1979 Yamaha XS750 conversion.

Joined
May 20, 2020
Messages
22
Alright, lets get this thread started.
I recently acquired the aforementioned XS750
I will add pictures later this week.

I have ordered the following parts:
17" by 6" 12kw rear hub motor from qsmotor (configured for 145kph)
300a ANT bms with screen.
Kelly KLS96601-8080I
A 220v charger for 96v lithium at 20A

I already have lying around:
A pile of matched nissan leaf batteries to make my battery
The bike itself

Things I still need to get:
A replacement swingarm that will accept the new wheel (stock XS750 is shaft drive)
Brakes for the rear wheel
J1772 adapter to feed the charger
throttle (considering a domino pot throttle if i can find one)
Dcdc converter (suggestions welcome)
Main power contactor


I did some looking about but I could not find any mention of anyone using this motor. I plan to document my entire build process thoroughly with lots of pictures and data.
There is a local place that is willing to let me use their dyno too when I get it put together.

I don't expect this to be a drag strip monster, but having some actual data out there should be informative.

Does anyone have any experience fitting brake rotors to these motors? I am trying to find a suitable brake rotor/caliper setup that will fit onto the existing mount holes for the motor.

Any other suggestions are welcome too.
 
biothundernxt said:
throttle (considering a domino pot throttle if i can find one)
You may wish to consider a cable-operated-throttle (COT), using whatever cable-type grip you like, or that it already has, and simply run the cable to a COT module inside the housing with your other wiring and electronics. Then there's no weatherproofing worries, etc., for electronics on the handlebar control.

LIke the one used here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=100859&p=1475133&hilit=throttle#p1475133
(see MJSfoto1956's build thread for pics of it in use on the bike)
or here, where I use one operated by a brake lever for proportional regen,
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1562688&hilit=atv#p1542626
or here, where I use one operated by an ATV thumb throttle as the actual system throttle
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1562688&hilit=atv#p1562688

I did some looking about but I could not find any mention of anyone using this motor.
Which specific motor model is it? You only give this info:
17" by 6" 12kw rear hub motor from qsmotor (configured for 145kph)


Does anyone have any experience fitting brake rotors to these motors? I am trying to find a suitable brake rotor/caliper setup that will fit onto the existing mount holes for the motor.
A number of the Chinese hubmotors use various Chinese rotor "standards", and some are even company and motor-model specific, with no source for them anywhere else (I have a bicycle motor from Fusin like this, and the company is long gone).

So your best bet for a rotor is to get it with the motor, if the rotor mount on the motor doesn't match standard motorcycle rotors you can just go out and buy. It should still work with any caliper that can accomodate it's thickness, mounted so it works with the diameter of whatever rotor it is.
 
I had considered using a throttle setup like that, but I have (possibly unfounded?) reliability concerns because the stock throttle is not dual cable.

This is the motor:
https://www.qsmotor.com/product/17-inch-12kw-hub-motor/
I don't have a model number.

For variable regen, I plan to use some kind of strain gauge on the rear foot brake. I havent figured out the details yet, but I am sure emulating the potentiometer input for that with a microcontroller based on the output of the strain gauge should not be too hard.

Thanks for the info on the rotor. That does not bode well for down the line when I need a new rotor...
I plan to keep this bike for a very long time.
 
biothundernxt said:
I had considered using a throttle setup like that, but I have (possibly unfounded?) reliability concerns because the stock throttle is not dual cable.

These cable throttles are real nice, never had any issue with them, you can go for it. Feeling is great too.

I suggest you to use one for the variable regen too, you can actuate it with a cable lever on the left handlebar since you won't have a clutch to actuate anymore. That's how we did it on a friend's bike, it's real nice to use and you keep the mechanical brake on the foot for safety in case something goes wrong with the electrics.

biothundernxt said:
This is the motor:
https://www.qsmotor.com/product/17-inch-12kw-hub-motor/
I don't have a model number.


I don't know anyone using a 12KW motor, but I know people using a 8KW motor and I'm myself using a 3KW motor. There's not much difference aside from the power they can tolerate, so finding someone who has exactly the same doesn't really matter.
You can expect some serious power with that, I tried the 8KW and coupled with a good controller it isn't weak at all.

Fitting brake rotors is pretty easy, just bolt it on there, the holes are already in place. You can find some kits on aliexpress for cheap. You don't need a powerful setup on the rear brake anyways, you'll have the regen so that's mostly dead weight. Just need it for safety and at very low speeds.

biothundernxt said:
I plan to keep this bike for a very long time.

Yeah QS motors are quite reliable usually.
 
biothundernxt said:
I had considered using a throttle setup like that, but I have (possibly unfounded?) reliability concerns because the stock throttle is not dual cable.
None of these COTs are dual cable either, becuause they have an internal spring return.

