Auto-Repeating Pneumatic Cannon

The questions I have:

- can I use an air compressor or do I have to use a CO2 cannister? Yes

If I must use a CO2 cannister (ughh):

- How many firings would a 20lb CO2 cannister support?

If I can use an air compressor:

- what PSI will be required in my pressure chamber? That would depend on how hard you want to launch the ball

- what size pressure vessel would I need? That would depend again on how hard and how often you want to launch.

- How do I figure out the SCFM / PSI rating before buying a compressor?

- what volume of air will be consumed in each cycle? That is a bit harder for me. It will depend on the launch pressure and the time the air is being expelled.

Ingersoll Rand's Aro division sells air valves that are controlled with electric signals. Use a valve that switches air from the reservoir to the launch tube when activated by your switch, then spring returns to the at rest position. While at this position the reservoir will refill from the compressor.

If the air valve has large enough flow, the on time would be 1 sec. If the cylinder consumes .10 cubic feet of air each launch, and you launch every 2 seconds, you will launch 30 times per min x.10. That means you will need at least a 3 cfm compressor to maintain that launch pace. To me that sounds too small. probably more air consumption than .10.

I will leave the 60 to 90 mph air flow calculations for the members who know how to drive a calculator better than me. Good luck and send pictures

Does it have to be air? If not have you considered using a nitrogen?

You can get a 4000 psi bottle or in some countries you get a 6000 psi bottle.

Or are you going to have difficulties with the density of the gas?

what is the velocity you wish? A linear electric actuator might work here, no gas needed.

It would be at the base and have a 6 inch travel and a stop and it will lift the ball. These run on short high current pulses and can have less than a 1% duty cycle (determined by the heat it can dissipate over time)

A baseball going fast and hitting a stop might turn into a frayed mass in short order, I take it you are testing baseballs? if so, there may ne a standard basaball test procedire and jig?

I did not know these existed. Sounds great, but I haven't been able to find any that would accelerate a ball to 130 ft/sec. Most are motor driven. Any companies you can point me to..?

Thanks!

Dave

You can try to find, or develop equations for this process. You can locate someone with experience in building pumpkin-chunking machines and scale those designs, or you can do what I would do. Get a piece of pipe to use as a barrel, a storage tank for compressed air that you connect to the barrel via a quick acting valve, and a small air compressor. After you have determined the storage volume and pressure required for a single launch, you only need to muliply that value by 30 to obtain the CFM required to launch every 2 seconds. Be prepared to anticipate some heating effects in your process.

Like this?

Here are some of my thoughts.

You want a ball to accelerate to 90 mph. This is equivalent to 125 feet per second. The acceleration will occur in approx. 0.25 seconds for an accelerartion of 500 ft per second squared.

F=ma=5/16x500=156 pounds of force

I would use a short stroke air cylinder to strike the baseball, rather than trying to push the ball with air, this will also simulate the bat hitting the ball.

Use an air compressor with 100 psi air. The air cylinder required will then be approximately 3/4" diameter. I believe you would only need about a 2" stroke.

To give the ball time to come to a rest at the back of the tube you would probably need at least 5 seconds. Therefore you would hit the ball 20 times per minute, cfm at 100 psi would be 20 x pi x .75^2 x 2" x 2 (return stroke)/ 1728 = 0.08 cfm = 0.6scfm.

Excellent suggestion. Thanks! I came across hydraulic cylinders (too slow) and totally missed air cylinders. Any suggestions for where to purchase low cost, 4" bore, long stroke, spring return, air cylinders?

My calculations:

m=mass of piston+ball

a=acceleration

b=bore diameter

P=Pressure

d=stroke distance

Using F=ma, F=PxArea, v=at, t=d/.5v I get the following equation to predict velocity (ignoring friction, pressure droop, air resistance, linear accel...):

v = 1.25b x (Pd/m)^.5

Plugging in .75" bore and 2" stroke, 100 PSI, and assuming 32 oz for the ball+piston (wild guess),

I get:

v = 10.5 MPH... mmmmh

Looks like I need a greater bore and/or more PSI and stroke length.

Increasing bore to 4", stroke to 4", I get 79MPH. Which is iffy given the things I ignored.

unit conversions courtesy of my favorite: http://www.digitaldutch.com/unitconverter/

I've always found Parker www.parker.com to supply good stuff. Numatics, Bimba etc. are all very good.

Along the same lines as this question: I need to get a pneumatic launcher for cricket balls to coach my Little Leauge cricket team of 10-12 year olds.

can anyone tell me if this is available .

I have seen 9 on TV) baseball batting practise machines which launch a baseball.

A cricket ball is about the same size as a baseball but about 4 ounces.

My email address is d_jacob9@yahoo.com for anyone who wants to direct a personal email.

I live in the Caribbean.

I would like to launch a baseball ------ 60/90 mph ------

Repeat cycle every 2/10 sec.--------- will hit stop---------

I suggest that you stop right where you are! The repeated bouncing of the baseball against a stop with such force and then expecting it to return for the next revolution of excelleration and sudden impact in such a fast cycle will quickly destroy the baseball. I suggest that you try some other type of ball. Maybe a WHAMO BALL. IT BOUNCES WITH SUCH FORCE THAT AFTER HITTING THE STOP, it will assist gravity in returning it to the starting position. It will try to continue bouncing as the result of it's molecular structure. Balls used to play requet ball may also work. At any rate timing will be critical but less force will be needed after the system is set in motion.

TMF