- How do you power a rail gun?
- What is a compulsator?
- How does a compulsator work?
- How do I build a compulsator?
Powering a rail gun is no simple task. Certainly you've heard of or seen rail guns powered by capacitors, car batteries, etc. If powering a rail gun were that easy, any terrorist worth his salt would be lobbing projectiles across the globe in no time. No, making a rail gun that can produce useful output is difficult indeed. The answer to this problem is the compulsator.
A compulsator is a compensated pulsed alternator. Basically this is an alternator designed to produce fast, high power, low rise time pulses by providing an impedance compensation system. The alternator produces an alternating voltage signal across the rotor coil terminals in response to being rotated through the magnetic field set-up in the stator. In addition, a conduction shell is mounted in the air gap between the stator and rotor, with a compensating coil mounted to it. So, the major components of a compulsator are: mechanical rotational input, stator with field coils, rotor with armature coils, shield with compensating coils, and lastly a switching system. The switching system allows the AC voltage signal generated in the rotor to be tapped and directed into the load (rails and projectile) at the desired time and thus desired voltage initiating a current pulse and then disconnecting the load from the rotor circuit stopping the pulse. The switching system is discussed in the Firing section.
A compulsator converts rotational energy into electrical energy. It requires two inputs, a rotational input and an electrical input to the field coils. The main difference between a compulsator and an alternator or generator is that the compulsator has an impedance compensation winding(s) that decreases the rise time of output pulses. In operation, the compulsator is spun by a suitable traditional electric motor or other source (gasoline engine perhaps...). The voltage is induced in the rotor in response to it's movement through the magnetic fields set up in the stator field poles and coils. Once up to speed, the switching system closes the circuit while the output voltage signal is of the desired polarity and amplitude. The extremely low impedance of the compulsator generates a large, fast rise time current pulse into the load (the rail gun). A counter-rotational force is exerted on the compensation winding housing and the rotor due to the current pulse so the entire compulsator must be fairly robust in construction. In addition, the rotor should have as little conductive material besides the armature coils as possible. This serves to further reduce iron losses and eddy currents that will reduce pulse rise time. Read the patent documents below to get a full understanding of compulsator operation.
Patent #4200831: Compensated Pulsed Alternator
Patent #4935708: High Energy Pulse Forming Generator
Building a compulsator is one of the biggest challenges to rail gun design. Theoretically you could modify an existing motor to perform as a compulsator, but of course a fully custom built unit will serve much better. Building a compulsator from scratch would allow the incorporation of custom feautures such as an incorporated switching system, internal cooling system, shaft position encoders, etc but at an enormous cost in materials and labor.
The best option is therefore to locate a suitably sized motor housing and use the field poles and windings. You may need to rewind the field coils depending on the type of motor. In addition the housing will also already have bearings to locate and support the rotor assy. The downside to this approach is that you will need to build a custom rotor and compensation winding (stationary or counter-rotating) as well as a conductive shell in the air gap. These hurdles will be minor compared to building a compulsator from scratch. Look to surplus (commercial or governmental) outlets or auctions as a good cheap source for large motor housings. The bigger the better. Use the patent documents above for guidance until full plans are available on this site.
Send
all comments to jmengel@insightbb.com
Page last updated 4/24/02
