Barry's Coilgun Mark I

What if I made a multi-stage coilgun, with digital timing to control the firing sequence? How well can it work?

Goals

My first model, the Mark I, will launch small projectiles at a modest speed. In this (my first coilgun) there's a few things I want to accomplish:

• Build a coil gun with predictable and controllable characteristics.
• Identify the main elements of design. That is, what variables affect performance, and how?
• Launch small (< 1oz.) projectiles at moderate speed. They should go fast enough to be fun, but not so fast as to cause permanent damage to body parts.
• Use inexpensive and common components.
• Simple mechanical assembly with a minimum of mechanical adjustments.

To be precise: My goal is tolaunch a 1-inch screw or nail 16 feet straight up . (That's the height of our living room ceiling, or about 5 meters. I hope it doesn't stick there!)

• Launch speed calculations

Design of the Mark I

I just hate to mess around with fiddly little mechanical adjustments, so my main goal is the "simple mechanical" part. I want to eliminate adjustments as much as possible. Therefore, the Mark I will have a few coils controlled entirely by digital electronics. (I am much better at electronic assembly than working with tools!)

I choose to run my coils in a pre-determined timing pattern. I know the performance would be better if there were a detector to fire coils according to position, but that would mean fiddling with the detector's position and the length of the projectile. So I won't use detectors.

Electrical

Building the electronics for a coil gun involves several components. Fortunately, today's electronics offer a rich variety of possible timing and power control devices. Here's what I chose for the Mark I:

• Oscillator circuit ('555 timer)
• Coil Timer circuit (8-bit binary counter, comparators, latches)
• Coil Driver circuit (2N2955)
• Trigger Logic circuit
• Power supply

Mechanical

Building the mechanical parts of this coil gun involves several components.

• Choosing the wire and winding coils
• Choosing tube material and dimensions
• Choosing a projectile
• Building the timing electronics on a breadboard
• Building the coil driver electronics at the business end of the coilgun

Timing

Because this coilgun is running open-loop, we need to calculate when to turn on/off each coil. Here's how:

• Measuring coil strength
• Computing maximum coil strength
• Computing Mark I coil timing (equations of motion) from the coil strength

Results

As of 20 Feb 1999, this coilgun has achieved 1.7 m/s with one coil:

• Mark I coilgun results