Cooking up a little something...

[Moonbogg]

lol, I'm fresh out of old tires.

[jackssmirkingrevenge]

It doesn't have to be tires, could also be a large sturdy box lined with old blankets or insulation material. The idea is to create a chamber that will absorb the pressure wave.

[Moonbogg]

It works! Did my first test session today and it worked out great. The cannon needs a chamber fan though. Performance is inconsistent with all the signs of improper fuel/air mixing. I may add a fuel dispersion manifold inside the chamber or just stick a little fan in there. Not sure which. That's relatively minor though. If I leave the mix sit in the chamber for a couple minutes, the cannon has that sharp sounding, powerful shot you expect it to have, but if I take the shot right away, it's less powerful and sometimes has that very telling "poomp" sound, which is a pretty sure sign of a bad fuel/air mix. I can't wait to get a chamber fan in there.

The best news is the piston works like I hoped it would. The piston housing stays pressurized, however, after perhaps a couple dozen shots, give or take, the housing does lose a few PSI after all those shots, so a quick top-up is needed. It only takes one or two pumps to fill the housing though, so maintenance there is super easy and not an issue.

The piston was reliable and worked the whole time. I still have to disassemble and inspect it for rubber wear and tear, but it seemed fine. I might even experiment with different diameter sealing faces, which I have a couple of. I might use a stronger rubber for the bumper, because in one of the videos I can hear the cannon ringing like a bell and I think maybe the piston is not cushioned enough? I can't tell. A little stronger rubber wouldn't hurt anyway and I am pretty sure I'll go ahead and step it up from durometer 50 hardness rubber to durometer 60 or 70 when I get a chance. I don't like hearing that ring sound during some of the shots. It might just be from the cannon being made from aluminum, but I am imagining the piston hitting the aluminum too hard. I'm paranoid like that.

The cannon passed the acid test with a full 12oz soda can at 3X and continued to work for additional shots. The first shot must have had a nice fuel/air mix because it shot hard and the recoil was kind of unexpected and hurt my wrist a little. It was sweet!

Golf balls are really what this cannon was designed for and they are incredible. They just haul ass. Also, huge-bore-sized potatoes are pretty awesome from the big barrel.

The cannon definitely needs a better pump. The little hand pump sucks, so a bigger bike pump is in order. Maybe some day I'll go nuts and get a big HPA tank to make life really easy (until I need to pay to have it refilled).
Looking good so far. I'll watch it closely and fine tune it and tweak it etc.

There are two triggers. One for hybrid firing, and the other button within finger reach drains the piston housing, so it can be used to fire pneubmatic shots

[youtube][/youtube]
[youtube][/youtube]

[D_Hall]

You may not need mixing fans. In fact, I doubt it. When I designed VERA I included an eductor inline with the fuel/air injection port. The effect is a constant recirculation of the gases inside the chamber during fueling/compression. Completely passive with no moving parts. Still, the result is that even on something the size of VERA fans are not needed.

[Moonbogg]

Thanks for the compliment and reply. I love the sound of not having to mess with wires and a fan. Is this the concept you are talking about? I can see how that might solve my issue.



As I add fuel, the pressure drags air through the inlet, starting the cyclic flow. When I follow up with air, it does it even more, causing the whole chamber to circulate fuel and air, is that right? If so, that's much better than even using a manifold inside the chamber with multiple fueling holes. I LOVE this idea. Now I have to figure out where to find something like that.

[D_Hall]

As I add fuel, the pressure drags air through the inlet, starting the cyclic flow. When I follow up with air, it does it even more, causing the whole chamber to circulate fuel and air, is that right? If so, that's much better than even using a manifold inside the chamber with multiple fueling holes. I LOVE this idea. Now I have to figure out where to find something like that.

Yup. You've got the idea. For bonus points, you have the inlet of the "suction side" of the eductor being fed via a pipe that goes the entire length of the combustion chamber. That way you're pulling gas from one end, mixing it with air/fuel, and then releasing it at the other end.

