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The Pipe Dream: I think it's going to happen

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: D_Hall » Wed Aug 06, 2008 8:05 am

McFear wrote:so has anything happened since the last rush job.

Yeah, an insane number of things have happened. We've got what would normally be consider 2 year's worth of work that we're supposed to get done within the next year.

Translation? Gun is on the back burner again. :(
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Unread postAuthor: SpudFarm » Wed Aug 06, 2008 10:51 am

S-A-D
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"Made in France"
- A spud gun insurance.
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Unread postAuthor: D_Hall » Thu Sep 11, 2008 10:24 pm

Found out today...

It got funded.

Which means it will very soon be an official project.

Which means three things....

1) I won't be able to talk about it once that happens (until press release).

2) It will have a defined schedule.

3) You folks will have contributed to something very real. Thank you.
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Unread postAuthor: frankrede » Thu Sep 11, 2008 11:11 pm

AWESOME!
Congratulations!
Goodluck!
Keep us informed onto when its going to be done
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Current project: Afghanistan deployment
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Unread postAuthor: LikimysCrotchus5 » Thu Sep 11, 2008 11:12 pm

Ok, so since its not official yet, can you give us,

1) a time estimation on completion

Two words "Awesome"
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4SPC, My 4" piston 3" porting cannon
Memo:
Fix up copper cannon
Fix up 4SPC
Start Stirrup pump
Start Toolies piston bazooka
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Unread postAuthor: SpudMonster » Thu Sep 11, 2008 11:48 pm

D_Hall wrote:Found out today...

It got funded.

Which means it will very soon be an official project.

Which means three things....

1) I won't be able to talk about it once that happens (until press release).

2) It will have a defined schedule.

3) You folks will have contributed to something very real. Thank you.


This is good. Very, very good :toothy3:
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Stupid quote of the now:
joestue "The chamber is rated to 100 psi, it don't say that on the side, but the 2 inch stuff is rated to 300, so by analogy..."
"only the last two feet hear the end is black cellular core"
"I'm taking it to 300 psi"
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Unread postAuthor: starman » Fri Sep 12, 2008 12:24 am

Sounds awesome! I assume the being quiet is a security clamp down? Or maybe just keeping quiet on account of hungry competition inside the great industrial complex....
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Unread postAuthor: Gippeto » Fri Sep 12, 2008 12:30 am

Congrats! An officially "funded" , ass kicking , name taking, spud gun. 8)


One small step for man,... one giant leap for spud kind. :lol:
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Unread postAuthor: starman » Fri Sep 12, 2008 12:33 am

Gippeto wrote:One small step for man,... one giant leap for spud kind. :lol:


:wink: Nice one Gippeto....
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Unread postAuthor: MrCrowley » Fri Sep 12, 2008 12:39 am

It got funded.

Just curious, how much was the funding?
Or will you have to kill me :wink:

I can't wait to see this thing finished.
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Unread postAuthor: psycix » Fri Sep 12, 2008 10:37 am

Awesome!
You will post pics, vids and result data when its done will you?
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Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

Spudfiles steam group, join!
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Unread postAuthor: jimmy101 » Fri Sep 12, 2008 12:45 pm

D_Hall that's great news!

Something that might help you...

In my setup I wanted to get the spark event in the data recording stream. You could record the trigger voltage to the HV system but there is usually a delay between when the HV circuitry is triggered and when the spark gaps actually fire. (My cheapo stungun takes anywhere from a couple mS to a few tens of mS to spark once the trigger switch is closed.) You would probably like to know when the sparks actually fired and not when the HV circuit was turned on.

It's not a good idea to have the tens of KV of the sparker anywhere near the analog to digital converter though since it'll fry it for sure. You can just step the voltage down to a more reasonable level with a big ass resistor and a small resistor but that tends to load down the HV a fair amount.

A small neon indicator bulb (NE-2) or a small zenon flashtube can be used as an additional spark gap in the HV circuit. Just wire one in series with the spark gaps and it'll flash when the gaps spark. No spark at the indicator means no spark at the gaps. (But spark/flash at the bulb does not necisarily prove there was spark(s) at the gap(s).) Point a photodiode (or phototransistor) at the bulb and you have a optoisolator that'll handle tens, perhaps even hundreds, of KV. Protect the whole thing from light by enclosing it in an opaque container. Here's my setup in a 35mm film canister. The HV input/output are the screws on the right, you can see the NE-2 bulb near the center of the perf board and the phototransistor is to it's left.
Image
This one is probably good to at least a few tens of KV. The voltage rating is limited by the nearest approach of the wires on the HV side to the wires on the low voltage side.

As I was fidling with the above setup I noticed that it gave a signal even if the light path was completely blocked. So, another way to get the spark signal into the data stream is to just run a length of wire near the spark gap. The spark generates a lot of RF noise and most AD setups, even with only minor amplification, will pick up the RF noise the spark generates. The line input to a PC soundcard easily picks up the RF noise as long as at least part of the wire is not shielded. I'm sure your much more sophisticated data system will pick the RF up as well.

I suspect you may be grounding the "pipe dream" for safety reasons, so the RF from the firing gaps inside the gun might not make it out of the metal gun. The wiring outside the gun to the spark gaps might still make enough RF noise, or you could add an additional gap outside the chamber as a "radio transmitter". I think a NE-2 bulb would work as the external spark gap / radio transmitter and it would be a bit safer than having an exposed spark gap.

Spark gaps were one of the first radio transmitter designs.
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Unread postAuthor: Ragnarok » Fri Sep 12, 2008 1:31 pm

Oh dear, I think Killjoy is going to have to give up on the muzzle energy record. :D

MrCrowley wrote:Or will you have to kill me :wink:

Working with the government gets you three surreptitious killings every year as a job perk, so it won't have to be him that kills you...

I could do it for you if you'd like. I've hardly killed anyone this month. :twisted:
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: rp181 » Fri Sep 12, 2008 4:26 pm

jimmy, thats a good idea, kinda like a rogowski coil (not really though :wink: )
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Unread postAuthor: D_Hall » Fri Sep 12, 2008 6:46 pm

jimmy101 wrote:In my setup I wanted to get the spark event in the data recording stream. You could record the trigger voltage to the HV system but there is usually a delay between when the HV circuitry is triggered and when the spark gaps actually fire.

Yes, we do that routinely on all our tests. We just use an inductive pick-up to gather this information.

Basically our set up is a cardboard tube with a coil of 50ish wraps of wire around it. The high voltage line goes through the tube. When current flows, we get an induced current/voltage in the coil. We record the signal put out by the coil.

Note that in some cases the current from the coil is fed into an old fashioned flash bulb (in addition to being recorded). This provides a blatant visual cue in all videos.
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