thanks Steffen and Mirek, your feedback is highly appreciated! I also
started reading the threads on the email archive about using rod end
bearings, what I found so far sounds good.
1) Alright, I've got to space the two joints as far as possible, I will
make sure to do so.
2) Sorry, I don't get this. What exactly needs to be precisely adjusted
in which way? What do you mean with "precisely adjust the distance of
the threaded parts of the joints"? I thought it was one adavantage of
the rod end bearings that they are not so prone to misalignment, or is
this a different problem?
Best regards,
Matthias
On 29.12.18 13:14, mircosoft@xxxxxxxxxx wrote:
Hello Matthias,
Yes, it would work. Just two things to be aware of:
1) M10 bolt is actually just about 8 mm in diameter at the thread bottom.
Quick release cannot be tightened as securely as a regular nut, so I wouldn't
rely on friction between the ball and the flange it rests on to carry the
shear forces. Load on the joints would have to be small enough so as not to
shear the 8 mm rod off. But that's just a matter of spacing the joints
sufficiently far apart, as Steffen says. For comparison: I used 12 mm joints
about 100 mm apart with no strength problems at all (picture here:
http://nightrider.xf.cz/galerie/python_wip08.jpg ;).
2) The quick release suggests you plan to disassemble the bike pretty often.
That means you need to work around the necessity to precisely adjust the
distance of the threaded parts of the joints during each assembly (if
misadjusted, the joints drag so much that it becomes impossible to balance
the bike). Fix one joint to a flexible part of frame (something like the
short strut under the seat in Dirk's design)? Or to a hinged "wishbone"
secured by another quick release which you tighten after the first one? I
haven't tried this myself yet.
Regards
Mirek
______________________________________________________________
Od: "Steffen R" <big.skangster@xxxxxxxxx>============================================================
Komu: python@xxxxxxxxxxxxx
Datum: 28.12.2018 21:31
Předmět: [python] Re: Would this quick release heim joint work as pivot?
Hello Matthias,
where to start with? In mechanics lots of things work by comparing forces
an their levers. In dirks design you see the pivot bearings are quite far
away from each other. So the lever between these two is big, which reduces
the stress on each of them. If your beam coming from the back is only 50 mm
high and thereby the bearings have a lever of about 70 mm between, the M10
rod ends likely will fail or the quick release shears away.
I hope at least some of the terms are used correct. It would be easier to
tell you in german.
Cheers,
Steffen
Am Fr., 28. Dez. 2018, 21:15 hat Matthias B. Schönborn <mbs@xxxxxxxxxxx>
geschrieben:
Good evening,
I've been thinking a lot how to realize the bearing for the pivot and
have made the attached sketches (fortunately the STLs of the parts can
be downloaded). The quick release bolt (light-blue) is an M10 bolt [1]
and the rod-end bearing (red) is a bearing with 10 mm diameter hole [2].
The idea is that the rod-end bearing would be connected to the rear
frame and the green part is part of the front frame with a M10 thread
inside (or a M10 nut on the other side). The construction would be
mirrored like 10 cm lower so that two bearings are forming the pivot,
just like in the design by Dirk [3]. In the sketch the quick release
bolt is not fully fastened to show where the bolt is actually located.
What do you think, would this pivot work?
Best wishes and have a nice weekend,
Matthias
[1]
https://www.norelem.de/de/de/Produkte/Produkt%C3%BCbersicht/Flexibles-Normteilesystem/Spanneisen-Spannelemente/Exzenterspanner/Exzenterhebel-mit-Kunststoffgriff-mit-Innengewinde-und-Au%C3%9Fengewinde-Stahl-oder-Edelstahl.html
[2] https://www.igus.de/product/?artnr=KCRM-10%20MH
[3] http://dirkb.dnsalias.net/python2.html
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