And you can buy them at McMaster-Carr. Probably lots of other places too, but I spend a lot of money at McMaster so that's the first place that comes to mind.

[Moonbogg]

I spent so much at McMaster for this project that I want to puke just hearing it again, lol. Amazon has a plastic one for $16.00. Maybe I can work that one in there somehow. It might be something I can mount to the piston housing and just have it install near the fuel injection port, since I don't have NPT threads inside the chamber. I like the tube idea to grab fuel from the far end, since that's where it will all get squirted after injection.
Thank you for stimulating my imagination in this area. I'm going to think on this and find a practical way to get something like that in there because it really needs some better mixing. Not having to drill any more holes sounds absolutely fantastic. Mounting onto that piston housing is a solution that's just begging to be taken advantage of.

[hectmarr]

Nice work your hybrid. Let's enjoy it !!! :bounce:

[Moonbogg]

I just inspected the piston. It looks exactly the same as when I installed it. The grease is still there and the rubber looks completely fine. I honestly didn't expect it to look so...fresh still.
There is a lot of moisture in the chamber and I don't like that. I am hoping that's just from pumping moist air in there because it was raining.
Even though the bumper is perfectly intact, I'm still wondering if it's compressing too much. I'm afraid it will impact the housing too much and the housing will shear a hole through the end cap and the housing will go through and impale me in the chest like a viking war victim. Thoughts on that?

[hectmarr]

Impossible to guess if it will break or hold.
During at least 50 or 100 shots, do not stay behind him. You will be taking confidence little by little, or not .... I am inclined to think so!
One question: How do you inject the fuel gas into your hybrid? What type of air pump do you use?

[Moonbogg]

I use a meter pipe for propane with a pressure gauge on it and just fill it to desired pressure for each shot. I then inject the propane through a quick-disconnect valve. I then pump in the air with a really crappy mini bike pump that I will be replacing with at least a better bike pump.

[hectmarr]

ok you have a manometric propane meter.
I use a butane meter, in my case, volumetric. The mixtures are quite homogeneous, enough to have regular shots in power, every 3 or 4 seconds.
I have a container of the same volume of gas that I need to introduce into the hybrid. Full of gas that container, at atmospheric pressure. Butane gas, (or whatever), displaces the air and fills it. Then I connect the suction line of my air pump, and when pumping, the gas dose is sucked into the air pump, mixed with the air, and then introduced into the hybrid.
I thought it would be another option to improve your mix.
From what you tell me, I do not think you can because you use another method, the manometer that injects gas at a pressure greater than that of the atmosphere.

[Moonbogg]

JSR, omg dude, you were so right about the fueling LOL. I was *only* off by 15% lolz. Instead of 38psi in the meter like last time, I was now at 32psi. Yes, it fixed the issue. Thanks! All I need now is for my bike pump to come in the mail. I have to pump about 100 times to exhaust the fumes with that crappy hand pump. A bike pump will help HUGELY.
I also moved the air inlet to the front of the cannon so it blows air the opposite direction of the propane inlet. Its also on the center plane of the chamber while the propane inlet is at the top of the chamber, so propane sinks and hides under the piston tube, thats what i'm thinking anyway, so the front inlet should help mixing and power was good today, so I think it's basically all sorted out. I will also experiment with reducing pilot pressure to see what happens there. Minor tweaking to do still.
Anyway, here are some decent shot vids. I had a great time in the desert today with it. 100deg weather. Very hot. I got a few minor things to improve but it's looking like a real success.

first 2 shots are full 12oz soda cans
3rd shot is a potato
4th shot is a golf ball
[youtube][/youtube]

Here's the money shot!
[youtube][/youtube]

[jackssmirkingrevenge]

Glad you sorted it out, working nicely now!

I will temper my praise however by chastising you for filming vertically and also not showing us any footage of the projectiles hitting something ;P

[Moonbogg]

I'm going back to try out my new bike pump, so I'll find an old board or something and shoot the thing with a can of soda. Also, I had to set my iphone in a coffee mug to hold it up since I don't have a tripod and don't make videos normally, so I suck balls at the whole youtube thing.