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Ask Jörg Sprave About Building Dangerous Projectiles

timothy posted about 2 years ago | from the so-this-is-what-business-school-does dept.

Toys 45

Jörg Sprave's day job is as a manager in the world of consumer electronics. But he has been for many years making manifest the sort of things that once filled my school notebook margins with doodles: slingshots and other devices for launching bolts, steel balls, and other stuff at high speed at targets or just into the air. (Some of his "slingshots" are hard to recognize as such; he eschews the classic American wrist-rocket braced design as well as the old Tom Sawyer forked branch in favor of things a bit more elaborate.) Thanks to the Internet, hobbies that were once obscure are now easy to follow, and Sprave's homemade slingshots are no exception; you can follow his exploits through an ongoing series of YouTube videos and a forum site that builds on these videos. He's doing it in Germany, too, where firearms may be harder to come by than in the U.S., but giant honkin' firecrackers are available (at least for part of the year), and acts accordingly. Amazingly, he has yet to lose an eye; his goggles are a wise precaution. Sprave has agreed to answer your questions about his own take on physics as a hobby. As usual for Slashdot interviews, you're invited to ask as many questions as you'd like, but please divide them, one question per post.

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Dangerous Gear (5, Funny)

smitty_one_each (243267) | about 2 years ago | (#42657377)

Dangerous gear
Need not cause one fear
First make the grade
On straight razor blade
Burma Shave

Re:Dangerous Gear (0)

gouahufa (2821779) | about 2 years ago | (#42660861)

http://www.cloud65.com/ [cloud65.com] my classmate's step-aunt makes $80/hr on the internet. She has been without a job for seven months but last month her payment was $12356 just working on the internet for a few hours. Go to this web site and read more

How Much Testing Do You Do? (4, Interesting)

eldavojohn (898314) | about 2 years ago | (#42657389)

From watching a few of your videos, I see a lot of end results which are fun to watch. Take, for example, the firecracker slingshot mentioned in the summary [slashdot.org] . But one thing I can't seem to find is any testing videos or explanation of testing (maybe you have it in German and I can't find it). So how much testing do you do on these? When I saw your firecracker launcher design I immediately thought that the worst case scenario is that the firecracker detonates before leaving the chamber or possibly barrel. Now, a firecracker that goes off in the palm of your open hand versus one that goes off with your fist wrapped around it produces two very different results. A short or dry fuse in your device could be problematic. Did you detonate firecrackers inside the chamber from a distance to see if there was enough room in the chamber to allow the explosion to vent without splintering your device? How much testing did you do on it before you were confident enough to pick it up and use the butane lighter on it? Is this discussed somewhere?

Re:How Much Testing Do You Do? (1)

Technician (215283) | about 2 years ago | (#42659057)

He has a youtube channel as well as a thread on spudfiles. Videos of his creations are plenty. He has some very basic slingshots as well as some very unique home creations.

Gun debate (2, Interesting)

schneidafunk (795759) | about 2 years ago | (#42657421)

What are your thoughts on the current gun debate in the U.S.A.

space launch (3, Interesting)

j00r0m4nc3r (959816) | about 2 years ago | (#42657517)

We still don't have terribly reliable/safe/cheap ways to deliver payloads into space. How about giant slingshots as a space launch platform?

Re:space launch (1)

M. Baranczak (726671) | about 2 years ago | (#42658275)

A normal spacecraft takes a few minutes, and a few thousand kilometers, to reach orbital velocity. If you try to reach the same velocity right at launch, you'd crush whatever is in the spacecraft. Then there's atmospheric friction.

So I see two possibilities:

1. A slingshot (or cannon, rail-gun, etc) to provide an initial push, then use a rocket. More complicated than what they're using now, but you'd need less rocket fuel, which could be a big deal.

2. A rail-gun that's thousands of kilometers long, and reaches above the atmosphere. Theoretically possible, but way beyond current technology.

Re:space launch (0)

Anonymous Coward | about 2 years ago | (#42659239)

1. A slingshot (or cannon, rail-gun, etc) to provide an initial push, then use a rocket. More complicated than what they're using now, but you'd need less rocket fuel, which could be a big deal.

Project HARP reached half the delta-v needed for low earth orbit in the sixties, using only a cannon with no plans of using a rocket for a second stage. It would be quite difficult for larger satellites, but for smaller ones, it should be within the realm of possibility. Electronics can be made to survive quite a lot of acceleration and would handle it just fine with a little forethought.

Re:space launch (1)

davester666 (731373) | about 2 years ago | (#42659185)

Trebuchet's work much more effectively than straightup slingshots.

And when they are large enough to launch things into space, they are called "Internapults"

DO YOU KNOW #6 ?? (0)

Anonymous Coward | about 2 years ago | (#42657525)

Do you know #6 !!

