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 64 users online :: 5 registered, 0 hidden and 59 guests


Most users ever online was 218 on Wed Dec 07, 2016 6:58 pm

Registered users: Bing [Bot], Exabot [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

Grom rifle

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
Sponsored 
  • Author
    Message

Grom rifle

Unread postAuthor: NeoTheFox » Sat Aug 03, 2013 1:11 pm

Hi guys, here is my first spud rifle. I made it using the remains from countryside home construction.
It fires well, but I have a problem - the cover of the blast chamber is always cracking after a few shoots - it happens because it is held by 2 bolts and metal frame, and bolts are tearing the cover apart. I want to enforce it somehow.

Image

Image

Image

It is not painted yet, because of my chamber problems. And yes, there are calamps and other stuff under the tape.

It fires screws covered with tape.

What do you think?
  • 0

User avatar
NeoTheFox
Private
Private
 
Posts: 4
Joined: Sat Aug 03, 2013 12:37 pm
Location: Moscow
Reputation: 0

Unread postAuthor: Gun Freak » Sat Aug 03, 2013 4:17 pm

Cool fueling, but that hose connection is unspeakably hurting performance.
  • 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: jackssmirkingrevenge » Sun Aug 04, 2013 3:21 am

I think I prefer the original Grom ;)

You don't need such a big chamber, and as Gun Freak pointed out, the way it's connected to the barrel is not the way to go for good performance.

Also, consider syringe fuelling :)

  • 0

Last edited by jrrdw on Fri Oct 18, 2013 7:30 pm, edited 1 time in total.
Reason: Fixed video.
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: NeoTheFox » Sun Aug 04, 2013 11:15 am

Thanks for feedback, guys!
When you are saying hose connection, you mean pipes connected to each other, or the hose I used to connect combustion chamber and the pipe?
I can see, how having funnel at the end of combustion chamber would help, but I never thought it is SO important. I'll build a new one soon enough, using an old teapot as a chamber, so I want to do everything right this time.
And yes, about syringe fueling - I am using spray as a fuel, and there is no way I can use syringe :(
  • 0

Image
User avatar
NeoTheFox
Private
Private
 
Posts: 4
Joined: Sat Aug 03, 2013 12:37 pm
Location: Moscow
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Mon Aug 05, 2013 3:45 am

NeoTheFox wrote:Thanks for feedback, guys!
When you are saying hose connection, you mean pipes connected to each other, or the hose I used to connect combustion chamber and the pipe?
I can see, how having funnel at the end of combustion chamber would help, but I never thought it is SO important. I'll build a new one soon enough, using an old teapot as a chamber, so I want to do everything right this time.


It's got to do with how the fuel burns.



That skinny pipe means that most of the energy is probably being wasted.

You should aim for a chamber that is short and fat, and if possible directly connected to the barrel.

And yes, about syringe fueling - I am using spray as a fuel, and there is no way I can use syringe :(


Yes you can! If you can't buy one from a Pharmacy in Moscow, then you could always try eBay ;)

Jimmy has an excellent page on how to use a syringe and cigarette lighter: http://www.inpharmix.com/jps/Fuel%20Met ... ghter.html
  • 0

Last edited by jrrdw on Fri Oct 18, 2013 9:57 am, edited 1 time in total.
Reason: Fixed video.
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: Technician1002 » Mon Aug 05, 2013 6:56 am

To get an idea of what the hose does to your performance, Exhale as quickly as possibly through the paper core from a roll of paper towels. Blow a marshmallow out of it.

Now repeat the above task but use a drinking straw between you and the paper towel core.

Your hose does the same thing to your flow from your chamber to your barrel. The same chamber pressure you get blowing through the straw is the same pressure your chamber feels being restricted by the small hose. The pressure can't get out, so it breaks things.
  • 0

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

Unread postAuthor: NeoTheFox » Sun Aug 11, 2013 8:25 am

Hi again guys, I followed your advices and removed hose connections, now I have a solid pipe coming from the chamber to the barrel. I also tried to reinforce the cover with a metal plank, but now the pressure bent metal corners of it. I then tries syringe fuelling with no luck, my calculations tells me I need 3 cm^2 of the propane, but even with twice as much gas it would not ignite (neither it will with less gas). However I figured out how to mod a lighter to fill the chamber, and now it fires even better, but it eats lighters very fast. Any idea why Propane fuelling failed? And thanks for advices I already took! :roll:
  • 0

Image
User avatar
NeoTheFox
Private
Private
 
Posts: 4
Joined: Sat Aug 03, 2013 12:37 pm
Location: Moscow
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: Blitz » Sun Aug 11, 2013 2:50 pm

Did you ensure you have the right mixture? ~4.2%. Beyond that, the more you add, the less powerful it'll be - until it won't ignite due to the lack of air (Too rich)

Also, just curious - how thick is that plate?
  • 0

User avatar
Blitz
Colonel
Colonel
 
Posts: 621
Joined: Sat Apr 07, 2007 1:48 am
Location: West Chicago, IL
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Sun Aug 11, 2013 11:51 pm

I could be that the large mouth of your chamber is allowing the gas to escape. Inject slowly, and with the syringe nozzle as close to the "bottom" of the chamber as possible.

Also, 3cm<sup>3</sup> sounds far too low for your chamber size. It looks like you have a volume greater than one litre from the photos, meaning you should be injecting at least 30cm<sup>3</sup>.

edit: units...
  • 0

Last edited by jackssmirkingrevenge on Mon Aug 12, 2013 5:13 pm, edited 2 times in total.
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: NeoTheFox » Mon Aug 12, 2013 9:21 am

The chamber's volume is 31cm^2, and the pipe is 2cm inner diameter, and 2,2cm outer diameter. When I decided to use syringe fuelling I sealed the cover, and made a small hole for fuelling.
  • 0

Image
User avatar
NeoTheFox
Private
Private
 
Posts: 4
Joined: Sat Aug 03, 2013 12:37 pm
Location: Moscow
Reputation: 0

Unread postAuthor: dewey-1 » Mon Aug 12, 2013 10:03 am

jackssmirkingrevenge wrote:I could be that the large mouth of your chamber is allowing the gas to escape. Inject slowly, and with the syringe nozzle as close to the "bottom" of the chamber as possible.

Also, 3cm<sup>2</sup> sounds far too low for your chamber size. It looks like you have a volume greater than one litre from the photos, meaning you should be injecting at least 30cm<sup>2</sup>.


Should it not be 30cm^3 (30cc) or 30mL?
Maybe I am missing something here! :)
  • 0

User avatar
dewey-1
Major General
Major General
 
Posts: 1298
Joined: Wed Mar 28, 2007 10:24 am
Location: NE Wisconsin USA
Reputation: 0

Unread postAuthor: jackssmirkingrevenge » Mon Aug 12, 2013 5:12 pm

dewey-1 wrote:Should it not be 30cm^3 (30cc) or 30mL?
Maybe I am missing something here! :)


I stand corrected :oops:

NeoTheFox, I'm pretty sure your chamber is much bigger than 31cm<sup>3</sup>... are you sure you calculated radius x radius x 3.142 x length?

http://www.online-calculators.co.uk/vol ... volume.php
  • 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

Return to Combustion Cannon Database

Who is online

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

Reputation System ©'