Mulling over ideas for mountainbike transmissions, as one does, and
thinking about both the Nicolai Nucleons (which use an epicyclic mounted
in the frame, driven by a primary chain) and Minaar's Honda downhill
bike (which appears to use a motorcycle type gearbox with a countershaft
between the bottom-bracket and the output shaft), I wondered why not use
a DAF type variomatic transmission, and wondered how efficient they
were.
The benefits, from a cycle design point of view, are that the input shaft
and the output shaft rotate in the same direction, so you don't need to
gear off a countershaft. So I did a bit of web searching to find out
whether a variomatic type transmission had ever been tried in a pedal
cycle, whether it could be made small enough, and whether it could be
made efficient enough.
Apparently, belt-and-opposed-cone transmissions have been tried in pedal
cycles, see
<URL:http://www.users.globalnet.co.uk/~hadland/old_derail.htm> (about a
quarter of the way down). But, more interestingly, I found that
Variomatic transmissions based on the old DAF design are widely used in
low-powered motor-scooters on engine sizes down to 30cc. This means that
(i) they can be miniaturised and (ii) they must be reasonably efficient.
I've found this
<URL:http://www.scooterpartsdepot.com/web_gas/x1_Pocketbike_transmission.htm>
in the States which makes it look as though the cones are in the boxy
part downstream of the reduction gear, and thus low revs, high torque,
ideal for push-bike adaptation. Furthermore, if, following the Nucleon
idea, you placed the driving cone on the bottom bracket axle and the
driven cone concentric with the swing arm pivot, you would have no
primary drive losses, and a fixed length rear chain which means that the
chain run could be enclosed in the swing arm and protected from
environmental dirt and damage.
So....
Does anyone know where in the UK one might get hold of one of these
things (ideally off a scrapped scooter, and cheap) to play with?
--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; All in all you're just another nick in the ball
-- Think Droid