Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 62 users online :: 4 registered, 0 hidden and 58 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Pressure Instrumentation

A place to ask general spud cannon related questions.
Sponsored 
  • Author
    Message

Pressure Instrumentation

Unread postAuthor: PeteS » Sun Sep 22, 2013 7:32 pm

I'd like to be able to graph actual chamber pressure over time. Is there a reasonably easy and inexpensive way to do this?
  • 0

User avatar
PeteS
Sergeant Major
Sergeant Major
 
Posts: 180
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Country: United States (us)
Reputation: 12

Unread postAuthor: Gun Freak » Sun Sep 22, 2013 8:15 pm

Pneumatic or combustion?
  • 0

OG Anti-Hybrid
One man's trash is a true Spudder's treasure!
Golf Ball Cannon "Superna"M16 BBMGPengunHammer Valve Airsoft SniperHigh Pressure .22 Coax
Holy Shat!
User avatar
Gun Freak
Lieutenant General
Lieutenant General
 
Posts: 4969
Joined: Mon Jan 25, 2010 4:38 pm
Location: Florida
Country: United States (us)
Reputation: 11

Unread postAuthor: Gippeto » Sun Sep 22, 2013 10:39 pm

Would you care to better define "reasonably easy and inexpensive"?

Pressure transducers have come down in price (hugely so), but would still require electronics of some sort to tie them into a computer and then custom software written to make sense of the input.

How much can you do yourself?


Another route is strain gauges.

http://www.shootingsoftware.com/pressure.htm
  • 0

"It could be that the purpose of your life is to serve as a warning to others" – unknown

Liberalism is a mental disorder, reality is it's cure.
User avatar
Gippeto
Donating Member
Donating Member
 
Posts: 2393
Joined: Sat Jan 19, 2008 10:14 am
Location: The Great White North...Canada eh!
Reputation: 11

Unread postAuthor: PeteS » Mon Sep 23, 2013 9:12 am

I have some wacky ideas for a two stage cannon that I won't go into right now that are combustion powered, but it is more complex than that. For practical purposes I think we can call it combustion.

Would I care to better define "reasonably easy and inexpensive"?
I am kind of a cheapskate so I probably don't want to spend hundreds of dollars. I am not too concerned about putting in quite a few hours of work.

How much can I do?
I am not too good with electronics, but am not afraid to solder. I spend some of my life as a programmer so I am reasonably proficient there. I do have and can use a mini lathe and mill, but am not an expert with them.
  • 0

User avatar
PeteS
Sergeant Major
Sergeant Major
 
Posts: 180
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Country: United States (us)
Reputation: 12

Unread postAuthor: dart guy » Mon Sep 23, 2013 2:42 pm

You could try making a pressure guage fit in the tank and then take a vid of it. :D
  • 0

User avatar
dart guy
Major
Major
 
Posts: 397
Joined: Mon May 13, 2013 7:54 pm
Location: not telling you
Reputation: 5

Unread postAuthor: Gippeto » Mon Sep 23, 2013 4:09 pm

If the goal is accurate data, I think you're looking at several hundred dollars at least.

Might be worth your while to check with Dewey or Poland Spud...they seem pretty handy with electronics and would likely be better able to advise you in that regard.

Perhaps an interface can be accomplished with some of the Arduino kits??
  • 0

"It could be that the purpose of your life is to serve as a warning to others" – unknown

Liberalism is a mental disorder, reality is it's cure.
User avatar
Gippeto
Donating Member
Donating Member
 
Posts: 2393
Joined: Sat Jan 19, 2008 10:14 am
Location: The Great White North...Canada eh!
Reputation: 11

Unread postAuthor: PVC Arsenal 17 » Mon Sep 23, 2013 4:11 pm

I am sure there is a cheaper solution, but: http://www.ebay.com/itm/0-250-PSI-Press ... 0402277797

Or make your own version of that, there are numerous ways.

Your run-of-the-mill barometric pressure sensor won't do it.
  • 0


PVC Arsenal 17
Major General
Major General
 
Posts: 1762
Joined: Mon Mar 27, 2006 4:18 pm
Location: United States
Reputation: 1

Sponsored

Sponsor
 


Unread postAuthor: jackssmirkingrevenge » Mon Sep 23, 2013 5:26 pm

PeteS wrote:I have some wacky ideas for a two stage cannon that I won't go into right now


Maybe you should, it might not be a new idea and others before you might have tried, so it would be good to learn from their experiences in that case :)
  • 0

User avatar
jackssmirkingrevenge
Donating Member
Donating Member
 
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: PeteS » Mon Sep 23, 2013 5:55 pm

jackssmirkingrevenge wrote:
PeteS wrote:I have some wacky ideas for a two stage cannon that I won't go into right now


Maybe you should, it might not be a new idea and others before you might have tried, so it would be good to learn from their experiences in that case :)


I might at some point before proceeding, but I want to mull it over a while first.
  • 0

User avatar
PeteS
Sergeant Major
Sergeant Major
 
Posts: 180
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Country: United States (us)
Reputation: 12

Unread postAuthor: jimmy101 » Tue Sep 24, 2013 9:37 am

The challenge with any pressure sensor in a spud gun is response time and the overlaid acoustic signature. Sound happens in about the same time domain as does the pressure signal making the signal from a transducer a bit of a challenge.

