Mid drive using hub motor

K

krombopulos_michael

10 mW
Joined
Sep 22, 2017
Messages
27
Currently planning out my next build and want it to have a range of 30+ miles and a top speed of 45-50mph. Although I much prefer mid drives, I was planning on using a rear hub motor like the qs204 or 273 for this high speed build but a couple weeks ago I came across the vector vortex (https://vectorebike.com/componentsss/vortex) which blew my mind. So I have two questions:

1) Aside from hub motors being heavier and not needing any gear reduction, what's the difference (i.e. rpm's, torque/power output, efficiency) between hub motors and high power rc motors?

2) What would be the overall difference (i.e. handling, acceleration, torque, top speed, efficiency, noise, etc.) between using a rc and hub motor located in same place in middle of high power bike.
 
You should think for a second how come Teslas don't have a huge 200kg hub motor suspended in the middle of the cars. Similarly neither do Zero or Harley bikes. While anything is possible, including powering your bike with compressed air, choosing the right tool for the job is better in the long run.

Btw, qs motor make a 3kw mid drive that is 15kw peak capable at 52v, and 21kw at 72.
 
Thank you for your response. Ideally I would like to use the 3kW mid drive from QS but I'm not sure how to mount it to a frame which is why the vector vortex interested me. Aside from figuring out how to mount the motor to a frame, my other issue is that I'm still a bit confused on if wether or not I'll need to use a gear reduction system and if I do I'm not sure what size sprockets to use or how to create said system. My end goal is to use a belt drive instead of a chain so the bike will be very quiet even at higher speeds. Any advice or knowledge about those two issues would be great.

***Edit*** Just found this post https://endless-sphere.com/forums/viewtopic.php?t=88909 that talks all about using DD hub mots as a mid drive
 
I set up a couple of tadpole trikes as mid-drives using hub motors a few years back. The first one started with a Nexus 8 transmission, which was replaced with a NuVinci auto shift. Both trikes worked great, but were heavy, and the NuVinci was quite inefficient compared to a derailleur system. I would never have attempted this on a two wheeler.

Short story, I now have two trikes with Bafang BBS02 crank drives and there is no comparison to the mid drives with the hub motors, and I would never go that route again. Here are links to my old builds:

https://endless-sphere.com/forums/viewtopic.php?f=28&t=18606
https://endless-sphere.com/forums/viewtopic.php?f=28&t=47043

Good luck with whatever you decide to do. :D
 
If you want to use eeb style frame, you can get a swingarm with a 4 or 7.5kw cyclone built into them, directly from cyclone, both with belt drive options. Just get a vector typhoon frame and buy the swingarm from cyclone.

[youtube]rHB26fDkhCM[/youtube]
[youtube]NBDZixtNaAE[/youtube]
 
For performance all that matters is power and weight, the rest is gearing. And hub motor mid drives are very very easy to gear since you don't need multiple stages. Yes you could get the same output from a much lighter motor (astroflight, neumotor, et al) but then you need a complicated reduction and more attention to cooling.

Tommm said:
Similarly neither do Zero
Click to expand...

Actually Zero basically does use the equivalent of hub motors. The motors are massively heavier than they need to be for thermal capacity torque fill and simplicity. Just a big motor with a heatsink around it peaking well below its potential.
 
Tommm said:
If you want to use eeb style frame, you can get a swingarm with a 4 or 7.5kw cyclone built into them, directly from cyclone, both with belt drive options. Just get a vector typhoon frame and buy the swingarm from cyclone.

[youtube]rHB26fDkhCM[/youtube]
[youtube]NBDZixtNaAE[/youtube]
Click to expand...

Never knew those existed but my new build is definitely going to use one of those. Do you have any experience using one of those motors built into the swingarm?
 
krombopulos_michael said:
Never knew those existed but my new build is definitely going to use one of those. Do you have any experience using one of those motors built into the swingarm?
Click to expand...

Yes, I have the 4(4.8)kw coaxial, it spins 750 at 72v, about 90kmh(55mph) with a 1:1 ratio to the rear which is a bit tall. You need to pay attention to your gearing so the rear sprocket is about 25-33% bigger than the front. My sweet spot is 30t front 42t rear. Good for 68kmh (~44mph) with field weakening.
Power wise it can take 72v 100a max, so 7.2kw peaks no problem, but since it is enclosed it is not great at shedding heat, and I think the material of the swingarm is steel which isn't as good at distributing heat as alu. Realistically you can take 3kw out of it continuous, which is just enough to cruise at the max speed at the ratio I mentioned.
The cyclone guy sells them with geared hubs, but they would get destroyed in short order above 60a, which is a waste to operate this motor at anyway. DT swiss ratchet hubs hold up to the abuse perfectly, because they don't use pawls, all teeth are engaged all the time. They are cheap to get when found used and included in wheelsets.
 
Could you explain why you said it'd be waste to use this motor above 60A? I was thinking about using a 72v battery that puts out 80a continuous so would that be too much for this motor? Also are you saying that the pulleys that cyclone includes with the swingarm aren't very good and that I should get higher quality ones? I like your gearing set up and will probably start with that since I want my top speed to be around 50mph
 
That seems like a sweet setup! Pretty close to what I envisioned for a high speed commuter build (been eyeing the vector vortex and Qulbix 140md). I to am curious about this swing arm and why higher currents would be “a waste”.
 
