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

  • From: Gerald <bepb@xxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Mon, 01 Aug 2011 22:57:43 +0200

Hi,
I made good experience with 48 degree pivot angle.

Even more than with the two wheel configuration, the front brake is the most useful brake.
Much more powerful because with the trike you don't risk falling if he front wheel slips.

The rear brakes are not only much less effective, but also lead to unusual reactions of the bike if not applied symmetrical.

Normally, one would expect that the bike will tend to the right if the right rear break is applied, but it is different with my python trike. I use the break on the right rear wheel, the  impulse of the python trike is to go to the left. And the other way around.
Actually the rear part turns to the right, but in this pushing the pivot to the right, which makes the front part of the bike turn left. This seem to get more pronounced if the track is more wide.

Somehow having separate breaks for the left and right rear wheel - as I have on the trike - does not make much sense. And it is obviously only possible if you run a coaster brake on the front wheel.

I include, an obviously outdated, picture of my python trike from last winter, showing the narrow track version:



Gerald






On 1.8.11 15:12 , Patrick van Gompel wrote:
Ah, thanks for your explanation! Yes, having just rear brakes on a trike is not a good idea. A front brake will make all the difference.

I can't help you with the geometries, as I haven't tried (many) different setups.
My 'magic moment' was there when I temporarily attached two wheelchair wheels on my Python. Although the construction was weak and the track was too small, it did give me a sudden insight of how the Python was steered. On this trike the cycling was very easy. It appeared to me that steering wasn't the actual problem, but keeping balance was. That might sound like an open door, but when you steer on a Python your centre of gravity is actually shifted to the outside of the corner. That means that you have to lean more than on a conventional bike. I still have problems with that when I make sudden sharp corners.

Thanks,
Patrick


> Date: Sun, 31 Jul 2011 21:34:39 +0100
> To: python@xxxxxxxxxxxxx
> From: Rhisiart@xxxxxxxxxxxxxx
> Subject: [python] Re: AW: Re: Questions about Python-Trike geometry (project similar to Howard Stevens foldable Python trike)
>
> Hi Patrick,
>
> Well since I wrote, I've put the trike back-end back on my Python,
> just to have another think about it.
>
> It rides really well, and I have literally instant control; had it
> from the very first try out in fact, and went out on the road in
> traffic that first day.
>
> So what I'm doing now is putting a brake on the front wheel (I hadn't
> done that before) and I'm fixing a method to pull on both back brakes
> by a single hand lever. I may also try two brakes on the front wheel,
> operated by both hands, if the back brakes are just hopeless. I'll
> report results.
>
> I must say too that being able to bank all of the trike, except the
> rear-wheels frame, into bends, just like on the bike, is a real plus.
> (Erik Wannee's training back-end photo shows you exactly the design
> principle) It feels just like riding the bike, except that you have
> those brawny handle-bars, fixed to the back end, to push down/pull up
> on. I find that I do both at once when I feel myself going over. Just
> like pushing frantically against the ground with your stretched
> fingertips, but so powerful by comparison that you can stop all
> fall-overs dead before they get going.
>
> And I've already noticed, even on my fairly short total time on the
> banking trike that there is indeed a training effect for staying
> balanced, so that you begin to be able to lift your hands slightly
> off the bars for a few metres at a time. I suspect that with plenty
> of use of the trike I should be able to ride the bike with
> confidence, before long. You can see from the videos that there's a
> knack; that first-time riders suddenly get it. That's the magic
> moment that I'm shooting for!
>
> It does occur to me, though, that since we've all made our Pythons
> ourselves, to no standard design, might it be that subtle, quite
> small variations in bike geometry make all the difference between an
> easy, sweet-riding bike where you get the knack easily and within
> minutes, and a really tough dog? I seem to have made a tough dog.
> Anyone got any ideas about that, based on experience with several
> slightly differing geometries?
>
> Hwyl, Rh
>
> >Are you saying that you abandoned a beautifull trike design because
> >of rear wheel skiding when braking? I want to build a python trike
> >myself, so I wonder why you would worry about it. I mean, if just
> >the front wheel is enough for braking, then why bother about the
> >rear? My two wheel Python doesn't even have a rear brake. Or is it a
> >safety concern? Though, you could always fit multiple brakes on just
> >the front.
> >Please let me know you thoughts,
> >Patrick
> >
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