Alternatives to Thera Band Gold & Springs? (4, Interesting)

eldavojohn (898314) | about 2 years ago | (#42657567)

I see the majority of your projects depend on Thera Band Gold and then the throwers (like your circular saw blade launcher) use a spring. Have you investigated other methods of using elastic energy (which I guess is technically potential energy?) to propel a an object forward by transferring to kinetic energy? Are you engaged in any areas of materials science study in order to find more efficient and reliable materials? Or do you just use Thera Band Gold as your gold standard and leave it at that?

Take it to the limit (4, Funny)

Sheetrock (152993) | about 2 years ago | (#42657583)

Have you looked into the feasibility of creating a slingshot that could fire smaller slingshots that, in turn, could perhaps fire something smaller themselves?

Re:Take it to the limit (1)

goertzenator (878548) | about 2 years ago | (#42660335)

Sounds analogous to the light gas gun [wikipedia.org] .

The car (5, Funny)

Anonymous Coward | about 2 years ago | (#42657619)

What was the wife's reaction after your one slingshot was off a bit and nicked her car?

Re:The car (0)

Anonymous Coward | about 2 years ago | (#42667057)

I think she was the one taking the video. Didn't you hear her make a disapproving sound?

Injuries? (4, Interesting)

BoRegardless (721219) | about 2 years ago | (#42657661)

I did similar things in high school, though not as elaborate. Made it through with all things, including eyes and fingers, intact.

How many injuries have you and your friends suffered?

Re:Injuries? (1)

Creepy (93888) | about 2 years ago | (#42658273)

I/my friends did crazy elaborate things in high school too... too bad there was no YouTube back then (or much of an internet), though I think I may have some 8mm movies at my parents' house. I mostly stuck with explosives and smoke bombs, but one of my friends built a portable rail gun that put a 6" nail through a 2x4 board (the 2" side) and fully embedded it into a cinder block (at least a couple of inches deep), and that wasn't even at full power. In fact, the AP physics teacher nixed a full power test, but we did fire it a few times "in the field" - aka in the forest, firing it through an old abandoned car and oak trees. The bad was it weighed about 45 pounds (actually, iirc it weighed almost exactly 20kg) not including the car battery backpack. He made that thing look pretty bad-ass, too, since he had to keep busy in class and essentially had finished the project about a week early (in the aforementioned class, we had a month to create any project we wanted to demonstrating physics - it was a pretty awesome class). Makes me wonder if he still has it, but I haven't been in touch since the late 1990s.

Re:Injuries? (0)

Anonymous Coward | about 2 years ago | (#42658861)

Any elaboration on the rail gun design? I always wanted to make one but was put off by the complication surrounding the coil timing. If I have time I'd love to revisit the idea, or even make one with some offspring (should they choose to turn up one day).

Ever made one big enough to propel a Doberman? (1)

Rogerborg (306625) | about 2 years ago | (#42657693)

If not, why not?

Re:Ever made one big enough to propel a Doberman? (2)

Keick (252453) | about 2 years ago | (#42657901)

As a followup, and generally high regard for canines, have you ever made a cat-ling gun? If not, why not? If so, how many lives do they have on average?

Legality (4, Interesting)

operagost (62405) | about 2 years ago | (#42657751)

What legal issues have you encountered? If your authorities are anything like they are in the more "progressive" states of the USA, they consider anything that looks like a firearm or throws any solid object (or not so solid [cnn.com] ), via any means of propulsion, a dangerous weapon.

Re:Legality (1)

tlhIngan (30335) | about 2 years ago | (#42657827)

On a similar note - what are the laws regarding projectile weapons in Germany?

How are your relations to your neighbours?

Is multi-shot more dangerous than single shot? (1)

mykepredko (40154) | about 2 years ago | (#42657973)

Jörg,

With the recent controversy regarding assault weapons in the US and the plans to reduce clip sizes, I'm wondering if you would think your, um, devices would be more dangerous if they could shoot multiple objects rather than just one at a time?

myke

Performance (3, Interesting)

PPH (736903) | about 2 years ago | (#42658001)

Have you tried to measure the projectile velocity (and calculate the energy) that your devices produce?

Re:Performance (1)

MartinSchou (1360093) | about 2 years ago | (#42681703)

He does that quite often using a chronograph

Not impressed (0)

Charliemopps (1157495) | about 2 years ago | (#42658145)

This is at least the 2nd time I've seen this guy show up on slashdot. While I'm all for people building stuff in their garage (I do it for sure) I see nothing impressive in this gentlemans designs. Nothing new or interesting. I built something very similar to his nailgun when I was in 7th grade and found a box of large nails at a construction site. His hobby is great, but he needs to come up with something far more insightful before I consider it news worthy. Why is this making it on slashdot?

Dangerous Projectiles (1)

rossdee (243626) | about 2 years ago | (#42658259)

As opposed to 'safe' projectiles?

