I don't have a good answer to your actual question, but we have spent spare hours for three years on a t-shirt launcher, which we finally got out to the games this year. It really helped our recruiting! Here's what we learned:
- Use large hoses/pipes from the accumulator to the barrel
- Size the barrel properly
- Make sure you can fit through the door of your build space
- Roll the t-shirts well
Hoses: we eventually wound up at a minimum of 3/4" diameter from the accumulator tank (about 3 gal, but probably didn't need to be this large) to the barrel, including the solenoid valve.
Barrel: We started at 2-1/2", but found that 3" was better, especially at shooting those foam rubber footballs. It also made shooting shirts easier. Make sure that you have a tapered transition from your smallest size to the barrel size to reduce losses to turbulence.
Fit: We messed this one up. We built a base chassis that would have fit with AM rubber-tread wheels, but when we went to the much-larger pneumatic wheels purchased at Harbor Freight, we couldn't fit through the door. We wound up rebuilding our robot during a four-week span of road games to be narrow enough to fit through our door without getting a couple of football players to carry it through sideways.
Rolling shirts: Some of our earlier attempts used duct tape to keep the shirts together through a launch, which makes the shirt rather less desirable in the stands. We developed a method that worked well for us and required nothing but the shirt itself to hold the package together:
- Lay the shirt out flat on a table
- Fold one sleeve over onto the body of the shirt
- pick up the waist hem and lift until there is a turn running from one armpit to the other
- come back down to leave the next turn at the shoulders
- repeat with armpit and shoulder until you've run out of shirt (usually five layers for a size L/G shirt)
- Roll the shirt up across the shoulders, starting at the side where you folded the sleeve under
- About halfway down the (short) sleeve at the end, flip the rest of the sleeve out over the cylinder you've created.
Each team should ask not what their alliance can do for them, but what they can do for their alliance. - [more] 
01-02-2015, 01:55
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