2001 KX125 Hub mid drive Build *multi megabyte picture/gif thread*

matt912836

100 W
Joined
Nov 25, 2012
Messages
122
Location
New York
How it all began:

Had a spare Vector Vortex swing arm and mid drive hub motor.

Also had a kx125 with a pristine frame that needed its engine rebuilt

Reduce, reuse, recycle is my motto, so I set out to make the two work together, with as little to no modification as possible to the frame
 

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Removed all engine components and started seeing how the chain line would work out
 

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Once I felt ready to commit, the swing arm met an angle grinder, and the rest was history
 

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Now it's just a matter of bracing this motor which I plan to feed around 20kw...

What's the stiffest solid pieces of metal we have lying around

A dig through some spare parts and some more angle grinder love led me down this path

Reusing crank arms and suspension rocker arms, the stiffest lightest pieces of aluminum I had lying around!
 

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Looks like a very interesting build, Kudos!

Also I really like the gif pictures, it's a very good compromize between static pictures and long (sometimes boring) videos. Great idea!
Keep the posts coming!
 
Dui said:
Looks like a very interesting build, Kudos!

Also I really like the gif pictures, it's a very good compromize between static pictures and long (sometimes boring) videos. Great idea!
Keep the posts coming!

Very appreciated! Going to optimize them as much as I can to cut down file size.

Drilled holes and mounted up what I call the "motor cradle" with the crank arms
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Also used this tube from the kickstand portion with a nut welded to it pretty strong as a brace for the bottom motor mount. This allowed me to hold the cradle in the offset position I needed it in to get the sprocket out far enough for a decent chain line.

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Seems to be pretty firm, this was okay for testing chain line under power but I definitely will want more bracing before throwing full power.

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Also reused some old burned out meanwells for their outer aluminum case. turned out to be the perfect size to mount as a radiator and use to mount the controller to, near identical size made it a perfect fit! Also a perfect location for airflow. Left side holds a 72v 80a yyk square wave for testing, will be changed to a 96v unlocked sabvoton. Right side can be used for mounting any peripherals, inverters, maybe even converted to small storage compartment?
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This was completely 100% freehand and even happened to fit into the plastics perfectly!
 

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Elektrosherpa said:
matt912836 said:
... mid drive hub motor...

I dont understand this expression.
Does this mean it was a hub motor and you transformed it to a mid drive motor?
Or does any manufacturer sell such motors?

Yes exactly, it is a hub motor used in a mid drive configuration with a sprocket bolted to it to run a chain driven drivetrain

Hubs are low RPM high torque motors so no need of a reduction and can be used with decent sized off the shelf sprockets. Removing the weight from the wheel but keeping the power and torque from a high powered hub is the best possible use of this motor in my opinion

This motor is a 3t qs205. so although it is the fastest wind hub, it also means it has the thickest wires used inside to wind it. Out of all windings, it's the one physically capable of taking the most amps through the wiring, and since it's being used as a mid drive, it can still be geared down for nice low end torque and not used for speed the way it's intended when laced in a wheel.

I plan on gearing it for 60mph top speed at 100v after flux weakening. Meaning it should hopefully have enough torque down low to make the front end light and pick up under power, Anything less would be disrespectful to this frame!
 
Bike had been riding well with yuyangking, time to step up the power and stress this mount.

Added some more bracing which is bolted to the rocker arms and braced to the old shock mount on the cradle, old 1/2 drive sockets :mrgreen:

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Bigger sprocket came in the mail!

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Originally found a 54t that was made for a Japanese CBR that had a 428 chain and the same bolt pattern as the KX

Further research into other 428 sprockets and I was able to find the biggest off the shelf 428 sprocket, which ironically just so happened to be for a kx125 from 1977, before they moved to 520 chain. also has the same bolt pattern as my 2001!

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Bike did 47mph with old 54t on 75v nominal + 15% flux weakening. Upping the sprocket to 63t and voltage to 92v nominal should get me a ~45mph top speed before flux weakening and 60mph with, and noticably more torque overall

Swapped out the yuyangking for an unlocked sabvoton 96100, aiming to squeeze as much power out as possible to lift the front wheel.
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Motor mount feels rock solid even at 120A and slide regen enabled. can barely get front wheel to lift off the ground if I'm going under 5mph and toss my weight way back, but definitely getting voltage sag due to these xt60s I was running from the yuyangking. probably holding me back a lot as theyre heating up noticeably now, got away with 80A but definitely now have to upgrade wiring.
 
One thing you should probably know about this controller is that the face that needs cooling is the one on the bottom. Meaning right now in your case if faces the rear, so there will be very little airflow.
It might still be ok if oriented this way, so I suggest you to try and see, but if it overheats then you might want to turn it the other way around. Keep that in mind during building so you can still be able to accomodate later if need be. :wink:
 
Dui said:
One thing you should probably know about this controller is that the face that needs cooling is the one on the bottom. Meaning right now in your case if faces the rear, so there will be very little airflow.
It might still be ok if oriented this way, so I suggest you to try and see, but if it overheats then you might want to turn it the other way around. Keep that in mind during building so you can still be able to accomodate later if need be. :wink:

Upgraded the battery wiring, Just ran around the neighborhood set to 150 battery amps and 450 max phase amps... I guess I finally got what I wanted, somewhat

Bike pulls like a train up until 40mph then power dies off fast. I can get it to pick itself up but still only <10mph, maybe I overestimated this motors ability to lift a 40 point front fork setup on a 57 inch wheelbase at speed.. feels like I'd need twice the motor to achieve the performance I'm really after, or twice the controller and battery.. I would say atleast 200 battery amps and 600 phase amps would be where this bike turns lightweight on demand.

