[python] Re: some thoughts
- From: Dirk Bonne <dirk_bonne@xxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Thu, 13 Oct 2005 10:44:47 +0200
On 10/13/2005 03:38 AM, 25hz wrote:
>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.
>
Hi Tim,
Great experimentation! 8-)
But the gyroscopic torque is 90degrees to the pivot axis. In fact the
gyroscopic torque was there, and it was working in on your bench. If the
bike would have been free standing, then the bike would have fallen over
when rotating the front end.
So that is why you didn't feel anything. The experiment does not model
the situation "coasting downhill" well.
>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.
>
>
AFAIK, The gyroscopic torque felt will be lineair with the speed. And is
quadratic in the wheel size.
>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.
>
That's okay, I'm not so ambitioned either ;-)
What I do feel is that from a certain (really high) speed the
*qualitative* feeling of the bike changes. On my bike it is at least
above 52kmh, dunno exactly where it happens.
My question is why would a bike be different at high speed than at low
speed? I can really not believe that the answer is "pivot angle". If you
are willing to drop the notion of gyroscopic torque, what is there left
to actually give you physically the feedback of that something is
qualitatively different?
> What I
>can do, is feel the effect, quite easily, of changing the pivot angle, and
>the wheel base, and the seat height.
>
>
It would be interesting to know how the mechanical trail has an
influence. Hmm, making the pivot angle more horizontal will make any
gyroscopic torque more vertical, creating less influence on the side pull...
Dirk
>
>
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