Any advantage to a mid mounted hub drive ?

sanjuro

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Would there be any advantage to mid mounting a hub drive over the typical real wheel set up?
 
sanjuro said:
Would there be any advantage to mid mounting a hub drive over the typical real wheel set up?

Do you mean converting a rear hub motor to a mid-drive motor? The advantage is being able to leverage the existing drive train gearing.

https://www.ebikes.ca/shop/electric-bicycle-kits/middrive.html
https://www.electricbike.com/mid-drive-cargo/
https://electricbikeaction.com/wp-content/uploads/2015/10/MotorHub.jpg
 
There's more advantages than disadvantages. A hub is a huge motor that only puts power up to a couple hundred RPM and is heavy and takes a lot of space.

You'll use up a lot of precious space that could be used for batteries by using a hub. Unless you're using something like a dual reduction geared hub, like the bafang G310, which is rather compact for the power it puts out, and could easily sit ahead of the bottom bracket and take minimal space. With brackets and chains and a high reduction ratio ( 5:1 or higher ), you could come out at a similar power density as a BBS02, but without as many mechanical, driveline, and Q factor problems.

I've thought about building a drive like that, as these mid drives with offset pedals ( 10-20mm outwards on one side!! ) really irritate my knees. And the ability to easily service the drive in the field ( just bring tools, another hub, and another hub to crank chain ) would be a huge plus.

Also you only really want a mid drive for hilly areas.. a DD hub is the most efficient thing on relatively flat ground with minimal hills.. The most efficient DD hubs get into 90-94% efficiency .. mid drives are usually 80-85% efficient once all the gears and drive chain take their little friction tax out of the power being delivered.

The example G310 mid drive would probably be in the upper 70% efficiency due to two chains eating the power. However, it does offer some advantage..
 
I've been contemplating a way to use the excellent and very quiet G310 in a mid drive without having the whole thing revolve so that I can remove as much from the outer casing as possible. 3:1 gearing to the crank equals something like 120nm at 90rpm which is impressive.

Haven't really figured it out yet without somehow spinning the axle.
 
Mount it like a hub.. use dropouts from a junk bike as the beginning of your mounting plate.

And go beyond 3:1 so that you can get as much power density out of the motor as possible. I think 400RPM is where the magnets wanna start flying off the rotor, so a 4.5:1 ratio once you consider the back EMF reducing the loaded speed by ~20% would be ideal.. of course adjust to taste for whatever voltage you're gonna throw at it, what winding you get, etc.
 
I want to mount it by the shell so I can remove as much of the axle and shell as possible. Maybe just one half of the shell could spin? But then I'd have to seal it somehow.
 
You'd have to remachine the entire thing.. just think about it.. mount it by the shell, and then the axle spins, thus the phase wires spin. Not an easy engineering problem.

Then you have to figure out how to mount a sprocket on to the axle.

Instead of just putting a single cog on the casette freewheel, or using a front motor and mounting a sprocket on the disc brake holes. Which would be a million times easier than reengineering the drive system.
 
The advantages of your proposed setup are mass centralization, easy mechanical regearing, and if there's suspension, reduced unsprung mass.

Disadvantages are an abnormally large spinning body inside the bike. You'll have less gyro influence on the handling, better packaging, and easier mounting with an inrunner mid drive.
 
There are many examples.

https://endless-sphere.com/forums/viewtopic.php?f=6&t=38553

file.php
 
A bicycle with an extended wheel base, like the 1) cargo bikes 2) bikes where the battery goes behind the seat tube 3) cruiser bicycles that are stretched out. I tried to do a mid mount dd hub in the triangle of a Norco cruiser, it was a half baked plan.

I liked the idea of bypassing the direct drives friction by using my Cyclone freewheel crank, which is a big bonus.

If I were thinking of doing it again, I'd look at these kinds of frames.

This picture below would be extreme, I would have 275mm space between the seat tube and the rear rubber. A large dd is 230mm, you can see the diameters at https://www.ebikes.ca/tools/spoke-calc.html?hub=MX_45&pair=false
Then you'd have plenty of room for a battery inside the triangle.
stretch bike 1.jpg




stretch bike 2.jpg




stretch bike 3.jpg



This one is unique, I kinda dig it.
https://www.electricbike.com/wp-content/uploads/2012/06/P10000801.jpg
Another unique design
https://farm8.staticflickr.com/7197/7098559047_3563e5d316_c.jpg
http://endless-sphere.com/forums/viewtopic.php?f=6&t=38553&start=25

What'd be cool is a custom frame job, where the crank, pedals and hub motor are all one piece, then it would look like a funky crank to a casual observer. Well kinda like this one, 20. Binova Flow - https://www.electricbike.com/mid-drive-kits/ thats the look from the side to any casual observer, obviously a hub would be a lot chunkier.
hub mid drive.jpg
 
Todd Fahrner of Portland OR invented Stokemonkey a long time ago, to make better e-bikes than most of us have today.

stoke-monkey-attached.jpg


His was the first crank drive I am aware of, but of course the same method could be used to drive the rear wheel directly, with a configurable ratio.
 
Those kinds of bicycles would be ideal for a hub motor mid drive. But I'd like a smaller axle-to-axle length, less of a frame stretch.
Kona Cargo - http://cargocycling.org/wp-content/uploads/2009/08/ute-1.jpg
Yuba Bike Boda Boda - https://yubabikes.com/cargobikestore/boda-boda





HPC
View attachment 1



I did a quick design of a mid hub crank, lots of fabrication and engineering! The force applied to the pedals and crank arms, the freewheeling action, the implementation. Complicated!
The bottom bracket is the hub motor. Maybe have tubular around the circumference then figure out mounting. Lots of WORK!
hub mid drive 1.jpg
 
neptronix said:
You'd have to remachine the entire thing.. just think about it.. mount it by the shell, and then the axle spins, thus the phase wires spin. Not an easy engineering problem.

Then you have to figure out how to mount a sprocket on to the axle.

Instead of just putting a single cog on the casette freewheel, or using a front motor and mounting a sprocket on the disc brake holes. Which would be a million times easier than reengineering the drive system.

Having a hub spinning away inside the frame with the attachment point being a set of dropouts is a huge set of engineering compromises which just aren't acceptable for my application. It's likely different for a trike/recumbent or cargo bike.
 
neptronix said:
You'd have to remachine the entire thing.. just think about it.. mount it by the shell, and then the axle spins, thus the phase wires spin. Not an easy engineering problem.

No, but Crossbreak did it for at least one motor, in his thread about that sort of thing.

https://endless-sphere.com/forums/viewtopic.php?f=28&t=45245


And Ferum:
https://endless-sphere.com/forums/viewtopic.php?f=28&t=95899#p1404823
 
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