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Topic: Compressed Air Pressure Meter (Read 17058 times) previous topic - next topic

Jeremy1998

Well, I want to make an automated compressed air rocket launcher... To do that, I need to know what the current pressure is in the rocket... Basically I need a compressed air pressure sensor that I can use with arduino. It needs to thread into a standard sized thread; 1/4", 3/8", 1/2" or soemthign close... Can someone please link me to a sensor?  

Jeremy1998

Also, any recommendations for solenoids? 1/2" would be best, and 12 volts is highly prefered...

Ran Talbott


Jeremy1998

0-150 would be good, I think. I'm not sure what pressure I would ever be using, and most compressors only go to like 125...

AWOL

You're thinking of using a compressor?
Are you aware of the potential dangers of using compressed air?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

retrolefty

#5
Sep 23, 2010, 08:59 pm Last Edit: Sep 23, 2010, 09:21 pm by retrolefty Reason: 1
Well I built a 2 liter (plastic coke) bottle launcher in the 80s from a mag article I had come across. Those plastic coke bottles will take a lot of pressure but I never got high enough to burst one as I put a 100 psi pressure relief valve on my setup. The tricky part is of course the pressure sealing device you build to fit into the neck of the bottle, that will allow pressure to enter the bottle but then has a quick release to allow fast discharge for launching.

There was no electronics used in my launcher. I used a rubber bottle stopper sealer that used a lever to release or tighten from inside the bottle's threaded neck. I took quite awhile to find the right modifications to allow a 1/4" filling tube to be fitted inside and through the stopper and still allow for compressing and releasing the stopper. I then had a one way check valve between the stopper and the foot pump with a 100psi relief valve T-ed between those two parts. Just pumped away until I heard the relief valve start to release and it was ready for launch. If I didn't pull on the release string in a min or so the bottle did have a tendency to gradually crawl off the stopper and self-release! Again the stopper mechanism was the most difficult part to get right.

I would fill using a foot bicycle pump up to around 90-100 psi and then release the stopper with a pull string. The sound it would make on release was great, people would come out of their houses to see what the hell the sound came from. The bottle, having somewhat poor aerodynamic characteristics, would only go up about 200 ft max and with such a light bottle any wind would take it pretty far from launch site. However the acceleration and sound was fantastic. Once I did one launch.  any avalible area kids would be so excited that they would supply the foot action for pumping air and retrieving the bottle for all future launches in a afternoon! The acceleration was so fast that often the glued paper coke label would be left at the launcher!

Anyway it was a real fun project that would hold a crowds attention for a long time. Never any safety problems, however I always tried to make sure no kid was standing over the bottle when filling or launching as I'm sure if launched into a peering face it could cause injury.

Tell us more about your launcher ideas.

Lefty

Jeremy1998

Well, I'm in 7th grade... As my 5th preiod class, I have "Mission Space"... We launch 2 liter bottle rockets and try to recover the egg inside without it cracking...

The launcher is made of 2 hinges with notches carved in... You set the rocket on a little plastic stopper thing, put the hinges over the lip of the bottle. You use a little bracket with a chain attached to hold the hinges together... You pull the chain, and rocket to WHIZ!

I want to make one, btu have it timed, pressure meatured, ect.

westfw

Such items are somewhat standard, but tend to be a lot more expensive than you'd think (you have your pressure sensor, and then you have the carefully designed housing designed to contain at least 5x overpressure, and you have some electronics that conditions the bare signal from the sensor to convenient voltages, with temperature correction and stuff.)
OMEGA is one popular manufacturer with a wide range of products.  This one looks like it would work:
http://www.omega.com/ppt/pptsc.asp?ref=PX209_PX219

($200 !)  A nice request from a teacher on a school letterhead might get you a free sample...  You can also check on eBay; all sorts of "pressure sensor" and "pressure transducer" there.  You want one with a 0-5V output.

Mere visual pressure gauges are mechanical and much cheaper.

100psi is pretty high for 2l rockets.  I was surprised just how low a pressure makes for impressive altitudes, using a mechanical gauge and foot-operated bike pump...

An interesting idea to look into is the pressure sensors you can now get for monitoring automotive tires.   Some of those are available as add-on kits.  Or you could use/convert a digital tire pressure gauge...


Jeremy1998

Yeah... I would like to divide that price by about 10... There is no way in heck that my mom will get that for me...

westfw

#9
Sep 24, 2010, 07:30 am Last Edit: Sep 24, 2010, 07:30 am by westfw Reason: 1
See if your teacher will request a sample.  It can't hurt, and sometimes companies are very generous toward educational institutions...

Also, this looks OK:  http://cgi.ebay.com/TI-PRESSURE-SENSOR-PPE-PA-GF30-0-100-PSI-PIGTAIL-/290477233182?pt=LH_DefaultDomain_0&hash=item43a1cad41e

Jeremy1998

That is good, but 125 or 150 would be better... 125 is like the highest it will ever go, so I would like to have some extra room for if there is a fualt, it doesn't break.

Ran Talbott

If you check your local Wal-Mart or PepCheckerZone,  you can probably find a digital tire gauge with a sensor that you can cannibalize.  Although you might need to hit a truck supply house to get one with a high enough maximum.

CSingleton

Jeremy1998

I think that this little $15 beauty from Harbor Freight might be the way to go:

http://www.harborfreight.com/air-tools/air-accessories/digital-air-flow-regulator-98426.html

While it is a digital regulator, I think that it will display the actual pressure delivered rather than the pressure set. You could crank it up to your maximum safe working pressure by setting it with a high-pressure shop source then install it into your model rocket system and just watch the gauge.

Or you could Arduinoize it and hack into the display to get digital signals and relay them to your Arduino.

Jeremy1998

Ironically, I was just looking at that... The problem is, I think that it measures speed (40MPH).

Jeremy1998

Brain blast! (Jimmy Nutron!!!) How do air compressers do it? If I get oen of those controller boxes, would I be able to hackify it?

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