Hi Dirk,
Just for you, I swapped out the rear wheels to vary pivot angles, from 26, 16,
12, to 6in to get 60-52deg. Surprise, they are all ridable. In fact the
smaller wheels feel more stable than 26in. Seat height may have something to do
with it, and possibly the wheels themselves. Here is video of the test ride.
http://www.youtube.com/watch?v=5JUg0zIHSuM
Regarding your program, assuming the geometry calculation is OK, the seat rise
peak still suggests a critical point, compared to the slopes on either side. I
will flip the rear frame back to normal and test 48deg downward until it scraps
the ground, to confirm the critical point hypothesis. Searching the archive, it
seems that Ray had written a program (python?) that included forces on the
geometry, http://rjs.org/Python/FrameGeometry.zip compiled for Windows, so I
have to figure out a way run it in Linux. I may take a shot at coding my own to
study dynamics, which may take a while...
Vi
________________________________
From: Dirk Bonné <dirk.bonne@xxxxxxx>
To: python@xxxxxxxxxxxxx
Sent: Thu, March 17, 2011 3:50:44 PM
Subject: [python] Re: Cool handlebar for 48deg 20in
Hello Vi,
I do doubt very much that the self centering graphs produced from my
program are very useful. Seat rise is only part of the thruth.
I tried the other end of the pivot angle scala: 70degrees and 80degrees, and
they were not very good - it was distinctly difficult to turn the bike. It
was difficult to overcome the seat rise, even though the seat rise for these
angles is less than with a 60degrees pivot.
There were as far as I can see two reasons for this worse turning behaviour:
* What the program does not deal with is forces. When turning, the seat rise
is counteracted by the front part (+legs+feet) weighing down. In 70 or
80degrees there was not enough mass falling over to get my body up.
* On 80degrees the ergonomics of turning got worse. Trying to swing sideways
with the legs is just not something the human body is made for.
I can see that 70degrees is in use by other python riders, I can only assume
that these work because they are short bikes and thus do not have to swing
as much to do the same turn.
You say 48 degrees is bad, would bei interesting to see what 55degrees does
;-)
Dirk
On 16.03.2011 05:08, Vi Vuong wrote:
60deg pivot rise @ 20deg turn is in range of Pythoon and Kauai. It
seems that 48deg is at some sort of critical point...
http://en.openbike.org/wiki/File:GuineaPigPivotAngle.png
Vi
________________________________
From: Vi Vuong <vi_vuong@xxxxxxxxx>
To: python@xxxxxxxxxxxxx
Sent: Tue, March 15, 2011 7:10:03 PM
Subject: [python] Re: Cool handlebar for 48deg 20in
Magic, I can ride it on first trial :) Ground clearance also
improved, but seat angle became a little too upright ~40 deg
to stop me from sliding off forward. I can also push it
forward by the headrest. Perhaps this is a good objective test
for ride-ability, independent of hip
coordination... http://www.youtube.com/watch?v=6yBjSGL_pd8
Vi
________________________________
From: Vi Vuong <vi_vuong@xxxxxxxxx>
To: "python@xxxxxxxxxxxxx" <python@xxxxxxxxxxxxx>
Sent: Tue, March 15, 2011 6:26:48 AM
Subject: [python] Re: Cool handlebar for 48deg 20in
OK, skip the cool handle for now. A quick change I can try is
to flip the back wheel upside down, which should lift the
whole bike by 12 deg, closer to the Pythoon. I don't want to
cut the beam just for this configuration, so perhaps 2 wheels
in the back with very narrow track to adjust wheel base, and
also pivot angle...
Vi
On Mar 15, 2011, at 2:45 AM, Jürgen Mages <jmages@xxxxxx>
wrote:
A python with your specs (48 deg pivot + überlong wheelbase)
will be unrideable, no matter what you try.
Jürgen.
On 15.03.2011 03:00, Vi Vuong wrote:
3/13/11 - Went on the street w/ the training wheels for a
longer ride, ~6km, but didn't gain much balance if any.
As is (48 deg pivot angle, 20in wheels), the bike must be
very flawed, so maybe a cool handlebar
[[http://2.bp.blogspot.com/_atq6Cg90KPY/SkT3mNsHN0I/AAAAAAAAAcE/ZG2SsF1AVOQ/s1600-h/Kouign+Amann-+soir+proche+de+l]]
will be my last attempt before donating it to a trike/quad,
then move on with the next guinea pig module (65 deg, 24 in)
which may be the limit for my inseam...
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