SpudFiles

I thought you guys might be interested in this:

Some time back I designed and built an Oxygen/Propane powered cannon for the 4th of July. It does not fire projectiles. However the sound itself is devastating enough. The barrel was made from a 330 cu ft 6000 PSI nitrogen tank with the bpttom cut off. The valve end eas welded and drilled and threaded to receive a spark plug. A stancion was welded on the bassness end that carries an axle for 2 10" pneumatic tires. The stancion also has 2 trays for the twin 24V aircraft batteries as well as the mounts for the Oxygen and propane cylinders and regulators. The gasses enter the barrel on opposite sides through 1/4" stainless steel tubing after passing through 2 check valves and the control valves. The ignition source is a HV automotive ignition coil that is driven by a IGBT transistor. The transistor is controlled by a pulse generation circuit interfaced to a PIC microcontroller MCU). The MCU also controls the gas injection as well as the data acquisition. The remote control console is a hand held held device on a 25' control cable. The control console has a BCD switch that the user sets for the quantity of gas to be loaded, the load/fire switch and a 4 digit display that reads out in decibels. The computer and electronics are enclosed in an aluminum chassis mounted to the barrel. The reason for 2 batteries is to isolate the electronics from the high voltage (50KV) ignition source. To fire, the user turns on the main power switch, sets the quantity of gas in the BCD switch, presses the load toggle switch, waits for the gas to finish loading which is indicated by the flashing red safety light on the barrel and presses the fire button. There is an instrumentation grade microphone in the mouth of the barrel that is sampled by the MCU and converted to decibels for display on the hand held control console. I calibrated the microphone and data acquisition system to an NIST traceable standard. I have seen an honest 185 dB's at the mouth. It is so loud that it shattered a plate glass window 30 feet BEHIND the cannon at a 90 degree angle from the reflection wave. Attached is a sketch of the layout. If anyone is interested, I will post pictures. It has won several awards and has been featured in Design News Magazine's 'Gadget Freaks' section. The University of Mississippi contacted me about borrowing it for a Naval Research contract they have. I am going to donate it to them for their use.

That sounds too amazing a post to not be illustrated, pics/videos please!

Also, paragraphs

I tried to attach a BMP, EPS, and WMF pic but all were rejected. How do you post a pic?

Can't you save the .bmps as .jpg or .png? Also make sure the size is less than 350k.

Sounds like quite an entertaining toy. Not sure why the university would be interested though...

Also, considering that decibels is a measure of RMS sound pressure, you'll be getting misleading results from that microphone which are dependent on your sampling time and artifacts in the equipment. A dedicated high speed pressure transducer would be a much more suitable piece of instrumentation.

I'm led to believe that the whole thing is left open ended and filled with the gas mix, then ignited from the rear. Is that correct? If so, you'll get a much sharper sound profile if you endeavour to modify the ignition system such that it detonates the gas mix. This can be done in several ways which I'd be happy to explain to you if you're interested.

A microphone is a pressure transducer. The one I used is an Endevco high intensity microphone designed for such use. The data is sampled at 100KSPS and has an analog butterworth filter on the front end to eliminate ailiasing. The pressure range of the microphone is good to 190dB. I calibrated the system in the laboratory. I was a flight test instrunmentation engineer for Lockheed's Skunk Works for 31 years, so I know what I'm doing.

Oh yeah, the university need a large, loud, repeatable point noise source in support of an acousitcs program.

Also,a decibel is a logarithmic function of a pressure ratio that relates to the human hearing curve. It can ve expressed in either peak or RMS.

Ah, excellent. You have much better equipment than most of us have access to then, and the assumptions made in my last post are totally invalid. I'm guessing the 185dB is your peak measurement then? What are you using as the reference pressure, the standard 20μPa?

If that's your peak barrel mouth pressure, then you would certainly benefit from detonating the gas, at least in the attempt to create a large single-pulse acoustic point source. Or are you trying to avoid shock waves in this application?

Also, I'm well aware of what a decibel is, and politely recommend that you refrain from triple-posting in the future
(There's an "edit" button at the top right of your post which you can use to append to it)

The application was simply to create a loud party favor to celebrate the 4th. I wasn't trying to sound snippy. I just nhit send before I was finished... twice

I will take some pictures to post tomorrow if time permits.

I'd love to see some photos if you have any, this might help when it comes to posting them.

enauman wrote:I was a flight test instrunmentation engineer for Lockheed's Skunk Works for 31 years, so I know what I'm doing.

Surely then posting pictures should be easy, don't leave us hanging

here is the PDF from desingnews where is also some pictures how its build: http://downloads.deusm.com/designnews/2 ... ctions.pdf

Your english professors would be proud. Starting off your paper with a picture of a massive fireball is a GREAT way to catch the attention of your audience! (They might dock points for not using paragraphs but who cares!)

I have seen an honest 185 dB's at the mouth. It is so loud that it shattered a plate glass window 30 feet BEHIND the cannon at a 90 degree angle from the reflection wave.

How far away will your audience have to be?

Is there any particular reason the gasses enter the barrel on opposite sides? I would have simply ran them into a T through 2 metering orifices and mixed them on delivery into the barrel from a single port for a better mix. The two flow rates would be in proportion to the desired fuel oxygen mix. A small diffusion tube with a baffle would complete the mixing as it entered the barrel. I was considering this for a future full auto combustion cannon of mine, but it would shoot projectiles.