User bkraz333 uploaded a new video a few days ago, in which he demonstrates how can someone make an air muscle with very simple and cheap materials. The stroke is not very impressive, but this is typical for all sort of air muscles, but the force is huge, again typical characteristic. bkraz333 was originally inspired by an instructable, but his video is very nice. Moreover, he uses 4 air muscles to make a force-feedback joystick. Good work.