[python] Re: Forwarding Ghislains Mail

Cool looking python.   Very similar to what I had in mind for my kids to try
:)  I would humbly suggest, that instead of changing the whole frame of the
python, which looks pretty nice, try just making an extension to raise the
seat, that could me removed later, if you wanted (and after the riders have
a good "feel" for the python).  Raising the seat on ours produced a
noticeable change and we only raised it 5 cm, not 10 like you propose.  10
might even be better still?

The next one I built I'll likely use some 1/2" female rod ends, like Mike
Channon did, instead of an actual bearing.  Why?  Well, I'm going to make a
frame with a static pivot angle aroung 66 or 67 degrees and use the
adjustment of the rod ends to experiment with pivot angles of low 60s up to
about 70 to see which angles help the rider learn, and which ones are better
for after they can ride and want more . . . . ?
(performance/handling/agility?)  As "ignorence is bliss" the 70 degree angle
doesn't seem to be posing a problem, but we haven't had a chance for some
high speed testing yet either.  While that angle might make the front end
feel too light, it also makes it easy for a beginner to quickly and
"lightly" react to tipping over.

My friend and I were also thinking of making a python front end with an
adjustable bottom bracket that could use a turnbuckle to raise and lower the
BB in relation to the seat, and see what effect that has on performance,
handling, speed, etc.


> Hi All,
> Why a 20" Python ?
> Dirk proved it could be made.
> Other personal reasons : smaller diameter of wheel, compared to 26",
> - makes easier the fixing of the bottom  bracket  shell; tubes instead
> of flats can be used.
> - more adjustment made possible for  various length of legs,  ok for a
> child 14 years old, or long legged adult, as I am. Moving the seat aft
> up to 10cms from its more forward position,  gives a different feeling,
> while the beast remain ridable.
> - overall dimensions less cumbersome, easier to put in the car and
> overall weight reduced compared 26"
> -  apart from 61or 64 teeth ring for the crankset, all parts can be
> found easily.( I found, cheap second hand, a flawless 61 teeth ring.)
>
> Why did we lower the seat height compared to Dirk's model ? low seat
> height can be used by children or adult, hands touching the ground.
>
> About the building itself :
> Front part steel 30x10x1.5mm with roller bearing pivot
> main beam,  steel exhaust pipe 42mm outside diam. x1,5mm
> rear fork, steel 22mm outside diam. x 1,5mm
> mig welding
> Feels strong and rigid , for my weigth 80 kgs.
>
> About the riding :
> Very odd, and a good challenge, children learn much more quickly than
> adults !
> We started getting used (?) to it, after a few minutes/hours depending
> on age. Conclusion for now is  it is ridable, low speed only, in open
> space.
> About the seat height, as mentioned in the freelist, we came to the
> same conclusion : the lowest the seat, the sharpest the balance. Having
> experienced we could  ride it, at low speed,  as it was, we are
> modifying seat height and trail. New goals : Pivot angle the same, 60
> degrees. Trail, reduced to 14 cm, seat height + 10cms. Which will make
> this 20" python look exactly the same as Dirk's !
> Do these figures remain good for him ? Or  would he change them a bit
> for his own python, If he were to do it again ?
> It looks like Dirk got it right the first time, when it took us twice
> to reach the same result :  a more forgiving ridable python, at last
> nearly  (: >) ! Future will tell.
> Well done Dirk ; thanks Jurgën for the challenge !
> Cordially
> Ghislain Pillet, Antibes, France.

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