# [python] Re: FWD-RWS-Recumbent

• From: "Bolle, Cristian A \(Cristian\)" <bolle@xxxxxxxxxxxxxxxxxx>
• To: <python@xxxxxxxxxxxxx>
• Date: Fri, 27 Mar 2009 09:12:16 -0500

```Well, I will contradict DirkS and tell you that the green line pivot will not

In a traditional bike, as you lean to the right the front wheel will also turn
to the right because that lowers the center of mass (the rider's hip) of the
bicycle. Try it out, for a small lean angle to the right the front wheel will
turn a bit to the right. If now you manually turn the front wheel a bit more or
a bit less (with the bike leaned over) you will see that the seat of the bike
will rise a bit in both cases. Therefore, bicycle leans to the right, wheel
leans to the right. Now if you drive the bicycle and you start to fall to the
right the front wheel will automatically turn to the right and prevent your
fall. It's like negative feedback.

The Python is different in that sense. As you lean the rear (you) to the right,
the front wants to steer to the left and eject you. Positive feedback. That's
why it is so hard to learn to ride a Python. You basically have to steer with
your body and feet, but once you learn it you can ride without hands. You ride
in the back and steer with the front.

I wrote a Matlab code that does the whole vector analysis of the rotations of
the bicycle as a function of lean and steer angles and calculates the potential
energy and it shows you how it all works. And I found the same geometry as
Dennis Renner. And that geometry  should work since it behaves in the same way
as a traditional bike. And I also have a prototype that is almost finished (but
little time to do it) that I started over a year ago. And it turns out that the
Renner geometry is actually the same as the Velaero geometry from Craig
Cornelius:
http://www.ihpva.org/HParchive/PDF/27-v8vn1-2-1990.pdf

And now to your question: For the green line the bike will behave like a python
but you only have your hands to control the rear wheel. As the front of the
bike (you) leans to the right the rear wheel turns to the left and you get
ejected.

In my 'Velaero' the rear axis is at 71 degree (I wanted 70 but got 71, blame it
on the Harborfreight Buzz-box) but not as far back as in Dennis' frame. I tried
with a direct steering for a while and just couldn't get it to work, I guess
the brain doesn't like it? Now I'm modifying that to be an inverted steering
like in the Velaero.

That's my 5c for now. I'll share the code I wrote in the next few months but
since the interpretation of the results is a bit tricky, I want to take some
time to add some examples and explanations. And then there is JBike6!

Cris

> -----Original Message-----
> From: python-bounce@xxxxxxxxxxxxx [mailto:python-bounce@xxxxxxxxxxxxx] On
> Behalf Of dirk@xxxxxxxxxx
> Sent: Friday, March 27, 2009 9:24 AM
> To: python@xxxxxxxxxxxxx
> Subject: [python] Re: FWD-RWS-Recumbent
>
> Hi,
>
>
> yes it should but i don't know if anyone tried yet.
> Jürgen claimed that his px5 was next to unrideable. There should be quite
> some documentation on the px5 if you search the python mail archive at
> freelists for it.
>
> what questions me is the direction of the pivot. in dennis solution he is
> using handlebars and the pivot angle is pointing towards the front part of
> the bike while located behind the center towards the rear part ... i
> wonder if this would result in just the opposite of self centering... i
> expected the pivot to point towards the rear part once located closer to
> the rear end in oder to keep the self centering effect. Maybe something to
> simulate with to beams with a pivoted joint.
>
> regards,
> DirkS
>

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