Q128c on mountain / hybrid bike

Jmcycles

1 µW
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I’m planning to use the Q128C to convert a 26” hard tail mountain bike which I use as for gravel riding mostly on level trails.
I’m hoping to use 48 volt system.
The variants on bms battery are 201 rpm and 328. According to my calculations, 201 rpm will top out at 15 mph ( no load rpm speed), which seems too low. The 328 rpm has a a no load speed of about 24 mph.
That seems too high, I don’t think the power band will support 20+ mph. But given the choice, that seems like a better solution.
What if I choose a 201 rpm motor 36 V and run it on 48 V? That Would did give a no load rpm of 4/3 * 201 = 268 which seems like a great compromise. Will 48V over stress the 36V motor?
Any suggestions for battery and controller?
I like the idea of BMS battery with built in controller, and the throttle etc comes with it. but they don’t tell you which controller it is.
Em3ev seems like a better battery choice, but the controller and other parts cost extra.
Thanks for any help!
 
Jmcycles said:
I’m planning to use the Q128C to convert a 26” hard tail mountain bike which I use as for gravel riding mostly on level trails.
I’m hoping to use 48 volt system.
The variants on bms battery are 201 rpm and 328. According to my calculations, 201 rpm will top out at 15 mph ( no load rpm speed), which seems too low. The 328 rpm has a a no load speed of about 24 mph.
That seems too high, I don’t think the power band will support 20+ mph. But given the choice, that seems like a better solution.
What if I choose a 201 rpm motor 36 V and run it on 48 V? That Would did give a no load rpm of 4/3 * 201 = 268 which seems like a great compromise. Will 48V over stress the 36V motor?

It depends....
One way to get a bit more speed is to go with a bigger tire....a 26" rimmed fat-tire bike effectively is 29" at the tread.
I found Q128C motor handles 800W sustained fairly well if you keep max RPMs down.
I'm running 42V into 36V Q128C 328RPM motor with a 20" wheel on my two tadpole trikes.
I run them hard (as in they get hot) also.
Performance wise trikes do 28MPH tops.
On three occasions over the past 5000 miles the motors have thrown magnets due to excessive motor RPMs.
I repaired them using epoxy specifically designed (very expensive) for magnet use in high-speed motors and all is well.
I really like the Q128C because it is so compact. For your use you should stick with the 201RPM motor though.
Pushing through loose gravel is going to take some watts, so Q128C may not work very well unless you overvolt it (and keep RPMS down as to not have magnet problems).
Another option is a Bafang 750W geared hub.....I'm running a 1000W Bafang geared hub (overvolted to just under 2000W) on a woods "e-dirtbike" hardtail 26" fat-tire bike. It is a beast!
 
Pullin-gs
That’s’ great information. Thank you. I have 2” knob us on the bike. The diameter is likely larger than I thought. Will measure.
What model Bafang motor did you refer to? There seem to be many.
Thanks,
Jmcycles
 
Never used a Q128, but have used every variant of the smaller (2Kg. vs 3Kg.) Q100 and the 201 or 328 as the only choice in most of the Q-series motors requires a less than satisfying compromise.
With the Q100, the best combo for a 26" whl.ed bike is the 201 on 52 Volts which will get it up to 20 mph, but that's still a little slow. Bigger whl.s/tires can gain another mph or two, but the bike will still be in the low 20's mph.
The Q128 could take and absorb more power than the diminutive Q100, but it's still stuck with 201 speed rating, so it's basicly the same scenario.
In general, the best geared hub motors for bikes with 26", 700cc or 29" whl.s will have a mid speed motor(260 to 270 rpm @ 36 V) and are run on 48 or 52 Volts.
Currently, I'm running a Bafang SWX02 rear cassette motor with 13 turn winding in a 26" whl. on 52 Volts for a top speed of 24 to 25 mph, the sweet spot for me. The 13 turn winding is a little slower than a true mid-speed, being in the 240 to 250 RPM @ 36 V range and a newer and more efficient design hub motor would be happy in the 10T to 12T range giving a 25 to 27 mph top speed.
 
The way I came by my current whl./motor combo is unusual.
The thread is interesting because the $45 whl./motors are still available, so I'll link it.
https://www.endless-sphere.com/forums/viewtopic.php?p=1620702
After I frt. mounted it, I realized it was a little too fast a wind for me on 52 Volts (27 mph!) and a little too powerful for a frt. mount, so I bought this....
https://hilleater.ca/bafang-swx02-rear-cassette-motor-slow-13-turn-winding/?tab=ProductReviews
...and swapped it's core into the Jump hub/whl. and ended up w/ a low to mid-speed range and CST (cassette mountable) rear motor/wheel combo.
Maybe not the least expensive way to do it, but I got what I wanted.
The well known Bafang BPM is a popular choice for rear geared motors, At 5 Kg., they fall in the large range of geared motors. They are larger diameter, smaller stator (narrower) form which can be a help for ease of install. Ck. BMS Battery for many Bafang whl/motor combos.
 
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