Kawasaki Z125 build

[Z000 Amateur]

Hello! I just finished up my Kawasaki Z125 conversion and I wanted to share it with yall. This forum was super helpful for ideas and info during the build.

Here was my totally stock Z125 Pro (excpe the bar end mirrors).

This is a small bike so I decided to go with a hub motor to conserve space. I ended up selecting an 8kW QS hub motor and a Kelly KSL-7275H controller. This system runs on 72V.

Next, I got rid of the engine. Sorry for the pictures in a dark garage. It’s a shared garage for the building and the landlord has the lights come on at night on a timer. That means it is always dark.

Since the hub motor doesn't take up any space the entire engine area is wide open for a decent size battery. Since I’m not a good welder trapped the battery between two plates separated by spacers, with closeouts around the outsides. I modeled it up in CAD to create a file for cutting the plates.

Next step was motor testing. Unfortunately I didn’t take any great pictures of this setup, but maybe that’s for the best so you don’t have to see how messy my bedroom is. I had the wheel/motor on my rear stand and then a rat’s nest of wires between components. This is all temporary and I cleaned everything up before installing on the bike.

I still had a bunch of gas guzzling parts on the Z that needed removal. I took off the grips, fuel system, tank, clutch lever and associated hoses and wires. Now we’re at bare bones. Extra fuel was donated to my Triumph (in the background) which happy drank it up that week.

Next I wrestled the tire over the wheel.

After that, I got everything mocked up on the bike. Overall I like how it looks! The battery fits really well (mounted to the old engine mounts) and doesn't really look all that out of place. The controller is a really tight fit on top. I took some measurements during this mockup install to make some brackets for the controller. I also needed to relocate the horn since that goes right where the controller is sitting.

The wheel/motor will sit slightly behind where the stock one was. I made plug that goes into the back of the swingarm and provides the slotted mount to hold the motor axle. The cable bundle from the motor runs up along the inside of the chain guard toward the controller.

Once I took the battery and ECU out, the DC-DC converter (72V battery step down to 12V to run lights and gauges) and the main contactor fit in there.

I painted the battery box black, then added a strip of black plastic around. This looks a lot better than bare aluminum and the blue battery plus I think the plastic will help protect against small rocks and debris kicked up by the front tire.

Things were getting a little tight with the new components so I also freed up some space by getting rid of the unnecessary wiring. There are a whole lot of wires once I cut the harness open and I really gave those Harbor Freight wire cutters a good workout. I even got a little too snip-happy and cut off the horn (oops). The only thing I really wanted to keep was the lighting circuit. However, it turns out everything runs through the speedometer so once I got rid of that I needed a separate standalone flasher relay. It works now and I reduced the the wiring by a lot.

I figured out some brackets once I had everything mocked up and cut them out of aluminum. I don't have a lot in the way of tools and workshop space so everything takes longer than it should.

The controller packages tightly right above the battery and picks up the old airbox mounts. There is barely any space with steering at full lock, but it does fit.

The DC-DC converter goes under the seat, where the battery used to be.

The bike looks super clean from the right side after installing the wheel/motor. Finally back on the side stand! I also installed the throttle and mirrors.

The wire extensions coming out of the controller are comically oversize since I only bought a few different wire sizes.

Next I trimmed all the wires and connected everything up, both the high voltage and low voltage (lighting) circuit. I also got the speedometer working and calibrated.

For my rear brake, I'm ditching the mechanical brake in favor of regen only. I figure emergency stops pretty much all come from the front tire anyway, especially with a wheelbase this short. The motor controller accepts a 0-5V signal for variable regen so I am getting this signal with a load cell. I mounted the load cell using a custom bracket off the rear brake master cylinder tab and the other end goes to the brake pedal. Since I think a fully rigid brake pedal would feel weird, I used rubber bushings in the mounting holes so there is a tiny bit of compliance like a real brake pedal. The output from the load cell runs through an amplifier to get the 0-5V signal for the motor controller. This turned out fantastic, braking feels really good and just like a firm conventional brake pedal.

I bundled the wiring a little better (still not super neat honestly) and then went for a test ride! Woohoo!

Next I got to work on the onboard (tank mounted) charger. First I cut a hole in the bottom of the tank. There is lots of open space to make sure I have good ventilation.

The charger fits inside (barely) and is fastened with square U-bolts to a bracket spanning the opening. For the picture, everything is in there temporarily since I wanted to add some foam padding where the U-bolts clamp and add trim around the edges to avoid cutting the wires. I cut off the excess U-bolt length after that too.

