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High Velocity Launch Systems

A place to ask general spud cannon related questions.
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High Velocity Launch Systems

Unread postAuthor: DYI » Sat Apr 10, 2010 8:48 pm

As some of you probably know, I've had an interest in high speed launch and impact for quite a while now. My initial approach at it didn't go so well, and wouldn't be permitted for discussion here anyway. I've had a good deal of success with electrothermal propulsion, but insufficient energy to test at high speeds not any more. One thing that really stood out during my research is a conspicuous lack of hypersonic launchers built by amateurs. They certainly aren't very accessible to the 13 year old with no job, building launchers in his bedroom, but people like Larda are not an extreme rarity. It strikes me as odd that the impressive resources of DIYers with machine shops have so rarely been turned toward such an interesting field.

This is a fairly wide-ranging thread, with two main topics:

1) Discussion of launch methods - There's a good deal of them; all the varieties of light gas guns, railguns, induction launchers (pancake and tubular coils), electrothermal guns, exploding foil launchers, a few other more difficult and uncommon EM-based methods, laser ablation, and all the ones based around compounds we are not to discuss here. Anything that interests you in this field may be posted here, along with theories and information from research papers.

2) Collecting links to actual launchers built by hobbyists - I've found one so far that may fit, built by a 4hv member:
Badastronaut's railgun
More links would be greatly appreciated, but don't bother with anything under 1200m/s or so, or we'll have a great mess of overly-long cannons powered by worrisome quantities of Pyrodex :roll:

Essentially, I'm looking for innovation here, done by people who don't charge the casual reader thirty bucks a pop to read about their results. Having a collection of such information assembled here could make it marginally more likely that people will build these things once in a while, so please post anything relevant to the topic. HPEL-1 lives
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Last edited by DYI on Fri Aug 13, 2010 9:10 pm, edited 2 times in total.
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Unread postAuthor: rp181 » Sat Apr 10, 2010 9:50 pm

I don't think Badastronaut got past 1200m/s. He wasn't able to chrono it, and as Andyman on 4hv said, the kinetic energy was probably less than 1.5kJ.

I would like to introduce a new topic: Explosively pumped flux compression generators. This serves to help all the electromagnetic launch systems. Just leave the Explosive part out :wink:

Also, I really dont think induction launchers have much promise in high velocity. Pancake coils offer high repulsion force, but the force can not be applied constantly or multi-staged. Tubular designs require quite a bit of power. The only place I can see use for these is when you have enough power that normal reluctance based designs saturate the projectile to easily.
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Unread postAuthor: inonickname » Sat Apr 10, 2010 9:59 pm

A ram accelerator would suit this purpose. Rather simple, and only needs around 500 m/s input.
Link.

Edit: Is decomposing a single material (solid, liquid, gas, whatever) by means of heat or impact within the forum rules- and no, I don't mean anything like NC or NG. Just fairly normal, inert substances.
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Unread postAuthor: DYI » Sat Apr 10, 2010 10:10 pm

I have suspicions that pancake coils aren't much use at higher speeds, but so far I've not seen evidence of anyone actually TESTING it, which is the entire point here. There are enough people with coin-shrinking rigs that you'd think someone would have tried already.

And "normal reluctance based designs"? Point me to any reasonably high velocity coilgun build that used a reluctance based design. From all information I've seen on the topic, it is essentially a dead end technology, useful for nothing but slow lobs even with excellent design and pulse shaping. Tubular induction launchers, on the other hand, are limited only by the possibility of melting the projectile in the barrel. I fail to see how reluctance, which is far more limited in materials and constricted in achievable acceleration, could even begin to compete.

@inonickname: What you describe is well within forum rules; so long as these substances do not contain fuel and oxidiser, and cannot decompose explosively (under release of their own chemical energy, as opposed to external input) there is no problem.

Could you post the link to the launch-to-space ram cannon paper which was floating around here a while ago? I seem to have lost it.
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Last edited by DYI on Sun Apr 11, 2010 1:42 pm, edited 1 time in total.
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Unread postAuthor: 245Tommy » Sat Apr 10, 2010 10:31 pm

Sam thinks his railgun is shooting at 1000 - 2000m/s. :roll: http://www.youtube.com/watch?v=OqeMGkye ... re=related
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Unread postAuthor: rp181 » Sat Apr 10, 2010 11:12 pm

And "normal reluctance based designs"? Point me to any reasonably high velocity coilgun build that used a reluctance based design. From all information I've seen on the topic, it is essentially a dead end technology, useful for nothing but slow lobs even with excellent design and pulse shaping. Tubular induction launchers, on the other hand, are limited only by the possibility of melting the projectile in the barrel. I fail to see how reluctance, which is far more limited in materials and constricted in achievable acceleration, could even begin to compete.


That is what I was trying to say, tubular induction launchers are well suited to high input power. My point in bringing up reluctance based designs is that reluctance is more efficient for low energies.

@245tommy: Oh I hate Sam....see his railgun design? He copied my design. That alone I am fine with, but previously he had emailed me claiming that I copied his design, and wanted me to give him credit. To show him my design was original, I sent him stress analysis reports of the enclosure, and a dimensioned drawing (Those are on my website). He seemed to have thought is was a better design so he used it....
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Unread postAuthor: DYI » Sat Apr 10, 2010 11:20 pm

"OH MY GOD, DO YOU REALIZE WE JUST PUT PLASTIC THROUGH PLYWOOD?!!!"

