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 78 users online :: 5 registered, 0 hidden and 73 guests


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

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

The Team
Administrators
Global Moderators
global_moderators.png CS

Help with combustion

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

Help with combustion

Unread postAuthor: Hubb » Sat Aug 25, 2007 3:52 pm

I am looking to build an advanced combustion cannon (you know; propane injection, fan, and all that good stuff). The problem I got is that I don't want it to be too big because I want my kids to be able to shoot it.

I figured on using a 1" barrel with a 2" chamber. I put these sizes in the ratcalc and it figured that for a .8:1 ratio, the chamber would be 6" and the barrel 30". I think that may be too long for what I am looking for.

I thought about using a 1.5" pipe for the chamber. This would allow for a shorter barrel to get the ratio.

The problem I have is that if I use a 1.5" chamber, I'm concerned about the power because, after all, I'm still a guy.

Does anyone have any experience with a cannon this size and, if so, does it have decent power for a "guy's toy"?
  • 0

User avatar
Hubb
Major General
Major General
 
Posts: 2390
Joined: Mon May 28, 2007 8:39 am
Location: South Georgia
Reputation: 2

Unread postAuthor: Gepard » Sat Aug 25, 2007 4:10 pm

Could you not make it standard size and then make a small tripod to rest it on for your kids? I'm sure they'd much rather you made a big one :D
  • 0


Gepard
Captain
Captain
 
Posts: 342
Joined: Mon Jun 18, 2007 11:12 am
Reputation: 0

Unread postAuthor: homedepotpro » Sat Aug 25, 2007 8:08 pm

the thing with going small is you have to be very precise in you fuel meter measurements
  • 0

Image
User avatar
homedepotpro
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 443
Joined: Sun Nov 26, 2006 1:00 am
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sat Aug 25, 2007 8:31 pm

I'm concerned about the power because, after all, I'm still a guy.


Love your reasoning :) Don't worry, with a fan in the mix the power should be there.
  • 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: Novacastrian » Sat Aug 25, 2007 8:54 pm

I made a cannon about the size you are talking about, maybe even a little smaller- Anyway i used one of those little pc fans but it only survived for about 10 shots if that, i don't know if it was on it's way out already.
It had lots of power though, your's should be fine with nice fitting ammo.
  • 0


Novacastrian
Major General
Major General
 
Posts: 1604
Joined: Sat Aug 11, 2007 6:59 pm
Reputation: 0

Unread postAuthor: Hubb » Sun Aug 26, 2007 5:16 am

Thanks guys. I mainly build pneumatics (after an incident with my first combustion, which can be read about in that "cannon accident" thread). However, after seeing some of the outstanding creations on this site, and then building my mini, I want one so bad. It should be posted by next weekend.
  • 0

User avatar
Hubb
Major General
Major General
 
Posts: 2390
Joined: Mon May 28, 2007 8:39 am
Location: South Georgia
Reputation: 2

Unread postAuthor: Hubb » Sun Aug 26, 2007 6:09 am

Another question:

In this combustion, I want to put a camera flash ignition with a homemade induction coil for the spark (I figured this would be harder to do than just sticking on a stun gun, and I always like a challenge).

I was wondering if anyone has made one of those homemade induction coils from this site and, if so, does it work good?
http://www.sciencebuddies.org/mentoring/project_ideas/Elec_p027.shtml

Another question:
I looked at the advancedspuds.com site. It said something about using a check valve on the chamber to aid in rapid venting. My question is if the fan opens the check valve to vent the chamber, won't it open it again when mixing the fuel? I'm pretty sure it does so is there a solution to this?
  • 0

User avatar
Hubb
Major General
Major General
 
Posts: 2390
Joined: Mon May 28, 2007 8:39 am
Location: South Georgia
Reputation: 2

Sponsored

Sponsor
 


Unread postAuthor: jimmy101 » Sun Aug 26, 2007 4:38 pm

hubb017:

Making a homebrew step-up transformer shouldn't be too hard (but a bbq piezo is a heck of a lot simpler, safer, and probably cheaper).

The cite uses bare copper wire for the primary so it is important that the primary coils don't touch each other. With insulated primary wire you can omit the PVC insulation between the two coils (and it'll work better without the thick hunk of PVC in there), the primary can be wound right on top of the secondary. A layer or two of electrical tape might be a good idea between the primary and secondary.

Obviously, you don't need the Neef vibrator. The setup in the cite is also called a buzz coil. Ford's used to use this as an automotive ignition system way back when. This basic circuit has also been used in cheapo hand held, battery operated "Sears Tower" radiation detectors.

12G wire for the primary is several gauges to small (the wire diameter is way bigger than needed). 15 to 20G or so wire should be able to handle the power that a photocap will supply. Since the cap supplies current for much less than 1 second you can use much smaller wire than what would be required for a continuously operating system. 30G for the secondary would be good. RadioShack sells (or at least they used to) a set of three spools of magnet wire; 20, 24 and 30G IIRC for $5.

Somewhere I have the equations for choosing the wire size for this type of coil. If you want I'll dig them up.

The photocap is 300~320V so a 30:1 turns ratio will give you ~9KV which should be more than enough for an ignition system.

The 2Meg resistor is probably not needed, neither is the capacitor. You probably will need a diode across the coil. When the current stops and the magnetic field collapses the coil will send a big negative voltage pulse back into the flash charging circuit. The photcap might be able to absorb that pulse, if not, it'll fry the transistor(s) in the circuit.

The power/fire switch is tricky. Most switches won't last very long at the 300V and tens (hundreds?) of amps the photocap will supply. A "trigatron" is probably the best way to go. (IIRC, "Trigatron" is SixMHz's name for it.) Basically, you leave the entire photoflash circuit intact, including the Xenon flash bulb. The primary of your coil is wired in series with the flash tube. The "switch" is basically the flashtube itself, the trigger is the trigger on the flash board for the tube. This setup completely avoids having to have a high power switch, any old switch will handle the flash board's trigger circuit.

If you do make a homebrew step-up transformer then please post it. If it works out well it would make a great "How To" and/or Spud Wiki page.

As to the check valve and venting, I don't think the fan is strong enough to pull the check valve open, IIRC you have to help it with a small push. When the gun is loaded the operation of the fan doesn't put any load on the check valve, it's a closed chamber, running the fan just moves the gases around it doesn't generate a significant pressure gradient. You might want to take a look at Burnt Latkes' vent valve.
Image Image
from here.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3127
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Doodmens, Google [Bot], Google Adsense [Bot], Yahoo [Bot]

Reputation System ©'