[python] Re: some thoughts
- From: "25hz" <25hz@xxxxxxxxxx>
- To: <python@xxxxxxxxxxxxx>
- Date: Wed, 12 Oct 2005 21:38:42 -0400
You are in fact correct, I only changed the rear wheel. So, as I didn't
think about the effect of the front wheel as far as gyroscopic effect is
concerned, there was an easy way to find out.
I took the BHP and clamped it on my steel table with the front wheel hanging
free and clear over the edge.
I next took the following:
- my electric drill and my high speed grinder
- a hockey puck with a 1/4" hole drilled through the center with a long 1/4"
bolt through it
I put the hockey puck/bolt in the electric drill. I steadied the python's
front end with one hand, turned the drill on (variable speed) and held the
puck against the front wheel. I went from 0 to 48 kph in 10 kph increments
except for the last, 8 kph, and while the wheel was turning, I tried to see
if I could feel any gyroscopic torque on the front end by slowly rotating it
from side to side. The result? Zero. When I take a 16, 20 and 26" wheel,
hold the axle by one end and spin it, I immediately feel the gyroscopic
procession kick in and it is very difficult to change the orientation of the
wheels with my bare hands. There is no such feel with the python's front
end. Interestingly, if I take the same 20" wheel, and put one axle end in
one of the king pins I make for my trikes
(http://bikes.jkcc.com/new%20king%20pin%20on%20wheel.jpg), and just hold the
kingpin with one hand, once again, the gyroscopic torque is completely
eliminated.
So, seeing as how I'm on the net, I did a little reading on gyroscopic
effect and bicycle wheels, and came across this:
http://www.sheldonbrown.com/brandt/gyro.html
I read it, and a couple other sites on gyroscopic effect and procession, and
it would seem that the wheel needs to be much more free to pivot around its
own axis to employ the "coupling moment" and generate some gyroscopic
torque. It would seem that the gyroscopic effect is very minimal and a
wheel doesn't need to be spinning fast at all to generate it, if it can be
felt at all, so even a bigger bike wheel, spinning slowly, can generate the
gyroscopic force, when it is mounted so it can be observed.
At any rate, I can't effect and kind of change on the laws of physics, but
what I can do is change the pivot angle, so that's what I'm going to do. :)
The physics descriptions and equations are over my head right now, and I'm
not really very interested in them. I can't "feel" the equations. What I
can do, is feel the effect, quite easily, of changing the pivot angle, and
the wheel base, and the seat height.
> >I don't think the wheel size has an effect on downhill stability. I
think
> >what makes your's stable on the downhill is primarily your pivot angle of
> >60 degrees. After experimenting with the PC2, I would LOVE to have 60
> >degrees or even less on my BHP. The BHP, right now, has about the same
> >angle with the 20" rear wheel as it did with the 26" rear wheel, to
within
> >about 1.5 degrees. The handling felt the same on the downhills with both
> >wheel sizes, even after I had about 350km when I switched to the smaller
20"
> >wheel.
> >
> But Tim,
>
> I thougfht you only exchanged the rear wheel??? Did you also change the
> front one?
>
> Dirk
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