Re: pneumatics or motors?
 

Ah, I misunderstood.

I still think that you should check to see if the valve/hoses will flow enough air fast enough to do what you want. Though I'm still not convinced that an air-cannon is legal.

Re: pneumatics or motors?
 

that plus if you use 4 1/2 inch cylinders vs 1 2 inch cylinder you have the same force but 4 times the flow. when you need speed and force in pneumatics use multiple small cylinders in parallel. and using a mechanical stop to allow the cylinders to charge like daniel said makes a huge difference.

here is a example of a multiple cylinder launcher.
http://www.youtube.com/watch?v=QeQSGmFnKAE


here is another example
http://www.youtube.com/watch?v=0c6mym04OGs


both of those shooters used multiple cylinders with a mechanical stop the breakaway bot used a door latch type mechanism and the overdrve bot had a delta p of about 1.5 psi so the pistons would deform into the ball until there was enough force to break the vacuum.
which with that amount of surface area was about 200-300 pounds

Re: pneumatics or motors?
 

OK. Lets go through this:

1: How do you charge the accumulator without using a valve(0.32CV) between the accumulator and the cannon?

2: In order to release the air that fast you would need either a vane valve or sprinkler valve. Both have CVs too high for FIRST.
3: Consider your mass flow. As the valve is opened the air starts to flow and pressure begins to build in the cannon (I'll ignore leakage around the ball, which you'd want to lower frictional forces). When the pressure gets to ~0.15PSI (12 oz acting on an 11 oz ball) the ball will start to move up the cannon.

4: Pressure will remain ~ 0.15PSI as the air fills the, now additional, volume created by the ball movement. giving you only .75LBf of the 15LBf that you need.

My guess is that the ball never leaves the cannon, as the leakage around the ball will probably have a higher CV than the CV of the valve used.

Re: pneumatics or motors?
 

Good point, but the release mechanism isn't a solenoid and would have to be exempt form the Cv limitation. Maybe low pressure systems (< 5 PSI) won't be considered "compressed air" rather "high energy fan system". :]

I'm also thinking of charging the cannon directly by the blower (no reservoir) and just tuning the blower ON/OFF. Modulation of the force would be done by varying the voltage on the blower motor.

At any rate, I'll be protoyping this today and let you know if the performance makes it worth pursuing.

Re: pneumatics or motors?
 

Dad,
Unfortunately, any pneumatics are inspected under the pneumatics rules regardless the pressure. Blowers on the other hand will be looked at for electrical, motor, mechanical and safety parts of the inspection checklist. Of particular concern would be exposed moving parts. They are pretty much handled the way ball launchers would be. We don't want fingers getting damaged or worse so things do need shields when they pose a threat to humans.

Re: pneumatics or motors?
 

Hi Al,

Thanks so much for the clarification. This makes sense as any stored energy from CA is a potential danger and following a standard CA safety standard is required.

Much appreciated,

Craig