I like how it looks from the other side. This is a J1772 connector which I have at the charging stations at my work. I was able to fit the stock silver trim ring around the plug housing.

Finally, I reinstalled the tank (now with the charger inside), then reinstalled the fairings. Here's how it looks all buttoned up and plugged into the charger.

Thanks for reading! This has been a fun project and the bike is a hoot to ride.

 

[dustNbone]

Awesome build, looks really tidy and practical.

Did you do anything in terms of registration? Or just don't mention it to the authorities?

 

[skeetab5780]

Nice build! Thanks for sharing. It looks like a ton of fun to rip around in such a small package nice and tidy

 

[Z000 Amateur]

Awesome build, looks really tidy and practical.

Did you do anything in terms of registration? Or just don't mention it to the authorities?

Thanks! It was registered before I started this project so I'm just keeping it on the books as a normal Kawasaki Z125.

 

[boars]

Fantastic work, love it.

What kind of speed and range are you getting out of that little beast?

 

[Z000 Amateur]

Fantastic work, love it.

What kind of speed and range are you getting out of that little beast?

Top speed is around ~60 mph, which is about as fast as you want to go on a bike this size.

I've been kind of scared to push the battery too low but I think the range is somewhere around 60 - 70 miles. I haven't run the battery down below around 70v (3.5v/cell) resting voltage yet.

 

[chazw]

Great build. Now that you have had the bike for a bit what have been some challenges or things you would have done differently?
Is it fitting in with your lifestyle. Have you found it easy enough to charge? Did you consider having a removable battery?

 

[maydaverave]

Is that the stock swingarm or custom? Very clean build! I have a kymco 125 k pipe I stuffed a 17 HP 155cc pit bike race engine into but I have been thinking of converting it. The swing arm seems way to wide for hub motor so I'm wondering how hard it is to source custom swing arm.

 

[Z000 Amateur]

Great build. Now that you have had the bike for a bit what have been some challenges or things you would have done differently?
Is it fitting in with your lifestyle. Have you found it easy enough to charge? Did you consider having a removable battery?

I'm about 600 miles in at this point and still really enjoying it. No I didn't consider a removable battery and have had no issues charging since I can plug in at work. If I didn't have daily access to that charger then I think I may have considered a removable battery.

Generally I am happy with the build and don't have any major things I would have changed but there are a few small ones.

• I don't love the stretched swingarm look that I got from the adapter plug. I think I could have made that tighter to minimize the stretch.

• I didn't add connectors or clean disconnect points between most of the components and the controller, even including the wheel/motor. Any servicing and replacing items or changing tires will be a pain.

• I didn't take much care to waterproof any connections. In southern California this isn't a huge issue, but I wouldn't trust this thing in the rain.

Is that the stock swingarm or custom? Very clean build! I have a kymco 125 k pipe I stuffed a 17 HP 155cc pit bike race engine into but I have been thinking of converting it. The swing arm seems way to wide for hub motor so I'm wondering how hard it is to source custom swing arm.

Thank you! The swingarm is stock but the plug in the end is custom. The 10th picture in my original post shows the CAD model of the plug next to the stock swingarm. This adapts the width and includes the right size slot for the hub motor.

I did add some thick washers as spacers to make up the width difference due to a wider swingarm like you say.

 

[TorgueRPM]

I'm working on a Honda Grom build, which is pretty much the same bike. I'm planning to get a 5kw QS hub motor, but I'm worried about heat issues and choosing the right kv. What phase current are you running? Have you noticed any issues with heat dissapation given that the motor is directly in contact with the tire?

 

[gogo]

Congratulations on choosing a frame that for the most part doesn't use the engine as a structural member, but instead uses a stout backbone. The engine/transmission did stiffen up the frame between its mounting points, however, and you must question whether that function is important, and if so, whether your conversion provides it.

The standoffs you have between the engine mounts and the plates can allow some flex where before there was solid attachment between all three. Just to be sure, I would bolt something directly to the engine mounts that connects the triangle between all three. Either one or two plates or a solid piece would work.

 

[Z000 Amateur]

I'm working on a Honda Grom build, which is pretty much the same bike. I'm planning to get a 5kw QS hub motor, but I'm worried about heat issues and choosing the right kv. What phase current are you running? Have you noticed any issues with heat dissapation given that the motor is directly in contact with the tire?

