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Community Project #1 - Handheld, High Mix, Hybrid

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: Hubb » Mon Sep 28, 2009 3:25 pm

POLAND_SPUD wrote:so what about the design I draw... of course it cartridge could be sleeved in PVC or ALU to keep the same OD... if it was possible to thread the inside of PVC pipe that could be even simpler...

nah wait a second... all you need is a female-female adapter (or pipe with theadeds on the inside)... and short lenghts of threaded alu pipe (pipe nipples) to hold the disk... the you can epoxy that part into a larger pipe


This was the same design I have envisioned for a cartridge and I think something similar to this is going to be the best way to go.
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Unread postAuthor: Moonbogg » Tue Sep 29, 2009 9:23 pm

Brian the brain wrote:Why not use an onboard high pressure pump like on a Benjamin airgun to draw in the mix and compress it.
All you would need is a checkvalve to insert the mix, then compress.

just make a 1x mix, keep a fan running and pump away.

The pumphead would just not get a checkvalve that;s all..


I think something like this would be a great way to make s self contained hybrid. We could inject mapp gas to desired pressure with a gage, and then simply pump the required ammount of air in via an attached pump and check valve. It seems too elegant and easy to not explore. We could make use of a single chamber this way making the design simpler. Once we decide I will start drawing up parts and submit them as a part of my contribution.
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Unread postAuthor: starman » Wed Sep 30, 2009 12:06 am

An idea for fueling could be to use the compact pressurized isobutane/propane canisters that is used for camping gear.

Image

http://www.jetboil.com/products/accesso ... erfuel100g

A standardized fuel "cartridge well" using common camping plumbing connected to the metering system (whatever that might be) could be designed to accept these relatively quickly. No, they aren't the capacity of 14 or 16 oz canisters, but they aren't the weight or near the size either, and you should still be able to get several shots out of it.
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Unread postAuthor: Technician1002 » Wed Sep 30, 2009 1:45 am

Moonbogg wrote:
Brian the brain wrote:Why not use an onboard high pressure pump like on a Benjamin airgun to draw in the mix and compress it.
All you would need is a checkvalve to insert the mix, then compress.

just make a 1x mix, keep a fan running and pump away.

The pumphead would just not get a checkvalve that;s all..


I think something like this would be a great way to make s self contained hybrid. We could inject mapp gas to desired pressure with a gage, and then simply pump the required ammount of air in via an attached pump and check valve. It seems too elegant and easy to not explore. We could make use of a single chamber this way making the design simpler. Once we decide I will start drawing up parts and submit them as a part of my contribution.


I don't like the idea of pumping a mix simply due to safety reasons. An accidental ignition for any reason will likely result in an undesired outcome. Pumping up an air chamber and filling a meter tube to the same pressure for mix on delivery makes more sense and keeps the explosive mix in the combustion chamber where it belongs.

For partial use for multiple shots, both the fuel and air can go through a check valve and mix in a T on delivery. Both gasses expand at the same rate, so volumetric metering of both propane and air can occur together. For example the air and propane are both filled to 100PSi and due to a guage accuracy the propane or air is 5 PSI high, an initial bleed/purge of the fuel system will bring down both prssures to say 95 PSI (both gauges move) and after that all deliveries are the proper mix. For example filling the chamber for a 5X mix could leave the air/fuelmeter at 80 PSI for example as the draw dropped both by 15 PSI. Care needs to be taken to prevent propane condensation at higher pressure.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 30, 2009 2:10 am

Technician1002 wrote:I don't like the idea of pumping a mix simply due to safety reasons.


True, true. In the case of cartridges I would be in favour of injecting the fuel with a syringe through the cartidge mouth, popping the projectile/burst disk on then filling to the required pressure with air from a schrader mounted at the other end. You could also make an adapter that screws on to the schrader and cracks it open while fitting a syringe so both fuel and air can go into the sealed cart.
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Unread postAuthor: Technician1002 » Wed Sep 30, 2009 2:45 am

jackssmirkingrevenge wrote:
Technician1002 wrote:I don't like the idea of pumping a mix simply due to safety reasons.


