Page 2 of 2
Posted: Fri May 15, 2009 2:54 pm
by Woody
Yeah thanks for the info. I don't think I'm gonna be making any pvc or abs hybrids though. 1.5 mix isn't that appealing to me, nor is 10x. I just wanna be able to take one up to 4x or so. Anyways I have 2 pneumatics on my list of things I want to make first before I move on to hybrids.
Posted: Sat May 16, 2009 9:07 am
by c11man
4x will get you some very good power expecaly for the beginer spudder.
and when you think you have a solid design for a hybrid just post it and we will help make it better/work
Posted: Sat May 16, 2009 10:03 am
by inonickname
Don't make a hybrid cannon from PVC. I know they can fail, even after being made from a 3 layer sandwich of PVC. And anyway, whats the point of a 1.5x propane hybrid? you could just use MAPP and get two shots in the same amount of time emssing around.
Things you should (could) do:
The sparkgap needs to be reduced (divided) by your mix. This is because the 'atmosphere' is thicker and takes more energy to pass through a certain area. Also, pointed electrodes lose less energy over a distance. If your feeling lazy an automotive sparkplug works fine.
Use a shorter, fatter chamber. At any mixes, you'll probably find you don't get deflagration to detonation transition as the main causes are fast burning fuels (acetylene, hydrogen) and the presence of an oxidizer (O2, NO2, KNO3, KMnO4 etc..). Though still, something good to avoid.
If you've never fired a hybrid before, a mix around 5x should impress you. Using fittings such as malleable iron, galvanized, copper for ease..threaded joints will get you there but remember to be fair with the teflon tape.
Then you need something to retain pressure, but release it upon ignition. A piston valve can be used, but this is more complex so a burst disk is usually a better approach. You can use camlocks (lower mixes only) or unions. Unions are simply sections which thread together with an o-ring. By sealing a thin sheet of material (eg. aluminum foil) between the union sections an airtight seal is given which tears away and opens upon ignition.
For metering your best bet is to make a meter that will supply a 1x charge, then use it as many times as required to get the charge you want. Then you can use it with whatever mix you want. An air supply is needed which can be regulated from a bottle or compressor or pumped with a manual pump. Easy enough.
Be safe, if you need any more help feel free to give us a bell.