Tech Arm

Start with a new document

Make a new layer. Make a rectangular selection, fill it with white and apply these settings to it:

It should now look like this:

Now create a new layer underneath this layer and make a new rectangular selection, but smaller then the one before. Again fill it with white and apply the same settings;

Create a new layer on top of the last one. make a small circle on top of the rectangle. Fill it with white and apply the same settings again;

Make a new layer underneath the circle layer. Create a new rectangular selection, fill it with white. go to Edit > Free transform and make it look like this:

This is the basic of your tech arm. To create some wires, do the following:

Grab your pen tool and make the shape of your wire. select your brush tool and select a 1px hard brush of the color you want. Now go to your path tool again and rigth click your path. select "stroke path" select "brush" and deselect "stimulate pressure" and hit "OK".

Create some more details and stuff and you might get this:

Click to enlarge