[python] Re: Python Plans

  • From: Henry Thomas <whpthomas@xxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Thu, 15 Feb 2007 21:55:23 +1000

Hi Mark,

Please don't feel responsible for the re-design, it was my decision alone...

Mark Schaaf wrote:
Hello Henry,

Am Tue, 13 Feb 2007 16:23:47 +0100 schrieb Henry Thomas <whpthomas@xxxxxxxxx>:

After Mark Schaaf voiced the concerns he had about the using the python
drive train on a tilting trike, Jetrike has been somewhat redesigned.

It was not my intention to let you build a Flevo - mini - Racer.

The new front was based on the Speculoos, but if you have a link for a Flevo - mini - Racer, I would be keen to see one...
The problems I have are substantiatet a) by the long wheelbase, b) missing weight of the big case, that would push the rear end to ground and c) missing rear breakes who hold the stability of the pendulous vehicle.

Never the less, as attracted I am to the Python drive train, my goal is to elucidate this tilting trikes self-centering effect. I didn't want to be in a situation where if it didn't work, I wasn't sure what the cause was. Once I perfect the tilting I will revisit the drive train.

BTW: how high was your bottom bracket from the ground. Having your BB to high would also cause wheel flop.
After re-reading Jürgen´s "Frame Geometry"-Page, I think, the Wheel Flop is also established in this:

"The optimal pivot angle is exactly the one where the weight of the whole front part (including the riders legs) is in equilibrium with the rest of the bike (including the rest of the rider). This is different with every bike and rider. To be more exact: It is the angle where the wheel flop effect is nullified by the seat rising effect."

I think the Pivot Angle at my trike is too low.

I thought Jukka's comment relating trail and seat hight, was also interesting. This would have been a issue for the Rev B design.
This has left me with the remnants of the Python drive train I had
already started constructing, so rather than let it go to waste, I have
designed a python frame to use it (Attached Photo).

Ok, nice, but i please you to build the old Jetrike first.
the new design of the MKII rear frame looks sporty, but in the old design you have a chance to append a carrier to Item 21 (rocker arm).

I actually made that change to the original Jetrike (now Rev C - Photo Attached) because I found it saved weight. The Rev C is 2 Kg lighter than Rev B, just from squeezing the frame in.

How would you couple the rocker arm with the swing arms?
Why 90° at the rocker arm, not 70° as by the Jetrike, rev. B?

I have a better simulation now. The first one didn't isolate the two planes properly, the new one does, and so is more accurate. I have begun rewriting my geometry page http://jetrike.com/geometry.html with some on the new info I have learned. I will finish it when I can confirm it with the finished trike.
The plans on my web site http://jetrike.com/plans.html are only a
preview, I haven't finished drafting them up.

Which Program do you use to create your drawings?

Solidworks -- it took a while to learn, but now I seem to have the hang of it. The best things about it are:

- it is parameter based, so you can change your mind, alter a dimension or angle, and it will update your drawing, - it supports weldments, so you can have all your structural member profiles, draw your frame with lines, and then select the profiles you want to apply to those lines, - it does the whole cut list thing, so you can find out how much metal you will actually need.

It has a 20" front and a
20" back, elastomer rear shock, M12 rod ends for the pivot and weighs in
at 6kg minus the seat. The specs are 1100 wheelbase, 60° pivot, 270mm
negative tail, 240mm seat height, 380mm BB height, 410mm BB-FWA.

The thing I haven't had a response about is what the best sear angle
should be, I set it at 40° for now... any ideas?

I used 20° - 35°.

Thanks Mark (20° - 35°) and Jürgen (30°), I wasn't sure if it was too low, whether it would make the Python too hard to balance, apparently not. On the MkII I set the seat angle to 21°, but for the Python 30° seems a good choice.


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