just need to bolt things together. Not sure about left-handed freewheel - personally, I don't mind 'fixed gear' assist mode, but than on my bike I'm using fixed gear left-hand setup as 'main' assist and crank drive is for a ton of torque pretty intermittenly...

Anyway, you said you are willing to pay 4-figure sum for a silent (well, reasonably silent - there is still some whine from the motor even in FOC mode, but belt is silent), efficient and powerful middrive - my estimate is that it will not cost you in total considerably more than 300$ or so, and would be even cheaper when VESCs cost 2x less (but than now we have a pretty handy e-bike 75100 vesc)

New flipsky 'battle hardened' motors with large bearings should be much more durable in the long-term and need no system of shaft support (though I've designed that too and it seems to work):
WAZhnDeh.jpg


Personally I'm using 170kv 6374 cheaper motors (less than 50$), they seem quite adequate but lack refinement of flipsky motors.
 
Honestly i would be happy with something as simple as a hub motor holder that holds a perhaps mid sized geared motor. The idea would be to do that for reliability. Motor burned out? swap a new one in! in fact i'd like to carry a spare motor in the field!

Both my cannondale and my maxaraya have 'mid drives' in the chain line. A 3-6.5lb geared hub motor could be hooked up to either side of the hub. I'd like to take advantage of the freewheel inside the motor so i have very few moving parts.

I would be happy to ship my frame back and forth and pay for you to build me such a thing if you're interested.
 
I was thinking mid drive via hub motor to keep your pedal width to a minimum.
https://endless-sphere.com/forums/viewtopic.php?t=38553#p562377
Chop the axles down
Like a narrow 27H 9C https://endless-sphere.com/forums/viewtopic.php?f=6&t=38553&start=25#p569087
A steel frame and a welder :thumb:
Change up the pedaling width to see what you like and fine tune or start another from scratch.
 
neptronix said:
Honestly i would be happy with something as simple as a hub motor holder that holds a perhaps mid sized geared motor. The idea would be to do that for reliability. Motor burned out? swap a new one in! in fact i'd like to carry a spare motor in the field!

Both my cannondale and my maxaraya have 'mid drives' in the chain line. A 3-6.5lb geared hub motor could be hooked up to either side of the hub. I'd like to take advantage of the freewheel inside the motor so i have very few moving parts.

I would be happy to ship my frame back and forth and pay for you to build me such a thing if you're interested.
Click to expand...

Erm... a recumbent frame to Russian Federation? That does not sound cost-effective :) (though possible, last I've had a bike frame shipped from Ebay it cost me about 150$ or so... that was a few years ago tho)
Since I do not weld at all and mostly deal with clamped/laser cut/3d printed fixtures that work quite well (though a bit heavier than can be to due to bolts, but than easily moveable/removeable, great for belt tensioning - I'm learning composites for lighter, permanent fixtures) and can be installed by anyone - I'm not sure that is needed.
Having access to your frame would be great and make things quite simple when it comes to tailoring 3d printed bits, of course, but than by using 6384 motor it would be possible to fix it to the *seat* (horizontal) tube (that comes with guide rail, very handy) and tuck it close to your seat because it is very small and should not interfere with your ingress and pedalling, unless I'm mistaken in my measurements. It is a simple round tube, right? OTOH, main tube seems pretty complex in geometry.

Using a single-stage (for the motor, that is) reduction will make the system very efficient, considerably moreso than typical hub motors - high speed motor with thin laminations is great in that regard, that's why I've chosen them (also, cheap :)).

Both of my cheaper motors (1.5 pounds) are happily capable of 1+kw at 26v (about 50a tops), and can be overdriven to nearly 2kw at peak, but care must be taken lest you burn them (though that can be managed by the choice of controller) and it would only be possible when the middrive is spinning much faster than you can spin yourself even given additional reduction from middrive to the cranks.

Those are just a no-brainer for a bent where you do not have as much problems with clearances...
 
An other interesting idea I'm current researching is attaching a NEMA23 planetary gearbox to the motor with 8mm axle using an adapter plate. I'm not 100% sure how it turns out and how much noise will it produce and what would be efficiency loss, but should double as first stage reduction AND shaft support AND chinese gearboxes are quite cheap and should be fine on motors that are not too powerful.
https://aliexpress.ru/item/1005002841759258.html

Since they have a massive output axle with a keyway, it should be possible to install a freewheel adapter and use a bicycle chain, so with a system like yours you'll have both freewheeling cranks AND freewheeling motor - so no losses when pedalling with motor off (those would be rather minor though).
There are even helical gearboxes avalable that should be much more silent, but cost 3x more at the very least...
 
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