I am also still running on run down knobbies and pavement, I do feel that's why my top speed is suffering, maybe a proper dual sport tire will give us more traction and also more lift?

The svmc96120 is known to do well over 3x the rated power reliably.. I wonder how much this 96100 could do? My battery absolutely maxes out at 180 amps and would be pushing the cells to the limit, battery cooling would be a must at that point. Controller gets luke warm after running around for 10 min trying to get the bike to lift with no mercy on the throttle, so I feel it can definitely do a little more... my low gearing definitely helps it only pull a lot of power in short spikes... Phase wires and motor also get a bit warm but nothing alarming yet, but Any further power from where I'm at now would definitely greatly benefit from or probably even require doubling phase wires, adding ferrofluid, and manual cooling fans hitting the motor since I dont have clearance for hubsinks.

On the bright side, the motor mount is holding up amazingly solid under full power. the sprocket honestly isnt even lined up 100% and still havent had a single chain issue. This chain seems to stretch every ride on the other hand, making a switch to a heavy duty 428 sooner than later
 
matt912836 said:
Bike pulls like a train up until 40mph then power dies off fast. I can get it to pick itself up but still only <10mph, maybe I overestimated this motors ability to lift a 40 point front fork setup on a 57 inch wheelbase at speed.. feels like I'd need twice the motor to achieve the performance I'm really after, or twice the controller and battery.. I would say atleast 200 battery amps and 600 phase amps would be where this bike turns lightweight on demand.

Your motor is geared down, so that's to be expected. On my bike, which is not geared down, the power remains strong up until 60mph or so, when it starts decreasing.

Regarding the controller, I pushed mine (unlocked Sabvoton 72150) up to 210 battery amps and 510Phase amps. Never tried to go higher because I don't want to destroy it, but its been working very well so far and it never overheated (about 4 years of daily driving)
 
The standard SVMC is to week for fast starts.
If you can get the unlock software try this first an raise phase amps , as it should be only a few clicks.

To speed up just try the flux weakening und raise flux current, but be aware that the motor generates more heat.

If someone has the unlocking software, please post it or send a link to it, I´m still searching it.
I want to try to raise my phase current too.
 
dominik h said:
The standard SVMC is to week for fast starts.
If you can get the unlock software try this first an raise phase amps , as it should be only a few clicks.

To speed up just try the flux weakening und raise flux current, but be aware that the motor generates more heat.

If someone has the unlocking software, please post it or send a link to it, I´m still searching it.
I want to try to raise my phase current too.

Your correct, if I was limited to the stock settings this controller would not be enough.

Luckily I do have mine unlocked. Right now running 160 battery amps and 475 phase amps max, This thing pulls like a freight train and easily picks itself up under 15mph. The extremely low gearing ensures those numbers are never drawn for any significant amount of time, never more than a few seconds, controller gets lukewarm at best with this settings and gearing combo. Even though the controller only gets warm and the motor isnt even close to overheating yet, or even have ferrofluid yet, I dont think I'm going to want much more power. If I did it would only be if I added more battery and needed more power to compensate for the weight, and probably would also upgrade to a 96120 for less worry about pushing the 96100 too far. but so far, I am very satisfied with the results I have.

skeetab5780 said:
Cool build! Sub’d

Thank you very much! Very appreciated

Been having a little too much fun lately... got a head of myself and found out the balance point of the bike before making covering the rear brake a reflex and looped out at like 20mph.. the bike is 100% fine, motor mount did not budge or shift one bit, controller didnt get hit at all or take any damage even though its sticking out pretty good.. was able to pick it right back up and continue riding. Only thing that's probably off or damaged in any way is the handlebars.

Laying it down does make me want to reconsider controller mount location, sucks because where it's at is now is so convenient and maximizes battery space and cooling, but also leaves the controller unprotected and exposed..

My knee didnt fair so well, nothing major, just a lot of swelling and a nice pepperoni, definitely wont be able to ride for atleast a week or two, so wont be able to make any new videos riding immediately, but heres a tiny clip of it showing off the power.

[Youtube]FsyTJ80z-AI[/youtube]
 
Wow, you made that build look easy even though it is a much taller order than most people realize when they decide they want to convert something.

Any Info on the battery you are running?

Congrats on the bike, best of luck on the recovery.
 
Awesome build!!

What about the airbox as a location for the controller. Might need to add a fan but its a nice large empty space to work with that's designed to stay relatively dry.
 
MorbidlyObeseKoala said:
Wow, you made that build look easy even though it is a much taller order than most people realize when they decide they want to convert something.

Any Info on the battery you are running?

Congrats on the bike, best of luck on the recovery.

Very much appreciated, I was definitely impressed myself how fast I was able to get something functional, and This amount of power too Is for no novice, triple digit voltage and amperage is a different ball game!

Running a 25s 10p ncr18650pf pack

DanGT86 said:
Awesome build!!

What about the airbox as a location for the controller. Might need to add a fan but its a nice large empty space to work with that's designed to stay relatively dry.

Unfortunately that is where I have a nice chunk of cells stashed to bring my series connection up so high 😔 even after I just now converted the original gas tank to a battery box: most I can fit in it is 18s10p. If I heavily modify the gas tank I *might* be able to fit *most* of them in that small remaining gap above the motor...
 

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