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

  • From: Steffen <big.skangster@xxxxxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Thu, 28 Jul 2011 17:17:21 +0200

May have a look at the foldable HP trikes. If you use the ability of a chain to twist thefolding thing is might easier as you think.



Am 28.07.2011 17:14, schrieb Frank Schmaus:
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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