[python] Re: Lean Steer Python/Hipparion Trike

  • From: dirk.bonne@xxxxxxx
  • To: python@xxxxxxxxxxxxx
  • Date: Thu, 04 Jan 2007 10:36:53 +0100

Hi Henry,

Following things I noticed (I could be mistaken!)

The forces on the pads of the swing arm (item 39) and thus the rod links are very high.  There is a lever between swing arm and pad. And the force on the pad will be about 360 / 60 = 6 times as high as the force on the wheel. Just to keep the swing arms in place the rod links will have to work hard.

Even if this is not a problem strength wise, it could be a problem because there can occur low frequency oscilations (is it called shimmer? because of the sloppy feel), and may the effect on speed stability.

Did you consider using an aluminium seat, you can save weight there. The seat is now 2.6 kgs. A alu seat is about 1kg.

otherwise a very nice design! :-)
best regards,

Henry Thomas wrote:
Hi Pythonauts,

This is my first opportunity I hope to contribute something meaningful to this great forum.

I got the recumbent bike building bug about a year ago, but living on a sugar cane farm (near Bundaberg in Queensland - Australia) I found the off road handling around the farm somewhat lacking. I looked into trikes, but for stability they need to be very low, and tufts of grass here will rip a derailleur clean of a bike. So I started investigating ways to raise the center of gravity of a trike by allowing it to lean independently of the steering.

My first prototype (Prototype-A.jpg attached) wasn't ultimately successful, aside from being heavy, the BB was too high and it suffered
from wheel flop on sharp corners causing uncontrollable over steer. So I
set off on a journey across the Internet to learn all I could about bicycle geometry and consequently came across many of this forums contributors sites like Jürgen's, Dirk's and 25mhz's. It got me thinking that their must be a way to design a trike that could lean, but like the python also have static stability that was self centering.

So I played around with many designs and simulated their geometry (Tilt-Geometry.gif attached). Finally I have settled on one (Jetrike-3D-View.gif attached), which I plan to start building next week. It raises the seat height by 30-40mm on a 30 degree tilt, which will push it back to neutral, yet be easily over compensated by leaning to either side.

I have drafted detailed plans with a cut list which anyone who is interested can download form http://jetrike.com/Jetrike-Plans.pdf

[In the design an M8 tie rod links the rocker arm to the swing arms, but these are not shown.]

I plan to take photo's and maybe even some video's of the trikes construction and post them to the site as I go.

The specs from the design table are as follows:

Pivot-Angle 55
Wheelbase 1230
Trail 250
FW-Radius 254
FW-Axle 125 (Sachs)
RW-Radius 254
RW-Axle 100
BB-Height 400
BB-FWA 380
BB-BOS 950 (Back of Seat)
Seat-Width 450
Seat-Height 240
Ground Clearance 105

I would be grateful if some of you could review my design and see if there are any glaring mistakes.

For the materials I plan to use high strength 316 stainless steel, mainly because it is the only steel I can get in a 40 x 20 profile. I could get 40 x 10 in mild steel, but I would have to purchase a ton, which is a little outside my budget. We have a good machine shop on the farm so fabrication and welding shouldn't be an issue.

I look forward to reading your comments.


Henry Thomas.


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