Enclosed gearbox at the cranks

[jag]

Likely there will soon be alternatives to the traditional hub or external gears. New solutions for bikes will put the gearbox at the cranks instead. There are many design ideas and prototypes, e.g. regular (car/motorcycle type) transmissions, enclosed chain drives, planetary gears etc. This report reviews several prototypes from manufacturers, and presents their own design, including a prototype. Lots of nice pictures in the .pdf file.
http://en.scientificcommons.org/49056998

Internal Gearbox for Downhill Mountain Bikes
Filgate, Joshua, Kuhn, Jesse, Misek, Morgan, Seiter, Jay, Witonis, Michael
Northeastern University

Abstract
Capstone Design, Final Report. In the realm of competitive downhill mountain biking, there is a need for advancement of the drive train. The conventional sprocket, chain, and derailleur drive train is not well suited for the high speeds, impacts, and harsh environmental conditions inherrant to the sport of downhill racing. The gearbox created in this project replaces conventional drive trains on downhill mountain bikes. The initial design and proof of concept were designed to provide a comparable gear range and capabilities of a conventional drive train, while providing increased protection, strength, durability, and performance. The scope of the project was to provide a working prototype capable of demonstrating the ability of the gearbox to provide the overall system gear ratio range of 2.1-3.3 when interfaced with industry standard components, as well as a detailed design of a complete prototype system.

A superlight eBike with motor, gears and batteries all integrated in the triangle would be nice. Gives optimal placement of weight. Would a 20kg bike be doable? E.g. 12kg bike + 8kg powertrain (1kg Astroflight motor, .5kg controller, 2kg gears for both motor and cranks, 3.5kg batteries, 1kg housing). Maybe a moderate downhill geometry on the bike.

If 20kg is pushing the limits (may need esoteric materials, and end up underdesigned) I feel that at least 25kg should be possible.

 

[Tom Tom]

Seems to be the holy grail.

Nice honda. I'd like more of a motorcycle type seat.

 

[AussieJester]

The e-bike made in OZ The Stealth Bomber uses such a gear box already

http://www.stealthelectricbikes.com.au/stealth_bomber.html

KiM

 

[TorEddy]

My downhill bike weights 18kg, and 20kg is not unusual for this kind of bike.
I Guess 25 kilo would be doable, with a 10 kg drivetrain.