High Angular Velocity PTO Driving

What is the best modern mechanical means to convert relatively slow power kite traction to high angular velocity generator input? The basic idea is to turn a shaft at high velocity with as small a diameter pulley/sprocket as practical.

Simple capstan reeling chews up kiteline in a matter of hours or days. Rope-driving is limited in how small a drive pulley diameter has adequate friction. Drive chain lasts far longer, but is comparatively heavy and sprocket tooth life can be low. Belt drives are hard to beat, but which are best?

The newest belt-drive technology is toothed Kevlar timing belts, but not just for timing, by keeping in register (not slipping), but as used for industrial power transmissions at all scales (in parallel as needed).

Short-stroke PTO pumping is favored by similar superior dynamics of short pistons for race-car engines. Just the pumping stroke length needs to be belted; kiteline itself remains outside of the PTO.

Here is a top modern belt and hardware supplier, a sample reference to what is available-



How would you estimate the life of the cable drive I propose?


Assume a cable speed of 10 met/sec (Dyneema?). If the tether length is 1000 meters, then the cable passes through a pulley every 100 seconds. This is much less taxing than capstan winding. I assume that the ground pulley at the generator has the most severe duty.


The cable life can be set by design trade-off. Massive large diameter bull-wheels and pullies and extra-thick cable can extend life to many years, while overly small diameter wheels and thin line can fail very quickly. There is also accelerated wear by surge-loads and high working load.

A curious advantage is that the higher (longer) a cable loop, the more cable to share the wear, for longer life. Its a complex estimation, subject to the designer’s specific case. One design trick is a rubber lining on pulley grooves. See Rope Driving Treatise.