[python] Re: spring leaf as pivot
- From: Pierre-Philippe Coupard <pcoupard@xxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Fri, 23 Mar 2007 18:01:07 +0100
Hi Jürgen,
Jürgen Mages wrote:
Do you mean steel as the leaf material? Any pictures of these leaves?
What dimensions and weight would these leaves have for our purpose?
Yes. I usually work with CK-75 spring steel that, with the proper
quenching and tempering, is really quite resilient, elastic and
fatigue-proof.
Assuming a single, say 10cm-wide leaf with a minimum work length of 4cm
(that is, the length of material where the steel is free to bend), on
top of my head, I'd say a 2.5 or 3mm-thick leaf would be resilient
enough to avoid crumpling, and soft enough to allow a good range of
motion without too much effort. If the leaf is made thicker, then it'd
have to be narrower to prevent it from being unacceptably strong. Bear
in mind that I basically pull those number out of thin air: these are
the dimensions I would be inclined to give a spring of this sort if I
were to make one. It would have to be tested for response,
fatiguability, range of motion, brittleness and whatnot, but it's
nothing a half-day of work can't fix.
... would have an angular range in the order or +-15 degrees on
either side, perhaps more.
That should do for most riding situations, but does not allow really
tight turnings.
Indeed, but I was under the impression that a Python isn't too agile as
far as cornering is concerned: am I wrong? can someone give a realistic
angular measurement when cornering at walking speed? What's more, with
my current USS recumbent, I doubt that I get much more than +- 20
degrees, and I can corner just fine with experience.
Unaided, the springs alone couldn't fight torsional efforts very well
when turning, so perhaps a pair of small guiding bearings or bushings
could be added, but at least the springs would bear the entire load
of the rider, which the bearings wouldn't have to withstand.
How to arrange these guidings?
Well, think of the arrangement as what you have now on a regular python
(i.e. a top and bottom bearing holding two large U-shaped brackets with
a boom welded to each), with the spring leaf bolted inside each boom at
the center, and the working section of the leaf going across the gap
between the brackets. Only the bearings wouldn't need to be so beefy
because they would simply prevent the front wheel twisting with respect
to the rear wheel, the load-bearing being taken care of by the leaf.
Depending on the size of the rear and front boom (which would have to be
hollow sections of course), the leaf would be more or less wide and
thick to give the proper response. Do I make sense?
In fact, if one has a Python with hollow booms, all it would take would
be to bore the brackets to have access to the inside of the booms, and
install the leaf with bolts and centering spacers.
... and perhaps an additional static turning effort wouldn't be
desirable ...
The leverarm of the legs is quite large. I would give it a try.
I can see if I might find some time to forge a leaf and send it to you
if you want to give it a shot. Not that I have much free time these
days, but I can try :)
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