A dual cable pulls boht directions, which with a mechanical ICE throttle might be a necessary thing so a spring can't fail and leave the throttle stuck open with gas pouring thru. Not an issue with electric motors--you just turn off the power. ;)


For variable regen, I plan to use some kind of strain gauge on the rear foot brake. I havent figured out the details yet, but I am sure emulating the potentiometer input for that with a microcontroller based on the output of the strain gauge should not be too hard.
You could use a COT for that, too, adding a cable pull to the foot brake, and a cablestop above it on the frame. Much simpler, and a proven electrical design. ;)

Alternately, since you won't need a clutch anymore, then if it has a clutch lever on the left side, you can use the clutch lever and cable to control the ebrake.

Looks like it uses a 3-bolt rotor design, so you would need to find a rotor with that many bolts in the right BCD (bolt circle diameter). I don't know what that is, because the page doesn't say. It just sayd "11) Brake: disc brake (220mm)" which is the outer edge of the rotor, not the BCD.

A simple search for 3 bolt brake rotor turns up a fair bit, don't know if any of them are the one you want
https://www.google.com/search?q=3+bolt+brake+rotor
 
I have been contacting a few suppliers from china about getting brake parts that will fit.
I will post here with some more info when I have confirmed a fit.

But now for those other photos I promised earlier!
Here is a picture from the day I picked it up:
TuojwY2-min.jpeg

I fitted one leaf module various ways to see how it might fit:
vq8MmKo-min.jpeg
nU6zliE-min.jpeg

And here is my progress so far disassembling the bike down to the frame.
TK7q3Uj-min.jpeg
HFs203d-min.jpeg

I finished up the battery the other day:
puJreUw-min.jpeg

I have a lot of restorative work to do.
I have a 3d printer and scanner, soI plan to scan in models of most of the parts as they are, and then sell the tank/plastic pieces to someone who wants to restore a stock XS750, and then print out replicas of the plastic parts and a shell of the tank for looks (I will likely put the charger inside the tank.
I'll post the models I scan if anyone is interested.

Today though, I am off to find a new swingarm so I can mount that monster 12KW motor.
 

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I don't see any pics; presumably you're using some external site to host them that isn't visible to everyone. (a common problem).

I'd recommend attaching all images directly to your post using the attachments tab, since if they're uploaded to the forum they'll be visble to anyone that can see your post, and wont' disappear whenever the external hosting site goes down or changes their mind about who gets to access the content the users posted there. :/
 
Nobody local had anything available, so i ordered a Yamaha fazer swingarm.
$_57.jpeg
I hope it fits. Some other conversions from shaft to chain for the xs750 used this swingarm, so fingers crossed that it will not require much modification.
We'll see. It should get here pretty quick, it is only going across town.
 
Also, here are some pictures showing a cardboard mockup that is the size of my battery floating around in my frame.
I'll need to make a box for this to sit in, but this looks promising so far.
IMG_20200706_153354_compress95.jpg
IMG_20200706_153410_compress48.jpg
 
Try turning that rectangular mock-up on its wide side, then leaning it down in the front of the frame. That will give you a better, lower center of gravity, and leave you room for the motor behind and slightly above it.
 
LeftieBiker said:
Try turning that rectangular mock-up on its wide side, then leaning it down in the front of the frame. That will give you a better, lower center of gravity, and leave you room for the motor behind and slightly above it.

The motor is a hub motor, so there is no advantage there, but a lower center of gravity is always better. I will move it around some more to see what the best position would be.
 
I recently converted a 1989 Yamaha FZR250 using a QS 273 6000W v3 motor, very happy with the results and happy to answer any questions you have. For the brake rotor I got QS Motor to supply one as it seemed like an unusual bolt pattern. To get the motor in, I extended the slots to make dropouts and made some solid aluminium blocks that slide into the back of the swingarm and clamp onto the axle flats. There will be a lot of torque on the axle (especially 12kW!) so you’ll need a good way to resist that force. Also I tried to use the original rear brake caliper but didn’t allow for the bulk of the hub motor so ended up buying a thinner one and getting a new mounting bracket made. The Fazer swingarm in your photo looks a little different to mine so not sure how useful my 3D models would be but happy to share if want. Good luck, looks like a great project. Those Leaf cells should be amazing!
 
Also very interested to see how you go with the Ant BMS, especially how you connect up the power cables to handle a lot of current.
 
soyachips said:
I recently converted a 1989 Yamaha FZR250 using a QS 273 6000W v3 motor, very happy with the results and happy to answer any questions you have. For the brake rotor I got QS Motor to supply one as it seemed like an unusual bolt pattern. To get the motor in, I extended the slots to make dropouts and made some solid aluminium blocks that slide into the back of the swingarm and clamp onto the axle flats. There will be a lot of torque on the axle (especially 12kW!) so you’ll need a good way to resist that force. Also I tried to use the original rear brake caliper but didn’t allow for the bulk of the hub motor so ended up buying a thinner one and getting a new mounting bracket made. The Fazer swingarm in your photo looks a little different to mine so not sure how useful my 3D models would be but happy to share if want. Good luck, looks like a great project. Those Leaf cells should be amazing!

