[python] Re: pivot quality

  • From: Jürgen Mages <jmages@xxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Tue, 17 Apr 2007 11:20:05 +0200

The long-term experience with rod ends as steering pivot
would be interesting. 500 or even 1000 km is not much. As far
as I know there are 5 pythons with rod ends, built by:

Tim (25hz)

Like Tim, I expect the rod end bearings to be a simple and
efficient pivot solution and I would give them a try in
my planned foldable.

Surprisingly to me, the cartridge bottom bracket of my P3
lasts much longer than I had expected. Mine now has 21.000 km
and shows no hint of play or wear yet. Considering that it was
already used for years as an upright BB, when I got it, that is
truly amazing.

In contrary to this, the cup and cone BB of my wife's P1 showed
plenty of play after 1000 km. Better do not use these.


On 12.04.2007 06:55, 25hz wrote:
For my first python, the BHP, I used sealed 12mm bearings very
similar to the ones Jurgen posted a picture of.  They worked fine,
were/are likely massive overkill and after 2000km+ they were as
smooth as when they were installed.  Hopefully they are still as
smooth for the brave soul who bought it :)

On the 2nd python of mine, the PC2, I used the "aircraft rods".
They're actually called (at least over here in North America) "rod
ends" or "Heim joints".  Anyway, they were not high quality, super
strong, or anything else.  They were just plain old farm grade, 1/2"
rod ends that were about $15 Cdn each that I bought at the local
hardware store.  I sued them because they were so much easier to
build for and I also wanted the pivot to be adjustable so I could
experiment with the pivot angle and find out what the optimum angle
was to make it easier to learn to ride. http://fleettrikes.com/python%202%20pivot%20final.jpg

There was no machining, all the steel used was stock dimensions and
the pivot bolt is a plain old 1/2" NC Grade 5 bolt with a Nyloc nut.
The plate they bolt to is nothing more than a 1/4" thick piece of
mild steel that is 1.5" wide and about 4.5" long.  I dabbed a little
3 In One oil on the rod ends every now and then for lubrication, just
in case, cranked the pivot bolt down good and tight, and that's it.
It steers smooth as silk, but not quite as freely as the sealed
bearings.  There was about 500km on it when a guy came running up,
asked a bunch of questions about it, and bought it on the spot.  In
less than 30 minutes he had learned to balance it and was riding
short distances on it. I weigh around 98 to 100 kg, and there is no hint of movement or play in those rod ends at all. They will likely
last as long as the bike, the selaed bearings or longer because there
is no real moving part to them like bearings.  Even if they do fail,
another $15 and about 5 minutes replaces them.  Keep in mind formula
1 race cars use 1/2" rod ends for their suspension and steering (of
course probably higher quality).  Racing go-carts that can go in
excess of 120kph only use 3/8" and 5/16" rod ends for their linkages
and steering.  In my opinion and experience so far, the rod ends work
very well, are cheaper than bearings, require much less custom
fabrication and adaptation.  If you want to use rod ends, get
inexpensive ones first.  If they end up failing on you, it won't be
catastrophic, you'll probably start to feel a little play first and
be able to see that there is a problem.  I think you will be fine
with them for quite a while and might not need to replace them at
all, and then you will have saved yourself a bunch of money.  Maybe
some of the other people who used rod ends on their pythons have
different experiences with them?


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