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 47 users online :: 4 registered, 0 hidden and 43 guests


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

Registered users: Google [Bot], Google Adsense [Bot], Majestic-12 [Bot], Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Fully Automatic potato cannon project.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
Sponsored 
  • Author
    Message

Unread postAuthor: Technician1002 » Mon Jul 12, 2010 9:18 pm

Note the ratio of one part Propane to 5 parts Oxygen by volume. Still think $10 for just over 1 cubic foot is still a good idea?

On second thought, it may be all over on the first shot.. :shock:

On a safety note, the range of combustibility is a much wider range with pure Oxygen than with air. The narrow band of flammability with Propane does not apply when it is in an Oxygen rich environment. Don't assume it won't ignite or explode because the ratio is not close to 5:1. That could be a lethal mistake.

Did you know that if you soak a piece of notebook paper in liquid Oxygen and then place it on a table and hit it with a hammer, it will explode! I've seen it done. Rich Oxygen environments can produce the unexpected with otherwise safe materials. Paper hit with a hammer is not normally explosive.

I work with Oxygen and Liquid Oxygen. It is very dangerous.
  • 0

Last edited by Technician1002 on Mon Jul 12, 2010 10:43 pm, edited 1 time in total.
User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Ragnarok » Mon Jul 12, 2010 9:28 pm

Okay, really... no offence, but in asking about "dulling down the mixture", you've demonstrated how little you know about this subject. And in such a potentially dangerous situation as this, that is a very bad thing.

As I've said before, there is a difference between what people want to know, and what people need to know.
For a subject like this, there's a lot you need to know in order to do it safely (and even then, safe is a relative term).

If I may, I'd like to talk about the Dunning-Kruger effect. (Cue people who've heard me ramble on about it before groaning.)

Justin Kruger and David Dunning wrote a paper a few years back called "Unskilled and Unaware of it". Summarized, it talks about how someone who is incompetent* on a subject will:
a) make poor choices
b) and more importantly, fail to realise they're making poor choices.
*That's the wording used in the actual Dunning-Kruger paper, not me directing an insult at you.

It's worth watching this video on the subject of Dunning-Kruger - it's more angled at the idea of debate than this particular subject, but the basic principles still apply. (In fact, it's worth anyone watching it. Simply recognising the existence of said phenomenon means you're far less likely to fall foul of it!)

Anyway, what that means, in this case, is that you don't know enough about the subject to realise how much you don't know. And that means you don't know what questions you need to be asking* (as opposed to the ones you want to ask). And in a word, that's dangerous.
*I don't know either. I don't know what you don't know.

In your case, you need to start off rather more basic, I think.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: Conrad2468 » Mon Jul 12, 2010 9:30 pm

fine...oxygen and propane will be used in MKII.....can i create a syphon effect by running propane through a T joint connected to the chamber with one open end?
  • 0


Conrad2468
Private First Class
Private First Class
 
Posts: 26
Joined: Thu Jul 08, 2010 10:51 pm
Reputation: 0

Unread postAuthor: Ragnarok » Mon Jul 12, 2010 10:04 pm

Conrad2468 wrote:fine...oxygen and propane will be used in MKII...

Well, I might leave it longer than that, but the results and lessons learnt from the MKI will help gauge whether you'll be ready to deal with these things.

Trust me when I say I'm serious about safety. One of my relatives was killed by a gun exploding.

...well, that's a bit over simplified. It wasn't immediately fatal - it was ultimately the infected wound that killed him, but the exploding gun is still listed as the cause of death on his death certificate.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: Conrad2468 » Mon Jul 12, 2010 10:07 pm

The reason i say that, is MKII will be all steel pipe rated to god knows how many PSI as opposed to PVC. Do i need to use a pressure regulator on my project?
  • 0


Conrad2468
Private First Class
Private First Class
 
Posts: 26
Joined: Thu Jul 08, 2010 10:51 pm
Reputation: 0

Unread postAuthor: Technician1002 » Mon Jul 12, 2010 10:45 pm

Just post the names of the next of kin.. and make sure your will is up to date.. I tried.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Conrad2468 » Mon Jul 12, 2010 10:47 pm

You do realize...that i said im not using oxygen anymore right?
  • 0


Conrad2468
Private First Class
Private First Class
 
Posts: 26
Joined: Thu Jul 08, 2010 10:51 pm
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: Technician1002 » Mon Jul 12, 2010 11:57 pm

OK, Off oxygen and now with air.

