Subject:
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Re: Pneumatic Arm
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Newsgroups:
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lugnet.technic
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Date:
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Sat, 17 Jul 2004 14:56:18 GMT
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Viewed:
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3590 times
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In lugnet.announce.moc, Philippe Hurbain wrote:
> It was featured on my site for a few days, but I forgot to announce it here:
> a [<http://philohome.com/pneumarm/pneumarm.htm pneumatic arm>]. Loosely
> modelled after human arm, it has 6 pneumatically actuated joints.
>
> <http://philohome.com/pneumarm/pneumarm.htm
> <http://philohome.com/pneumarm/pneumarm1-v.jpg>>
>
> You will find <http://philohome.com/pneumarm/pneumarm.htm there> detail
> images, movies...
>
> Note: I first tried to build the support tower using only studless beams, but
> the result was not stiff enough, and I had to rebuilt it using the more
> traditional beams-and-plates method. Any tips and tricks to build a similar
> structure with studless beams?
Philo,
Congratulations on a beautiful creation! I like it a lot. I appreciate all
the thought that went into the design.
I'm also envious of all your clear pneumatic hose ;^)
Studless beams work well in some applications, and not well in others. As I'm
sure you know, I'm a studless beam advocate, but I'm also a studded beam
advocate. For compact, lightweight structures, studless beams have an advantage
over studded beams. For structures where you need to worry about static
stresses and strains (which your arm has especially when fully extended),
studded beams abnd plates are superior.
Studless beams have much more flexion than studded beams. To overcome the
flexion you need to use cross bracing.
I was a coach for an Oddessy of the Mind team, and our specialy was to build
weight bearing balsa wood structures. We were blessed with a very gifted
builder. We typically had to build a structure that weighed 14 grams (balsa
wood and glue). If I remember correctly, the structures regularly held in the
range of 700-800 pounds.
How it do it? Given that we knew that the structure had to be strong
vertically, almost *all* the balsa was in four large legs forming a square. A
small, but important part of the balsa was invested in horizontal and diagonal
beams providing cross bracing. The lesser successful structures' failure mode
was due to twist (allowed by too little cross bracing). The more successful
structure failure modes were where the large legs themselves shattered due to
compression.
Studded bricks and plates hold up better against twisting and compression.
You can build a replacement structure using studless beams, but you need to
understand where the stresses and strains are in the structure. I'd guess that
your beautiful arm's failure mode for studless, would be in the face where the
arm is attached. This face of the structure would experience compression, while
the opposite side would experience expansion.
Did the connections between the beams fail, or did the beams fail themselved?
Or was it that the structure twisted?
The structure below shows your typical cross bracing arrangement. You will
want cross bracing in all three dimensions.
_____
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> Enjoy,
I certainly did. Thanks!
Kevin
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Message has 1 Reply:
 | | Re: Pneumatic Arm
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| Hi Kevin, (...) Thanks ;o) (...) Here is their source: (URL) (...) I'm convinced too now... but maybe someone has found (will find) a way to build decent studless braced structures? (...) I had not much trouble in one direction, but couln't find (...) (20 years ago, 17-Jul-04, to lugnet.technic)
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Message is in Reply To:
| | Pneumatic Arm
|
| It was featured on my site for a few days, but I forgot to announce it here: a (URL) pneumatic arm>. Loosely modelled after human arm, it has 6 pneumatically actuated joints. (URL) You will find (URL) there> detail images, movies... Note: I first (...) (20 years ago, 16-Jul-04, to lugnet.announce.moc, lugnet.technic, FTX) !!
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