I haven't noticed any heat problems. The motor gets warm but not really hot. I'm at 72V and the current limit set in the controller is 150A.

Usually I do short rides (~10 miles) and don't spend the whole time at full throttle so that probably helps too.

I would definitely recommend the 8kW motor. That extra speed and power is really nice.

 

[swiftyds]

Congrats on a great build.

I’m just about to use the same KLS7275H controller and QS hub motor for a conversion of an Aprilia RS50. Motor is only 4Kw to keep equivalent 50cc power rating for the bike.

Any chance you could share/post your controller settings? I’m using the Android app via Bluetooth on mine to set the controller up and want to set a max Amp rating of 150A our of the controller. There’s a load of settings there that don’t seem relevant like three speed switch that I understand you still need to set parameters for.

Many thanks

 

[maSch]

Hi Zooo
I followed your build and pics in detail, and I love your build, however I dont like the modern style of the bike, I am oldschool, I love bikes from the seventies (which has an advantage here in Germany with extremely strict legal restrictions: for bikes before 2000 no EMC, Electromagnetic compatibility test necessary). My plan is to go with similar components like you did, but use a Yamaha XT 250 or Honda XLR 250 as donor bike.
I am researching this great forum before I start to order parts and came over your solution for the rear-brake:

For my rear brake, I'm ditching the mechanical brake in favor of regen only. I figure emergency stops pretty much all come from the front tire anyway, especially with a wheelbase this short. The motor controller accepts a 0-5V signal for variable regen so I am getting this signal with a load cell. I mounted the load cell using a custom bracket off the rear brake master cylinder tab and the other end goes to the brake pedal. Since I think a fully rigid brake pedal would feel weird, I used rubber bushings in the mounting holes so there is a tiny bit of compliance like a real brake pedal. The output from the load cell runs through an amplifier to get the 0-5V signal for the motor controller. This turned out fantastic, braking feels really good and just like a firm conventional brake pedal.

could you please elaborate on that?
- is it really "braking" or just a bit of "delay" ? this is crucial to get it over the tech-inspection here in Germany
- what parts did you use exactly? "load cell", "amplifier"
- could you please up some details pics of your rear brake?

thank you very much, ride on!
mark

 

[Z000 Amateur]

Congrats on a great build.

I’m just about to use the same KLS7275H controller and QS hub motor for a conversion of an Aprilia RS50. Motor is only 4Kw to keep equivalent 50cc power rating for the bike.

Any chance you could share/post your controller settings? I’m using the Android app via Bluetooth on mine to set the controller up and want to set a max Amp rating of 150A our of the controller. There’s a load of settings there that don’t seem relevant like three speed switch that I understand you still need to set parameters for.

Many thanks

Sorry for lack of response and I'm guessing you figured it out by now. This is my understanding of the current limiting parameters. The "current percent" limits the phase current to some percentage of the controller's max rating. The "battery limit" is a percentage that further limits battery current draw.

In other words:
max phase current = controller max rating * current percent/100
max battery draw = controller max rating * current percent/100 * battery limit/100

For me, I wanted to limit the motor and battery current to 150A so I used current percent as 30 and battery limit as 100.

 

[Z000 Amateur]

Hi Zooo
I followed your build and pics in detail, and I love your build, however I dont like the modern style of the bike, I am oldschool, I love bikes from the seventies (which has an advantage here in Germany with extremely strict legal restrictions: for bikes before 2000 no EMC, Electromagnetic compatibility test necessary). My plan is to go with similar components like you did, but use a Yamaha XT 250 or Honda XLR 250 as donor bike.
I am researching this great forum before I start to order parts and came over your solution for the rear-brake:

For my rear brake, I'm ditching the mechanical brake in favor of regen only. I figure emergency stops pretty much all come from the front tire anyway, especially with a wheelbase this short. The motor controller accepts a 0-5V signal for variable regen so I am getting this signal with a load cell. I mounted the load cell using a custom bracket off the rear brake master cylinder tab and the other end goes to the brake pedal. Since I think a fully rigid brake pedal would feel weird, I used rubber bushings in the mounting holes so there is a tiny bit of compliance like a real brake pedal. The output from the load cell runs through an amplifier to get the 0-5V signal for the motor controller. This turned out fantastic, braking feels really good and just like a firm conventional brake pedal.

could you please elaborate on that?
- is it really "braking" or just a bit of "delay" ? this is crucial to get it over the tech-inspection here in Germany
- what parts did you use exactly? "load cell", "amplifier"
- could you please up some details pics of your rear brake?

thank you very much, ride on!
mark

The braking strength will depend on your batteries. My batteries have a max charge rate of 3A per cell so with 20 cells in parallel I can brake using 60A. That generates a significant amount of braking force and I can usually ride around most of the time with only using the regen brake. I have a feeling this might not pass tech inspection just because it is unconventional and would not work if the controller turned off. Maybe you would be better off using the clutch level for braking but also keeping the rear foot brake?

