Out stretching surgical tubing.

[Jon Stratis]

We use a fish scale to periodically measure the force on our catapult at a specific pull distance. This tells us if the tubing is losing its pull, and lets us either adjust it or replace it as needed, ensuring we can get consistent results each time we modify it.

[Peter Matteson]

Use the Bobcat solution:
Buy these: http://www.mcmaster.com/#extension-springs/=rh55nd
Replace every event for consitant performance.

Trusted source of spring force on Bobcat designs since 2008.

[jijiglobe]

Our team had a similar problem but we came up with a 3 point solution to it that made us not have to change our surgical tubing for both of our regionals(besides the ruined stuff from build season). The system is as follow:

1) Have a system where you can take off surgical tubing without cutting the zipties or whatever holds it. We accomplished this by using an eye bolt with a hole to hook surgical tubing into. Then only put surgical tubing onto robot while in queue.

2) Never stretch surgical tubing more than half of its initial length.

3) Find out how much force it takes to move your catapult using a spring scale(use the same one every time in case it's off) You have to measure from a specific point in the motion of the part every time. Then check that you match that number before each match.

It's a little tedious but we went through 2 days of competition at the Buckeye and 3 days at New York without having to change and without having noticeable drops in accuracy.