My team is currently looking at building a t-shirt cannon, and no surprise we are looking at arguably the greatest of them of all. From their build blog, we have gained much valuable information, but we still have a few questions?
How does 254 roll their shirts? 2.375 ID seems really small. Why not the ranger roll?
200 shirt capacity, isn’t that excessive and expensive? Or is it for the convenience of not charging the air tanks all the time?
How difficult is it to add a rotating barrel? How is the barrel mechanism sealed to the air hose interface? Any closeups?
We roll our T-shirts by simply folding the sleeves/edges up to the collar and then rolling from the collar down to bottom edge. We typically use 1-2 rubber bands to hold the shirts together. While this is not the most compact way to roll a shirt, they end of pretty small and also don’t fly like bullets, making them a lot safer to shoot.
We tried to have such a large shot capacity purely for ease of maintenance. We will typically go to 2 or more outreach events with Shockwave before we have to take it back to a scuba shop for re-filling.
The large block in the back that holds the globe motor and a pneumatic cylinder for rotating/indexing was the most complex part on the robot. However, we found that a rotating barrel is simpler is better at managing the indexing of the shirts that a linear magazine.
There is no special sealant between the block and the barrels. The block simply has a conical-shaped output that lets the air through a polycarbonate plate that the back of the turret slides nearly flush against.
You can look at shooting sponsor t-shirts. For team 4004, Buffalo Wild Wings in our area gives us free shirts for promotion, so we shoot them off with team shirts.
Our football team booster club provides us Tee shirts from their sponsors. They also give us a small stipend. It is kinda of neat that the football jocks help sponsor the geeky robot team.
A lot different than way back when I was in high school.
As mentioned above, we shoot sponsor provided t-shirts usually. We rarely shoot shirts purchased with team funds, as that is cost prohibitive as you noted.
There are two regulators. One regulator is mounted on the scuba tank itself, which regulates the ~3000 psi air down to around 150psi. That air is used to fill the secondary scuba tank which the main shooting valve is hooked up to. The secondary regulator is used only for the pneumatic functions of the cannon, which is primarily just the indexing mechanism.
When the scuba tank is depleted, it gets removed and filled at a local scuba shop. We do not have the capability to fill the scuba tank at our school or lab. High pressure compressors are extremely expensive.
Nothing fancy. Feed it 12 volts for as long as you want it open. We use a VEX controller. A cRio is more than sufficient to do that. You could use an RC controller if you wanted.
For t-shirt shooting since you only need to turn the air supply on and off I am a fan of these valves. http://www.airbagit.com/Brass-Air-Valves-p/airvalve-06.htm They do make them smaller too. They are cheap, completely rebuild-able, fast acting and are very simple and reliable. They do need a bit of power to operate, around 4 amps per valve, IIRC. They have smaller versions available too.
We used them in testing for our abandoned T-shirt shooter project and we were able to control the distance of the by the amount of time the valves were opened.
