Rail 3

Project Summary

This Railgun was designed to be easily transportable, simple to assemble, and "safe" around drunks, children and animals.  The system, when setup, will have NO exposed high power/voltage conductors so there shouldn't any way to get shocked from it.  The controller also has EMO (emergency machine off) which automatically engages the discharge circuit, and everything else (charging, loading, firing) is disabled until it is reset. 

The design of the gun, although similar to Rail 1, has been improved upon considerably. Design changes include rail design, rail containment and compression, and automatic BB loading. I'll just get into the pictures and describe each system as it is pictured.

Below is a picture of the new design of the rails. they are made of 3/16" x  1" copper buss. The connection tabs (sticking off the sides) are made of the same stock, just cut in half and machined. The rails and tabs were clamped in place (close together) while they were soldered witha propane torch.  The gap between the copper pieces was minimized to produce the highest conductivity.  If there is too much solder the joint will act like a fuse when the gun is fired. Sounds funny talking about large solder joints as fuses but I've seen pictures of just such catastrophic failures on other Railgun websites.  The cut in the rail is another improvement over the Rail 1 design.  The notch cut out of the rail forces the electricity to follow a more linear path along the rails, where the shape of the magnetic field is most important. A linear magnetic field is caused by linear current flow. This part of the design can never be "ideal" so balances and tradeoffs are made. Hopefully I made good design choices.

Pictured above is the rail containment structure.  Remember, most of the force created by the magnetic fields is trying to split the rails apart so rail containment and compression is very important. Rail 1 was held in place by compressing the rails from top and bottom, not from the sides.  This caused the rails to migrate during a shot.  The new design solves this. It holds them in place from the sides, with a layer of compressible plastic (acts as a spring and electrical insulator), aluminum supports and through bolts between supports. The new design is tough, and infinitely adjustable with shimming.

Below are pictures of the pneumatic injector with the rails set in place (left) and with the containment in place.  The pneumatic injector is used to accelerate the projectile to an initial velocity so it does not arc weld into place.  A new addition in this iteration of rail gun is the auto loader seen at the end opposite of the rails.

A front view of the rails, injector and containment.

The auto loader was created to add repeated firing and a safe way to load the gun. This design is simple yet effective way to load a BB moments before each shot.  The vertical tube if stacked with BB's. There are two adjustable bolts aligned with the end of the tube. in a natural state a BB falls into the gap between the bolts.  When the solenoid fires, both bolts are shifted aligning them to the gap over the injector channel and the BB falls into the channel.  The solenoid is de-energized and the spring returns it to home position where another BB falls in. Its simple, guarantees single BB release, and reliable.  During testing it was able to release 2 BB's a second without jamming or missing. It'll do.

Here's where I get into the creation of the controller.  It is based around an Atmel ATMega8 microprocessor (uP).  There are many safety features designed into the system. Each will be discussed in time. The system was designed using ExpressPCB schematic and layout software.  It is a useful program that allows you to design a board and order it over the internet for a good price. I have used their services for several years and have been impressed by the quality on the "prototype" boards. For a simple circuit such as this; I use the software to design the board and then make it myself.

Above and to the left are the supplies needed to make the board. The PC board has a positive photoresist layer on top and bottom. The photo resist is exposed using a black light, UV, bulb over several minutes. The pattern, printed on transparency paper, is transferred to the PC board blocking the UV light. The light softens the photoresist, allowing the developer to remove it.  The pattern is then etched onto the board using the Ferric Chloride acid.  The acid removes the copper where the photoresist was exposed to light and removed.  The above right picture is after etching but the photoresist is still visible (as green).

Below are the top and bottom of the board with thier masks after the resist was removed. (notice the copper shine)

Now we get into the Construction of the box that will contain the control system, charger, discharger, energy storage and pneumatic controls.  Below is the face plate and CPU plate. The face plate is made of soft aluminum that was sanded and polished to a near mirror finish (you can see my hand, camera phone and verticle blinds in the reflection) after all holes were cut. The CPU plate mounts the PC board I discussed manufacturing earlier and the 24V power supply solely used to fire the pneumatic solenoid.

The divider plate separates the finicky electronics from the high power equipment.  One side shows the pneumatics and high power inductor, the other side has a couple power supplies and the power resistors.  The large cylinder in the left picture is an air charge holder. When the air is fired the bulk of the air comes from this small chamber and afterward its refilled by another air tank. The large power supply in the right picture, is a 5V@3A  and 12V@2A switching power supply used to power the relays and processor. The small one is a high voltage switching supply for a cold cathode florescent tube that illuminates the LCD screen.  The resistors are all 50W aluminum enclosed panel mount type resistors.  Four are discharge resistors and three are current limiting resistors for the charger.

Following are some shots that show the system mostly assembled.

Here's some shots of the caps all hooked up.  The caps are 450V, 2400uf but the each measure ~2600. The surge voltage is 525 but I've never fired them with more than 500 in them.  They are connected with aluminum buss in series with balancing resistors along with a bypass diode to absorb the reverse voltage spike after the shot.

There's its new home.  The entire system was designed to fit inside this ambiguous brown metal file folder box I picked up from goodwill.  There's enough room under the lid for all the cables needed for firing.

When turned on, the controller lights up from the cold cathode light and the illuminated buttons. The giant red buttons are fire and EMO, the green are right and left, and the blue is "select". The fire button also illuminates but only when the CPU tells it to.  It will flash when the system is dangerous (caps are energized) and it will go solid when ready to fire.  There's the startup screen below, it reads "WELCOME TO THE INSPIRED RAILGUN."  The other picture is of the screen while its being programmed. There are a bunch of arrows pointing to the programming cable on the left of the screen. As soon as it finishes programming it restarts the software and the arrows disappear.