I'm very impressed. Next thing you know, these geniuses are going to invent something powerful enough to put a POTATO through plywood.
Oh, wait... :lol:

Wood targets and huge distances between muzzle and target seem like a deliberate attempt to obscure actual results. Knowing the general arc of Sam's projects, this one will sink before it produces anything useful. A good place to watch for the rare and coveted electrothermal fireworks though :P

Better add a third permissible topic to the thread; protracted mockery of Sam Barros. :D

@rp181: Do you have any numbers to compare tubular inductance and reluctance launchers at low energies? It is interesting that reluctance designs seem to be considerably more popular among hobbyists when they have so little application in "serious" research.
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Unread postAuthor: rp181 » Sun Apr 11, 2010 10:23 am

DYI wrote:@rp181: Do you have any numbers to compare tubular inductance and reluctance launchers at low energies? It is interesting that reluctance designs seem to be considerably more popular among hobbyists when they have so little application in "serious" research.

Blah, you pull that out again :wink: (with good reason). I had read a paper detailing the differences between induction, reluctance, and coil armature PLIM's, but I can't find it again. It was linked some where on Barry's site, so you can look through his site.
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Unread postAuthor: Ragnarok » Sun Apr 11, 2010 10:35 am

rp181 wrote:I don't think Badastronaut got past 1200m/s. He wasn't able to chrono it, and as Andyman on 4hv said, the kinetic energy was probably less than 1.5kJ.

Yeah, but 1200 m/s with a 2 gram projectile is still only 1.44 kJ, so it's not an impossible velocity at sub 1.5kJ kinetic energies.
And based on the damage to that steel plate, I would expect more than 1000 m/s, and 1200 m/s really wouldn't surprise me.

DYI wrote:Better add a third permissible topic to the thread; protracted mockery of Sam Barros.

Perhaps we should make a mockery machine, that would be able to mock people automatically.

But for a comment from me, not the mock-o-matic, He might get lots of nice toys to play with, but surely someone of his supposed intelligence (and claimed experience with high velocity projectiles) should know that if you send something doing several hundred metres per second at something else, it may well make a hole.

It is interesting that reluctance designs seem to be considerably more popular among hobbyists when they have so little application in "serious" research.

Interesting, but I'm not exactly surprised. Inductance launchers demand greater effort than reluctance launchers, and often, the hobbyist looks for something that works without too much effort, rather than something that's necessarily possessed of a "serious use".
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Unread postAuthor: 245Tommy » Sun Apr 11, 2010 11:10 am

This is the only amateur tubular induction gun I've seen, is shoots just under supersonic, 1kj stored energy. http://www.rapp-instruments.de/index6.htm
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Unread postAuthor: rp181 » Sun Apr 11, 2010 12:10 pm

Translators are failing for me, but from looking at the pictures, it seems they used a high voltage pulse around the main work coil, to induce a a low rise time pulse in the main coil, for faster current ramp. That was something Ragnarok was talking about in reluctance based designs.
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Unread postAuthor: 245Tommy » Sun Apr 11, 2010 12:23 pm

rp181 wrote:Translators are failing for me, but from looking at the pictures, it seems they used a high voltage pulse around the main work coil, to induce a a low rise time pulse in the main coil, for faster current ramp. That was something Ragnarok was talking about in reluctance based designs.
Google "rapp instruments" and click translate. I think that's part of the triggering system.
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Unread postAuthor: Ragnarok » Sun Apr 11, 2010 1:42 pm

rp181 wrote:That was something Ragnarok was talking about in reluctance based designs.

While the idea was to reduce current rise time, and create a "squarer" pulse, the idea is based around a single coil.

Two banks of capacitors (fed through some slightly more complex switching than usual) into the same coil. A high voltage, low capacitance bank that could provide a burst of power to overcome the coil's inductance, and then a lower voltage, high capacitance bank which provided the energy to sustain the current in the coil.

You'd burn off quite a bit of energy in the current rise, but you'd not use a lot to sustain the current - a lot of energy's already in the coil. As a result, I think this design could muster 20% or greater efficiency relatively easily.

But as I'm not expecting more than about a 120 m/s muzzle velocity from the project, it's hardly the kind of high velocity launcher this thread wants to focus on.
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Unread postAuthor: 245Tommy » Sun Apr 11, 2010 5:47 pm

Is anyone working on an ETG? They're probably the easiest high velocity gun for an amateur, here's the latest updates on mine. http://4hv.org/e107_plugins/forum/forum ... .php?87092 The barriers I found are having a fast enough discharge time and getting the chamber to stay together.
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Unread postAuthor: rp181 » Sun Apr 11, 2010 9:23 pm

Ragnarok wrote:Two banks of capacitors (fed through some slightly more complex switching than usual) into the same coil. A high voltage, low capacitance bank that could provide a burst of power to overcome the coil's inductance, and then a lower voltage, high capacitance bank which provided the energy to sustain the current in the coil.


Using a second coil in a air cored pulse transformer setup may well work just as well, and simplifies issues like semiconductor protection.
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