Step 20: Joebot’s right arm begins with a grey brick 1x1 with headlight, and a grey brick 1x1 with studs on four sides.
Step 21: Connect the two pieces with a blue 1x2 tile with grille.
Step 22: On one of the studs sticking out to the side, attach a 1x4 hinge plate. The hinge plate only connects to one stud, so it’s a bit of a flimsy connection. His arm will fall off. Repeatedly.
Step 23: Add some decorative stuff -- a 1x2 tile and a transparent blue 1x1 plate. Attach a grey 1x1 plate with horizontal clip for Joebot’s hand.
Step 24: Attach the arm to the shoulder by inserting the t-bar into the “headlight.” The trick here is to not push the t-bar all the way in, otherwise ...
Step 25: ... you won’t be able to swivel Joebot’s arm downwards.
Don’t stop now! The poor guy only has one arm! Onwards ...