# [python] Svar: Re: Svar: Re: children's python

• From: "Thomas Paul Jahn" <tpj@xxxxxxxxxx>
• To: <python@xxxxxxxxxxxxx>
• Date: Sun, 09 Nov 2008 13:13:13 +0100
```hey python fans,
we made a new short movie yesterday to demonstrate how to learn/teach riding a
python.

In the beginning I was a bit irritated by the fact that we always had to put
the bikes in the car, just to get to the park where we could have our training
safely. So we tried to ride next to each other while I am holding on to Luka.
The learning effect is great. And now we go 25+ km/h if we feel like. And
absolutely straight. So, the car is not needed any longer.

And although we feel quite safe now going by ourselves, even on bikepaths, we
still enjoy going 'python duo'
greetings
Thomas

>>> Thomas Jahn <tpj@xxxxxx> 17-10-08 11:22 >>>
Hej Dirk,
thanks a lot for you calculations and the interpretations! Considering
that the pivot angle is okay, there would be not much to play with the
trail at the moment because of his short legs. This would only have
been possible by choosing even smaller wheels I guess. But I wanted to
avoid that. The 305 mm front wheel just fits between pivot and crank
at the moment.

Luka is doing very well on the bike. We did not practise as often as
we planned, but after about 6 exercises of 30 min to 2 hours max where
he mainly tried to get into move he managed a few meters:

Once he understood the principle (which was really a 'head thing') he
became better and better. His learning curve is definitely more steep
than mine. It is sooo great to see him enjoying the python. We both
love it!

cheers
Thomas

Den 17/10/2008 kl. 10.08 skrev dirk.bonne@xxxxxxx:

> Hi Thomas,
>
> I finally got off my lazy ass and made the graph I promised.
>
> I compared it to the baby python, monty and the P4 of Jürgen. The
> graph
> depicts the rise of the seat versus turning angle. As you can see it
> is
> the smallest on Lucas bike. The monty is similar to my bike on purpose
> (me and Olaf decided it that way). P4 is in a totally different level
> because of the "extreme" trail.
>
> Compared to monty the self centering is smaller because of the lesser
> trail (monty has -170mm, luca -114mm). I tried setting the trail to
> -170
> for Luca's bike and the self centering got considerable bigger then
> that
> of the monty or my bike. This is due to the larger wheelbase. If you
> would shorten the wheelbase the self centering would go down more.
>
> If you want to have more self centering you need to change the trail.
> The wheelbase cannot sensibly be lengthened and the second graph shows
> that the pivot angle is already at its best. Another idea would be to
> use a spring (silent block) as like on a flevo.
>
> How is Luca doing on the bike?
>
> Sorry about the long delay. Anyways, the mailing list here has been
> very
> very quiet, so everybody seems to have had a time out.
>
> Dirk
>
> Thomas Jahn wrote:
>> Hi Dirk,
>> here are the data for Luka's python:
>> Wheel size 305 (in front with a Schwalbe 47 mm).
>> pivot angle at 60°
>> Trail 114 mm
>> seat height 235 mm
>> Wheel base 1,04 m
>>
>> cheers
>> Thomas
>>
>>
>> Den 04/08/2008 kl. 13.48 skrev Thomas Jahn:
>>
>>> Hej Dirk,
>>> I am just back from vacation. Luka and me went by bike to Jottlands
>>> westcoast. He on the Brompton and me on the trike. Next time on the
>>> pythons. He did his first experience on the python yesterday. And
>>> although it looks rather challenging, I can already see some first
>>> progress. And he did not give up. Great!
>>>
>>> Den 15/07/2008 kl. 9.51 skrev dirk.bonne@xxxxxxx:
>>>
>>>> Thomas Paul Jahn wrote:
>>>>> Hej Dirk,
>>>>>
>>>>> Luka's first trial reminded a lot of his first time on an upright.
>>>>> He was very eager but it will take some time!!
>>>>>
>>>>> The bike is a little too big still and so is the seat. He says,
>>>>> the
>>>>> seat is hard. The latter can be solved. The former will solve
>>>>> itself.
>>>>> The front part is rather heavy. With a Sram 5 speed hub. Am I
>>>>> surprised?!
>>>>> And the pivot made of brass bushes is pretty rigid. With his low
>>>>> weight, the self centering is minimal.
>>>>> Also the long rear part probably reduces the self centering. I
>>>>> wonder if I simply cut it shorter.
>>>>>
>>>> On my bike the self centering is also minimal - just enough to keep
>>>> the front piece upright when sitting on it. I don't feel this is a
>>>> problem at all, on the contrary, I like it because it allows for
>>>> quick & sharp turns. Maybe Luka just needs the chance to learn it
>>>> first a bit?
>>>>
>>>> The weight of the front part should be as low as possible. Why
>>>> should the sram hub have something to do with that? To me the bike
>>>> looks already quite light - the tube at the front could be
>>>> shortened, but then you would need to weld it back as Luca gets
>>>> older.
>>>
>>> You mean, the hub does not have any impact, because it is part of
>>> the
>>> rotating mass!?? I see.
>>>>
>>>> You could shorten the rear, yes. It looks anyway disproportional
>>>> long compared to the rest of the bike. But I think the self
>>>> centering will get smaller. Do you have some data about the bike, I
>>>> can calculate a comparisation to my bike. I need:
>>>> * wheel size
>>>> * pivot  angle
>>>> * trail
>>>> * seat height
>>>> * wheel base
>>>
>>> I will give you some data about the bike's geometry soon.....
>>>
>>>>> And at the axis of the rear swing, or at the back wheel, I
>>>>> probably
>>>>> fix some supporting wheels to each side. So I don't have to walk
>>>>> bended down next to the bike, while Luka is doing his first
>>>>> exercises.
>>>>>
>>>>
>>>>> And the seat lean should be less inclined for him to reach the
>>>>> ground with his hands. I just hesitated reducing the inclination,
>>>>> as the beginner is not relaxed enough to go very recumbent. I
>>>>> seems
>>>>> now it would be better anyway...
>>>>>
>>>>> What do you think?
>>>>>
>>>> May be better to recline the seat (and not add support wheels), so
>>>> he can touch the ground so he kind find his own balance.
>>>
>>> Luka and me agree!!
>>>>
>>>>> About the seat: It was extremely easy to make and is very rigid
>>>>> and
>>>>> stable. After assembling, I glued it with expoxy. I will definetly
>>>>> make one for my python as well, where I still lack the proper seat
>>>>> solution. The wooden seat is very easy to attach too. Because its
>>>>> construction can be adapted to the bike structure. It seems the
>>>>> idea for the seat brought me a large step further, while doing the
>>>>> final work on the bike. I strongly recommend it:
>>>>> http://hebike.borec.cz/sedlo.htm
>>>>>
>>>> Very interesting solution and very light!!! Don't understand the
>>>> language but the scale I can read: 616gr. How well does the seat
>>>> fit
>>>> (lumber support)?
>>>
>>> I am not an orthopaedist, I made the seat a little too big. But Luka
>>> is in a potentuially fast growing age. Now he just measures 126 cm.
>>> But soon.....
>>>
>>> Thomas
>>>>
>>>> dirk
>>>>
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>
> <luca.jpg><luca2.jpg>

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• » [python] Svar: Re: Svar: Re: children's python - Thomas Paul Jahn