[python] Re: AW: 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 17:14:06 +0200

That ist true yes. But on the other hand I realy like the python-foldable thing, that I postet in the first mail. The whole python idea is very cool for a foldable construction, as there is no chain going along the bike. But maybe I will give a rear wheel drive alternative a good thought. Maybe it can also be build foldable when using a second chain with a chain wheel exactly at the folding-axis.


But on the other side I remember a video of an eastern european guy who built a python-lorry, carriying his whole family uphill on some sandy tracks. I think I have to search for that video once more...

Am 28.07.2011 17:05, schrieb Gerald:
Hi Frank,
Obviously You can ride a trike uphill as slow as you like. But, at least in my expirience, going uphill with a front wheel drive trike - or bicicle at that - your limit might not be your power to pedal, but traction. If your front wheel slips excessivly, you will have a poor and exhausting ride going uphill with a trike, even more so with the bike.

The issue is that if you pedal uphill, you dynamicaly deload the front wheel, and load the rear wheel. Good for rear wheel drive bike.












-----Ursprüngliche Nachricht-----

    *Von: *Frank Schmaus <frank.schmaus@xxxxxx>*
    An: *python@xxxxxxxxxxxxx*
    Gesendet: *Do., 28. Jul 2011, 13:53:34 GMT+00:00*
    Betreff: *[python] Re: AW: Re: Questions about Python-Trike geometry
    (project similar to Howard Stevens foldable Python trike)

    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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