Want to build a small railgun

[TheoPetro]

title says it all. i know basically how these work (kinda) but im not aware of things to watch out for. im thinking a track with a series of electro magnets that are turned on then off by a timer. im thinking that the time inbetween one magnet going off and the next one going on has to be something like 1/x^2 or somethen like that so the object will keep accelerating.

neone have any links or insight on this project? i dont want it to bee too large but would like to shoot a small bb or ball baring 20-50 ft. just as a little project to keep me busy.

 

[Painman]

This answer isn't highly technical by a long shot - Google "railgun" - the first 3 hits are very relevant...

 

[cheesehead]

Hackaday.com has several links.
Also, I should mention that asking for help is entirely reasonable. I'm still a little fuzzy on the mechanical aspects, and anything involving enough electricity (in the larger variants, anyway) to kill multiple elephants should be approached with caution.
A slightly easier option (you can find plans at hackaday, as well) is a coilgun. All it needs is a high-voltage DC power source, such as that found in a disposable camera's flash, a coil, and a non-ferrous barrel. The projectile (usually a ball bearing) is placed before the coil, the coil is momentarily energized, and the BB is pulled twoards it. However, the surge ends at roughly the same time it passes through the coil, so that it continues moving.

 

[TheoPetro]

i dont want plans to make one tho. i dont use plans or instructions for nething i build. i like to make them from scratch. im just curious about anything i should watchout for.

 

[silverpig]

Originally posted by: Cheesehead
Hackaday.com has several links.
Also, I should mention that asking for help is entirely reasonable. I'm still a little fuzzy on the mechanical aspects, and anything involving enough electricity (in the larger variants, anyway) to kill multiple elephants should be approached with caution.
A slightly easier option (you can find plans at hackaday, as well) is a coilgun. All it needs is a high-voltage DC power source, such as that found in a disposable camera's flash, a coil, and a non-ferrous barrel. The projectile (usually a ball bearing) is placed before the coil, the coil is momentarily energized, and the BB is pulled twoards it. However, the surge ends at roughly the same time it passes through the coil, so that it continues moving.

That is called a Gauss gun I believe. And you have to turn it off when the projectile reaches the halfway point as it is at equilibrium there. Keeping the power on past this point will only serve to decelerate the projectile until it comes to a stop at the other end and is accelerated back towards the middle.

 

[silverpig]

Originally posted by: TheoPetro
i dont want plans to make one tho. i dont use plans or instructions for nething i build. i like to make them from scratch. im just curious about anything i should watchout for.

Your idea is not quite correct. You need two rails of a good conducting metal like copper. Attach one rail to the + side of a huge bank of capacitors, and the other rail to the - side of a huge bank of capacitors. Charge up the capacitors, use a gas gun to inject your conductive projectile in between the rails, and watch out. You have to be careful because if you don't inject your projectile with enough velocity, it will melt and form a smear of liquid metal along the inside of your rails. Secondly, in order for this to be fun, you have to get a LOT of capacitors, and the higher the voltage the better. Using low voltage ones means that in order to get the same power output, you will need an extremely high current. High current = high temperatures = melted projectile.

 

[Evadman]

If you are just doing this for fun, you may want to start with a gauss gun before moving up to a railgun. A Gauss gun acts like a solinoid and will accelerate a projectile from zero velocity, so you do not need a projectile injection method.

My first gauss gun was a 2 bic pen tubes with about 400' of magnet wire wrapped around it. (IIRC there were either 2 or 4 current paths, I don't remember. I do remember it was close to 8 ohms) I plugged it directly into the wall (120v ac current, so it pulled about 15 amps) and used a momentary contact switch to fire it. It would shoot a 16 penny nail about 15' or so. It got very hot after being fired a few times and the tube finaly colapsed because I let it get too hot. Still fun though, and only cost about $30.

 

[TheoPetro]

Originally posted by: Evadman
If you are just doing this for fun, you may want to start with a gauss gun before moving up to a railgun. A Gauss gun acts like a solinoid and will accelerate a projectile from zero velocity, so you do not need a projectile injection method.

My first gauss gun was a 2 bic pen tubes with about 400' of magnet wire wrapped around it. (IIRC there were either 2 or 4 current paths, I don't remember. I do remember it was close to 8 ohms) I plugged it directly into the wall (120v ac current, so it pulled about 15 amps) and used a momentary contact switch to fire it. It would shoot a 16 penny nail about 15' or so. It got very hot after being fired a few times and the tube finaly colapsed because I let it get too hot. Still fun though, and only cost about $30.

is a gauss gun the one you have to turn off once the projectile passes through the coil?. if so can i rig something up like a motion light that will shut it off for me?

 

[Matthias99]

Originally posted by: TheoPetro
is a gauss gun the one you have to turn off once the projectile passes through the coil?. if so can i rig something up like a motion light that will shut it off for me?

Sometimes any sort of electromagnetically-driven accelerator is referred to generically as a 'gauss' weapon, but yes, a 'gauss gun' is usually used to refer to that type of device (where you pull the projectile into an electromagnet, usually a coil, located partway up the barrel, then shut it off so that it continues down the barrel). A 'railgun' is a different sort of accelerator, where current passing through the projectile and two 'rails' that form the barrel induces electromagnetic acceleration.

You should be able to use a feedback system to shut a 'gauss gun' or coilgun off at the right moment, in theory. Getting the timing exactly right may be difficult without equipment to measure projectile velocity.

Also:

i dont want plans to make one tho. i dont use plans or instructions for nething i build. i like to make them from scratch. im just curious about anything i should watchout for.

