Thank you everybody for your input and ideas. Our team will discuss what we will do and possibly post how it works if we do it. If you have an epiphany and get a great idea, feel free to still post it; we can never run out of ideas. I don’t know if we will try a choo-choo, our team is still discussing it and we will probably have a decision within the next week.
So thanks everyone.
He meant to have the bike pump attached when you are testing the psi and how much it drops every shot, not during the match! 
I bet with some creative use of solenoids and rubber bands, you could use a piston as an air pump. Then you could drive up against the wall many times to repressurize your system.
Of course this would be completely impractical and the time you would waste pumping up your pneumatics by driving repeatedly into the wall would allow your opponents to majorly outscore you, but if could be done for fun or for show on a robot.
Maybe in autonomous, the robot grabs and shoots a large ball, robot returns to the alliance tile and driver runs it into the wall for one pump. The process repeats for the second ball, and for the remainder of the period(3ish seconds without practice maybe?), the driver just replenishes air as much as possible.
I think everyone has missed the point here. We tried the catapult both ways, one motor, a small turntable, some latex tubing and a few miscellaneous parts (perhaps $50 in parts total) gave similar, if not better, performance than 4 pistons (cost for two double acting kits $460 ).
Yes, but we didn’t use much air in Autonomous anyway, so that wouldn’t need to be replaced.
We are trying to build an intake launcher, not just any catapult.
This was our thinking exactly!
I understand how the choo-choo retracts, and I may use it this year, but exactly how does it release the tension with the friction that the motor would cause? Or does it require pneumatics to shift a gear out of place to fire?
What if a VEX U team 3D printed an air pump that could be pumped using motor power?
By rotating. Team JVN put together a nice video explaining it but I am on my phone traveling so I can’t find it.
Best way to think of it is that a joint has no torque around it when the force goes through the joint. This means when the catapult is ready to fire it maintains a state of equilibrium. If the mechanism is turned more however it will no longer be in that state and the built up energy will release.
The cho cho is a method of storing and releasing potential energy with only rotational movement. It still requires something to actually store the energy in. This should be obvious but I wanted to ensure everyone knew for when this thread becomes popular again.
Not allowed to custom fabricate parts that will be under pressure.
Kinda obvious application of G1 but feel free to QA it.
Sorry about multiple posts, multi quoting is hard on phone
What would be the maximum rate of fire you could get using a device like this?
Your just spinning a gear so the only limiting factors on rate of fire should be imposed by you. Length of desired shot, amount of motors and efficiency of the build will all effect the rate of fire while all other factors should just be derived from the original 3.
It should be able to perform a far more consistent shot that a standard piston catapult because of the change in pressure and I’m pretty sure that will be one of the most important factors this year even before range.