pneumatics or motors?

[JamesCH95]

Originally Posted by DavisDad

The 10 CFM fills an accumulator (reservoir) until charged to about 2-3 PSI. The compressed air is released directly into the end of the cannon; like a potato cannon. The air is released very fast and the 2 psi acts against the 50 sq.in. surface of the ball = 100 lb force at initial release. My calcs say I need about 15 ft-lb energy to accelerate the ball to about 31 ft/sec. The size of the accumulator will determine the final exit pressure on the ball. Of course leakage around the ball is a big variable.

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.

[cmwilson13]

Originally Posted by Daniel_LaFleur

Neither of you are thinking outside the box

Take a 12" cylindar. lock it 1/2 way (mechanical lock like a fence latch). pressurize the cylindar. release the lock and see how fast the cylindar reacts and how far you shoot the ball.

oh, I'd put a hard stop on the rod so you dont damage the cylinders end cap

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

[Daniel_LaFleur]

OK. Lets go through this:

Originally Posted by DavisDad

The 10 CFM fills an accumulator (reservoir) until charged to about 2-3 PSI.

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

Originally Posted by DavisDad

The compressed air is released directly into the end of the cannon; like a potato cannon. The air is released very fast and the 2 psi acts against the 50 sq.in. surface of the ball = 100 lb force at initial release.

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.

Originally Posted by DavisDad

My calcs say I need about 15 ft-lb energy to accelerate the ball to about 31 ft/sec. The size of the accumulator will determine the final exit pressure on the ball. Of course leakage around the ball is a big variable.

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.

[DavisDad]

Originally Posted by Al Skierkiewicz

The valve you would need to release that pressure still would need to be higher than 0.32cv (not 0.35) correct? ...

Originally Posted by Daniel_LaFleur

OK. Lets go through this:
1: How do you charge the accumulator without using a valve(0.32CV) between the accumulator and the cannon? ....

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.

[Al Skierkiewicz]

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.

[DavisDad]

Originally Posted by Al Skierkiewicz

Dad,
Unfortunately, any pneumatics are inspected under the pneumatics rules regardless the pressure. ...

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