rob.northcott said:You're effectively using the rider's ankle as the torque arm of the
gear system, right, even if the pedal was firmly attached to the shoe?Also, the pedals would move in a freaky way round the circle unless the
rider kept their feet at the same angle for the whole revolution (which
they don't) - a bit like PowerCranks as somebody else mentioned. That
may make unicycling feel pretty bizarre, but might not be a problem.
Ioan-
I agree with Rob that this would add some very strange feel to the
pedaling motion. The pedals are going to want to rock back and forth
while riding. Our pedals don't stay flat throughout the entire
revolution of the cranks. In your system as the rider rocks the pedals
the cranks must rotate slightly about the wheel axle. In fact, for the
2:1 system for every 2 degrees of pedal tilt the crank will rotate 1
degree about the axle. For 150mm (6"😉 cranks this constitutes 2.5mm
(0.1"😉 travel at the pedal.
One of the disturbing things about riding a geared unicycle (as many
now know) is the backlash felt at the pedals. In my design I had to
accept 0.5-1.0mm of variation at the end of a 150mm crank due to
inherent gear backlash. I knew this ahead of time and wondered how
difficult it would be to adjust to. I think it must be about the same
for Florian's hubs. In your geared crank design, for just 2 degrees of
pedal tilt throughout the crank revolution this is already 2.5 to 5
times as great as the gear backlash of an epicyclic hub and would be
perceived the same way. I have not included the backlash already
present in the crank gears but that would be a cumulative effect.
The "long pedals" are required to permit the body to exert a force with
the heel to counteract the tendency of the pedals to rotate around with
the cranks. This is useful only while applying pedaling torque. On a
unicycle the rider must constantly adjust the applied torque to
maintain balance in the forward/backwards axis. When the torque is
suddenly reduced on a unicycle to correct and balance, the toe rather
than the heel would be required to maintain the pedal in a horizontal
position. Because of the short lever arm on the front of the pedal, it
would rather easily try to rotate under the foot right at the very
moment that the rider attempts to correct his balance. This would be
unnerving to say the least.
You have made several references in your posts to small wheels, of
order 12" in diameter. Small wheels do not fare well over rough
surfaces, especially at high speeds. The small wheel size amplifies
road irregularities. These irregularities need to be corrected by the
rider by varying torque at the wheel axle. This takes physical energy
and concentration. The portability of a small wheel becomes moot if the
vehicle is not ridable. I would recommend that you not suggest using
small diameter wheels on a unicycle driven by your gearing scheme. Long
distance unicycle riders use large diameter wheels for a reason that it
quite obvious to unicyclists but not so apparent to those who do not
ride.
Can you make some comments about these issues? Maybe you already have
some design refinements in mind. Again, these may not be significant
issues for other pedaled vehicles but for unicycles they certainly are.
--
harper
-Greg Harper
*jc is the only main man. there can be no other.*
"In general, I'd like everyone to just stop treating one another like
[censored]. I see it every day. It sucks." - SqueakyOnion
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