[python] Re: Improving the Python

  • From: "25hz" <25hz@xxxxxxxxxx>
  • To: <python@xxxxxxxxxxxxx>
  • Date: Mon, 12 Feb 2007 21:44:01 -0500

Old message, but been busy building . . .

I'm not sure what the slant of your post was intended to be, but if you
found that using handlebars helped you, great - whatever gets another person
on a python and person on a bent.  Also, by "handlebars" most of the list
members (that tried them, anyway) would refer to handlebars that are
actually attached to the front end of the python, and not rigid/non-moving
bars that hold the controls. I tried handlebars on the front end and it was
worse than without them - so I took them off.  Marcel, who was riding it and
balancing the python in less than 10 minutes, also tried handlebars on the
front end, and he went from being able to ride, to being able to immediately
crash - so we took them off.  We also tried temporary bars for two other
guys that learned to ride the python, and same result - absolutely not a
help.  The easiest for all of us was to keep our upper arms against our
torso, keep our forearms out to the side and roughly parallel to the ground,
and sort of use our arms like a tight rope walker uses a balance pole.
Afterwards, when we could ride pretty confidently, again, temporary
handlebars seemed to put forces in all the wrong places and we immediately
crashed.  After a couple hundred KMs on the python, we could actually use
the static handlebars, under the seat, to enhance turning by gently pushing
down on them, using the side we wanted to turn to.  I didn't use that
technique much because with the shoulders, hips and feet - I had more than
enough stuff in the mix and didn't need one more.  I did end up riding with
my hands on the bars most of the time so I had quick access to the brakes -
especially in areas with lots of sideroads.

Comparing a python to a diamond frame bike is like comparing apples and
bricks.  While your analogy is flawed, you actually can ride a DF bike when
it doesn't have handlebars.  Why?  Because it is inherently stable.  Push a
DF with no rider on it and it will roll off, turn into a lean by itself and
roll for a while.  Push a python with no rider and it'll be on it's side
seconds after it leaves your hand.  A python needs a rider for balance,
while a DF does not.  On a DF, you counter steer and then lean and steer
into the turn.  On a python, you have to lean into the turn first, then
shift your weight to the outside and hope you've balanced the speed, lean
and weight shift.  For control, the two bikes are almost the complete
opposite.


| One way to deal with "It is difficult to ride initially" is to put
handlebars on it. It seems that without handlebars, one needs to ride 300km
before ventruing out into traffic. (According to Jurgen and others on the
list.) With handlebars, I rode between 300m and 3km beforehand. Think about
trying to learn to ride your old diamond frame bike without handlebars; it
would be pretty tough. The handlebars actually facilitate learning to ride
no-handed. Remember riding with your hands a few inches (centimeters) from
the handlegrips, then suddenly being able to go no-handed? It's the same on
a python.
|
| Please, I hope someone points out how I must be developmentally challenged
if I need handlebars. It makes me feel good. I hope these guys have taught
their kids to ride diamond frame bikes without handlebars.
|
| -Rod
| -------------- Original message -------------- 
| From: Paul Lowing <plowing@xxxxxxxxxxxxxxxx>
|
| > OK, here goes. I've been intrigued by the Python for a quite a while
| > now and a build is next on my bike building list. However my perception
| > of the Python (having never built or even ridden one) is that it has
| > many advantages but perhaps two major failings.
| >
| > 1) It is difficult to ride initially. This can be overcome by practise
| > but has to be taken into account before building. I hypothesize that
| > this is due to the steering geometry not providing a correcting force
| > that increases with increased steering lock.
| >
| > 2) This is the big one for me, apparently there can be stability issues,
| > particularly when coasting down hills at high speed. On one of my
| > routes to work I can hit 48 mph and exceed or approach 40 mph a number
| > of times. This speed is then put to good use climbing the next hill.
| > Having a bike that I can't use fully under these conditions is a
| > problem I hypothesize that this problem is caused by the steering
| > geometry not providing an increasing centring force with speed. This I
| > would find difficult to live with.
| >
| > There have been suggestions for altering the steering to provide a
| > virtual steering axis, but this solution suffers from making the front
| > wheel move differentially with the feet which probably would cause
| > interferences, it also adds quite a bit of complexity as the solution is
| > often on the lines of a four bar linkage.
| >
| > My solution (which I was going to keep under wraps until I had tried it
| > out) is the following:-
| >
| > Assuming the turning force on the steered wheel of a cycle is
| >
| > proportional to sin(steering head angle) X distance from the point of
| > contact of the wheel with the ground
| >
| > Then by introducing a second steering head that steers the rear wheel
| > the tendency of the Python front wheel to turn away from centre at high
| > speed can be overcome.
| >
| > By having a more vertical rear steering head a smaller turning of the
| > rear wheel is required relative to the front.
| >
| > My plan is to start with a standard Python configuration but with a
| > vertical steering head for the rear wheel. The ratio of front wheel
| > steer to rear wheel steer I was originally planning to try at 2F:1R.
| >
| > Although this idea is adds some complexity (an extra steering head and a
| > linkage) it retains all the other advantages of the Python layout, the
| > increased centring force with steering angle may make it easier to ride
| > and increased centring force with speed should promote stability.
| >
| > Does anyone have any comments on this? As I said I was going to try it
| > out myself first but since I haven't had time to try it yet I thought
| > I'd share it.
| >
| > Paul Lowing

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