[python] Re: Lean Steer Python/Hipparion Trike

  • From: Henry Thomas <whpthomas@xxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Fri, 05 Jan 2007 10:26:18 +1000

dirk.bonne@xxxxxxx wrote:


Henry Thomas wrote:

It is my theory that the reason why we hear reports of non tilting
python trikes experiencing shimmy at higher speeds is a function of
the static forces on the bike caused by road camber. I imagine that on
a perfectly flat road there wouldn't be a problem, but on a normal
road shoulder the trike is on a slight lean, so the weight of the
rider is always forcing the steering to turn up towards the road
center. At higher speeds this would be the likely cause of these
oscillations. My expectation is that my trike design will eliminate
this shimmy, because the rider and steering forces will remain
vertical and thus neutral to the road.

Yes, you are right. The oscilation should be vertical and should not
affect the steering. Very nice!
Yes, at this point I would stress the word SHOULD in that sentence. I have simulated it, made models in Meccano, but at the end of the day, until I build and ride it, this is all conjecture.
For those of you who may be having trouble visualizing how the rear end works, I have attached another photo of Prototype-A (which works in a very different way to the new design) which shows how the tilting action works. In Prototype-A the steering and leaning were coupled, and I tried to calculate an optimum lean ratio based on the average cruising speed. I have some tables here http://jetrike.com/banking which I calculated and used for this design. But ultimately I now believe that one must decouple the tilting from the steering.
Dirk, I must confess that it was after reading about your baby python and looking over your "self centering" data that I got the idea of having the tilt geometry center the rider. I do not have a mathematical model for it like you, instead I simulated it using CAD software (easier for me).
I have a CAD design for a real python, with my drive train, and using the data recommended by 25mhz's field tests. I will post once I have a chance to draft it up -- but that will have to wait until I finish building this one.
I am a bit nervous riding the real thing around here. Drivers will give you a wide birth on a trike, but not on a regular bike. We have sugar can haul outs and semi's on the road most of the year during the sugar cane harvest. On a bike compared to these things you feel like a gnat. 

Thanks for your kind words

Henry.

JPEG image

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