Has anyone built a mid drive from a QIWO 48V motor

[richj8990]

Tongsheng TSD Z8 didn't fit my carbon frame. Two brushed MY1018 motors fried in 30 miles total. Back to square one. Here is the link:


https://www.amazon.ca/brushless-Square-Diameter-Sensor-48V-400W/dp/B0CSJV496Y?th=1

DC 48V brushless DC Motor 60mm Square 14mm Shaft Diameter 400W brushless Motor with Hall Sensor (48V-400W 14mm Shaft Diameter Motor)​

The one I got was only $108



This looks great because:

1. It's only 140mm across besides the output shaft, so add another 30 mm or so for the shaft to 170 total. That can just barely fit between a standard Hollowtech crankset. If needed, a Superboost crankset is 181mm wide, or an extended 141mm square-tapered bottom bracket. I have both in the garage (I actually sold the Superboost but can buy again if needed). The 300W version is 150mm wide total including the output shaft, a significantly more amount of wiggle room between the pedals if you need it. And I may need the 300W version instead, we'll see. Free 30 day return for this unlike the damn Tongsheng.

2. It has four M5 bolt holes on each side.

3. I luckily have 2 1/2 sets of mounting plates: GNG 450W MY1018 brushed motor plates, Yalu 450W 48V brushless mounting plates, one used Cyclone mounting plate to mix and match. This motor is only 2.5 x 2.5 inches for height/width. The GNG drive side has about 2.7 inches for the sprocket part of the motor. Can shim/mending plate the empty space for a tight fit. Probably can only use one bolt on each side and other bolts can be mated to mending plates or even zip ties since I will not be using more than 800W peak.

4. The motor weighs less than 4.5 lbs, peak torque is around 75 nM with a 2.5x 1st phase reduction w/16T freewheel and 40T chainwheel. Not BSSHD level but good enough.

5. Output shaft is 14mm, beveled on one side for a keyed 15mm freewheel sprocket adapter. Another extremely important variable for a DIY mid-drive dual chain drive: the shaft width and if it's keyed or not.

6. It's brushless. That is priceless. I can't stand brushed motors on bikes, especially up hills. The internal heat increase on brushed can be faster than you can even react to.

I'll install this weekend. BTW Microsoft's Copilot was much more helpful than Alexa for choosing this motor. Alexa kept sending me to the wrong motors over and over again. Copilot listened to what I needed. The only complaint I have is that Copilot insists that I can use a larger motor than what can fit between my pedals. They say I can install a 230+ mm motor in front or on the side of the bottom bracket. Ummm...no. That can't work. The motor must be 100% transverse to the frame and parallel to the bottom bracket so that first it can bolt on to the bb mounts, and second the sprocket chain is parallel (in line) with the chainwheel. The only way you can mount something longer than the pedal spacing is way up in the triangle or far up the downtube. The pedal cranks are 7 inches long and the pedals themselves have about 1.5-2.0 inches on each side so that's around 9 inches away from the bottom bracket to clear. That is a long way folks.

I'll let you know how it goes with 400W and 170mm wide.

 

[scianiac]

Is an interesting motor choice, I wonder how efficient and power dense these a NEMA frame industrial motor is. Should at least cool reasonably well being an inrunner but hard to say what the inside looks like. Probably not as power dense as an outrunner though but is more water resistant. I would have probably gone with a outrunner and heavily varnished the stator.

 

[E-HP]

Tongsheng TSD Z8 didn't fit my carbon frame. Two brushed MY1018 motors fried in 30 miles total. Back to square one. Here is the link:


https://www.amazon.ca/brushless-Square-Diameter-Sensor-48V-400W/dp/B0CSJV496Y?th=1

DC 48V brushless DC Motor 60mm Square 14mm Shaft Diameter 400W brushless Motor with Hall Sensor (48V-400W 14mm Shaft Diameter Motor)​

so only 1.27NM of torque???

 

[richj8990]

so only 1.27NM of torque???

View attachment 388752

That's before gear reduction. For MY1018 36V 350W:

• Base Motor Torque: \(\approx 1.22\text{ Nm}\) (Standard for the 350W core).
• Internal Stage: The internal gearhead multiplies torque by 9.78.
• External Stage: Your 16t sprocket to 40t chainwheel multiplies torque by 2.5.
• Total Leverage: \(9.78 \times 2.5 = \mathbf{24.45:1}\) total reduction.

