[Jeffrafa]

Sanddrag's got it right - the PVC tube is simply covering up our 50 lb spring, to keep it from pinching wires and fingers as the arm moved.

The spring was added at our second regional to reduce the amount of air needed to lift the arm, making it possible to cut the working pressure on the main cylinder down to 45 psi instead of 60.

As for how high we could stack, we still aren't entirely sure. The highest we ever stacked in competition I believe was either 4 or 5 tetras on the center goal. Last Thursday we were able to stack 2 on top the center goal while it was sitting on a lunchroom table, which is approximately 2.5' off the ground. We only have 4 tetras total, so we haven't been able to test our maximum on our own.