[python] Re: wheel flop vs pedaling induced steering
- From: dirk@xxxxxxxxxx
- To: <python@xxxxxxxxxxxxx>
- Date: Fri, 04 Jan 2008 18:08:58 +0100
Hi Jürgen,
Had some time to study the PX.5 pictures.
btw: should this one - http://www.flickr.com/photos/python_uploads/2073763738/
- be named PX.5 as well?
So you cleverly moved the seat forward, while having the drivers back still
leaning against the rear part of the bike. So it is in essence a normal python
with increased trail and b>>a-distance
Do you think, this is somewhat related to the position of the hip joint in
front of the pivot, as on of your pictures suggests?
Or isit related to the added weight of the front part, because it is longer?
I'm going to do some rough sketches and try to document this in the wiki.
Regards,
Dirk
>I uploaded three better pictures of the PX.5 to
>
>http://www.flickr.com/photos/python_uploads/
>
>Maybe the seat/pivot arrangement is better visible now.
>
>Jürgen.
>
>
>On 29.11.2007 07:42, Dirk Steuwer wrote:
>> On Wednesday 28 November 2007 21:08:50 Rhisiart Gwilym wrote:
>>>> On 28.11.2007 16:50, Kevin Bailey wrote:
>>>>> I had assumed that PSI was dependent on the ratio between the
>>>>> pedal "width" (distance from the center of the pedal to the
>>>>> centerline of the bike) and the BB to pivot distance. Basically,
>>>>> that PSI was caused by the sideways component of the pedaller's
>>>>> stroke (which attempts to turn the wheel) and corrected by the
>>>>> foward component of his stroke (which attempts to straighten the
>>>>> wheel.) This ratio is equivalent to that between the pedal width
>>>>> and the BB to pivot distance. Put plainly, the further back you
>>>>> move the pivot (without changing the pedal width), the less the
>>>>> PSI. I assumed this was why the Python was better in this
>>>>> respect than the Traylor/Cruzbike designs.
>>>> Hello Kevin,
>>>>
>>>> I thought this too - until I built the PX.5, an
>>>> experimental prototype where the pivot was moved
>>>> 25 cm further back than the normal position:
>>>>
>>>> http://python-lowracer.de/pics/Python%20PX.5.jpg
>>>>
>>>> PSI was clearly noticeable and the bike was hardly rideable.
>>>>
>>>> Cheers,
>>>> Jürgen.
>>> Siwmae Jurgen,
>>>
>>> That picture seems to me like a very striking
>>> image of a man actually sitting on a unicycle,
>>> with the one-wheel trailer towed behind, rather
>>> than the rider sitting on the trailer to drive
>>> and steer the front-end/unicycle from behind, so
>>> to speak. Wonder if that has anything to do with
>>> PSI. It's certainly surprising that it comes back
>>> in that layout, and makes the bike hard to
>>> manage. Mysterious!
>>>
>>> Cof, RhG
>>>
>>
>> i had the same impression like RhG. Is this correct Jürgen? i think it could
>
>> be crucial to have a persons back pressed against the back of the bike to
>act
>> like a stabilising element instead of allowing free wobble of this part...
>>
>> Imagine you push into the right pedal, this would steer the bike to the
>left.
>> But you back would be pressed against the seat on the opposite site - left,
>
>> the resulting force should swing the rear part round and steer the bike to
>> the right side - hence balance out a possible PIS effect.
>>
>> Are there bikes with "conventional" python design, but with increased
>> FWA-pivot distance?
>>
>> Regards,
>> DirkS
>
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