24.45 x 1.22 = 29.8 Nm. Remember this is nominal torque, peak is probably twice that amount or around 60 Nm.



This other motor unfortunately doesn't have internal gearing, so I need to make the sprocket smaller and the chainwheel larger, then make the 2nd stage chainring smaller and I already have 11-52T in back, that should work.

 

[richj8990]

The direct drive was actually a blessing in disguise. Because now I can mount the long end of the motor parallel to the frame, then purchase a 14mm input to 18mm output worm gear reducer 15:1. Output shaft is at a 90 degree angle to it's now perpendicular to the frame and parallel to the right crank and double chainrings. I may need to put the motor chain on the inner chainring. 18-20 mm sleeve with a 20mm ID freewheel adapter.

Plan for now is 16t freewheel to 44t 1st stage (probably inner chainring now that the motor is so far under the frame), then 40t outer chainring mated to 11-52t cassette. Plenty of room now to keep a Hollowtech crankset with 104BCD adapter to double 30T or greater sized chainrings. This on paper gives:

1. Motor to worm reducer​

• Given motor peak torque:

Tmotor=3.84 N\cdotpm

• 15:1 worm reducer (torque multiplied by 15):

Tworm out=Tmotor⋅15

2. Worm output (16t) to 44t chainwheel​

• First chain stage ratio:

i1=44/16

• Torque at 44t chainwheel:

T44=Tworm out⋅i1=Tmotor⋅15⋅44/16

3. 40t chainring to cassette (11–52t)​

Let Nc be the tooth count of the cassette sprocket in use (between 11 and 52).

• Second chain stage ratio:

i2=Nc40

• Torque at cassette sprocket (wheel input):

Twheel=T44⋅i2=Tmotor⋅15⋅44/16⋅Nc40

4. Min and max wheel torque (for 11t and 52t)​

• For 11t sprocket:

Twheel, 11=3.84⋅15⋅44/16⋅11/40≈43.6 N\cdotpm

• For 52t sprocket:

Twheel, 52=3.84⋅15⋅44/16⋅52/40≈205.9 N\cdotpm

 

[richj8990]

Is an interesting motor choice, I wonder how efficient and power dense these a NEMA frame industrial motor is. Should at least cool reasonably well being an inrunner but hard to say what the inside looks like. Probably not as power dense as an outrunner though but is more water resistant. I would have probably gone with a outrunner and heavily varnished the stator.

#1 problem with this motor: it's direct drive, no gearing. #1 solution is a worm gear reducer (I'm hoping lol). I went with an inrunner because it has M5 bolt holes on both ends. However, now I'm going to mount it longways under the frame (with the output shaft pointing toward the handlebars and not the right-hand side of the crankset) so the bolt holes are not critical actually. It would not have fit transverse anyway through any bottom bracket motor mounts that I know of because it's 140mm wide and the separate bb mounts are 68-73mm, even offset they are not more than 100mm wide. So the goal is to cradle the 63 mm wide motor between the mounts and bolt underneath, probably going to need a lot of zip ties to finish it up, and that's OK because it's 750-800W peak, it's not a Cyclone or anything. With the worm gear reducer I have unfortunately doubled the weight from 4.4 lbs to around 9 lbs. Can't have everything. But I like the idea of mounting longways under the down tube, that solves a lot of problems.

 

[scianiac]

I don't think that's going to work as well as you think. The problem is worm gear reducers are pretty inefficient and I think more so as you increase the input RPM. So you have an under powered motor and your are loosing power from the inefficient reduction and then have to figure out how to mount it. I mean it will work but don't expect too much from it.

If I was going to design a low powered drive like this I would go with a decently powerful outrunner with a tiny 219 chain or belt pulley fit to the largest one I could reasonably fit around the crank. Actually this exact thing has been done before and the guy said it worked really well for a lower power assist (I don't recall the thread unfortunately). A powerful outrunner will easily fit between the cranks, be much lighter per power and have more torque. With the reduction I describe you won't get a massive amount of reduction but if you oversize the motor slightly so you aren't driving it that hard much of the time it will be reasonably efficient even at a lower speed. Like maybe an 8085 motor so you get a little bit more torque and lower KV than a 63 size motor but still nice and short.