Lock, Stock, and Three Smoking Coils: The Electric Musket Ryan Eder David Grothe Jason Kamuda Thomas Minor

Introduction Gauss Rifle Features: Charge status/readiness Three stages Store previous shot records and statistics

Design Constraints Power Projectile velocity vs. energy control Weight/Portability Hand-held, or Jeep-mounted? Speed/Timer resolution Speed/accuracy of calculation vs. overkill on I/O

Coils & Capacitors Coils will be made of 14-AWG copper magnet wire Provide high conductance, and large force on projectile Concerned about weight Tentatively three banks of 15 photo-flash capacitors each.

All that power! How do we control it? SCRs? Provide very high voltage isolation and very high current. Exactly what we need! Can’t switch them off mid-pulse No good IGBTs Very fast switching time (MOS-speed) Not many hobbyist coil guns have used them Relatively new (~10 years)

All that power! How do we control it? High-current diodes Used for inductor energy recapture Similar to inductive kickback dissipation, but we’re actually getting the energy back to the capacitors Microcontroller/LCD on a completely separate, low-voltage circuit from separate 9V battery All communication goes through optocouplers

How do we store the energy in the first place? Use a DC-DC converter 9V battery input (really only 4.8V), 990V draw, provides 700mAh, or 42 minutes of continuous charging Won’t actually need continuous charging except for boot-up Need PWM to drive transformer

Sensors Want to measure velocity, estimate IGBT switch times Essentially, use optocoupler with light path crossing projectile path Hopefully BBs ≠ Black Cats Want high precision for accurate reporting/control Need fast microcontroller clock! Want lots of input captures ports, need at least one.

Program Requirements Program shouldn’t be too big Store lots of statistics Help with determining timing Interesting to user: “How well did we kill ‘em?” Want lots of Flash! Single point of data can’t give velocity Want fast arithmetic, including multiply/divide Want SPI to interface with cheap LCD Pushbutton User Interface (PUI TM ) needs GPIO

Microprocessors Freescale MCF51QE128 Series V 32-bit 1 6-channel, 2 3-channel Input Capture/PWM, SPI 24-channel 12-bit ADC 71 GPIO FPU

Microprocessors Microchip PIC32MX Family 2.3V-3.6V 32-bit 5 Input Capture, PWM, SPI 16-channel 10-bit ADC Unknown GPIO, 100-pinout No FPU Single-clock multiply, fast divide Better support?