Using Propane the fuel is very sensitive to the mix. Too rich or too lean and it is very hard to ignite. For best results, plan on a way to change out the air after each shot so there is fresh air and measure the dose of propane carefully. This can be with a syringe, meter pipe and pressure, calibrated venturi, or other means to deliver the proper ratio of Propane to air. Unmetered blasts of fuel lead to non-uniform performance, often failure to ignite. There is a great Wiki article on proper fuel use with Propane.

http://www.spudfiles.com/spud_wiki/index.php?title=Propane
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: Conrad2468 » Tue Jul 13, 2010 6:43 pm

Ok, heres the new plan, ill have a tank of air attached to a regulator attached to a solenoid. The propane will be attached to a regulator and a solenoid also. The solenoids are attached to a T joint and the other end is attached to the cannon. Im fairly sure this should work.
  • 0


Conrad2468
Private First Class
Private First Class
 
Posts: 26
Joined: Thu Jul 08, 2010 10:51 pm
Reputation: 0

Unread postAuthor: ramses » Tue Jul 13, 2010 10:58 pm

so you'll control the dwell time of the solenoid valves with a microcontroller or similar? You need some kind of control for the propane at least, unless you are using a very accurate low pressure regulator for it. If that is the case, a couple of 555/556 timers should work.
  • 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

Unread postAuthor: Conrad2468 » Tue Jul 13, 2010 11:03 pm

If i get a barrel from here (http://www.launchpotatoes.com/cart.php?act=cart) the compressed air may push the ball out the barrel :/ any ideas? Also, Ill probably use a BASIC stamp seeing as i SUCK with 555 timers (yes, ive worked with them before). However, the Solenoids are 12 volt and the basic stamp is 9...how do i use 9 volts to operate a 12 volt solenoid?
  • 0


Conrad2468
Private First Class
Private First Class
 
Posts: 26
Joined: Thu Jul 08, 2010 10:51 pm
Reputation: 0

Unread postAuthor: Ragnarok » Wed Jul 14, 2010 9:05 am

Conrad2468 wrote:i SUCK with 555 timers (yes, ive worked with them before)

555 timers are pretty simple kit. If you can't work with one of them, I'd say you probably have quite a high chance of burning out the BASIC stamp.

However, the Solenoids are 12 volt and the basic stamp is 9...how do i use 9 volts to operate a 12 volt solenoid?

Well, you shouldn't be driving anything like that directly off an IC output pin anyway.

What you really need is to feed the stamp output into a transistor, then use that to drive a relay.
By using a common ground, you could do it without the relay if you can find a high power transistor (where the required base current is low enough that the IC can drive it properly), but the solenoid is an inductive load, so you'd need to put a high-power diode in reverse parallel to it avoid it damaging the other electronics.
However, you should really be doing that either way (and for both the relay and the solenoid).

However, you'd need to be more careful if you were wiring the 9V and 12V systems as one.

Of course, I'm not much of an electronics guy, so don't be too surprised if someone who does know what they're taking about comes and contradicts me.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: ramses » Wed Jul 14, 2010 9:10 am

put two in series, use one of them for the BASIC stamp, and the other two for the valves. use one of these if you want to follow the specs, but depending on the solenoid valve, it may work better at 18V. You will eat through 9 volts, though.

you could use a rechargeable NIMH battery and make a [url]boost converter[/url] for it. you may even be able to use the solenoid valve as the inductor.

it looks like the BASIC stamp 2 can run anywhere between 5-15V, so...

EDIT: wow. beaten to it. yes, you would need a transistor, yes you should use a freewheel diode, but it needn't be a large one. a standard 1n4007 or something should be fine.

I also struggle with 555 timers, and with a micro-controller, you can digitally control the timing to the microsecond (at least you can with a 16MHZ arduino). They're cheaper cheaper, too, or at least the clones are.
  • 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

Unread postAuthor: Technician1002 » Wed Jul 14, 2010 10:14 am

Compared to a stamp or Arduino, a 555 is dirt cheap. Trying to pwm or precision time a solenoid is not easy. Best bet is to supply air and fuel at a regulated pressure such as somewhere between 5 PSI and 50 PSI. A capillary tube for the air to limit the flow to a known rate and then use a needle valve to calibrate the fuel rate, a pair of solenoid valves on a single timer can take care of the purge/fill cycle for you. This would work just like the beverage dispenser at the local 7-11. Carbonated water and flavored syrup are delivered and mixed right into your cup at a 6:1 mix. Small cup, large cup, same mix and same flow rate, just the time varies. Properly done the vent/purge/fill cycle can happen while the projectile is reloaded as part of a full auto sequence.

The output of most digital control circuits only require a single power MOS transistor, I believe a N channel enhancement mode with an insulated gate is compatible with most low current sources and can directly drive the high power solenoids.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: ramses » Wed Jul 14, 2010 11:15 am

Technician1002 wrote:Compared to a stamp or Arduino, a 555 is dirt cheap.


I was thinking an ardweeny $10.00, plus a USB-serial adapter.

Why would it be hard to precision time a solenoid valve? I mean, pressure would be regulated still, but at a higher pressure so drift/ friction would be lower. Our methods are essentially the same, but yours has a longer time-scale. Would there be an issue with building back pressure (read: Hybrid).with either?
  • 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

PreviousNext

Return to Combustion Cannon Discussion

Who is online

Registered users: Google [Bot], Google Adsense [Bot], Majestic-12 [Bot], Yahoo [Bot]

Reputation System ©'