Arms and Shoulders

In the previous article I made an opening forearm structure, which we now need to mount the hand to as well as adding some features. I’ve design and 3D printed a repulsor piece, which will also partially act as a mounting structure:

I’m using cordless screwdriver motors to drive the features, these are mounted in pairs on each arm on a 3D printed bracket with a pulley assembly to pull the finger cords:

Shoulder and elbow parts next:

These parts have to support the arms and allow movement in multiple axis, so I have two spaces for bearings on each axis:

The upper arm is largely wood and metal, with a large 3D printed elbow hinge:

The elbow hinge will also act as a pulley with another motor to drive the joint, I’ll be springing the arm in the middle of it’s range of motion so that the motor only needs to pull it off centre rather than supporting the whole load around the pivot point:

The arm is suspended with a combination of bungee cord and wooden dowel with 3D printed ends. I’m using some larger metal geared motors to drive the elbows – this are Como-Drills 919D motors with an 810:1 gearbox:

The bungee and dowels are covered with fake pistons made from PVC pips and 3D printed spacers:

Here are all the part fitted, The biceps will eventually cover the ends of the pistons where they meet:

More to follow…