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I wanted to try a big pneumatic construction
(my pneumatic parts collection is at last large enough) I settled
on an arm, loosely modelled after the human one. Here is a detailed
description...
The
arm
![](handopen-v.jpg) ![](handclose-v.jpg)
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The hand has three fingers, a single piston is
used to open and close it. |
![](handcloseobj-v.jpg)
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The shape of the hand adapts itself to the object
grabbed. Chrismaker told me about this page
that describes the trick, he also used it in his
outstanding robotic
hand |
![](wristup-v.jpg) ![](wristdown-v.jpg)
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The wrist can flex... |
![](wristrot1-v.jpg) ![](wristrot2-v.jpg)
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...and rotate too. Piston linear motion is converted
to a rotation one by a lever, gears and a universal
joint transmit motion to the wrist turntable. |
![](wristtop-v.jpg) ![](wristunder-v.jpg)
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Wrist and hand viewed from top and bottom. |
![](elbow-v.jpg) ![](elbow-flex-v.jpg)
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The elbow has a lever mechanism to increase flex
angle. But there is a cost: two parallelled pneumatic
cylinders have a hard job lifting the hand. This
is also the reason why this arm remained skeletal:
I originally intended to add a skin, but the weight
would have been too much to be properly moved. |
![](shoulder-lowered-v.jpg) ![](shoulder-raised-v.jpg)
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Two parallelled pistons raise the shoulder. |
![](shoulder-rot1-v.jpg) ![](shoulder-rot2-v.jpg)
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Rotation of the shoulder. |
![](shoulder-top-v.jpg) ![](shoulder-mechanism-v.jpg)
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Details of the mechanism used to rotate the shoulder. |
The control
unit
![](controller-side-v.jpg) ![](controller-top-v.jpg)
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The control unit contains a battery pack, the
compressor and the command switches.
I had to carefully select the switches I used:
some of them were leaky and did not allow the pressure
to build up enough to move the elbow or the shoulder
joints. |
![](compressor-detail-v.jpg) ![](pressure-switch-v.jpg)
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The compressor is based on two small pumps, working
in opposition. They are driven by two clear "monkey"
motors that are faster and slightly more powerful
than regular ones. A small piston, loaded by two
rubber belts, moves an electric switch when pressure
is too high. The compressor motors are then switched
off. |
![](tubes-v.jpg) ![](compressor-v.jpg)
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The opened console shows some gory details... |
The stand
![](stand-v.jpg) ![](stand2-v.jpg)
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I first tried to build the support tower using
only studless beams, but the result was not stiff
enough. So I rebuilt it using the more traditional
beams-and-plates method. |
![](foot-v.jpg)
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Balancing the arm requires a pretty big foot! |
LDraw files
I have modelled the arm and the compressor.
![](pneum_ldraw.jpg)
Arm ML-cad file
![](comp_ldraw.jpg)
Compressor ML-cad
file
Movies
The pneumatic arm in action (AVI movies, Divx
5.1 compression)
![](hand-movie-v.jpg)
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Hand and wrist movements (400kb). |
![](arm-movie-v.jpg)
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Exercising the arm (900kb). |
![](object-movie-v.jpg)
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Moving an object (800kb). |
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