[python] Re: your Jetrike

Mark Schaaf wrote:

Hello Henry,
I have build my own three wheeled Python, lean steering, but no tilting mechanism. 
In different to yours, i have used the FlevoTrike lean steering.

There is one big problem i have while riding the Trike:
while breaking by driving curves, also in walking speed, the front frame tips over to the outer site of the curve. I think the positive Trail of the Python is here responsible for it; in combination with only one Breake at the Front.
Esko Meriluoto who built the Hipparion trike, built a prototype first to test out the effect of different variables on the stability and comfort of the ride 
http://personal.eunet.fi/pp/davinci/osa4eng.html
His trike has a python style drive train (or the Python has a Hipparion style drive train -- depending on how you look at it ;-) ) and he recommends a wheelbase of between 900 and 1200, with 1050 being about optimal. Yours looks like it is quite a bit longer.
However, re-reading 25mhz account of his PC2 riding test, http://www.freelists.org/archives/python/10-2005/msg00017.html he concluded that 1200+ was preferred. So maybe this is not the biggest issue. 

What is your seat height and pivot angle?
At the time, I re-build the rear part of the Frame; I treat him two drumbreakes at the rear frame and 30cm less wheelbase. In this way, i would lean the wheels 5° and increase the track width up arround 85cm.
My track is really quite narrow, and on the other trike designs I have done http://jetrike.com/plans.html that don't lean, the track is 90cm - just like the Greenspeed GTR.
Once again this was actually forced on me by the geometry. A 585mm with the 360mm swing arm length was kind of a sweet spot for the 20" rims. So that was what I went with. Wide enough that the wheels won't hit my shoulders, but narrow for a trike. It will only work because the thing tilts.
Your geometry looks as though it is essentially pivoting around the front contact patch like a normal bike, with an elastomer to dampen it a bit. This would lead me to suspect that it would be important for your design to work well as a 'normal' bike does rather than as a trike. So the long wheelbase would be a problem, as others have noted, a long wheel base it less twitchy if you can get it balanced, but harder to get started on. 
Do you mean, that it´s better by your´s?
I don't know yet because it is still being built it. But I will let you (and everyone) know as soon as its done and I get a chance to ride it.
I am optimistic though, because I really liked the feel of riding my first prototype, despite all its problems, and I have a sense from that experience of what to expect from this one.
The only way to describe is to say that its was like having a gentle hand holding you steady as you slowed down to a stop, but while you were riding it felt like a normal bike -- as long as you didn't lean too sharply because the first prototype had a penchant for wheel flop. It was that ride experience that has compelled me to continue to try and perfect this design. 
And one thing i think, there you would have a problem:
Do you want to transport any baggage?
You can´t put hardly anything on the middle Part of the frame, cause it changes the driving characteristics enormous.
This is an interesting observation, and I will keep it in mind. From what I understand about the Python, the weight needs to push on the pivot, in your design the weight of the load in the back is pushing on the rear end, and in that case, I would expect that the negative caster of the Python front end could be a big disadvantage.
If you are looking for a proven FWD trike design that will haul stuff about, there is a company in the US called Organic Engines http://organicengines.com/ that has a trike they call the SUV, I have attached some photos. It seems to have no trouble hauling big loads. 

-h

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