Hub motor to crank drive. Motor & Sensor chat appreciated

Pretty much. Except that the gearing isn't within the width of the motor on the Optibike. That's what I was illustrating. It's a motor with a 2 stage epicyclic reduction..... How else could you do it? :)
 
this config seems to makes most sence. Works just like a power drill. I can only imagine few different configurations that would ma ke little sence at all. One is similar to the RC-Hub drive I once tried to design:

ring%20gear%20hub2.png


Another one would be using a cycloidal drive, using planet gears to drive the excenter, if I have time, i'll post a cad picture of it next week.
 
as you teached me, reduction ratios of this one aren't so high. A 1:20 reduction would be the least I would calc with when designing such a crank drive. That would be about 40T for the planet and sun gears, which seems to get quite large. But I also think again about this. Building a crank drive seems to be easier from my todays point of view than building a hub drive. Also since the motors used in bafang hubs are suited almost perfect for such a drive, much better than using an RC one.
 
crossbreak said:
A 1:20 reduction would be the least I would calc with when designing such a crank drive.
Click to expand...
The reason I was trying to get the gearing within the width of the motor, above, was to get as much torque as possible at the motor shaft. Look at the airgap radius/area on the Opti, it's tiny...
 
Thanks for the input there guys. Miles, I'm with you on your idea for the motor/axle/gears configuration - that looks like a great solution. However it is making me think I may have been biting off more than I want chew in designing a motor and gear system from scratch. It is definitely something I will consider in the near future, but I think it will add too much time into what is already a long design process. For the time being I think I will continue with my original plan and mount an in-line drive motor. There will be two chains anyway so that the bike can fold in the middle about the pivot of the chains' intersection. I still have the challenge of combining the Patteson crankset with the Thun sensor, but that'll be much easier without having to build a motor around it too!

Here's how the drive system looks with a hub motor in the middle (modelled is a Tongxin micro motor with the spoke flanges machined off)

drivetrain31102012.jpg


With this gearing configuration (28t-45t:9t on the front chain + 16t:16t on the back chain + Nuvinci) in a 20" wheel, 50rpm at the pedals will mean speeds between 5 and 30mph, resulting in the motor spinning at 156-250rpm. The Tongxin micro motors interested me because of their very low weight and noise, and their rated RPM speeds match this figure perfectly. I'd custom mount a 9 and 16t cog onto one side of the hub motor and mount it in the middle of the bike via the axle like a normal hub.

This seems like a good solution to me, but discussion, advice and other options is why I'm here. :)

M.
 
Yes, the bottom bracket set-up was quite ambitious :)

Your latest plan seems pretty reasonable. Can you not get a larger chainring on the Patterson? The 9t sprocket is pushing it a bit....

Look forward to seeing what you come up with for the frame. Judging by your trials bike it should be awesome...
 
Miles said:
Yes, the bottom bracket set-up was quite ambitious :)

Your latest plan seems pretty reasonable. Can you not get a larger chainring on the Patterson? The 9t sprocket is pushing it a bit....

Look forward to seeing what you come up with for the frame. Judging by your trials bike it should be awesome...
Click to expand...

9T Sprocket may be pushing it, but achievable! I'll use cogs from the BMX micro-drive system mounted on a custom carrier fixed to the hub. See here.

I'll be going with the Tongxin motor set up, Thun sensor and a CAv3. I've been talking to a battery supplier in China to produce the batteries for us from Panasonic NCR18650 cells (coming in at around $6 a cell), so I'm looking at a 48v system, around 700Wh, which should weigh about 3.7kg. :)

I've not begun any research into motor controllers yet, but something small, lightweight, and suited to this system (duh) is what I'm after. Could you point me in the right direction of where to be looking?

Having toyed around with an elegant and flowing frame shape, I'm now leaning towards the idea of straight tubes. Whatever happens, it will be a truly beautiful machine. However, the real beauty is going to come when the thing's being ridden, so things like smooth throttle curves and instant power delivery/cut off are more important than how it looks!
 
note that a tongxin build into a middrive consumes about 20-30% more energy for the same distance compared to a rim mounted geared hub motor. I built such setups and could compare it on my daily commute. I used a 9-speed internal geared hub for my tongxin middrive, which should be still more efficient than a Nuvinci. Both nuvinci and tongxin use friction drives which are known to be not very efficient.

I compared those batteries you wanna buy. They really seem to push the limits. If I calc 70 cells for your 700Wh, the whole cells weight only 3.15kg, which introduces a energy density of about 222wh/kg which is about 60% more than a standart Lipo :shock: :shock: :shock: did i miss some new battery technology?

Datasheet: http://industrial.panasonic.com/www-data/pdf2/ACA4000/ACA4000CE240.pdf
 
I just saw these batteries are also available with 3.1ah per cell and still weight 45g per cell. Thats about 11.50wh per cell, thats a energy desnity of more than 250wh/kg. I somehow doubt that and will search for an independent evaluation.

I will do the above described mod to my 24V MBG Goldenmotor which just arrived. It's a 2012 model, which has stator carrier with more surface to mount a heat bridge to the hub housing, which is quite promising. Maybe you rethink buying a tongxin when I post pics and specs about my mod, i'm curious about this :)
 
I found an independent source: http://budgetlightforum.com/node/5269?page=1

They see yabout 9wh per cell at 1C for the 3.1ah cells. They can reach almost the claimed 3.1ah when discharged with only 0.1C. Thats sounds quite promising.
 
crossbreak said:
note that a tongxin build into a middrive consumes about 20-30% more energy for the same distance compared to a rim mounted geared hub motor.[/url]
Click to expand...

Would you mind explaining that for me? I would have thought mounting it as a mid drive, making use of the gear ratios at the back would make it more efficient, as the motor will remain in it's optimal rpm range.

I'm going to get some quotes on a pack with the NCR18650A batteries, it makes sense for the extra juice they'll offer - hopefully they're not that much more expensive.

M.
 
my above sentence is only true for my daily commute. There are no gains of more than 5percent on this route. A hub mounted motor can be more efficient here cause it doesnt suffer from transmission losses. Since i drive this route constantly going 35kph, the hubmotor is used actually always in its best efficiency region. On hilly routes it may be the opposite, since - as you said- the middrive can be used at it's best efficiency region-even at hills.
 
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