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moot1337 · 08-04-2003, 04:53 PM

I've been into the whole spud gun thing for a few years now... I started out with a very simple PVC gun like the one described in the first post... used a coleman lantern ignitor instead of the bbq thing though... i was a bit low on funds at the time. For fuel I use Right Guard in the aerosol can - contains butane, propane, and isobutane so it has a decent rate of combustion at the least...

The best fuel I've found so far (without use of oxygen gas as well) has been calcium carbide - it comes as little rocks which release acetylene gas when they come in contact with water... you can either put a couple rocks in the square impression in the endcap with some water and screw it on/wait/deal with mess later, or you can put a bunch into an old fire extinguisher (empty and with straw removed) with some water, let that react for a while, and turn it upside down and squirt out the water when it's done. If you do the fire extinguisher method, a small release of acetylene will do the job... it's really strong stuff.

After the first PVC one I made a real monster out of ABS: 2.5-3 feet of 3" abs pipe, then a 3" to 1.5" threaded reducer, then a 1.5" to 3" threaded reducer and another section of 2.5-3 feet of 3" abs. The choke in the middle of the whole thing really increases the power... a 6" section of 3" pipe just wouldn't do anything :/ This gun also has a barbeque ignitor in the cap, though I might try the screw method some time soon.

I also constructed a pvc pneumatic spud gun in a U shape with 4 feet of 2" pvc threaded into a 1" solenoid sprinkler valve and a 4 foot long 2" diameter pressure chamber... wedged between both chambers is a battery pack of three 9 volt batteries linked together to switch the solenoid - one thing to remember about solenoid valves is they can require a lot of volts to make them open properly, some as much as 18-24 volts. Both the ABS combustion gun and this PVC pneumatic shoot pretty comparatively, though there are drawbacks to both... the ABS one is sometimes sensitive to cold when using right guard, though with acetylene it will fire almost no matter what. The ABS gun also sounds like Hiroshima all over again, and the PVC pneumatic sounds a bit like the sound a goose being strangled by a 240 volt power cord would make. There is also the drawback of mobility when you have to use an air compressor, as the ABS one will go just about anywhere, especially while in the 3 foot long segments.

Hope this helps... or is at least a testament to my insanity! woot!

08-04-2003, 04:53 PM	#52 (permalink)
moot1337 Insane Location: Learning to Fly...	I've been into the whole spud gun thing for a few years now... I started out with a very simple PVC gun like the one described in the first post... used a coleman lantern ignitor instead of the bbq thing though... i was a bit low on funds at the time. For fuel I use Right Guard in the aerosol can - contains butane, propane, and isobutane so it has a decent rate of combustion at the least... The best fuel I've found so far (without use of oxygen gas as well) has been calcium carbide - it comes as little rocks which release acetylene gas when they come in contact with water... you can either put a couple rocks in the square impression in the endcap with some water and screw it on/wait/deal with mess later, or you can put a bunch into an old fire extinguisher (empty and with straw removed) with some water, let that react for a while, and turn it upside down and squirt out the water when it's done. If you do the fire extinguisher method, a small release of acetylene will do the job... it's really strong stuff. After the first PVC one I made a real monster out of ABS: 2.5-3 feet of 3" abs pipe, then a 3" to 1.5" threaded reducer, then a 1.5" to 3" threaded reducer and another section of 2.5-3 feet of 3" abs. The choke in the middle of the whole thing really increases the power... a 6" section of 3" pipe just wouldn't do anything :/ This gun also has a barbeque ignitor in the cap, though I might try the screw method some time soon. I also constructed a pvc pneumatic spud gun in a U shape with 4 feet of 2" pvc threaded into a 1" solenoid sprinkler valve and a 4 foot long 2" diameter pressure chamber... wedged between both chambers is a battery pack of three 9 volt batteries linked together to switch the solenoid - one thing to remember about solenoid valves is they can require a lot of volts to make them open properly, some as much as 18-24 volts. Both the ABS combustion gun and this PVC pneumatic shoot pretty comparatively, though there are drawbacks to both... the ABS one is sometimes sensitive to cold when using right guard, though with acetylene it will fire almost no matter what. The ABS gun also sounds like Hiroshima all over again, and the PVC pneumatic sounds a bit like the sound a goose being strangled by a 240 volt power cord would make. There is also the drawback of mobility when you have to use an air compressor, as the ABS one will go just about anywhere, especially while in the 3 foot long segments. Hope this helps... or is at least a testament to my insanity! woot!