Reading old Velovisions is a dangerous thing to do. On page 5 of Issue
16 is an innocent looking article about a rowing bike - a Dutch
recumbent propelled by a rowing action. What's interesting about this?
Well, an extremely novel and interesting CVT system, claimed to be
significantly /more/ efficient than conventional chain drive.
<URL:http://www.rowingbike.com/main.php?sNewPage=The_snek>
The critical part is an aluminium 'cone' (which has in fact has somewhat
concave profile) in which a spiral groove is cut. The cone is driven not
by a chain but by a steel cable, which runs in the groove. In earlier
versions of the design the cable was wrapped one and a half turns around
the cone, much like a sheet on a self-tailing winch. If I understand
correctly, on the CVT version the end of the cable is actually attached
to the small end of the cone (this works on a rowing bike with a
reciprocal action, but obviously would not work with a pedalled bike).
Although the transmission is stepless it is not automatic - the cone has
to be declutched from the driven wheel to change the ratio.
The makers of the system don't say whether they've tried wrapping a
continuous loop of cable round two opposed cones, and clearly for that
to work you'd need a sliding 'stripper finger' mechanism like that on a
self-tailing winch, but it does not look infeasible.
Reasons why might /not/ work include
* Too much slip: the cable might slip in the groove under load and fail
to transmit power - this may be why Thys anchor the cable end to the
cone.
* Too little slip: if the cable would not slip in the groove, it might
tend to ride up too high on both cones at once putting excessive loads
on the system
In fact getting the right amount of tension in the cable is clearly key
to making the whole idea work, but that might work in its favour if you
could use cable tension to drive the lateral motion of the stripper
fingers, which would give you fully automatic CVT.
--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
<p>Schroedinger's cat is <blink><strong>NOT</strong></blink> dead.</p>