Search found 3197 matches

by jimmy101
Mon Apr 09, 2007 11:40 am
Forum: Combustion Cannons
Topic: Ratio of marble cannon
Replies: 16
Views: 4063

Spudblaster put it very well. The Latke spark strip / multiple spark data is of only limited use. Indeed, I looked at his comparison of two versus three sparks on the strip and there is no statistically significant difference in muzzle velocities. http://home.earthlink.net/~jimsluka/_images/Latke_sp...
by jimmy101
Sun Apr 08, 2007 6:04 pm
Forum: Combustion Cannons
Topic: Ratio of marble cannon
Replies: 16
Views: 4063

If the chamber is too big, the cannon will be too loud, but there's no real negative effect. For this reason, I always tend to go chamber-heavy. This is not true for combustion guns. A too-big chamber will decrease the muzzle velocity of the gun. The maximum muzzle velocity for a combustion gun occ...
by jimmy101
Sun Apr 08, 2007 8:58 am
Forum: Combustion Cannons
Topic: Ratio of marble cannon
Replies: 16
Views: 4063

If the chamber is too big, the cannon will be too loud, but there's no real negative effect. For this reason, I always tend to go chamber-heavy. This is not true for combustion guns. A too-big chamber will decrease the muzzle velocity of the gun. The maximum muzzle velocity for a combustion gun occ...
by jimmy101
Sat Apr 07, 2007 12:53 pm
Forum: Ammo & Parts
Topic: How the heck do you rifle PVC pipe??
Replies: 32
Views: 16960

Instead of cutting the grooves into the barrel you might consider building up the lands instead. Wild Ass, Untested, Method 1: Get some, say, 1/8" thick by 1/4" wide plastic (PVC would be perfect) and glue it in a spiral inside the barrel. Wild Ass, Untested, Method 2: Get on old metal slinky. Stret...
by jimmy101
Sat Apr 07, 2007 12:37 pm
Forum: Off-Topic Hobbies
Topic: I'm still waiting for a credible answer to this
Replies: 9
Views: 2264

The peak chamber pressure in "typical" combustion spud guns (propane + air) has been measured a couple of times. IIRC nobody has ever measured a peak pressure greater than about 60 PSIG. Unfortunately, measuring the peak pressure isn't as easy as it sounds. The pressure peak is so short that many ty...
by jimmy101
Sat Apr 07, 2007 12:02 pm
Forum: Combustion Cannons
Topic: propane help
Replies: 11
Views: 2275

I don't believe anyone has ever gotten a combustion gun to fire from sparking in a brushed fan. Too bad really, it would have been an primo ignition system. DR regularly uses the "personal fans" from Kmart and has never had a premature firing (of his spudgun anyway). Still, with a brushed fan all th...
by jimmy101
Sat Apr 07, 2007 12:01 pm
Forum: Ammo & Parts
Topic: Laser pens
Replies: 13
Views: 3595

Wrap a rubber band around the laser so it covers the switch.
by jimmy101
Sat Apr 07, 2007 11:37 am
Forum: BB, Airsoft, and Pellet Guns
Topic: Backspin
Replies: 12
Views: 3190

For BBMG's people have cut a narrow slot perpendicular to the length of barrel a short distance before the muzle. Then use a small rubber band or O-ring around the barrel that fits into the slot as the "hop-up" mechanism. Making the slot deeper allows the O-ring to block more of the barrel. Too chal...
by jimmy101
Fri Apr 06, 2007 11:28 am
Forum: Off-Topic Hobbies
Topic: Can E-BAY Sellers Really do this???
Replies: 8
Views: 2136

Re: Can E-BAY Sellers Really do this???

... He requested a divers license because he assumes all buyers are under 18, i just dont see where he has the jurisdiction to do this. Can he do this??? ... Of course he can. He can do whatever he f'ing pleases. He can only sell to left handed Martians if he wants. Why would he have to sell to you...
by jimmy101
Thu Apr 05, 2007 2:30 pm
Forum: Combustion Cannons
Topic: new way of using camera for ignition
Replies: 20
Views: 5334

Hunter1992-
Very clever. Have you actually tried this in a cannon yet?

I wonder how much recoil there will be on the trigger.

Of course, if you do touch both leads... disposable camera flash units have ~7 joules stored in the cap.
by jimmy101
Thu Apr 05, 2007 12:15 pm
Forum: BB, Airsoft, and Pellet Guns
Topic: legitimate count per second
Replies: 19
Views: 4052

Measuring the ROF is pretty easy if you have an old PC or laptop laying around. (I can't believe how backwards this forum is.) Just use the PC to record the sound of the gun firing, or, the sound of the ammo hitting a target. Use any old sound editing software to display the waveform and measure the...
by jimmy101
Thu Apr 05, 2007 11:43 am
Forum: General How-To & Discussion
Topic: c:b ratio to destroy the cannon???
Replies: 12
Views: 2103

Well, you could make a chamber that wouldn't hold up to the pressure. Since the volume of a cylinder increases much faster than the inner surface area when you increase the size of the chamber, the pressure exerted by the force of the combustion on each square inch increases. I'm not sure how quick...
by jimmy101
Tue Apr 03, 2007 5:40 pm
Forum: Combustion Cannons
Topic: peizio wont work!
Replies: 13
Views: 2795

If it's an electric arc it is hotter than the surface of the sun, makes no damn difference if the spark is 0.01" or 0.5" long, it is more than enough to ignite the fuel. With aerosol fuels, mixing is often inconsistent, and so an ignitable fuel mixture is often not achieved between the ignition ele...
by jimmy101
Mon Apr 02, 2007 1:46 pm
Forum: Off-Topic Hobbies
Topic: Help me with electricity (Making a new taser)
Replies: 10
Views: 2271

You really can't wire up several transformers in series and expect them to boost the voltage to an "interesting" level. There are all kinds of limitations; the inductance and saturation of the transformers, resistance ... Besides, when you start getting into the "interesting" voltage range you'll ha...
by jimmy101
Mon Apr 02, 2007 1:42 pm
Forum: Combustion Cannons
Topic: peizio wont work!
Replies: 13
Views: 2795

If lengthening the spark gap solved the problem then the spark gap wasn't the problem in the first place. A spark is a spark is a spark. If it's an electric arc it is hotter than the surface of the sun, makes no damn difference if the spark is 0.01" or 0.5" long, it is more than enough to ignite the...