Big Stuff

[Jimmy K]

Actually I'm powering it with a 9v 500mA transformer. At 12v the thing doesn't want to cooperate. The 30A relay is for the hydraulic pump. For $5.50 you can't really go wrong.

[Jimmy K]

[youtube][/youtube]

[Jimmy K]

The console is done. It has a 10 foot cable attached to it so that you're not super close when it goes off. The light up trigger works amazingly well, as does the actual triggering mechanism.

[Jimmy K]

I added a support for the trigger and forgot about the recoil, so both ends of the 1/2" PVC leading to the trigger sheared off. Here's the new pilot and trigger assembly:



The hydraulic system is now fully functional too. Just need to find a 12VDC 30A power supply and do a little more wiring.

[Technician1002]

A UPS battery and small charger may be less expensive than a full size power supply. Your use is intermittent. A 12 volt 7.5 AH battery would suit the job fine.
http://www.nextag.com/yuasa-np7_-_12/shop-html

[warhead052]

Wow, thats all I can say. Bet you wish that could go up to higher pressures huh?

[Jimmy K]

Shot at 70 PSI:

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And Technician1002:
You may have noticed that I still have 45's connecting the tank to the valves. I made sweeps, but they did not handle pressure too well. They broke open around 30 PSI. I bent the pipe to have a 1 foot radius, but I guess it got too thin on the outside rim of the pipe. The 45's will work for me for now. I'll revisit the issue if I have time before the cannon is due.

[mark.f]

That recoil is impressive for something which weighs that much...

Also, what's the leaking noise after you shut the compressor off? Is it the cannon or just the airline/compressor/etc.?

Looking great so far.

[Technician1002]

Very nice. The 45's seem to do the job well. With a properly secured barrel that will be quite the field artillery piece. I don't know if it is echoes in the room, but the discharge time seems to be a little long. That should work well with an oversize barrel.

There is no sign of honking which indicates good flow into the valves. Well done.

I bet that sound is much louder than the recording can show.

[Fnord]

You really, really need to make some type of clamp/mount to keep recoil stresses from being tranferred through the pvc pipe, even during test shots like this.
If you put on some heavy boots and kicked the tee hard enough to make the whole thing jump like that, would you be worried about potential damage? Cause' that's exactly whats happening.


Oh, and good job.

[Jimmy K]

Mark:
You're hearing a very stubborn quick connect - it probably leaks more air than what it transfers

And the recoil was 28" for that shot.


Technician1002:
Speaking of oversize barrels, I cut mine to 15 feet to get it on the trailer. Even then, it sticks out about 2 feet. The Ohio BMV needs to inspect the trailer for plates once everything's mounted, so I need to keep everything within trailer limits.

The noise... Wow. I've shot AR-15's, R700's, and some large caliber handguns, but nothing comes close to this. It is by far one of the loudest things I've heard. Protection is a must.


Fnord:
After watching the playback of that shot and reading your post a couple of times, I've decided that I really shouldn't be setting it off without proper mounting. I planned on using a 3pt boom for a barrel support and as a mount for the tee, but I haven't bought anything for that yet nor have I drawn out plans. After I weld the hydraulic mounts to the trailer and cannon I'll work on bracing.

[mark.f]

Just a thought, but you needn't limit yourself to a 15' barrel. You could always magic up some stands and use modified bushings/threaded adapters to join the barrel pieces together. I'll admit this has always scared me a bit (who want's a few thou ft.-lbs catching the last bit of your barrel and tearing your valves out of the chamber? ), but if done correctly (perhaps by tapering the outer and inner surfaces where the two pipes join so they seat together, and then giving the inner pipe a slight inner chamfer), it could possibly be a viable option.

[Technician1002]

In oversize, I was referring to either length or diameter. The recoil is going to be immense with a larger diameter barrel. The larger diameter can provide some very high forces.

[saefroch]

Recoil would be lower with no projectile and a larger barrel, actually.
Conservation of momentum, remember?

[Technician1002]

Are you sure? Why do rocket nozzles have a bell shape?

Air expanding after it left the barrel will have less thrust than air expanding in a nozzle. Oversize will result in less thrust.