So, now you have your frame but now you need to make the arms, the arms are made from aluminum rails because they are less heavy than wood, the first thing you need to do for making the arms is attaching them to the body frame, to do these we will take three pieces of wood and make a hole through them, then we will put a nut and a bolt, make sure they are not so tight because the center wood needs to move.

Now attach the first and the third wood to the frame at the height of the shoulder, now repeat this process two times so you now have two shoulders.

Now that you have your two shoulders its time to attach the first halve of the arms, to do this, cut two identical lengths of aluminum rail (one for each arm) and attach them on an angle with two screws on the middle wood, note that they have to be on the outside part of the middle wood.

Then, you will have to attach the pneumatic piston to the middle wood, to do this simply secure an L bracket to each end of the pneumatic piston and attach the rod with the L bracket to the middle wood and the body of the cylinder to the frame of the robot, do this twice.