Simple mid-drive e-bike

yabert · Apr 23, 2016

Hello all
I'm used to share and learn about electric vehicle on Diy Electric car, but it's my first post here.
I've quite of experience with batteries, motors and fabrication as you can see below, but i'm here to have help to build a nice E-bike (my first one).

http://www.evalbum.com/4155
http://www.evalbum.com/3020
https://nomadbikeco.com/

So, about the project. My goal is to build a low cost / low power e-bike to cruise at 30-35 km/h.
I would like to don't have throttle, but a PAS system seem to cost a good amount of money (Torque Sensing BB and Cycle analyst).
I really like the idea of converting a cheap gear hub motor in a nice mid-drive system like here:
https://endless-sphere.com/forums/viewtopic.php?f=28&t=45245

Well, my questions:

1- Motor. What should be a good gear hub motor for my plan of building a mid-drive motor? I like the small diameter of few gear motor on BMS battery (example Q100H)

2- PAS system. Is it possible to have a cheap PAS who will work correctly?

3- Battery. Is there people here who tried the experience to build e-bike batterie from wreck electric car or plug -in car battery (Volt, Tesla, C-Max, etc)?

Thanks

yabert · Apr 25, 2016

Thanks for the tips about searching and reading about PAS.
So, if I exclude Torque Sensing BB because of the price, there is cadence PAS and the torque simulation PAS.
Well, if I'm right, the first one simply increase motor power while the crank spin faster and the torque simulation is a cadence PAS who simply increase torque while remaining the same speed.

So, if it's a good idea, I plan to link a gear hub motor to the crank sprocket without a freewheel and the signal to feed battery power to the motor controller will come from the cadence PAS monted on the crank.
In this case, while I start to pedal the motor will help me.

The down side of this idea are:
-I'm forced to pedal (it's ok for me)
-The crank will spin if a problem happen (chain broke, controller fault, etc.) and I will only have the kill switch or e-bike brake lever to save me from injuries... Right?

riba2233 · Apr 25, 2016

Hi yabert, it's really nice to have you here!

From my experience, if you must go with PAS, take torque sensing type, otherwise it really doesn't make sense. Speed sensing types are pure shit, even the best ones. Throttle rocks 8)

dogman dan · Apr 26, 2016

I also like a throttle, but that's the old motorcycle rider in me. Throttle gives me the most control. If you do have PAS, then you need the brake cut offs, so you don't start riding just because you unthinkingly changed your pedal position while waiting at a light.

Runaway bike is very rare, so most of my bikes with throttle don't have the brake cutoffs installed. Really don't need them.

Best approach for you might be to get a controller than can run on PAS or a throttle. Cheap pas is affordable, and so is a throttle. Try them, and choose what you like best.

Throttle to take off, then continue on PAS is pretty popular.

yabert · May 1, 2016

Ok, I tried a cheap e-bike with PAS and throttle. Cadence PAS is not that bad considering I want to continuously pedal my bike.

So, what could be the best motor to achieve my goal to build a nice middrive with a cheap hub motor?
Personnaly I like: 14mm axle (double flat = 10mm), small diameter hub motor (100-120mm) and front hub motor (only 100mm wide).
What are your suggestions?

dogman dan · May 2, 2016

You will want a rear motor, because you need to be able to attach the gear to it. But it can be one gear, not 7, and fit in about 110 mm.

yabert · May 2, 2016

dogman dan said:
You will want a rear motor,...

No really. I'm looking to build a middrive system where the shaft is turning and the hub is fixed. https://endless-sphere.com/forums/viewtopic.php?f=28&t=45245#wrap

dogman dan · May 3, 2016

Ok, but that's not how it's done with hub motors for bikes. Because if you try it, the wires feeding the motor will start wrapping around the axle. It won't work.

But hey, try it. I want vid of the first test run. :mrgreen:

You can do it fine with any other type motor, where the axle turns.

izeman · May 3, 2016

Sure this works. But only for some GEARED hub motors. DD motors can not be converted that way. Take a look at my signature to see another project based on crossbreaks' idea.

amberwolf · May 3, 2016

izeman said:
DD motors can not be converted that way.

can too, more complicated. see my post about it
https://endless-sphere.com/forums/viewtopic.php?f=6&t=38553&hilit=bearing+axle+cover&p=1158449#p1133333

izeman · May 4, 2016

And after having it read a second time : i have no idea how you would like to do it. And as posted in the other thread, a sketch could help a lot.

amberwolf · May 4, 2016

maybfe when iget ovr tiny. dont care rihgt now

izeman · May 4, 2016

amberwolf said:
maybfe when iget ovr tiny. dont care rihgt now

oh. sorry to hear that. my thoughts are with you! all the best ...

yabert · May 4, 2016

izeman, I like your mid drive on your Kona and it's what I want to do with a small gear hub motor. I remarked that you build a new shaft for your motor because you snap the hollow part of the shaft.

izeman said:
Sure this works. But only for some GEARED hub motors.

Considering this and the fact that some hollow shaft can snap under load, what should be a good choice of small gear hub motor for my project?

izeman · May 5, 2016

thanks. and yes, i made a new shaft. i maybe just had bad luck and overdid it a bit, rolling backwards and giving throttle, and again and again.
but with the new steel shaft made all is fine. 17mm of tool steel is more than enough.

dogman dan · May 5, 2016

Maybe I misunderstand. I meant you can't let the axle spin on a bike hub motor.

I do get it that you can bolt a gear to a front hub motors cover. But if both cost the same, why? Sure, if you have the front hub laying there, invent a way to put a gear on it.

I merely meant, if you are buying the damn motor, buy one a gear screws on to.

amberwolf · May 5, 2016

dogman dan said:
Maybe I misunderstand. I meant you can't let the axle spin on a bike hub motor.

can too see crossbreaks thred or one i linked to

d8veh · May 5, 2016

This one is already sorted and comes with a fitting kit:

http://www.gngebike.com/36v350w-48v500w-2015-gen-2

Here's mine - an earlier version.

dogman dan · May 6, 2016

Well, I just don't understand it, It needs to be a "simple mid drive e-bike" for me to understand it. There's a reason I don't get into home made mid drives. I like things simple.

yabert · May 7, 2016

dogman dan said:
Well, I just don't understand it, It needs to be a "simple mid drive e-bike" for me to understand it.

Well, the mechanical parts don't seem complex to me.
Of course, use the motor casing as large aluminum heatsink seem a really good idea to me.
More important, always used the motor at his efficient rpm by shifting rear gears make a lot of sens to me.
That why I would like to modified a small gear hub motor to build a mid-drive.

Thanks for the link d8veh. Although, the kit are relatively pricey if I compared to a more powerful Cyclone kit.

dogman dan · May 8, 2016

FWIW, my degree in Agriculture, not engineering. So I stay out of the non hub motor section.

Definitely, mid drive rocks for power levels low enough for the bike chain and gears. Fantastic torque in low gears.

heavymetalthunder · May 10, 2016

Mid drive system have advantages over the hub drives in low speed torque and lower weight. In actually there is no simple mid drive E-bike. Mid drives systems require more maintenance than the hub drive systems, more broken chains and damaged derailleurs. If I did most of riding off road and looking for performance, I would go mid drive. I built my hub mounted e-bike over three years ago and with over 10K miles of riding, the system is still going strong.

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