Re: Surgical tubing stretched too far
 

Be careful leaving bungee tensioned for long periods of time, we used bungees on our climbing arms last year and when tensioned they lose a lot of strength over time. If you can take the tension off when the robot is bagged or stored it will last a lot longer.

Re: Surgical tubing stretched too far
 

The stretching of your rubber tubing is a phenomenon known as hysteresis. As you pull on the tubing, long-chain rubber molecules absorb the energy. Releasing the force returns most but not all the energy. Some stays in the deformed molecules which don't all bounce back to their starting shapes.

What this means is that any rubber tubing will exhibit a loss of power over many stretches, so plan on an easy way to tension or replace the tubing, and try to design your mechanism so that you aren't stretching it so much. Changing the tubing to a better grade may help, but you most likely will still have a significant loss of power until you redesign your mechanism.

Enough for today's physics lesson, let's go play robots!

Dr. Bob
Chairman's Award is not about building the robot. Every team builds a robot.

Re: Surgical tubing stretched too far
 

Thanks for all the useful information. We went ahead and implemented this change.

We were able to attach the tubing to a pair of eyebolts on the top of our practice bot's superstructure, and tested it yesterday. The results were quite gratifying.

The ball has a lower trajectory, implying that the energy transfer is occurring through a greater portion of the arm's stroke. This means that we can tune the shot for greater distance without over-stressing the winch system.

Re: Surgical tubing stretched too far
 

We use surgical tubing and love it. We scored 2 perfect 75's in auton at Howell last weekend and have a system that gives us a very reliable dynamic ranging shooter.

Get a little creative and you can shoot any distance and trajectory you want. The surgical bands on our bot remain loose until the second we shoot. so set is not an issue. We have a max shot wrap. Large amount of loops with minimum starting length. We can shoot most distances on the fly (pretention hapens in less than 1/2 second). Full load is just over 1 for full field shot.

Re: Surgical tubing stretched too far
 

My team did a fair amount of testing with surgical tubing and our robot has a surgical tubing powered catapult.

A few things we learned from testing (On our practice robot we've fired our catapult at least 500 times and it's still consistent):

1. We had some problems with the KOP tubing and found that it lost its elasticity much faster than what we bought off McMaster.
2. After testing, we opted for more wraps that are only slightly tensioned when the catapult is up and ~150% stretched when the catapult is down. More than that and we started noticing wear and loss of elasticity.

Best of luck!

Re: Surgical tubing stretched too far
 

Another follow-up - we used the lower stretch of about 50% on the bot at Arizona today, and we're shooting quite well. Consistency is way up. We're in fourth place! Thanks again for the help.