The load cell and amp were similar to these. You may need a slightly different load cell range depending on how you mount it and how big your brake lever is. You can also fine tune the brake pedal force required using the controller dead zone limits.
https://www.ebay.com/itm/S-Type-Beam-Load-Cell-Scale-Sensor-Weighting-Sensor-100kg-with-Cable-Waterproof-/312663368471?nma=true&si=RpQSiE7so5QD8i8AzgOctW5oowU%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557
https://www.ebay.com/itm/0-5V-0-10V-4-20MA-Load-Cell-sensor-Amplifier-Transmitter-strain-gauge-transducer/272844412249?hash=item3f86cb5559:g:6q4AAOSw~4NZt-5d

What else were you trying to see from the pictures? I basically just connected the load cell in the same spot where the master cylinder used to be.

 

[swiftyds]

Thanks for replying on the controller settings. Very helpful.

Can I ask - did you use mild steel or aluminium for your swing arm plugs? I’ve used mild steel as I was worried the axle on the hub motor would chew through steel but they are quite heavy

 

[maSch]

yeah, thank you so much for these helpful infos!

I have a feeling this might not pass tech inspection just because it is unconventional and would not work if the controller turned off. Maybe you would be better off using the clutch level for braking but also keeping the rear foot brake?

Here you see the sheer difference between California and Germany. You are just doing what feels logical to an engineer. I totally agree that in my normal bikers day, I use the front brake for heavy (emergency) braking and the rear brake either to support or just to decelerate a bit. So more than logical to use it as pure regen. Now I understand basically how you constructed it. Unfortunately the link with the load cell itself does not work for me. (make/model?)
I would apreciate a lot seeing some more pics of that load-cell you used.

I was thinking to build such a load cell "in parallel" with the original brake pedal. Find some way to adjust the load-cell that it first only regen-brakes and the more you press the pedal, the more the disk-brake grips.
I believe still indigestible for German tech-control. But at least there is the foot-pedal with a real disk-brake.

I asked Damon of QSmotors if they could supply this 8Kw motor with a 320mm axle, and he confirmed they would. That would ease the construction of the swing-arm plugs enormously for my build.

I am still trying to figure out, if it would be possible to machine the outer plate of the motor, that it can hold a Yamaha disk with 6 bolts. This tiny 3 bolt disk that QS suggests doesnt look tough to me...

 

[Z000 Amateur]

Thanks for replying on the controller settings. Very helpful.

Can I ask - did you use mild steel or aluminium for your swing arm plugs? I’ve used mild steel as I was worried the axle on the hub motor would chew through steel but they are quite heavy

I used 6061-T6 aluminum. The motor axle and the plug shouldn't be moving relative to each other, so in theory you shouldn't have any wear problems with any material.

 

[Z000 Amateur]

yeah, thank you so much for these helpful infos!

I have a feeling this might not pass tech inspection just because it is unconventional and would not work if the controller turned off. Maybe you would be better off using the clutch level for braking but also keeping the rear foot brake?

Here you see the sheer difference between California and Germany. You are just doing what feels logical to an engineer. I totally agree that in my normal bikers day, I use the front brake for heavy (emergency) braking and the rear brake either to support or just to decelerate a bit. So more than logical to use it as pure regen. Now I understand basically how you constructed it. Unfortunately the link with the load cell itself does not work for me. (make/model?)
I would apreciate a lot seeing some more pics of that load-cell you used.

I was thinking to build such a load cell "in parallel" with the original brake pedal. Find some way to adjust the load-cell that it first only regen-brakes and the more you press the pedal, the more the disk-brake grips.
I believe still indigestible for German tech-control. But at least there is the foot-pedal with a real disk-brake.

I asked Damon of QSmotors if they could supply this 8Kw motor with a 320mm axle, and he confirmed they would. That would ease the construction of the swing-arm plugs enormously for my build.