I strongly recommend at looking at some plans and things other people have done, at least if you want to build anything that pulls more than ~1A of power from a wall socket. At high power levels, it's awfully easy to fry yourself, blow something up in your face, or set your house on fire if you screw up.

 

[TheoPetro]

that sounds like some good advice matthias99. maby taken a look at some diagrams isnt a bad idea. ill post some pics and details when i get this thing done. (itll be a month or two tho too much school to concentrate on)

 

[Alexstarfire]

Ok, maybe I'm just a little to stupid to understand the concepts, but couldn't you just use elctromagnets? I would say either one big one at the end of the rail, though that's probably not the best idea, or several throughout the gun. You would have to use timers so you could turn them off when they reached the elctromagnet. If you wanted it to work with any size/weight projectile then you could use motion sensors.

It's be best if you could direct all of the magnetic force into the barrel of the gun, but I don't know how to do that.

Just $.02 from a dumbass.

 

[TonyG]

Originally posted by: Alexstarfire
Ok, maybe I'm just a little to stupid to understand the concepts, but couldn't you just use elctromagnets? I would say either one big one at the end of the rail, though that's probably not the best idea, or several throughout the gun. You would have to use timers so you could turn them off when they reached the elctromagnet. If you wanted it to work with any size/weight projectile then you could use motion sensors.

It's be best if you could direct all of the magnetic force into the barrel of the gun, but I don't know how to do that.

Just $.02 from a dumbass.

That is the general idea of how a rail gun works. You just have an arrangement of electromagnets set to be activated/deactivated as the object passes each one. Also, I believe I have seen a design in the past which used motion type sensors, or it may have been a beam sensor to trigger the electromagnets.

 

[TheoPetro]

i was thinking something along the lines of motion detectors set like a cm before and after each electro magnet, the sensor before would shut off that magnet and the sensor after would turn on the next magnet. im not sure how many ill have yet.

we havnt gotten to magnatism yet in physics just on electricity now. are there some equations you guys know that relate the current to the force of the magnetic field it produces?

also im assuming i just wrap the wire around the non ferrous pipe then run a current through it. -----0----- <- Side view of pipe ( ---- ) and wire wrapped around it ( 0 )

to supply the wire w/ a current i need to create a potential difference between one end of the wire and the other. im assuming i store charge in a capacitor and when i turn it on it connects the capacitor to the wire(magnet) and then back to the battery? i guess my question is how do i charge the capacitor? do i just let it go and not complete the circut?

 

[silverpig]

Originally posted by: TonyG

Originally posted by: Alexstarfire
Ok, maybe I'm just a little to stupid to understand the concepts, but couldn't you just use elctromagnets? I would say either one big one at the end of the rail, though that's probably not the best idea, or several throughout the gun. You would have to use timers so you could turn them off when they reached the elctromagnet. If you wanted it to work with any size/weight projectile then you could use motion sensors.

It's be best if you could direct all of the magnetic force into the barrel of the gun, but I don't know how to do that.

Just $.02 from a dumbass.

That is the general idea of how a rail gun works. You just have an arrangement of electromagnets set to be activated/deactivated as the object passes each one. Also, I believe I have seen a design in the past which used motion type sensors, or it may have been a beam sensor to trigger the electromagnets.

No it's not. Read above for how a rail gun works.

 

[TonyG]

Originally posted by: silverpig

Originally posted by: TonyG

Originally posted by: Alexstarfire
Ok, maybe I'm just a little to stupid to understand the concepts, but couldn't you just use elctromagnets? I would say either one big one at the end of the rail, though that's probably not the best idea, or several throughout the gun. You would have to use timers so you could turn them off when they reached the elctromagnet. If you wanted it to work with any size/weight projectile then you could use motion sensors.

It's be best if you could direct all of the magnetic force into the barrel of the gun, but I don't know how to do that.

Just $.02 from a dumbass.

That is the general idea of how a rail gun works. You just have an arrangement of electromagnets set to be activated/deactivated as the object passes each one. Also, I believe I have seen a design in the past which used motion type sensors, or it may have been a beam sensor to trigger the electromagnets.

No it's not. Read above for how a rail gun works.

Sorry, its been a while since I have looked at rail guns. Looks like I am thinking more along the lines of a multistage coil gun. I know I have heard of something along this line in the past, maybe it is time for me to look a few things up.

 

[silverpig]

What you described is more like a LINAC. It works well on extremely small charged particles.

 

[networkman]

Railgun reference info

Excellent site on Railgun development

 

[bobsmith1492]

You know, I wanted to do something like this also. My idea was to use a series of contacts within a length of pipe to activate electromagnets. The idea was that when you drop/force a small, metal cylinder into the tube, it hits the first contacts, activating the first coil just above the cylinder, and launches it forward. The coil is deactivated when the cylinder leaves the first contact. It then hits the next.. and the next... and you could put in however many stages you want. You'd just need a huge bank of capacitors - actually, several, one for each coil stage. Then I realized how much work it would be....

 

[imported_Seer]

I think the best thing to use for detecting where the projecile is would be laser gates. We use them in physics all the time. These are different from motion detectors, which are sonic in nature and pinpoint distance. A laser gate just says on or off depending on if the laser is broken or not.

 

[TheoPetro]

Originally posted by: Seer
I think the best thing to use for detecting where the projecile is would be laser gates. We use them in physics all the time. These are different from motion detectors, which are sonic in nature and pinpoint distance. A laser gate just says on or off depending on if the laser is broken or not.

im tryen no to spend alot of $ (most of the materials i have at home or work) how much are laser gates?

 

[imported_Seer]

I dunno, they are pretty small, and it's just a little beam and a sensor.

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Yikes, $50 >< http://froogle.google.com/froogle?q=photogate&btnG=Search