Creating the animated arm

(Arm added to the circular disk)

To create the arm shown above, I first created a standard chamfered box, making sure that the fillet level was correct to match the rest of the model. Converting this to an editable poly, I then selected all of the end vertices on the right hand side and used the scale tool to pull them slightly closer to each other. This in turn made the end of the arm slightly narrower. I then scaled the rest of the arm so that it matched my original source photograph.

(Box and NGon created to make the end of the arm)

First, I created an NGon within the splines object type. This created a 2D object with six sides. I then converted this to an editable poly and selecting the polygon mode, I extruded it. Next, I created a chamfered box at the end of the arm, and sized it accordingly. So that I could get the cut-away shape inside this box, I used the NGon that I had created, and placed this within the box, as shown above.

(Boolean tool applied and cylinders added)

Selecting the box at the end, I used the Boolean tool and chose the NGon as the operand B. This gave me the nice cutaway that you can see at the end of the arm. I then added a chamfered cylinder and sized this accordingly. This was then cloned across to the other side, and placed in the adjacent position to the other cylinder. All that was required then was another chamfered cylinder similar to the one I had just created, only this one needed to be slightly smaller. I will add the relevant textures to the model towards the end of the project.