If you fire anything fast enough, it wouldn't be considered safe

Re:Dangerous Projectiles (1)

vlm (69642) | about 2 years ago | (#42658453)

If you fire anything fast enough, it wouldn't be considered safe

Low density is the key. I suppose I have to officially discourage this kind of activity, but in the early 90s my friends and I had indoor potato gun fights using balls of crumpled paper as ammo. Virtually harmless projectiles even at point blank range assuming you use gas fuel and not liquid fuel. Liquid fuel sets the projectile on fire, which sounds cool but usually isn't unless you're on dueling pontoon boats pretending you're re-enacting naval battles, which is a whole nother story. One broken glass window, but that was heavily debated as being due to the sonic backblast of the potato gun itself rather than the projectile which might not have hit the window anyway. It is obviously capable of knocking stuff off shelves or pix off walls. Frankly running around screaming like lunatics caused more injuries than the projectile itself. Its a fun way to play tag, a little more "sporting" than merely using NERF weaponry.

I would imagine a DRY sponge or a mooshy foam ball would be pretty safe at anything below supersonic.

Re:Dangerous Projectiles (1)

lxs (131946) | about 2 years ago | (#42667553)

...unless you're on dueling pontoon boats pretending you're re-enacting naval battles...

I like the way you think.

Re:Dangerous Projectiles (1)

bellers (254327) | about 2 years ago | (#42658887)

*Why* is so much of our science dangerous? Why not *marry* safe science if you love it so much? In fact, why not invent a special safety door that won't hit you in the butt on the way out, because *you are fired!*

Re:Dangerous Projectiles (1)

tibit (1762298) | about 2 years ago | (#42659977)

Whooooooooooooosh!

Re:Dangerous Projectiles (0)

Anonymous Coward | about 2 years ago | (#42661285)

Whooooooooooooosh!

For those unaware, that whooshing noise is a perfectly anticipated part of the test, just ignore it and try not to look out the window.

I enjoy watching The Slingshot Channel. (2)

RatherBeAnonymous (1812866) | about 2 years ago | (#42658619)

Partly for the slingshots, but mostly for hearing Jörg giggle after every shot.

Have you considered publishing CAD files (1)

WillAdams (45638) | about 2 years ago | (#42658643)

suitable for 3D printing or milling?

If you've already done this, where are they?

William
(who made a crossbow using a truck leaf spring when he was a teen-ager and used his father's ratchet lever hoist to cock it --- was fortunate to be to on the opposite side of the tree when the stock split and things went flying)

It goes without saying but (0)

Anonymous Coward | about 2 years ago | (#42658791)

Thiss Gye is uh Moreon!

Whats up with the cool "ZS" shirts you wear? (1)

bellers (254327) | about 2 years ago | (#42658871)

Are you in Zombie Squad? Do the slingshots work against Zombies?

Re:Whats up with the cool "ZS" shirts you wear? (0)

Anonymous Coward | about 2 years ago | (#42660693)

Any Jeorg fan knows that he is. He's got a specialized zombie-killing slingshot. There's a video.

Bad Title (1)

JockTroll (996521) | about 2 years ago | (#42659293)

Ain't no such thing as a dangerous projectile. What's dangerous is the one who does the throwing. Btw, anything even remotely interesting has an element of risk involved. That's why it's "interesting" as opposed to "shit".

ACME Corporation (0)

Anonymous Coward | about 2 years ago | (#42659845)

I think ACME Corporation makes stuff like this. Although they're pretty generic and typically failure prone. Look into the Ajax Corporation too.

http://www.cracked.com/article_16647_5-insane-devices-from-kids-cartoons-that-actually-exist.html

Sell Sprave=designed slingshot? (1)

JeffElkins (977243) | about 2 years ago | (#42660249)

Outsource a design to be manufactured. I'd love to buy one.

French don't surrender? (1)

HornWumpus (783565) | about 2 years ago | (#42664289)

How do you keep the French from surrendering to you?

My buddy Wendel. (1)

HornWumpus (783565) | about 2 years ago | (#42664363)

This is a suggestion: Credit to Wendel for doing this back in the 70s.

Get high pressure tank, narrow and long.

Build fins and nozzle that screw into tank neck. Insert burst plate designed to go 10% below tanks burst rating.

Fill tank 3/4 with water.

Stand tank on fins.

Build bonfire around tank.

The last step for Wendel was 'get arrested by airmen in helicopter while putting out scattered fires, deny anything to do with ultimate water rocket, just good citizens abating a hazard. Get away with it.'

Their rocket made about 30,000 meters and was seen by the Russian launch detection satellites.

Re:My buddy Wendel. (0)

Anonymous Coward | about 2 years ago | (#42664871)

Wow! Steam Punk Rocket!
I guess the warter would turn in to steam as the pressure droped du to the burst plate opening. I wonder if all the water converted to steam or just most of it. Sounds like it needs more development!

Re:My buddy Wendel. (1)

HornWumpus (783565) | about 2 years ago | (#42665369)

There were implementation details. I believe the nozzle went part way up into the tank. Apparently he promised the air force to never ever do it again, he's told me as much as he's going to.

I doubt I'll luck into the cylinder he described ether.

It's neat stuff, but... (1)

BobandMax (95054) | about 2 years ago | (#42664855)

...there's something unsettling about a German saying "Achtung!" and then firing a weapon. Maybe it was that three day war movie marathon on Spike.
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