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    Pneumatic Arm

 

     

    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

    The hand has three fingers, a single piston is used to open and close it.

    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

    The wrist can flex...

    ...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.

    Wrist and hand viewed from top and bottom.

    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.

    Two parallelled pistons raise the shoulder.

    Rotation of the shoulder.

    Details of the mechanism used to rotate the shoulder.

     

    The control unit

    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.

    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.

    The opened console shows some  gory details...

     

    The stand

    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.

    Balancing the arm requires a pretty big foot!

     

    LDraw files

    I have modelled the arm and the compressor.

    Arm ML-cad file

    Compressor ML-cad file

    Movies

    The pneumatic arm in action (AVI movies, Divx 5.1 compression)

    Hand and wrist movements (400kb).

    Exercising the arm (900kb).

    Moving an object (800kb).

       

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