Subject:
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Re: Excavator Pics
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Newsgroups:
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lugnet.technic
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Date:
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Thu, 21 Feb 2002 15:22:16 GMT
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Viewed:
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4129 times
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"Rebecca Taylor" <arellcat@NOSPAMyahoo.com> wrote
>
> It's my first post to the group so by way of an introduction I suppose,
> there are a few pictures at
www.brickshelf.com/cgi-bin/gallery.cgi?m=techgrl .
The modifications to the JCB are very interesting, especially making the
boom offset.
> Jennifer, correct me if I'm wrong, but isn't a kinematic singularity a • point
> in the motion of a mechanism whereby the direction of the applied force is
> exactly opposed by the final positions of the indirectly connected
> components? In other words, you get to a point where everything lines up
> just right and the thing locks up. A bit like trying to run a • one-cylinder
> engine without inertia?
Well as it happens that, like William, my degree is also in computer
science, so not strictly speaking being an engineer your definition is far
more rigorous than anything I had in mind :-) What you describe is indeed
the case though; when the actuator driving the bucket linkage is fully
retracted, it moves past a point conceptually similar to top dead centre on
a piston where subsequent extension (in the real world) could move it either
clockwise or anticlockwise. If it goes the wrong way it will end up in a
locked configuration.
You can actually see it happening a *tiny* bit at the start of one of the
excavator videos, despite the fix; I hadn't noticed this until I had
finished editing the video, and by then I had had enough. The force of the
pneumatic actuator is enough to overcome it and shunt it back into the
correct configuration! The video is here; the effect is a slight "pop" at
the start of the bucket motion.
http://www.telepresence.strath.ac.uk/jen/lego/images/js70/movies/skip_short.
mpg
Jennifer
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Message is in Reply To:
 | | Re: Excavator Pics
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| (...) Hi all, It's my first post to the group so by way of an introduction I suppose, there are a few pictures at www.brickshelf.com/c...?m=techgrl . Jennifer, correct me if I'm wrong, but isn't a kinematic singularity a point in the motion of a (...) (23 years ago, 21-Feb-02, to lugnet.technic)
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