This is an arm model I made mostly from picture analysis, but based somewhat on Starbuck Cylon parts and Gordon Tarpley's YouTube vids. The forearm is all one piece and the bicep is two. This was done to get a flat surface from which to start. The two pieces key together for alignment. This is intended for a large format printer like the CR-10 and I'm posting another version that might be more appropriate on smaller printers. I used 35% infill but it honestly probably doesn't matter too much where that's set. Most of the shaft is solid.

The forearm and bicep cuff are the same on both arms. The bicep body is handed so you'll want to reflect it when you print the left. The bar across the bottom of the bicep body is how the cuff is located rotationally so once you glue the parts together you can just trim that and sand it flush to the inside of the cuff. It also provides a little more surface area to adhere the part to the bed.

2/16/18 - update I changed the holes at the elbow to be dimples instead. I noticed that during printing, the retraction when it went from one side of the hole to the other side made the inside of the elbow kind of weak. The dimple allows a continuous bead for the whole layer and it provides a positive locating feature to drill a clean hole. I also added a small nub on the outside of the elbow to locate the piston anchor. I'll be uploading the other greeblies and bits to complete the assembly.

Better late than never: I promised at some point to add some detail about the piece I intended for the piston connector. I just attached a snapshot of the model and a PDF drawing. The piece is made from some extruded aluminum I bought. It's a 1"x1" 'L' shape that is 1/16" thick. I printed out the drawing, cut out the profile in actual size and then used a hacksaw and files to shape it to the paper. Once it's all fitted, I just expoxied it in place.