10kW 72v Electric mini bike build

Jacka98

Jacka98

10 W
Joined
May 9, 2020
Messages
79
Location
Finland
Specs:
Motor: qs90
Controller: Kelly kls7218s
Battery: sony vtc4 20s7p with 300A peak ant bms

Really fun bike to ride. Surprisingly the qs90 has been holding up pretty good with the kelly kls7218 controller :D The gearing is pretty low so the acceleration is very good.

IMG_20230527_204525.jpg

Here is youtube video:
 
Sick build! I have a similar project that will use a similar fork. Those front fork triple tree clamps usually have a pretty small hole for the shaft that goes through the stem. It doesn't seem to be the right size for typical bearings. How do you have it mounted to your stem?
 
Thanks. if I remember right the shaft is 10mm for that fork. The bearings was already also 10mm so I didnt need to change the bearings, but I think the bearings was just typical bearings that you can find at any store. I didnt have 10mm shaft so I just cutted right lenght piece from the 10mm threaded rod. Its probably not best solution but it has been working good so I havent changed it to the better shaft.
 
That looks the same as what those Coleman mini bikes use, and they have to change out their bearings rather frequently. I might try to see if I could use tapered roller bearings to better handle the thrust load.

Just watched the video, that thing really rips. How much does it weigh? How did you decide on how much power you wanted it to have when you did the planning for it? Are you happy with 10kw or would you want more or less? I'm planning to use about 6kw but my build will likely be a bit smaller and lighter. What's the top speed with your current gearing?

Overall very tidy build, that battery box looks neat, very impressive.
 
It weighs about 38kg. I had the battery and kelly kls7230s already from my old ebike so I used it in this bike. And then I thought that the qs90 would be suitable for that controller. I think the 10kw is enough power for this bike. Of course you always want more power, but then battery and motor needs to be bigger. I think 6kw will also be good power for small bike like this. Top speed at the current gearing is little over 50kmh. Not much top speed but the torque is really good, and small bike like this I want more torque than top speed. With taller gearing I think it could go 80-100kmh, but torque would not be so good.
 
Wow this is so sick. I love this project.

I have this motor which I am working hard to mount on my bicycle. I have not seen many people using this motor it's been difficult get info about it's perfomance in the real worls

Can you please share the Teeth count of your rear sprocket and the diameter?

What is the size of your wheels?

Do you know your gear ratio?

Cheers
 
brazilianboy said:
Wow this is so sick. I love this project.

I have this motor which I am working hard to mount on my bicycle. I have not seen many people using this motor it's been difficult get info about it's perfomance in the real worls

Can you please share the Teeth count of your rear sprocket and the diameter?

What is the size of your wheels?

Do you know your gear ratio?

Cheers
Click to expand...
Thanks. front sprocket is the stock one and rear sprocket is 43 teeth. And the wheel size is 12 1/2.
 
Nice, a new pancake I havent seen..... good job on the pancake(y)
The kind of damage that all goes straight into the rubbish bin.

You going new rim or used rim with real spokes?
 
calab said:
Nice, a new pancake I havent seen..... good job on the pancake(y)
The kind of damage that all goes straight into the rubbish bin.

You going new rim or used rim with real spokes?
Click to expand...
I had a spare rim so I replaced it with it. But I think that I will upgrade the rim to something more strong so its not going to break so easily.
 
It doesn't look like you have any problem with the rim itself. The problem appears to be with the cast wheel as a whole, the spokes are unable to handle one or more of the modes of loading it sees at the hub because it's not designed correcly--it brings 12 rim connections down to only six hub connections, instead of keeping them all to pass the load thru.

You might want to look into spoked wheels instead.
 
Looks sweet!

How are you handing your battery charging/discharging in the cold? Presumably, you have somewhere indoors to store it, let it come to room, temp, charge it, then take it out for a ride while the battery is still warm/room temp.
 
harrisonpatm said:
Looks sweet!

How are you handing your battery charging/discharging in the cold? Presumably, you have somewhere indoors to store it, let it come to room, temp, charge it, then take it out for a ride while the battery is still warm/room temp.
Click to expand...
Yea I have little storage room where I can warm my bikes if I need to charge batteries. If the storage room is full then I can charge right after riding because batteries are heated from the riding, but then the charging current needs to be high enough so the batteries stay warm from the charging current.
 
SlowCo said:
Nice!
What a large playing "field". I would almost want those freezing temperatures here. Almost...
Click to expand...
Yes its fun to ride on ice, but its also pretty cold 🥶 At some point its going to rain so much snow that its almost impossible/harder to ride with small bikes like this.
 
Last edited:
what are your battery and motor temps after snow plowing for a while? Do they stay low with the fresh powder hitting the enclosures?
 
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