True, true. In the case of cartridges I would be in favour of injecting the fuel with a syringe through the cartidge mouth, popping the projectile/burst disk on then filling to the required pressure with air from a schrader mounted at the other end. You could also make an adapter that screws on to the schrader and cracks it open while fitting a syringe so both fuel and air can go into the sealed cart.


I would prefer an air chuck on the mixing T and simply press the chuck on the valve to charge it with mix. No measuring, no guessing, simple as filling a tire. If doing carts, instead of using metering volumes, metering jets (like a torch head orifice) can be fitted to the mixing T connected to a chuck. Both gases (air and fuel) would be regulated and would mix on delivery based on the ratio of the two metering orifices. A tracking fuel pressure regulater can track the air supply pressure if desired for multiple filles from a field compressed air tank.

The outlet would simply be a single air chuck.

Think soda fountain dispenser. The syrup and carbonated water mix in the nozzle, 5 parts water, 1 part syrup. Mixing on delivery the air and fuel can be done the same way.
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Unread postAuthor: psycix » Wed Sep 30, 2009 4:01 am

As I said, you shouldn't pump a mix, but you should pump the air and fuel separately.
Inject fuel (regulated manometrically) and then pump the air in.

Cartridges take too much time to refuel and reload in my opinion. Sure, the cannon can be fired very rapidly as long as you've got filled cartridges, but you need lots of preparation before doing so.
A filled cartridge shouldn't be stored for a long time (safety issues, and the mix might leak away), and thus youshould fill them right before shooting anyway, making you fire less shots per hour overall.
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Unread postAuthor: Moonbogg » Wed Sep 30, 2009 5:42 am

I wasn't talking about pumping a pre mix. I meant it qould be great to add MAPP, and then pump in air to the chamber. The mix would only take place in the chamber.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 30, 2009 5:50 am

psycix wrote:Cartridges take too much time to refuel and reload in my opinion. Sure, the cannon can be fired very rapidly as long as you've got filled cartridges, but you need lots of preparation before doing so.
A filled cartridge shouldn't be stored for a long time (safety issues, and the mix might leak away), and thus youshould fill them right before shooting anyway, making you fire less shots per hour overall.


Seems the jury's still out on the issue, should we put it to a vote? I would prefer to see a cartridge fed mechanism but would back the project either way.
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Unread postAuthor: inonickname » Wed Sep 30, 2009 6:19 am

I say cartridges. The cool factor does it.

By the way, I mucked around with low voltage ignitions and steel wool would work fine. A single strand of fine steel wool and a nine volt battery will throw glowing bits of metal around a meter and will easily ignite the entire chamber.

Edit: not worded well. Would ignite the chamber easily even if fuel mixing was poor.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 30, 2009 6:31 am

inonickname wrote:I mucked around with low voltage ignitions and steel wool would work fine. A single strand of fine steel wool and a nine volt battery will throw glowing bits of metal around a meter and will easily ignite the entire chamber.


Does this mean the strand needs to be replaced fpr every shot?
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Unread postAuthor: inonickname » Wed Sep 30, 2009 6:45 am

Yes. Nichrome would negate this issue and only need to be replaced rarely. You could use more strands of steel wool, but you would end up with inaccuracies in fueling (in smaller chambers) and less reliability.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 30, 2009 6:57 am

inonickname wrote:Yes. Nichrome would negate this issue and only need to be replaced rarely.


Better, since the major objection to cartridges seems to be the time it takes to prepare them.
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Unread postAuthor: Hubb » Fri Oct 02, 2009 7:30 am

Obviously, the biggest concern now is the preparation of cartridges. To an extent, I do agree. I can see this being a real PITA. This means that we should probably come up with a solution to filling the cartridges.

I'm still leaning on something like the Gen 3 hybrid to do this. If it is set up right, cartridges could be filled and reloaded in less than a minute a piece.
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Unread postAuthor: Moonbogg » Fri Oct 02, 2009 7:59 am

A manifold system could be used to fill all the cartridges at the same time. If a rotary chamber design we used, there could be check valves on the back of each chamber and they could all lead to a single fill point, allowing all the chambers to be refilled at once without having to be dismantled or ejected from the gun.
Cartridges could work the same way, but would have to be connected to a fill manifold of course seperate from the gun.
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