[python] Re: Question for the experts
- From: George Durbridge <gdurbrid@xxxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Mon, 17 Jul 2006 23:55:10 +1000
On Mon, 2006-07-17 at 05:09 -0400, Recumbent Country wrote:
> The way I am envisioning this is as follows.
>
> 1) Rear wheel drive.
> 2) Standard Tadpole boom setup
That is, the chain runs from a central bottom bracket to the rear wheel,
as on, say, a Speedy or a Greenspeed? In the absence of cheap, light
differentials, most tadpoles will continue to use rear wheel drive.
> 3) The front Cross bar of the tadpole will be completely horizontal with
> the standard python steering frame joints on the outer ends of the cross
> bar.
I assume you mean the crossbar will be horizontal at all times, and
rigidly mounted to the tadpole boom? If so, you cannot use lean-steer.
> 4) Standard Python front sections using a front wheel instead of a rear
> wheel.
> 5) Where the bottom brackets on a python normally is, having a linkage
> join the two python booms together.
So the two Python booms, the crossbar and this linkage form a
parallelogram (or perhaps a trapezium, to allow for some Ackermann
effect). The linkage can join the two wheel centres, rather than being
in front of the wheels.
> 6) some type of handle bars to allow the rider to induce the lean for
> the steering.
This I still find difficult. Assuming the tadpole boom is rigidly
connected to the crossbar, that the Python pivots are not inclined
transversely (only fore and aft, as on Pythons) and that the front
wheels remain on the road, the seat and the rear wheel will remain
upright in a corner and, as far as I can see, the trike cannot lean. As
the front wheels are steered, the angled pivots will lift the rest of
the trike by the small amounts indicated by Dirk's graphs. But this
rise will be the same on both sides, so the trike will squat a little,
rather than lean. It will be possible to steer, but not by leaning:
only by manually pushing the wheels sideways.
> The purpose of this is to design is as follows:
>
> 1) A self centering trike that can be the base platform for a velomobile.
The large amount of sideways displacement of the wheels by the steering
will shift them out of line with the fairing.
> 2) It will allow the use of standard bicycle parts without relying on
> special hubs for the front wheels.
BMX hubs with 20mm axles are now widely available. If you want to
support the front axles on both sides, you can use the same layout as
the MR Swift, with a tube running from the kingpin over the top of the
wheel.
> 3) Allow higher gearing using as 26" rear wheel and using 16" or 20"
> front wheels with disk brakes.
This does work, but a large chainwheel or an intermediate step-up drive
will also give the necessary gearing. Most recent tadpole designs use
the same sized wheels at each corner. One reason is that a large rear
wheel makes for greater difficulty in designing the chain line.
> 4) If building a velomobile the python frame joints could be built
> into the faring design for the front wheel mounts and to total encase
> the front wheels for aerodynamics.
The wheels can't be totally encased, and can't be fully faired except in
the straight ahead position.
> If someone is good with a sketchup I can try to provide further details
> if need be to help developing the plans.
Alternatively, did you have in mind that (a) the Python pivots should be
inclined transversely or (b) the crossbar should pivot on the tadpole
boom?
A pivoting crossbar needs a linkage to the Python pivots, and I have not
yet thought of one which would work.
If the Python pivots are inclined inward and upward (that is, their axes
lie on the arms of an A with its apex above the tadpole boom), you would
have a sort of lean steer: when the steering was deflected, the wheel on
the outside of the corner would move down and the wheel on the inside
would move up, so the rider and the rear wheel would be tilted into the
corner. I assume this would work in reverse: the rider could steer by
leaning. The upward movement on one side would be roughly equal to the
downward movement on the other, so the rider would not lose as much
potential energy as he would in other leaning mechanisms, and could
probably straighten up without special machinery or much effort. But
the layout would be more liable to tip over than a standard tadpole,
because the centre of gravity would move outwards in corners.
> Doug Morency
> Osgoode, ON Canada
> ============================================================
>
> This is the Python Mailinglist
>
> //www.freelists.org/list/python
>
> Listmaster: JÃrgen Mages jmages@xxxxxx
>
> To unsubscribe send an empty mail to
> python-request@xxxxxxxxxxxxx
> with 'unsubscribe' in the subject field.
>
> ============================================================
>
--
George Durbridge
+61 3 9481 3500
+61 409 413 945
============================================================
This is the Python Mailinglist
//www.freelists.org/list/python
Listmaster: Jürgen Mages jmages@xxxxxx
To unsubscribe send an empty mail to
python-request@xxxxxxxxxxxxx
with 'unsubscribe' in the subject field.
============================================================
Other related posts:
