[python] Re: python stability, again...
- From: <peter.svancarek@xxxxxxxx>
- To: <python@xxxxxxxxxxxxx>
- Date: Tue, 16 Apr 2013 16:02:19 +0200
Thanks for your response...
Well, python is maybe special in this scope, because whole front end with
bottom bracket is moving while steering. What I’m aiming for is rather clasical
low racer, or semi low racer based on this
http://rowingbike.com/site/EN/Models/Carbon-THYS-209/ with some modifications .
20/12inch wheels(12 inch wheel is OK for road, I tried it quite enough),
different rail system... I think I will go for wheel base of 120-130 cm...
maybe even different way to unlock the revolver(i have an idea how to get rid
of the bowden, but maybe it wouldn’t be necessary.
I gave up to build an python, because I want to have little more practical
bicycle(to move some cargo, maybe up to 20kg) and also to whole body workout.
Once, till 2 years ago, I used bike nearly whole year to ride to my work, to
make necessary shopping... but my wrists started to be sore... something like
carpal tunnel or what... so I’m trying to build bicycle on which I wouldn’t
need to be bowed over handlebars.
While it is true, I built model from wood with a few steel parts, it is rock
solid. Distance between wheels is between 100 to 115cm depending on steering
configuration. Maybe I have problem with steering bar... I’m not used to it(but
I know how to modify steering, only it is more difficult to aply it because I
need more variability to change steering configuration for tests. I thought
that reclined seat(I aim for 25degrees from horizontal) could be problematic,
but experimenting with that showed me, that I could ride much more stable in
reclined seat (25 degrees) than at 80 degrees... there we go- centre of gravity
is at 80degrees angle of seat higher... And... hmmm... you know, my little
daughter knows how to ride that model much better than I Stability may not be
good, but she is better in finding it Anyway, after many attempts I found best
configuration to this date is 18 degrees headtube angle, 6cm trail. Wheel load
is cca 50% on each. I didn’t like wheel flop at 45 degrees headtube angle, and
even when I turned it down to 30degrees from vertical it was real pain in the
ass ... so I lovered it to current 18 degrees and it is much better.
Program I mentioned earlier was inspirational, I made a few attempts and found
also configuration with only 5-6degrees headtube angle and 8cm trail... very
stable, according to program. But that stability may be changed horribly by
some of those things I mentioned in first mail.
Peter
From: Patrick van Gompel
Sent: Tuesday, April 16, 2013 2:23 PM
To: python@xxxxxxxxxxxxx
Subject: [python] Re: python stability, again...
Hello Peter,
I don't know that program and I don't have answers to all your questions about
it, but a stable bike is not only about centre of gravity (CoG). Just a simple
example: you have a bike which seems to be stable with a 100kg load right in
the middle. Now, take 50kg and put that 1 meter to the rear and put that other
50kg 1 meter to the front. Your CoG hasn't changed, but your (steering)
stability has. For example, I think it's almost impossible to drive a Python
with a 50kg load on the front near the pedals. Your front end will probably
flip left or right and your legs won't be strong enough to keep it centre.
Keep in mind that CoG is an idea to simplify things. Although it can be used to
calculate things like the load on both wheels, for stability you need quite a
bit more.
A good question might be why your other bike isn't stable. Is it because of the
steering, position of mass or a weak construction?
Hope that helps a bit, but I am sure others know much more about it.
Patrick
> From: peter.svancarek@xxxxxxxx
> To: python@xxxxxxxxxxxxx
> Subject: [python] python stability, again...
> Date: Tue, 16 Apr 2013 13:52:44 +0200
>
> Hi,
> I was looking for bicycle stability calculator becase I ran into problems
> with stability of my little rowing bike project model. It is model(to this
> time without drive) where I could change to some degree parametres of
> steering. But that beast is is not very stable, even if it is possible to
> ride it. So before I will built final recumbent I must obtain reasonably
> stable model :)
>
> I found this little program on this mailing list (
> http://rjs.org/Python/FrameGeometry.zip ). I even changed a few values to
> obtain selfstable bike at 6.4 km/h, but while I understand some of
> variables, others I don’t understand.
>
> Front mass to pivot, front mass to height... Why not give there only data
> about centre of gravity? While on projected bike will be mass moved(both
> legs and torso of rider) during driving, the centre of gravity would be more
> or less in the same position. And centre of mass is what is loading the
> wheels, isn't it so?
>
> what is "tortional K to pivot axis" ? What is inertial factor and "inertial
> angle of front mass from horizontal"? "inertial angle of front mass from
> horizontal? Front mass and main mass???
> Cheers Peter
>
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