A $1 piezo transducer could be used but calibrating it is pretty tricky. A piezo produces a voltage that is proportional to the rate of change of pressure so you need to integrate the signal. For qualitative work, of you just want to know the timing without need for the actual pressure, it might be OK. You can plug a piezo directly into the MIC input of a pc and record the signal directly. A voltage divider, or just a series resistor might be a good idea to keep from over-voltage into the MIC input.
http://www.inpharmix.com/jps/Piezo_Spud.html

You can try to use a standard dial pressure gauge but usually they (1) react much too slowly and (2) the rapid change in pressure may well trash the gauge even if the gauge's max pressure isn't exceeded.
See the sequence of images near the bottom of http://www.inpharmix.com/jps/Chamber_Temperature.html

You can use a $1 tire pressure pencil gauge but again the high rate of change of pressure makes the reading pretty inaccurate. In particular, the rapid pressure change gets the scale moving too fast, it then overshoots the actual peak pressure by a lot. In the image below there is a dial and a pencil gauge installed on a test combustion chamber.
Image

In guns, the solutions it typically to use a strain gauge. They can be had for fairly cheap but will need a bit of electronics (but you can use the laptop's MIC input for the data logger and save some $). A strain gauge will need to be calibrated. A good page on strain gauges and guns is http://www.ktgunsmith.com/straingauge.htm

As an alternative you might consider measuring temperature instead of pressure since they are often related (though the relation might be pretty complex). A typical temperature sensor is much to slow, and requires much to much heat, to work inside a gun (combustion or pneumatic). But there are other ways to measure temperature, for example, the speed of sound is very sensitive to temperature (and pretty insensitive to pressure). So if you put a piezo inside the chamber, wire it into a laptop MIC input, record the sound of the gun operating, then extract the resonant frequency of the chamber as the gun goes off, you can extract out the average temperature in the chamber. For a gun you would also need to be able to correct for the increased length of the chamber as the ammo moves.
http://www.inpharmix.com/jps/Chamber_Temperature.html

A final way to measure the pressure might be to accurately measure the projectile position versus time (and the static and dynamic friction of the ammo to the barrel) as the gun fires. You could then calculate the pressure versus time data for the chamber.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3128
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Unread postAuthor: PeteS » Tue Sep 24, 2013 11:26 am

Interesting... I think maybe for my purposes temperature might be a good metric to use.

BTW, I think I might be satisfied with just peak pressure rather than pressure over time and figure that might simplify this whole thing quite a bit.
  • 0

User avatar
PeteS
Sergeant Major
Sergeant Major
 
Posts: 180
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Country: United States (us)
Reputation: 12

Unread postAuthor: PeteS » Wed Sep 25, 2013 7:52 am

It occurred to me that if I was satisfied with peak pressure only that having a small metering chamber connected with a check valve would be pretty accurate. It could have a gauge attached or just a schrader or presta valve. If using the valve a tire gauge would work up to the pressures that you can find one for. I have one that does 160 PSI and I think they probably make some for presta that go higher. The reading could be taken at your leisure after firing.

Am I missing any flaws with this idea?
  • 0

User avatar
PeteS
Sergeant Major
Sergeant Major
 
Posts: 180
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Country: United States (us)
Reputation: 12

Unread postAuthor: jimmy101 » Thu Sep 26, 2013 12:33 pm

PeteS wrote:It occurred to me that if I was satisfied with peak pressure only that having a small metering chamber connected with a check valve would be pretty accurate. It could have a gauge attached or just a schrader or presta valve. If using the valve a tire gauge would work up to the pressures that you can find one for. I have one that does 160 PSI and I think they probably make some for presta that go higher. The reading could be taken at your leisure after firing.

Am I missing any flaws with this idea?
Yes you are.

For a combustion the pressure drops very rapidly in a closed chamber. Figure within one or two seconds the pressure will have dropped back to atmospheric.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3128
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Unread postAuthor: PeteS » Thu Sep 26, 2013 12:51 pm

jimmy101 wrote:
PeteS wrote:It occurred to me that if I was satisfied with peak pressure only that having a small metering chamber connected with a check valve would be pretty accurate. It could have a gauge attached or just a schrader or presta valve. If using the valve a tire gauge would work up to the pressures that you can find one for. I have one that does 160 PSI and I think they probably make some for presta that go higher. The reading could be taken at your leisure after firing.

Am I missing any flaws with this idea?
Yes you are.

For a combustion the pressure drops very rapidly in a closed chamber. Figure within one or two seconds the pressure will have dropped back to atmospheric.


Due to temperature change? Or do you mean too quickly for the check valve to pass the pressure to the measuring chamber? Something else?
  • 0

User avatar
PeteS
Sergeant Major
Sergeant Major
 
Posts: 180
Joined: Wed Sep 11, 2013 5:53 pm
Location: Maryland
Country: United States (us)
Reputation: 12

Unread postAuthor: ramses » Thu Sep 26, 2013 4:52 pm

PeteS wrote:
Due to temperature change? Or do you mean too quickly for the check valve to pass the pressure to the measuring chamber? Something else?


Temperature. My hybrid will actually pull down to a substantial vacuum after the piston valve closes from the cooling effects.
  • 0

POLAND_SPUD wrote:even if there was no link I'd know it's a bot because of female name :D
User avatar
ramses
Major General
Major General
 
Posts: 1679
Joined: Thu May 29, 2008 6:50 pm
Reputation: 3

Next

Return to General Spud Cannon Related

Who is online

Registered users: Bing [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'