[PAR_WIG1350]

My suggestion would be to do everything you can to make the segments farthest from the attachment point of the arm as light as possible. and those closest to the attachment point as strong as possible. Flexing and torque are your enemy. I suggest very thin wall high-strength aluminum round tubing for the last section or two, 1/16th for the second segment, and 1/8th for the first. I also recommend that all segments except for the last one be constructed from two parallel sections. this makes the load distribution more symmetrical and results in less twisting. Your first joint will need either a strong motor, or large bore pneumatic cylinders. to reduce the torque caused by the large cantilever, place the motors at the beginning of the segment before the one that it moves. Also, the first segment should be balanced with surgical tubing so that it is stable with the arm folded. To get an idea of the kind of load the arm will be under, bolt three pieces of aluminum together and bolt one end down to something sturdy so that it pivots at that end. Then try to lift it from the pivot end.