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Originally Posted by Andrew Blair
Pneumatics are nice for two position action, but for variable control they don't seem to be very capable. I'm thinking however that variable control can be achieved by using two cylinders in parallel, such as with a bicep and tricep. however, when applying pressure to your "bicep" the second cylinder would be applying some back pressure, so that the cylinder would not contract all the way. I don't know if this is what you're using, but it makes sense that it could work.
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Team 614 uses a single piston w/ variable control... the advantage here is much greater reliability and less chances of stripped gears, stuff broken, etc. We have not had any issue with the arm breaking, except for the claws being slightly bent.
The problem is that the weight of the tetras necessitates a large cylinder which consumes a lot of air. Because of this we are somewhat limited on how many tetras we can lift before we run out of pressure (roughly 4-5, though w/ proper consideration of time needed to charge cylinders, this may be extended to 6- once the tetra is above 45 degrees, the pressure required drops dramatically though). Those who have seen us today at the Annapolis regional have probably noticed the slow lifting of the last tetra....
It would have been nice to attach a potentiometer for dialing the angle of the arm for autonomous, but that was deemed unnecessary (which it was, due to having a broken autonomous (now fixed, but unused since not many other robots can do autonomous either, and the benefits are questionable compared to the risks of getting something stuck, since we do not have time for testing).