Okay so I am back again. After my last post my team decided to use a spring powered linear launcher but after some browsing on Mcmaster I came to realize that most extension springs that have a bunch of power don’t extend very far and vice virsa. I looked into the issue more and found gas springs and am again worried about extention speed. Will they move fast enough to move the ball? I like them because I have so much more control over size, stroke, and power.
We actually just played around with them briefly today, we tested up to 90lb gas springs that we had in-house and they do not extend at a rate capable of launching a ball.
Under our testing, an 8" stroke, 90lb gas spring took roughly 2-3 seconds to fully extend.
This is probably a good thing, or more people would get hit in the face by their car trunk doors… 
-Mike
Okay that is what I thought time to continue brain storming. Thanks for the reply.
Have you thought about trying constant force springs?
You may want to search for unrestricted gas shocks
I briefly thought of the idea of using constant force springs. However, with them you’re really not going to benefit too much. The largest one that I have seen while looking around holds a max load of 41 lbs and that results from the amount of deflection that you have. You could design to reach that deflection where greater deflection is negligible in result to generating force. Also, packaging them would be a bit of a pain because of the width of that size spring. (2 in wide)
I would certainly take a look at the surgical tubing that FIRST gave every team in the kit. You’d be surprised at the force to % elongation trends that associate with tubing. There can be a LOT of energy stored in a system from surgical tubing alone.
Our testing of surgical tubing yesterday resulted in 60lbs of force required to stretch 2-1ft loops of tubing to a length of 3ft - YMMV
We did see a lot of wear on the tubing and had some failures. If we go this route, will be sure to bring plenty of extra tubing and be ready to replace between matches
The tubing we tested was purchased from ACE. Hardware, don’t know any of the specs on the tubing
If you’re using tubing or springs, keep in mind what happens when such high-tension items “spontaneously disassemble”. Build in some shielding so team members and volunteers don’t get hurt if it suddenly decides to explosively deconstruct itself!
I grabbed the following data trends from Vulcan Springs. (major supplier of many different springs available)
In regards to the following trend, they are saying that your peak load hits around a small to moderate deflection with their constant force springs. Now later down the road, I’m sure we can test some springs out and make sure it accurately matches the trend.
What I tried to mention above before is that you will get your max load but under a certain amount of deflection as you can see here. (I should have posted this initially)
I hope that clears the air a bit on them.