I am still trying to figure out, if it would be possible to machine the outer plate of the motor, that it can hold a Yamaha disk with 6 bolts. This tiny 3 bolt disk that QS suggests doesnt look tough to me...

I don't think using a load cell in parallel will work because the brake pedal needs to move significantly for the disc to engage, but the load cell doesn't move much at all.

The load cell is identical to this: https://www.ebay.com/itm/S-TYPE-Beam-Load-Cell-Scale-Sensor-Weighting-Sensor-With-Cable-1PC/383134188537?hash=item593493c3f9:m:mTY8v7pWL9qjqjvxZwHsexw
And the clevis ends are these: https://midwestcontrol.com/shop/MMC-12

The picture in the original post shows all the pieces so I'm not sure what else would help. I attached a new picture with the pieces highlighted since it is hard to tell them apart with all black. The green is obviously the brake pedal. The red is the custom bracket that I made which is bolted fixed to the frame. It uses the bolt holes from the rear brake master cylinder. The blue is the load cell, which is connected to the fixed bracket and the brake pedal through the clevis ends. You can see that when the pedal is pressed, it will compress the load cell.

 

[gregstantonlauer]

This is perfect. Ive been looking to build something similar out of a Honda Groom. Might I ask where you purchased your battery from, and also how did you assemble the motor to the rear hub?

Thanks!

 

[swiftyds]

I used 6061-T6 aluminum. The motor axle and the plug shouldn't be moving relative to each other, so in theory you shouldn't have any wear problems with any material.

Thanks - I went ahead and got a set of adapter plates machined in 6061-T6 aluminium that slot into the box section of my swing arm. Just mounted the motor and test wired everything up - seems pretty solid with the brake disc mounted as well.

Will redo my build thread as it’s still based on the Aprilia RS50 I’d originally set out to convert.

 

[Z000 Amateur]

This is perfect. Ive been looking to build something similar out of a Honda Groom. Might I ask where you purchased your battery from, and also how did you assemble the motor to the rear hub?

Thanks!

Here's the motor and battery. I'm not sure I understand the question about assembling the motor and hub? They are integrated when you buy it.
I think it was this hub motor: http://www.cnqsmotor.com/en/article_read/QS%20Motor%208000W%20273%2050H%20V3%20E-Motorcycle%20Spoke%20Hub%20Motor/264.html
This is the battery: https://www.aliexpress.com/item/32938333114.html?spm=2114.12010612.8148356.13.39a94cfd90IdVn

 

[Dui ni shuo de dui]

Awesome build, very clean.

Just a few remarks and suggestions, if I may:
-You should put a second nut on your motor axis, to secure the first one. If it gets loose because of vibrations then you'll ruin your motor.
-150A seems quite weak since you're using a 8KW motor. I dont know if your battery and controller allow you to go for more, but your motor is way overspec. You could double that amount of current and still be totally fine with such a motor. :wink:
-If you can, don't hesitate to change this puny front brake and upgrade to something better. You can find some really good brake kits, stuff like frando or clones like that. They re very affordable and you'll see a clear difference agains the stock ones!
-Carbon vinyl might look nice on your battery box. It is already ok in black, but everything looks better with carbon :wink:

Again, kudos on your build, really well done.

 

[Z000 Amateur]

Awesome build, very clean.

Just a few remarks and suggestions, if I may:
-You should put a second nut on your motor axis, to secure the first one. If it gets loose because of vibrations then you'll ruin your motor.
-150A seems quite weak since you're using a 8KW motor. I dont know if your battery and controller allow you to go for more, but your motor is way overspec. You could double that amount of current and still be totally fine with such a motor. :wink:
-If you can, don't hesitate to change this puny front brake and upgrade to something better. You can find some really good brake kits, stuff like frando or clones like that. They re very affordable and you'll see a clear difference agains the stock ones!
-Carbon vinyl might look nice on your battery box. It is already ok in black, but everything looks better with carbon :wink:

Again, kudos on your build, really well done.

Thank you! You're right I should get a double nut in place. I maybe need to cut one down since there isn't much thread sticking out.

You're also right about the motor power, but my battery is the limiting factor for current draw. Maybe in a few years as batteries get better and cheaper I can upgrade and keep all the same motor and controller. The cost difference between 5kw and 8kw hub motor was pretty small so I just went with the bigger option that will run cooler and allow upgrading later.

With the rear regen brake, it's like a game for me to try not to use the front brake as much as possible so I probably won't upgrade it. I want all that energy back!