[python] Re: vertical steering axis

On Wed, 2007-04-25 at 08:13 -0700, Ray Schumacher wrote:
> At 10:58 PM 4/24/2007, you wrote:
> >On Tuesday 24 April 2007 18:25:22 Oupa wrote:
> > > Bill Patterson <wmpatterson@xxxxxxxxxxxxx>, an engineer, ex-academic
> 
> I bought Bill's book while building my low racer
> http://rjs.org/recumbents/images/IMG_4276.JPG
> which has an 88 degree headtube and 3" trail. (Bill recommended more 
> for speed, but it turns better with 3; it is also speed limited by 
> the torsional flex of the long rectangular tube - it's twisty).

Your bike has a normal steering head above the front wheel, and I can
see how that will work.  Tony Foale and Mike Burrows both say that their
experiments show that a vertical steering head works OK, provided there
is adequate trail.  Jim Papadopoulos says that you need some steering
rake for best control (particularly riding no-hands).  What was your
experience?  

> He doesn't have any vertical Flevos in his book, only a normal one 
> with low angle and positive trail. I assume from the text that the 
> vertical ones also had positive trail. With the trail the same, 
> vertical heads just seem to make the response of small steer 
> adjustments faster, my long WB bent is ridable at 3mph.

How would you design a Flevo with a vertical pivot and positive trail?
Put the pivot somewhere near your knees?  That would be difficult to
pedal with the steering turned from straight ahead, particularly as the
wheel might foul both legs.

Alternatively, I can imagine a Python-ish design, with a vertical pivot
under the seat and lots of negative trail, but I don't want to try
riding it.

If you put the pivot near the rider's hips and the centre of the front
wheel 2" behind the pivot, you will have positive trail, but the rider
will be more or less directly above the front wheel.  This might suit a
really short wheelbase tandem, with both riders cantilevered outside the
wheelbase, but would probably be pretty unstable for any other sort of
bike.


-- 
George Durbridge
+61 3 9481 3500
+61 409 413 945

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