[python] Re: AW: Re: Questions about Python-Trike geometry (project similar to Howard Stevens foldable Python trike)

  • From: Frank Schmaus <frank.schmaus@xxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Thu, 28 Jul 2011 15:53:34 +0200

Thanks for the input. I anyhow have to place the backwheels far behind, to be able to roll the collapsed box around and still have enough room for my laguage. But somehow I thought the wheelbase should not be too wide as it will increase the danger of tilting to the side, the more lengthy the triangle of the wheel becomes.


Traction is an important issue for me, as I have one specific track in mind, that I will use quite often, that is a steep mountain road. That's also why I prefer a trike with 20 inch wheels instead of a small foldable bike with a trailer. The trike can be run as slow as you like, if the gear is choosen well.

Am 28.07.2011 15:07, schrieb Gerald:
Hi,
based on my own expirience with a Python trike, I suggest to aim for more weight on the front wheel, if possibe ~50% on the front wheel, ~25% on the rear wheel. Otherwise going uphill will give problems with traction. This can be archieved by place the rear axle/wheels far enough back, behind the seat about as far as for a two wheel python.
For the pivot angel, I made good expirience with 50 degree.


Gerald






-----Ursprüngliche Nachricht-----

    *Von: *"gdurbrid@xxxxxxxxxxxxxx" <gdurbrid@xxxxxxxxxxxxxx>*
    An: *python@xxxxxxxxxxxxx*
    Cc: *Frank Schmaus <frank.schmaus@xxxxxx>*
    Gesendet: *Do., 28. Jul 2011, 11:19:25 GMT+00:00*
    Betreff: *[python] Re: Questions about Python-Trike geometry (project
    similar to Howard Stevens foldable Python trike)

    Frank,

    I assume you propose to build a delta trike (two rear wheels), as a Python
    tadpole (two front wheels) is a challenging thought. There are several
    trikes in Jurgen's hall of fame, but the best documented front-wheel drive
    centre-steer delta trike I know of is the Hipparion (Google for it, but
    avoid the horses). It isn't strictly a Python, because Esko Meriluoto
    built it before Jurgen built the first Python. But it's very much the same
    sort of design, and is now in its fourth iteration.

    Most successful trikes have a wheelbase of about 1 metre, and a track of
    60 - 80 cm. Tadpoles generally have about 1/3 of the weight on each wheel.
    Rear-wheel drive deltas such as the Anura and Kettwiesel often have more
    than 1/3 on each rear wheel. These are not golden rules, just experiences.
    Your front wheel must provide traction, steering and braking, so don't
    unload it too much.

    On any trike, the wider the track, the less the trike will tend to tip
    over sideways when cornering. On a Python trike, your weight must be close
    behind the front wheel, so the wheelbase should be short. Draw a triangle
    on the ground, connecting the points where your wheels touch the ground.
    Mark a point under your centre of gravity: the longer the line from one
    side of the triangle to the other through this point, the stabler the
    trike will be. How wide a trike can be made usually depends on space in
    the house, door widths and so on. If the seat is low enough, a track of 66
    cm is satisfactory on tadpole trikes. I would not use less on a delta
    trike, unless you mean to ride very slowly and carefully, because delta
    trikes are very tippy: see the Hipparion site.

    One golden rule is that the lower the centre of gravity, the better the
    trike will corner and brake. This really means your own centre of gravity:
    riders weigh a lot more than trikes. Trikes are completely different from
    bikes as regards cornering (though not braking). You should have the seat
    as close to the ground as you can arrange: 15 cm is high, and 10 cm is
    better, unless you will be riding off road, or over gutters and rocks. The
    low seat does make it harder to get off, but you can put a loop of webbing
    around part of the front frame and use it to lift yourself up.

    Python trikes seems generally to work best with lower pivot angles than
    Python bikes. I don't know why, but it seems that 57 - 60 degrees has
    generally been found preferable. Since bikes lean when they corner, but
    (most) trikes do not, it does make sense that the inverse pendulum should
    work differently for bikes and for trikes. Perhaps the lean of the bike
    increases the effect, so that a steeper pivot angle is satisfactory, but a
    trike depends entirely on the inverse pendulum, so needs more of that
    effect i.e. a shallower angle. Dirk may have a view on this.

    Best of luck,

    George

    ---- Frank Schmaus wrote:
    > As I got quick reply and really good help last time, I try it again:
    >
    > I'm planning to build some foldable python trike like this one:
    > http://en.openbike.org/wiki/Python_Trikes#Howard_Stevens_Mk2.2C_Australia
    > But with larger laguage capacity. On the python page
    > (http://www.python-lowracer.de/geometry.html) there's a lot of good
    input on
    > geomtry questions concerning pythons. But how is all that with a python
    trike? I
    > gues the requirements and the conditions are quite different. Is there any
    > written summary about trail and angle for a trike? I would like to
    follow well
    > approved standards instead of having to build several trikes, just
    because the
    > first ones are ugly to stear.
    >
    > Any other parameters e.g. wheelbase, minimum ground clearance, track
    width...
    > are also still quite a myth to me, but those are more bound to other
    > requirements of the vehicle, whereas angle and trail are free of choice to
    > assure the best performance possible.
    >
    > Hope to get a lot of good suggestions,
    > Cheers from Germany,
    > Frank
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