disc shooter

[danman1453]

I know there will be a lot of physics involved, but i would like to build a electromagnetic disc shooter. I have seen it on various railgun webpages. I have never seen any schematics for it or even any real detail in its construction. i have no idea what kind of power supply is needed. Thnx!

 

[mechie]

Magnetic Rocketry et al

Not an answer to your request but we did discuss something along these lines a while ago ...



Nothing much was revealed but to keep history from repeating itself :|

 

[Mikkel]

On https://4hv.org there is some discussion on that topic.

 

[charcoal]

The basic principle of a magnetic disc launcher relies on Lenz’s Law; that an electric current induced by a changing magnetic field will flow such that it will create its own magnetic field that opposes the magnetic field that created it. These opposing fields occupying the same space at the same time result in a pair of forces. In order to create a pulse in order to throw a ring/disc off of a metal guide you’ll need some form of inducing a large current in the metal disc in a short period of time.

One tried and true way is using capacitor bank capable of discharging in a very short period of time. A bank of 12x 800uF 330V caps (photographic flash capacitors would work best, as they are designed to produce a fast pulse) should work nicely. If you arranged them in a 4x3 grid you’d get an equivalent cap with a value of just over 1000uF and a max. working voltage of 990V.

This still leaves you with 4 problems in making your disc launcher.
A power supply capable of charging the cap bank to about 800v.
Some way of switching the capacitor bank over the coil in a very short period of time.
A coil capable of inducing current in your disc.
Manufacturing the frame, projectiles and wiring.

Starting with the power supply, which was your original question, I’d recommend building a simple switched mode power supply (SMPS) driven by a 12v lead acid battery. This can be done using a 555 timer driving IRF530 mosfet transistor connected in series with the primary of your transformer. There are schematics for these types of power supplies available on the web. The transformer would need to be some form of flyback type to provide the sort of pulses needed to charge the cap bank.

Switching the pulse generated by your capacitor bank to the coil will be one of the most difficult steps to overcome. Trying to use a relay for this sort of job will give you a good introduction to spot welding and I have seen people use triggered spark gaps (loud, dangerous and good at wasting energy) or high current SCRs (solid state relays about the size of a hockey puck and quite expensive). I’d go for a thyratron/triggatron tube. Call it overkill but you can pick them up at decent prices off of eBay or from a tube wholesaler. All three of these methods need some form of trigger pulse (not too sure about SCRs) and the best way to get a suitable pulse is by using a xenon tube trigger transformer and a diac. You can get both of these from most electronic parts stockists.

The coil is pretty simple to describe, about 30 feet of #12 enamelled magnet wire should do the job ok for a 2¼” coil, but you need to manufacture this part as accurately as possible for a smooth acceleration and minimum wasted energy.

The majority of the physical construction is probably beyond the scope of these forums, with the exception of wiring the caps together and to the coil, which will have to be done using copper braid or low gauge bus-bars.

Overall projects like this require a large amount of time in manufacture and testing, and can be dangerous with even slight imperfections (even in only moderate velocity pulse launchers like the one above). Make sure you’re familiar with what you’re doing before you start building.

If you want more detailed instructions on how to build something like this then Information Unlimited do some very good plans/kits in this area.