HW projects - Multi stage optically triggered 5 kilojoule coilgun (under construction)

When people see this thing, their first question is usually something like this: "whoa!, cool!.....can you shoot through walls with it, like in some sci-fi movies?". But unfortunately the answer is no, you can't. 5kJ is not a huge amount of energy, especially when the efficiency in conversion of electrical to kinetic energy is usually somewhere between 0,1 - 4% in these kind of setups.

projectiles

The coilgun or gauss gun is actually not more than one example of a linear motor, a motor that has its stator "unrolled". Instead of rotation as in normal motor it produces a magnetic force along the length of the stator. In this case, the coils are just simple solenoids, triggered one after another. The projectiles are made from large silicon steel solenoid cores and weigh ~130 grams each. Lighter cores would, of course, accelerate better and reach higher velocities but at higher speeds the coils would misfire or the pulse duration might be too long. As the velocity increases, the time to transfer energy to the accelerating core decreases. Also, the triggering circuitry has a delay in the microsecond range and it is a long time to "wait" for the coil to energize if the projectile is passing through it at high speed.

Unit has been tested with low power shots and it works, but not without problems.

A single power supply is responsible for charging, SCR triggering, IR optics and powering the control circuitry but it cannot supply enough current for drive electronics when enabling more than five stages.

Note: Almost all of the pictures are crappy since they were taken with a camera phone. I will put better ones as the project continues....

Related links:

http://en.wikipedia.org/wiki/Coilgun
http://www.powerlabs.org/emguns.htm

Power source:

133 x 450V/470uF of electrolytic capacitors, having the total capacity of
6,3kJ @ 450V, 5kJ @ 400V & 4,5kJ @ 380V. Caps arranged to 11 separate banks.


Switching devices:

Stage 1: Semikron SKT130/12C (1200V / 130A SCR)
Stages 2-6: Semikron SKT80/14C (1400V / 80A SCR)
Stages 7-11: Semikron SKT55/14C (1400V / 50A SCR)

The current handling values mentioned are for continuous operation, these SCRs can actually survive few millisecond pulse currents from 1,5 to 4kA.

Note: These thyristors were actually manufactured in the mid 70's, modern GTO:s would probably be very nice replacements....

Coils:

coils

11 pcs. (1 manually & 10 optically triggered)

Single coil specs:
Wire: 1*3mm rectangular magnet wire, 4.4 metres.
Dimensions: In 18*22mm, Out 40*45mm, Length 33mm.
Construction: 4 layers, 10 turns / layer (40 turns total).
Weight: 130g + coilform 8.5g.


Drive electronics:

trigger circuitry

SCR triggering is done manually using push button for the first stage and in stages from 2 to 11 by using infrared LED and phototransistor gates. The phototransistor output is passed to 74F14 fast inverting schmitt trigger logic chips that switch 2 amp mosfet driver ICs. Driver ICs are connected to the SCR gates through current limiting resistors.

Future upgrades:

-Power supply upgrade (to enable more than five stages)
-Redesigning the charging circuitry
-Improving the SCR triggering system
-Getting faster photodetectors

to be continued.....

(click for larger image)



top section



side view



capacitor bank