I am glad to see others converting old motorcycles. I would love to see the cad files you mentioned, even if they do not work for my swingarm, they could provide inspiration for me on my build.

Did you make a thread on here for your motorcycle project? I would love to see some photos.

soyachips said:
Also very interested to see how you go with the Ant BMS, especially how you connect up the power cables to handle a lot of current.

The version of the ANT bms I ordered says it can handle 300A continuous, and my controller should only pull 240A max for a short time, so it should work out. I plan to utilize the existing wiring on the BMS for the power input and outputs, but the rest of my main power wiring is going to be 2/0 AWG for DC, and probably bigger for AC (maybe? I am not sure if that would be needed at 600 phase amps or not)
In any case, my BMS was supposed to be here on wednesday, but the tracking says it is stuck in San Francisco right now.
Oh well. I just hope they do not lose it along the way.
 
I know it has been a while, but I am posting an update, albiet a short one.
My motor should finally be coming in next week. (after I got hit with 250 dollars in import fees... Ouch)
I plan to post a lot of pictures of the motor, and as soon as I have time to, I will be testing the motor controller with it on the bench.
 
UPDATE DUMP

Sorry for the delay, the fires around me (Oregon) have made things hectic.

Anyway,

(Sorry if you cannot access imgur for some reason, I will come back and edit this post and embed the images directly later, but I don't remember how to do that right now)

Here are some photos of the motor:
https://imgur.com/gallery/6WgJGl1

Then I built a little stand and hooked up all the electronics for a first test:
[youtube]zs7Qzl2n8bo[/youtube]

And here are some photos of how it lined up with my chosen swingarm (from an old yamaha Fazer).
https://imgur.com/gallery/Jt3FXZp

I was thinking about slotting the swingarm to allow the wheel to mount, but some of my engineering minded friends advised against it, siting concerns that slotting it would make it lose it's structural rigidity.
I decided to make an adapter instead that would slot into the existing ends of the swingarm.
https://imgur.com/gallery/mvdoUt2

My next move is going to be to 3d print this adapter to check fitment, and then have it CNCed out of 6061 T6 aluminum.
 
The extensions looking very smart!
Have you thought about to get the long axle of Hubmotor in between the swing arm later on?
Maybe you have to mount the brake later on at least vice versa to get it out.
 
I
Rovii said:
The extensions looking very smart!
Have you thought about to get the long axle of Hubmotor in between the swing arm later on?
Maybe you have to mount the brake later on at least vice versa to get it out.

Hi Rovii!
Yes, mounting the motor was an interesting challenge because I cannot slide the axle into my swingarm.
Instead, I designed some adaptors in Fusion 360 and 3D printed them to check fit:
isometric bottom.png
isometric top.png
2YgarXNsmall.jpg
aFAJiAesmall.jpg

With these, I can attach them to the hub motor, then slide it into the swingarm and bolt them in place.
 
Over the past few weeks, I have made some more progress.
I mounted most of the components in a temporary fashion:
Af4FATMsmall.jpeg
C1phQq8small.jpeg
uuN6rCYsmall.jpeg
 
I would highly recommend thickening the metal on the extension where the axle is going. Better yet, thicken it and make it clamp on the axle. That motor is probably capable of at least 30kw bursts, and the torque at those levels may shred those holes. I know some qs motors come with small torque arm things, but even those might be pushed to their limit.
 
Great work so far.

I do hope you'll shorten the swingarm as much as possible to get a shorter wheelbase. That will ride much better.



rear swing arm extension.jpg
 
TorgueRPM said:
I would highly recommend thickening the metal on the extension where the axle is going. Better yet, thicken it and make it clamp on the axle. That motor is probably capable of at least 30kw bursts, and the torque at those levels may shred those holes. I know some qs motors come with small torque arm things, but even those might be pushed to their limit.

That cut-out on the back of the bracket is to hold the hardened steel torque arm that came included with my motor:
Inkedisometric top_LIsmall.jpg
IMG_20201008_162621Small.jpg

I ran some static analysis on it in fusion 360, assuming the maximum rated stall torque, and it did not show any damage.Stress analysis.png
(the warping of the part is exaggerated to allow for ease of viewing, stress warping happens around 6,the minimum shown in my analysis was 8.239)
 
SlowCo said:
Great work so far.

I do hope you'll shorten the swingarm as much as possible to get a shorter wheelbase. That will ride much better.



rear swing arm extension.jpg

If you mean for me to chop the swingarm, that is not really feasible because it stops being a square tube.
rear swing arm extension detail.jpg
If I were to cut it down, my adapter would no longer fit into the swingarm.
I am trying to avoid any welding if possible.

If this swingarm does not work out, I will probably just have to have one custom fabricated from scratch.
Anyway, we'll see.
I know that a longer wheelbase will affect rideability, but I am hoping it will not make it unrideable.
 
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