alternate power

[jon_89]

Are there other power sources besides pnuematic and combustion? I am looking for something just to try out.

[Novacastrian]

In a word HYBRID
I would not recommend building one without first constructing both a Pneumatic and Combustion.
Why not build a "Mini" Combustion?

Edit: Or a Coilgun, but they usually have nadda power. There are some railguns out there too.

[jon_89]

i have built 3 combustions and 5 pnuematics. hybrids seem to dangorous to me.

[Novacastrian]

They are only as dangerous as their owners or builders, kind of like owning a dog- they are what you want them to be.
If built properly a Hybrid is most probably safer for the user than any other spudgun. A "properly" built hybrid IS made out of metal, unless you fill it with nitrocellulose you are safe as houses, (unless you use a coke can for the chamber).
There are no other power sources except for steam that i know of and that would just be a pain. Other "sources" are not allowed on this forum i.e. Gunpowder, but if you are worried about Hybrids there is no chance that you would go down that path

In Conclusion, i can not help you

[jon_89]

well i also live in a city so hybrids would be just to loud. i not looking to shoot potatoes but more like bbs and darts. oh its ok i am just throwing the idea out there to see what people come up with.

[Novacastrian]

Ok, what about a small rubber band powered "crossbow"?
I'm sure that there was one posted a while back, looked quite good too.
Maybe have a look through this http://www.spudfiles.com/forums/office- ... 11318.html
Hoped that helped.

[jackssmirkingrevenge]

There's spring power but it's impractical for amateur builders.

For something really alternative, have a look at my airsoft crossbow - I made it using very basic tools and materials when I was 16, it should be easy to replicate or improve.

[BigGrib]

how about a a spud gun powered by a small nuclear reactor?? Ragnarok any ideas

[Ragnarok]

And on cue...

Well, other than combustion and pneumatics, other common launching methods include, stored strain energy (like in an onager, or crossbow), gravitational energy (like in a trebuchet), solid propellants (not safe, legal, or quiet, don't mess with them) or electric power.

Electric power can be split into two subsections:
- Electromagnetic
- Electrothermal

Electromagnetic can be spilt down further into reluctance, and inductance.

In simple terms, reluctance is using an attractive force, inductance a repulsive one.
Railguns and Thompson's coils are always inductive, coilguns can be either. When people normally talk about a coilgun, they're referring to a reluctant coilgun, using magnetic fields to draw in a steel armature (or projectile), but they can also be inductive, producing high currents within the projectile itself with sheer electromagnetic brute force (which creates a magnetic field), and then repelling that with the same field that created the currents in the projectile. That takes a lot more power, but it's also I believe how the world's fastest coilgun currently works.

Electrothermal cannons use electric power to create heat to expand gases to force a projectile with pressure. You can either heat the air with a vast spark, but that's obviously inefficient.
A common variant is the atomisation of water with a high power electric impulse. Basically, if you apply enough power to water quickly enough, it turns to steam almost instantly, and you can create huge pressures with enough application of power.

That brings me on to one last type of cannon. The steam cannon, which flash boils water in a fraction of a second, again, producing vast pressures.

That lists all the main ways I can think of to launch something. There are other ones, but those are the variants that a home hobbyist might be able to achieve.

For more info on Electric based acceleration, I'd advise taking a look around: http://www.powerlabs.org/emguns.htm
Also take a look at the atomisation of water section on the high voltage section of that site.

[jackssmirkingrevenge]

gravitational energy (like in a trebuchet)

I always wanted to make something like the attached diagram, of course it wouldn't be at all portable but the power potential would be there. It's always how I imagined the dart-firing traps in Indiana Jones and similar would work. Such a system would be more likely to survive for centuries in a hidden tomb when compared to a tension powered device.

[Twitcheth]

Simple = onager/treb/slingshot. Difficult (depending on who you are) electromagnetics .

And JSR thats actually a good idea/theory. I mite put that to the test one day.

[Ragnarok]

Such a system would be more likely to survive for centuries in a hidden tomb when compared to a tension powered device.

That would depend on how well the seals on that piston survived. If the seal was degraded enough and large amounts of air were esacping, you wouldn't get much power out of it at all.

[jackssmirkingrevenge]

if it was a stone piston that fit tightly in a stone chamber (I'm thinking primitive technology here) you wouldn't need seals at all, of course it would leak a bit but the pressure generated would be enough (given a large enough weight and piston) to propell a dart at lethal velocity into an unsuspecting grave robber.

[Ragnarok]

I always thought the lethal would come from a poison, and for that, you don't need much velocity. Blowpipes are fine, and that's only using a few psi from the lungs.

However, whether a poison would survive several hundred years is yet another matter. The next problem is if they've developed an antidote for it in that time.

[Twitcheth]

OK lets test. JSR be the Indianna Jones I get to be a native guy who makes the traps