Mark Drela's Flex-Shaft Drive System

MIT professor Mark Drela proposed this flex shaft drive system for the Open Waterbike.

In his original message, he wrote:

«Here's a potential system to consider for your open waterbike project.

The attached sketch shows an HPB drive system which I and two other guys built back in 1994, right after the Decavitator project. It worked very well. The thin shaft was quite stable, and did not exhibit any whipping tendency even at full sprint power.


The nice features are:
•only a simple and cheap 1:1 bevel gearbox is needed,
•no complex mechanism or seals under the water,
•no additional axial-loaded bearings besides the gearbox itself,
•very simple prop replacement system.
•The "screwdriver" shaft-end system mimics a bike crank axle taper
•and allows a much smaller flex drive shaft than what a shear-pinned joint would need.
•The 1/4" pitch chain and sprockets are easy to get.
•The only special item was the large 120 tooth chainring, but that was a fairly simple CNC job from aluminum plate.»


You're invited to download the original pdf file Mark gave us. Please make good use of it and give the community your feedback.


If you don't know who Mark Drela is (shame on you! ;-) you may be interested in this video and in this link.


Our boat is better than mine.