[python] Re: report: pythoon first ride
- From: Ken Pendergrass <kenp794@xxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Mon, 12 Oct 2009 20:21:33 -0400
Hi Dirk and Dirk,
I had a very similar thought just shorten the wheel base. I think the
rear wheel between the passenger's legs is an elegant solution. It
seems you may have to mount a seat which could be removable to cary
only cargo. I like the idea of the cargo area extending back behind
the rear wheel. You could even make the rear of the cargo area
removable so that if you don't need a truck you don't have to ride
one. Best of all this would get your wheel base back to that of a
normal bike, where you know your pivot angle would work. However this
being your bike not mine you doubtless have our own ideas of how to
fix it.
best regards,
Ken
On Oct 12, 2009, at 5:11 AM, dirk@xxxxxxxxxx wrote:
Hi Dirk,
Great design!
I also think along the lines, that the self centering effect is
related to the torque as a driving force to bring the bike back
into the straight position.
Many dimensions, like mass of rear and front part, pivot angle,
distances to the wheels, weight of the driver (weight of the
drivers legs before the front wheel axis..), etc, have a major
impact on this, and not all of them are used by your program. (You
should be easily able to verify the correctness of your calculated
data by measuring pivot/ground distance in straight and defined
angular positions.)
Beyond that, you would have to consider, how the mass is
distributed - relative mass with respect to distance from pivot
(front & rear part). This, and the change in seat height/turning
angle, make up for the correcting torque. The more mass you lift
and the higher, the more correcting torque you get.
However, when building bigger, heavier bikes, increasing the pivot
angle, to have less torque probably gives you more wheel flop. It
probably turnes out that if the overall mass of the bike rises, you
need more force on the pedals to work against that. You could
probably fine tune a little, but what happens when you ride it with
and without passenger?
I wonder, if the rear wheel would sit betweeen the passengers legs,
far closer to the pivot, how the bike would handle. In this
configuration, the mass of the "optional load" would sit around the
rear axis, somewhat balancing itself around it, and not changing
the effect on the pivot that much. At the same time, the wheelbase
is greatly reduce, generally givin the bike a more agily feeling.
Also, there is the inverse pendulum effect as seen on any bike. If
you tip over to the left, how much do you need to steer/drive
towards the left side, in order to overcome this and start tipping
to the right? The longer the wheelbase, the more steering it takes
to get back to the other side. The heavier the bike is, the more
pushing force you need to put into the pedals, to work against the
mass of the bike and its load.
It would be great, to have a program, that would caculate/simulate
all of this...maybe we could contact some university research folk :-)
greetings,
DirkS
> The bad news is that the bike steers like a truck. Before I
started the
> project I actually made a graph comparing the pythoon, the baby
python
> and the p3 and I didn't see anything unusual. I recalculated and
put it
> on picasa:
>
> http://picasaweb.google.com/dirk.bonne/
Pythoon#5391423541426608210
>
> It shows the change in seat height when turning the front part. The
> pythoon has a stronger self centering then baby python, but still
less
> then the P3 of Jürgen. But in practice the self centering feels very
> strong, stronger then I remember from trying a 26" python
(birdcage of
> Serge). Either my program to calculate the curves is wrong (quite
> possible), or it has to do difference with weight distribution
caused by
> the long wheelbase. On this bike there is more weight on the
front wheel
> then on any other python. In any case this shows that the graphs
are not
> useful at all. What is needed is a graph depicting the needed
torque to
> sustain a turn.
>
> I am considering my options. I don't like the idea of putting a wide
> steer on the bike to help with turning (the current steer is very
> narrow). I think I am going to increase the pivot angle. It is now
> already on 70degrees - I could try 80degrees. This is a lot of work
> because I have to re-braze on both the rear and the front. But on
the
> other hand it would be interesting to see what such a high pivot
angle
> has as an effect. I calculated the graphs:
>
> http://picasaweb.google.com/dirk.bonne/
Pythoon#5391428883434182962
>
> The graphs show that the self centering (in seat height change)
should
> be smaller even then then baby python. In term of torque, I do
not know.
>
> Dirk
>
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