[python] Python frame with virtual front wheel pivot steering (instead of center pivot steering)
- From: Michael Rienstra <ageless@xxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Thu, 29 Jul 2004 13:46:14 -0700
Hello All,
[ POSTSCRIPT: This was supposed to be a quick sketch of an idea, but I
got carried away trying to explain it 'clearly' and ended up with a big
mess of words which is way more confusing than it needs to be!
Executive Summary: Frame that looks like a monotube Python
(single-sided rear fork and front end), but the center pivot is gone,
and instead there is a small four bar linkage near the front wheel
which creates a virtual pivot point to emulate the steering of a taller
FWD recumbent ]
Been thinking about this abstractly for a few weeks, and concretely for
a few days now.
This is another Open Source Idea. No proprietary profiteering.
Start with a basic Python frame.
Now, imagine that the front end in a monotube design, like that carbon
fiber tricycle, so that the front wheel is attached to the left of the
monotube and the cassette and rear derailleur are attached to the right
side of the monotube.
Next, get rid of the center pivot. Instead, have a simple transition
from the rear to the front. Either a bent monotube, or a welded or
lugged connection, with or without gussets or other reinforcements.
Finally, make a new virtual pivot point using a four bar linkage. This
new VPP can be almost anywhere you want (I was thinking right in the
center of the rear wheel hub to eliminate pedaling-induced steering
torque, but I keep getting confused about the right location) -- choose
your rake and trail, and tweak them by changing the lengths of the four
bar linkage (see http://www.edgebikes.com/gallery_prodi01.html ). You
can try to ride a FWD Lowracer with any kind of
'steering'(exaggeration): try out road bike, mountain bike,
cruiser/comfort bikes, SWB/MWB/LWB 'bents, etc. Actually you can only
change the virtual pivot point's virtual location, but the virtual head
tube angle is fixed by the angle of the four bar linkage -- reducing
the size of the front wheel or increasing the size of the rear wheel
bring the virtual head tube angle closer to vertical just like it you
would expect.
The four bar linkage would consist of:
1) a stationary bar, attached to the rear frame (seat and rear wheel).
It's long axis is parallel to the long axis of the front monotubes
2) & 4) two rotating bars connecting the stationary bars to form a
floppy parallelogram
3) a stationary bar, attached to the front frame (front wheel and BB).
It's long axis is parallel to the long axis of the front monotubes
The monotube rear frame would need to flare out near the trailing edge
of the front wheel to allow the front wheel to rotate CCW.
PS: I really want to build a Python soon, but I need a new bike ASAP to
replace my BikeE, and I ride with heavy bike trailers almost everyday,
so I need a bike that I can get used to riding in a few hours or days.
I've been really into the idea of a FWD lowracer for months, and it
seems like it would be hard to make a twisted chain FWD lowracer that
was simple, dirt cheap, efficient, and very quiet (noisy idlers are
slightly awful). That leaves moving BB FWD designs ( Tom Traylor:
http://traylorfwd.home.mindspring.com/ Paul Keen:
http://www.users.bigpond.com/pekay/recum.htm No Weld Recumbent:
http://hometown.aol.com/david5430/order.html ), or center pivot, i.e.
Python (flevo is cool but too tall for my tastes). I wanted the Python
frame with the handling of a moving BB FWD design, and a virtual pivot
point bike with a monotube frame would be so cool! And I could make a
carbon fiber version this winter if it was cool enough.
PPS: I still really want to build a Python, and my neighbor is also
very interested (he just got an ActionBent SWB, wow it's fast, man my
BikeE is so slow!), I just need to settle on a simple design that I can
build and use to replace my BikeE ASAP.
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