Lightweight 250w 700c 120mm Rear Hub Motor on a Budget

[SPho3nix]

Hi!

This post is very specific. I am trying to build a lightweight rear hub setup on a single speed track bike, with 700c wheels and 120mm dropout spacing.

I am under the impression that some motors, such as the q100h / akm-100h, are very capable of being modified for 120mm rear hub spacing.

I believe that both of the following kits would work for my purposes:
https://www.greenbikekit.com/24v-250w-bgk100r-e-bike-conversion-kit.html
https://bmsbattery.com/ebike-kit/633-16315-q100h-36v350w-rear-e-bike-motor-wheel-ebike-kit.html#/327-rpm-260

My issue is that shipping on these kits is astronomical! I'm trying to save a hundred bucks - does anybody have tips on any parts or vendors that would help?

Has anybody build anything like this before? Any advice?

Appreciate it!

 

[Drunkskunk]

Welcome to the forum. We're kind of international here, so what part of the world are you in?

 

[SPho3nix]

Thanks for the welcome!

I'm in California, USA!

 

[neptronix]

bmsbattery likes to offload the cost of their products onto the cost of shipping. It's a trick they've been doing for quite a while.
Many of the products they sell are also kinda low quality, so you gotta ask yourself if it's really worth it.

One thing to mind is that most rear motors are 100mm or 135mm. I imagine you'd need to remove the axle, machine it, and heat treat it to remove the axle shoulders.

It would be a lot easier to convert a multi speed bike that already had the right dropout spacing for sure.

 

[wturber]

https://endless-sphere.com/forums/viewtopic.php?t=85154

This thread shows the spacing issues. I think you may need to just suck it up and pay a bit more than you'd like. Either that or spend a lot of time looking. But it looks like you can get the motor in hand for around $150 which isn't horrible. If you are really on a budget, then do a lot of craigslist cruising.

 

[motomech]

A Q100 for rear fitment can be mod'ed down to fit a 125 m/m dropout by cutting the lip of the spline right up to the recessed bearing, but of course the cassette/free whl. would have to be cut-down as well because a 16T "fixie" won't work w/out a lot of machining. It is possible to ptu a single gear on the spline, but some spacers would need to machined(no, stacks of washers won't work) to put the gear in the driveline position.
Changing bikes is might be less money and is certainly less work than modifying motors and you might want to think about something w/ 130 m/m dropouts.
Those big Chinese vendors are about it for the Q100. The idea is to order all the accessaries (there are quite a few needed), plus maybe the battery to difuse the cost of shipping. If you are shocked at he cost of a Q100, you might want to also think about a less expensive hobby. That's about the most reasonable start and these things have a way of having the costs escalate along the way. Have you priced a battery pack??
I could build a "Spokey" (gas engines bicycle) and operate it for less than my electric bikes, but I like the electrics for the challenge and the results. But I don't build and ride them to save money.

 

[Drunkskunk]

yeah, if you were in Asia, there might have been hope, but outside of their, not so much.

See, the problem is, the Q100 and it's siblings are really $180 motors. Some rather shady pricing by greenbikekit/BMSbattery lists them for about half what they're worth, then gets the rest of their value by super high charges on shipping. Same idea as a Pizza shop selling a pizza for $10, but then hitting you with a $10 delivery charge.

You can try Ebay. Looks like you can get the CST version for ~$160 shipped, although the CST can't easily be made to fit a 120mm frame, while the freewheel version might work for that. getting a motor like that laced into a wheel and with all the other parts needed to make it run is going to be over $350, plus another $400-500 for the battery