The arm is already taking shape, now the joints. I installed 3 joints, one of those is the wrist that need an entire post.
At first I thought of making a telescopic extension. The idea was a square profile with a nut anchored go through a cylindrical profile. A threaded rod would rotate to move the square profile.
This system easily solved several problems but getting engines that could move the bar quickly was almost impossible, so I switched to a 3-point joints, hereafter ‘Shoulder’, ‘Elbow’ and ‘wrist’.
The profiles are rectangular aluminum of 12 x 10 mm.
Now that were already in place came the part of the movement .Luckily, a friend had just cleaned the attic and had given me several things, including two power windows car engines. These motors are 12V DC and have the characteristic of having much torque, just what I need.
The motors are hooked by aluminum frame to the structure. In the third picture the square frame(which makes motor shaft) inside cylindrical frame. It’s like a tread. This assembly is wrapped by a sheet of aluminum of 10 x 2 mm.
To transmit the movement thought of using ropes, but only temporarily, because they have the disadvantage of stretching the load weight, a situation to be avoided in a system designed to be accurate. In the future they will be changed by metal chains.
And just it left wrist, but that deserves a separate post.