[python] Re: Jetstream

  • From: Henry Thomas <whpthomas@xxxxxxxxx>
  • To: Ghislain Pillet <gh.pillet@xxxxxxxxxx>, Python List <python@xxxxxxxxxxxxx>
  • Date: Wed, 28 Feb 2007 20:45:06 +1000

Ghislain Pillet wrote:
Hello Henry,
Congratulations for yours extensive works and the way you're unfolding them to us !

Its not quite there yet, but getting closer every weekend :-)

Looking at your JetStream design, as a python rider I'm puzzled about the amount of negative trail induced by the distance between the pivot and the fwd wheel ; the recommendation on the list being to try to reduce it to the minimum.

Well I guess I based it on the specs for 25hz PC2 which has a 10" -trail, and his riding report http://www.freelists.org/archives/python/10-2005/msg00017.html, put now that you bring it up, he does have a much larger front wheel, so I guess this is something that I missed when reading through the forum archives. Reading Dirk's notes I guess I thought bigger negative tail was better, so I thought I would ask the group: Is the smallest negative trail the best?

About JetTrike, may I suggest you to not bury too quickly your speculoos drive version, it should remind you what stability means.

I am actually really struggling with this. I think the 100mm positive trail may not be enough. So I have been doing some research into trail, and plotting the results for comparison. I looked up the table in Bicycle Science and they seem to place it somewhere between 1/2 or 1/3 across from zero to the intersection with the axle (see attached). Using these ratios, it would appear that the 100mm +trail with 57.5 pivot angle of the Speculoos is too far for the 504 wheel radius. Maybe 55mm or less would be better.

Does anyone have any experience or suggestions.

As we, Python riders, know that going downill on Python, at speed, (for me it is over 40km/h), is adventuring in unstable world where Python can get definitely very lunatic, even on empty road with nice surface, with no beam wind at all, and a totally relaxed mood !

I haven't given up on the Speculoos version just yet, but I am pulling my hair out in exasperation. The trail is all wrong, maybe too much, it flops from side to side and upsets the rear balance.

By contrast, it would appear that the python self-correcting would center and thus balance the trike with much less hassle, but maybe the grass just seems a bit greener over in that pasture right now.

-h

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