[python] Re: Lean Steer Python/Hipparion Trike

  • From: George Durbridge <gdurbrid@xxxxxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Mon, 08 Jan 2007 07:57:56 +1100

On Fri, 2007-01-05 at 21:13 +1000, Henry Thomas wrote:

[I have snipped quite a lot.]

> It is very exacting and hard to get your head around at times. 

Agreed - I am still trying to think out a lot of it.

> Have you seen Bram Smit's http://www.fastfwd.nl/eng/tiltingtrike.php 
> which has a similar tilting mechanism to mine, but without the self 
> centering effect. It is actually based on a Spanish builder, Carlos 
> Calleja http://www.moebius.es/ccalleja/ which in turn is based on Curtis 
> Princes 1987 Patent. The cover page for which I have uploaded to my site 
> http://jetrike.com/US4887829.pdf for those who are interested.

Thanks for those references.  The previous trikes all used a rocker arm
moving in a vertical plane about a horizontal pivot, but your current
design has the rocker arm moving in a horizontal plane about a vertical
pivot: did you make that change to achieve self-centring, or for
construction reasons?  Either way, had you thought of substituting a
stiff leaf spring for the rigid rocker arm, to allow some suspension
movement, other than pure roll?

> I have attached two screen captures of the geometry simulation. I assume 
> that the CoG is @500mm above the ground and the seat height is 240mm. The 
> first image shows the trike when it is centered. I have added 
> annotations and circled the two driven dimensions that reflect these 
> values. In the second image, the trike is leaning 25 degrees and the CoG 
> is almost unchanged, yet the seat height has raised 17.8mm.

> I have drawn the lines you describe into the geometry for reference. The 
> CoG does move outwards but only marginally, and simply applying a bit of 
> extra body lean will bring you back to true center. Yet at the same time 
> leaning back just a bit the other way will cause the trike to move back 
> to center. On the old Prototype A, it had the effect of allowing you to 
> stop without taking your feet off the pedals, yet once you were riding, 
> it was like a normal recumbent, you would lean into corners etc...
> 
> Whether the new design actually works as expected is anyone's guess, we 
> will just have to wait and see.

By leaning the wheels, we are loading them with cornering forces they
are designed to resist, unlike trikes cornering with upright wheels.
And, unlike so many leaning trikes, you do it with all three wheels.
While that has to be a good thing, it really affects how long the wheels
will last, rather than the cornering forces we can generate in the
meantime.

However, if the CoG neither falls nor moves inward when the trike leans,
have we improved the trike's cornering power at all?  The cornering
force it can generate (if the tyres and everything else are up to it) is
limited by the location of the CoG: the maximum cornering force in g is
equal to the tangent of the angle to the horizontal of the line from the
outer contact patch to the CoG.  Unless we can reduce that angle, can we
improve the cornering?

Of course, all of this assumes you are strapped to the seat, not leaning
further into the corner than the seat: maybe the real point is that the
leaning seat will facilitate your moving the CoG into the corner,
without hindering you straightening up again.

-- 
George Durbridge
+61 3 9481 3500
+61 409 413 945

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