[python] Re: frame geometry and pivot angle

  • From: Patrick van Gompel <patrick_van_gompel@xxxxxxxxxxx>
  • To: <python@xxxxxxxxxxxxx>
  • Date: Fri, 30 Mar 2012 16:08:50 +0200

Hey Vi, thanks for sharing. You never stop to surprise me with your new bikes 
Haha yes, you are sitting on the 'wrong' side of the bike. You are sitting on 
the non-fixed side, whereas on a normal Python you sit on the fixed side.
For your trike I think your pivot direction is correct, though I wonder about 
the position. The Python 'guidelines' say that the pivot axis should go through 
the center between the riders hips to minimize PSI. It seems your pivot should 
be like 20cm more to the rear. It would also help with less body weight leaning 
into the corner. A pivot lock seem kinda dangerous to me and you might not need 
it if the pivot is optimized ;-)  More testing? :-)

Haha, a paper Python! It would need quite a bit of epoxy to make is drivable.

Date: Thu, 29 Mar 2012 22:23:31 -0700
From: vi_vuong@xxxxxxxxx
Subject: [python] Re: frame geometry and pivot angle
To: python@xxxxxxxxxxxxx

Hi Patrick,
Yes, pivot does move up but rider falls down (leaning).  I do miss the self 
centering effect, and feel like I am sitting on the wrong side of the trike. 
However, for a tadpole with pivot pointing backward like pythons, the rider 
would lean the wrong way, very unnatural...
Well, the trike started out with RWS, which was scary with direct steering.  
Then I moved the pivot up front to try out leaning.  It does seems arkward 
making a u-turn, but a normal turn just need a little bit of leaning, and feel 
quite natural after a while.  Some sort of speed-variable pivot would be nice 
:)  Going fast is another story - I have to lock my
 arms to reduce steering influence; here a locking disc at the pivot would be 
super nice, but maybe getting too complicated (what happens to hands free).  I 
may build a RWD leaning tadpole to compare steering influence.  A really nice 
things about leaning design is that the track can be narrower, and maybe higher 
Besides the leaning experiment, I started making a wire-frame velo shell and 
got a little carried away with abstract painting.  Not sure what to do with the 
thing now, but I may participate in the 
http://fbuc.org/2012/03/fbuc-figure-8-track-pedal-car-racing/ if this thing 
qualifies (w/ 4 wheels).  Meanwhile I started a 2nd FWD leaning folding 
tadpole, http://www.youtube.com/watch?v=5rkPKDMDk9E, but the axle is rework...
So adding more wheels should be reserved for necessity (safety, stability, 
speed, cargo etc).  It would be tough to beat the experience on python bike 
cruising.  By the way, your video makes it much easier to understand the paper 
pivot concept.  How about an actual python model made out of paper :)?  
        From: Patrick van Gompel <patrick_van_gompel@xxxxxxxxxxx>
 To: python@xxxxxxxxxxxxx 
 Sent: Thursday, March 29, 2012 1:50 AM
 Subject: [python] Re: frame geometry and pivot angle

Yes Vi, you have a nice example of a fixed front. I just wondered: if you steer 
that bike, does the pivot point go up? I would guess yes, but I think your 
upper body is falling into the corner and making the overall CoG go down. What 
is your experience with your bike?
Are you still experimenting with this bike? I think the pivot point should be 
more to the rear (for more body rise when cornering and less pedal steer). Not 
sure about the pivot angle though... seems you need to lean quite a bit for a 
tight corner, right?


Date: Wed, 28 Mar 2012 22:11:41 -0700
From: vi_vuong@xxxxxxxxx
Subject: [python] Re: frame geometry and pivot angle
To: python@xxxxxxxxxxxxx

I have a video showing that front \ back configuration is not self stabilizing, 
and requires arms to stay upright, at ~1:30sec, 


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