Constructing a Railgun: My Cousin's Science Fair Project

[Nistlerooy]

My cousin is thinking about entering a science fair. Originally, we were going to build a small RC robot from scratch. Then he heard about rail guns on tv. You can guess which won.

I have a light university background in physics (graduated in 09), but electronics and electromagnetism were not my strong points.

I have searched this forum for other rail gun postings, and haven't found any solid information of what I'm looking for.

I understand the concept of a railgun, but have a few questions, and could use some expert advice on my design layout.

I've looked all over the internet at different designs for railguns, and found a fairly simple one http://scitoys.com/scitoys/scitoys/electro/railgun/railgun.html" . However, my cousin wants to be able to embed an object into a wooden log from 4-6 feet away. Not sure if that'll work out, but I said I'd take a look.

I'm trying to construct it out of basic materials. I see many designs which use point-and-shoot cameras (usually disposable ones) and other which use home-made capacitors. We don't mind spending the extra $$ to make a descent one in order to achieve the desired effect. However, we may go for all home-made for style points if we can't get the outcome we're looking for.

I"ve attached a rough layout/schematic of the design. I was thinking of using a 9V for the power source, or a car battery (12V) if needed. I think you get the basic idea. The transistor is an idea I stole from the design of camera flashes, which (as I understand), use transformers, transistors, and diodes to create an AC current, change it back to DC, and "pump" a capacitor with more voltage in order to get a greater output than the 1.5, 9, or 12 volts of the power source. (I've heard disposible cameras, which run off 1.5 V batteries, can produce 1,000 - 4,000 V.

The transformer is just 4 steel bars, wrapped in electrical tape, with 26 or 28 magnetic wire wrapped around it.

For the rail I plan on using thin (maybe 1/8") aluminum bars, abut 2"-2.5" wide.

The idea behind the trigger is to be able to place the projectile on the rail and have it stationary until the trigger is activated/depressed. So now I'll begin with my questions:

1. What are the design flaws?
2. As for the transformer, do I need to encase it with something for fire/safety reasons?
3. what specifications on the capacitor should I choose for a 9v battery? a 12v?
4. Will the trigger work as planned? Normally triggers complete a circuit, but in a rail it seems that the circut remains broken (until projectile closes it)
5. If I were to place the projectile on the rail, will it remain stationary until until the trigger is activated?
6. What kinds of things can I use as a projectile? Does the progectile have to be magnitized with 2 poles (similar to the one in the above link)?
7. Will the rails need to be mounted? I don't believe the will as there is no "recoil" like a gun, but if so, what are some good ideas for going about this?
8. Are there any other sources, tutorials, or plans I should be looking at somewhere on the net for help?

Thank you in advance for your time and help!

-Taylor

 

[cesiumfrog]

I was thinking about this recently.. I would suggest first getting a rare Earth magnet and making a 1.5v homopolar motor (using a screw and a wire.. wikipedia has a good picture up). Understand how it works. Then, trying to keep everything else the same (as much as possible) add some short rails and a rolling lightweight projectile (like a small ball bearing or a short wire segment). It should be easier if you're starting small from something that does produce movement, plus you're not needing to muck around with high energy power supplies. Very easy to experiment quickly on that scale.

There exists a type of railgun that does not require an external magnetic field (or rather, suffices with the field from its own single-winding circuit, given enough current). I don't recommend embarking on such a design (especially not if you're still having trouble understanding what you're doing). But you should do some research on the web (for example, you'll see a common problem is that you need so much power that the rails start to melt and deform).

A mistake I once made was trying a mercury projectile (on aluminium rails). I was hoping for low-friction movement and arc-free contact (and may even have been inspired by magnetohydrodynamic propulsion), but hadn't considered the chemistry (if there was any thrust, the projectile had become anchored by amalgamate cement).

If all he wants is to shoot stuff out electrically, a coil gun might turn out better than the railgun , and something run by a conventional spinning motor is probably more effective again (I think mythbusters have done things like this, e.g., for the card throwing episode).

 

[Nistlerooy]

Hello cesiumfrog, thank you for the reply.

After doing more reading and watching some videos of rail guns in action, I convinced my cousin that trying to create a railgun powerful enough to impale a solid wooden object was probably not a good idea.

We found a pretty cool video of simple spin-off of a gauss rifle http://scitoys.com/scitoys/scitoys/magnets/gauss.html" , and I think we'll go with that.

However, now I'm curious about this rail gun for myself. I may try to create one just to see it in action; not looking to create one powerful enough to kill something, but stronger than the one I linked above.

I'll probably start off small, foregoing the capacitor, transformer, diode, and transistor...for now. Does the projectile have to be magnetic, or can it just complete the circuit between the 2 rails?
Lastly, are aluminum plates too large to use with a AA battery? Should I stick with foil?

TIA,

Taylor

 

[Sakha]

Was reading an article about rail guns on HowStuffWorks,
Quoting it:
"Notice that the Lorentz force is parallel to the rails, acting away from the power supply. The magnitude of the force is determined by the equation F = (i)(L)(B), where F is the net force, i is the current, L is the length of the rails and B is the magnetic field. The force can be boosted by increasing either the length of the rails or the amount of current."

Wouldn't the L in the Lorents force (iLB) be the length of the armature instead of the rails?
While the work done would be W=iLB*length of rail?