I'm working on ebike like this. It will works on QS205 and 273 - universal frame

]
 
Hub motors tend to have issues spinning fast (e-rpm and mechanical limits) so the power density stays pretty low even though they have fantastic torque.

Having huge exposed spinning objects in the middle of your bike when you don't have to is probably also no good.

Inrunner is the best for mid drives. Not like there aren't plenty of inrunners with crazy power density peaking well over 2kw / lb.
 
sure, but at what cost differential vs widely available cheap hub motors.. mid mount solves unsprung motor mass, just make the motor mounts interchangeable for various different motor mounts?.. (and maybe a safety cover for the spinning motor type)..
 
efMX Trials Electric Freeride said:
kcr said:
I'm working on ebike like this. It will works on QS205 and 273 - universal frame

Click to expand...

nice:) link?
Click to expand...

I don't have link, its my design and you are The first person who see it :)
 
flat tire said:
Hub motors tend to have issues spinning fast (e-rpm and mechanical limits) so the power density stays pretty low even though they have fantastic torque.

Having huge exposed spinning objects in the middle of your bike when you don't have to is probably also no good.

Inrunner is the best for mid drives. Not like there aren't plenty of inrunners with crazy power density peaking well over 2kw / lb.
Click to expand...

In both motors you can find tuning elements.
In hub drive you can see big outer body of motor but in mid drive you have it too inside body. I agree that mid have lover tuning mass but its not a big difference especially that there wasn't be a more than 120 rpm. Its not a grinder with 12000 revolutions per minute ;)
 
kcr said:
efMX Trials Electric Freeride said:
kcr said:
I'm working on ebike like this. It will works on QS205 and 273 - universal frame

Click to expand...

nice:) link?
Click to expand...

I don't have link, its my design and you are The first person who see it :)
Click to expand...

have you built a prototype type yet, or just a computer rendering?? are you planning serial production and global distribution or maybe just a one off or for domestic market.. plz keep us updated if you build or plan to sell these.. I like the design so far, good luck:)..
 
efMX Trials Electric Freeride said:
kcr said:
efMX Trials Electric Freeride said:
kcr said:
I'm working on ebike like this. It will works on QS205 and 273 - universal frame

Click to expand...

nice:) link?
Click to expand...

I don't have link, its my design and you are The first person who see it :)
Click to expand...

have you built a prototype type yet, or just a computer rendering?? are you planning serial production and global distribution or maybe just a one off or for domestic market.. plz keep us updated if you build or plan to sell these.. I like the design so far, good luck:)..
Click to expand...

Tank you, nice to see that someone like my job, i waste for this project many work hours. This is 5th version and i think that this one will be produced.

It isn't render - its almost complete project from autodesk inventor showed in real view.

I will create new topic with it but first i have to start production od frame :)

It will be prototype but if everything will be good and people will be intersted i will make next for sale

For now i am happy for comments like yours and i feel that im doing right;) thank you and sorry for my english (im from Poland)
 
kcr said:
efMX Trials Electric Freeride said:
kcr said:
efMX Trials Electric Freeride said:
nice:) link?
Click to expand...

I don't have link, its my design and you are The first person who see it :)
Click to expand...

have you built a prototype type yet, or just a computer rendering?? are you planning serial production and global distribution or maybe just a one off or for domestic market.. plz keep us updated if you build or plan to sell these.. I like the design so far, good luck:)..
Click to expand...

Tank you, nice to see that someone like my job, i waste for this project many work hours. This is 5th version and i think that this one will be produced.

It isn't render - its almost complete project from autodesk inventor showed in real view.

I will create new topic with it but first i have to start production od frame :)

It will be prototype but if everything will be good and people will be intersted i will make next for sale

For now i am happy for comments like yours and i feel that im doing right;) thank you and sorry for my english (im from Poland)
Click to expand...
I am interessted in that frame, i am a big fan of middrive hubs :D
 
kcr said:
efMX Trials Electric Freeride said:
kcr said:
efMX Trials Electric Freeride said:
nice:) link :thumb: ?
Click to expand...

I don't have link, its my design and you are The first person who see it :)
Click to expand...

have you built a prototype type yet, or just a computer rendering?? are you planning serial production and global distribution or maybe just a one off or for domestic market.. plz keep us updated if you build or plan to sell these.. I like the design so far, good luck:)..
Click to expand...

Tank you, nice to see that someone like my job, i waste for this project many work hours. This is 5th version and i think that this one will be produced.

It isn't render - its almost complete project from autodesk inventor showed in real view.

I will create new topic with it but first i have to start production od frame :)

It will be prototype but if everything will be good and people will be intersted i will make next for sale

For now i am happy for comments like yours and i feel that im doing right;) thank you and sorry for my english (im from Poland)
Click to expand...

do you have a facebook or YouTube account?? if not then consider making them for free advertising and ideas sharing.. I think this design will have wide appeal and its great to see localized design and production (instead of everything made in asia then shipped across the globe;) .. looking forward to see more of your progress soon!
 
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