This will probably look fairly familiar seeing as I was inspired by SpudBlaster15's piston hybrid that he posted the other month. I've been working on this since early September and now it's in working order. I'm sure, like SpudBlaster, I'll change a few things over the coming weeks but for now this is its completed state.
I've fired about six shots out of it since I completed it yesterday. Five shots at a 5x mix and one at a 7x mix. After that, the piston bounce damaged the sealing face causing it to leak and damaged the gasket on the pilot valve part of the piston. I've now increased flow out of the pilot valve to minimize piston bounce. So it should be up and running by Monday or Tuesday and hopefully some videos will follow.
Specifications: Chamber:50mm galvanized iron pipe and fittings about 750mm long Barrel:2m length of 51.8mm O.D. x 1.5mm thick stainless steel tube Valve:1.5" porting bolt and washer piston valve, double o-ringed, rides in 50mm diameter galvanised iron pipe and fittings. Pilot valve:Unbalanced spool valve. Ignition:wireless 100kv stungun circuit wired up to two sets of electrodes like those seen in Hubb's homemade spark plug. Metering:Manometric Fuel:MAPP gas Venting:So far I have been using the cannon as a pneumatic to vent it (put pressure behind the piston, fill the chamber, vent the pilot volume), but that takes a lot of effort with a track pump so I might try other methods.
The fuel meter disconnects from the cannon when it's ready to fire. There is an air regulator between the ball valve and 0-15PSI gauge to protect the gauge from being over-pressurized on accident, the regulator is locked in at 10PSI. The whole thing weighs around 17kgs. HGDT predicts ~500ms golf balls at a 10x mix if I remember correctly. Testing will come in the next few weeks once everything has been fine-tuned, sorted out and University is finished for the year. Now for pictures...
Edit 14/11/11:
Increased pilot porting to 25mm because piston bounce has been destroying my sealing faces. New barrel support. New remote ignition. New piston sealing face. Added chamber length. New barrel. You will probably notice the 1" galv pipe sticking out of the chamber. I removed the second ignition electrodes and put the pipe in its place to help deal with recoil. Recoil will still be a [female doggy], but hopefully not so bad. The Steyr rifle sling is there to help distribute the weight.
Ha, soon we piston hybrid builders will conquer the entire world.
That's the plan.
jackssmirkingrevenge wrote:
Not this part of Europe you won't, friction seals FTW!
Friction seals/detent systems limit projectile choices too much to fit the model of what a spudgun is - A device capable of launching whatever the heck you can fit in the barrel at high speed. As such, those systems will never be practical for anything other than small scale experimental launchers. The future of hybrid technology will most certainly involve a main valve of some sort.
Joined: 23 Jun 2006 Posts: 10057 12582.50 Spud Bux
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also Crowley, your mythology reference wasn't lost on me. You should read "The Long Dark Tea Time of the Soul
Maybe I'll get round to it but I'm still working my way through the Prose Edda
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so you're saying that manometric metering works fine, right ?
Yup, I prefer it over volumetric. My 0-15PSI gauge isn't even that expensive, cost me $20 secondhand. No idea what the accuracy is but it would be around 1.0-2.0% F.S. If I recall correctly, I worked out that even a 2.0% F.S. accurate gauge would give either a lean mix of 4.2 mapp:air ratio or a rich mix of 5.0 mapp:air, which is still right in the zone for ignition.
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WOW, I've seen some WIP pics, but I'm still amazed! great work MrC
Thanks How are you coming along on your hybrid?
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Not this part of Europe you won't, friction seals FTW!
Shouldn't be too hard to takeover your part of the world then...those 1mm BBs are really scary, I might have to wear a sweatshirt
Joined: 23 Jun 2006 Posts: 10057 12582.50 Spud Bux
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so you're not using a reg ? well I paid less than 10$ for a 0-51psi reg so I am pretty sure you can find something similar in NZ
Na, the regulator shown on the metering setup is only there to protect the 0-15PSI gauge from over-pressurization. If I forgot to close the ball valve and open the air inlet, 50PSI or so could run through the 0-15PSI gauge and ruin it.
You want to use manometric metering with just a regulator? I guess that would work as long as the regulator is accurate enough. I assume you meant 0-15PSI and not 0-51PSI reg?
Joined: 23 Jun 2006 Posts: 10057 12582.50 Spud Bux
Lockednloaded wrote:
Eh, mine's coming along, just slower than I planned. I broke a spark plug yesterday
Also, I thought you were going to put a BV vent, when's that coming?
I got sick of looking for a sparkplug that I could tap in to some fitting so I just made my own like in Hubb's guide
Don't think I will put one in. I can run the cannon like a pneumatic which will vent out the chamber, I also need to try SB15's method of just pressurizing the meter to 140PSI and venting it through the chamber.
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but pretty is as pretty does, let's see it in action!
