Is this a viable idea? Disc Brake driven bike?

[azneinstein]

I've been a long time lurker and an avid cyclist, manage a small bike shop actually. I'm a recumbent rider, and have ridden quite a few hub motor bikes, they're great but feel a bit weight sluggish. (Thank god Lithium batteries were invented)

I recently came across this:
http://www.gizmag.com/velological-worlds-lightest-e-bike-drive/31976/

The idea doesn't seem bad except the constant need to replace the tiny rubber wheel and not sure if I want to wear down a rim's sidewalls.

That got me thinking, with many available forks that offer both a V-brake option as well as disc brake tabs, would it be possible to do something similar to the above but mount the motor instead to the disc tabs and have it run a rubber wheel friction against the disc rotor? (Using the Vbrakes as brakes)

Rotors are cheap to replace and meant to grip and dissipate heat well. I really like the small motor design and think driving the wheel at the center would also give it more torque.

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My other idea was to copy the one above but instead bolt the motors directly to a pair of vbrakes as Vbrakes would already have all the adjustments and tensioning options built in.

 

[meelis11]

Driving wheel near center gives you less torque.
Probably you cannot get enough traction there and rubber wheel starts to slip.
Small geared hub is much better.

 

[DanGT86]

I think getting enough traction on the slick rotor would be hard. Using a gear attached to or instead of a rotor would be good because you could probably get away with just that single reduction stage. Have a very light RC motor with a small gear driving a big rotor sized gear. Only problem there is you would be feeding the gears lots of road dirt and moisture.

So yes friction drive on the rotor is possible but not without some tough engineering challenges and material choices. As mentioned, moving the drive surface out to the larger diameter of the wheel requires less torque so less friction at your contact point.

Something like the disk drive would be great as a booster so you could ride an inefficient bike like a downhill or trials bike to a location and then quickly remove the drive to use the bike in its totally unmodified state.