Hello,
Ok. I have no experience with that kind of bike so my ideas might be totally
wrong but here are my thoughts.
I have included 5 pictures. They show the position of the wheels, the axle
position/direction and the pivot line of the front part. For my writings below
and the trike you are talking about, I only consider the Centre of Gravity
(CoG) of the front part, since most of the weight is there and is most
important for the steering. Also, the rear doesn't lean when steering into a
corner. Keep in mind that the CoG is not only about the position of your seat,
but also your legs, bottom bracket, pedals, wheel, etc.
In my eyes there is a self centering effect for the steering if the CoG is in
the green zone. But, the closer it goes to the dashed line, the weaker the
effect will be. (Though, the strenght of rise of the CoG also depends on the
position of the steering axle.)
So to answer your two points:
1 - No, it is not about the seat, but about the CoG. And yes, the CoG should be
under the pivot line. Keep in mind that the steering axle is not the same as
the pivot line in the pictures. They run parallel, but not at the same position.
2 - Yes, the steerings axle should be inclined.
I can't give a direct answer to what is the best for the inclination of the
steering axle, since I have no experience with such a bike. Probably it's best
to ask the owner of that Sirio.
Whether there are 2 linkings or joints from the rear to the front frame doesn't
matter. That is just to make the construction more stable. If you had only 1 or
even 5 joints, the pivot and axle line would still be the same.
The inclination of the seat is mainly a comfort and air resistance thing.
Again; the position of the CoG is what is important for the stability of the
bike. I think a inclination of the seat between 20-40° would be ok. My bikes
are about 30°, but that is a personal preference.
What I do not really understand is why the inclination of the axle would effect
the inclination of the seat. Those two are separate things, right?
Sorry, but I didn't receive any attached pictures.
Some more thoughts about my pictures:
Example1 shows the steering axle somewhere in the middle between the wheels. In
my eyes there are two things why the CoG will rise when you steer: 1 because of
the inclination of the steering axle the CoG goes up the same as with a normal
Python, 2 because of the inclination of the pivot line and if the CoG is in the
green zone.
Example2 shows a axle inclination that gives a lot of CoG rise when steering
(although hardly because of any CoG rise caused by the 'Python effect').
Though, there will be a lot of leaning but without much steering.
Example3 shows the opposite of example2. Steering will hardly give any rise to
the CoG.
Example4 shows a steering axle that is placed further to the rear. I assume
that this will make the trike behave more like a rear-steering one, which means
the rear will go to the right if you steer to the left. Also, putting the axle
far to the rear will lessen the rise of the CoG because the Python effect will
be less.
Example5 shows a steering axle far to the front. Again; the Python effect will
be less. Though, the trike will act more like a front steering bike. Not sure
in what way it will change the driving experience, but the swing of the CoG
from left to right will be rather different from example 4. If you for example
put the CoG at a great distance from the pivot line, it will swing a lot to the
right if you steer to the left. In extremes, I suspect this will make the trike
unhandable as it will throw the CoG outside of the corner when you steer into a
bend in the road.
Quite a lot to think about. Talking to somebody who actually built and drove
such a bike would be great.
Greetings,
Patrick
> Date: Thu, 4 Oct 2012 12:54:57 +0200
> Subject: [python] Re: question about pivot angle - 63-65 degrees
> From: mtzolo@xxxxxxxxx
> To: python@xxxxxxxxxxxxx
>
> Hi
>
> * sorry, in the video the "sirio" trike is the second one! the number
> 2! ("a combination of steering and leaning (leaning of the seat).")
> * in that video the steering goes straight (when sitting on the bike
> and doing nothing) because of the fact that
> 1 - the seat is under the steering axle
> 2 - the steering axle itself is inclined
> I think for both of that reasons (am I right or wrong?)
>
> From that considerations my questions: how much COULD BE the steering
> axle? (that is the same of pivot axle) 40°? 65°?
>
> Because, unlike python where the seat is a single blok with rear frame
> (seat is rear frame) and there is only a point linking rear and front
> frame (the pivot), in my case the seat "is" front frame, and it is not
> so easy to find a good combination of
> 1 steering axle
> 2 inclinations of seat
> for the fact that here there are 2 linking from front and rear frame,
> and they affect the inclination of the seat, changing the trike from a
> city-trike to race-trike...
>
>
> I enclose some drafts hoping they'll help.
> * there are 2 square (behind the head and under the seat), it is
> supposed that they should be 2 silent block, in the middle of which
> the steering axis goes through;
> * the draft is not completed, anyway there is a rear frame and a front
> frame (the seat is part of front frame) and the couple of silent block
> are the (only) con
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