From what I gather the tether is in place to stop the flipper going further than it should past the rams stroke especially these new breed of robots that use static rams eg gravity where the flipper is not connected to the ram, this way if the cylinder end did blow off the tether would be designed to stop the movement of the arm to say just above its highest point rather than all the way over and possibly hitting someone behind if they are loading the robot into the arena or powering up. Apologies if I have the wrong end of the stick would not be the first time :P

Francis

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