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Lock, Stock, and Three Smoking Coils: The Electric Musket

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

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Lock, Stock, and Three Smoking Coils: The Electric Musket

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

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

  3. 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

  4. 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.

  5. 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)

  6. 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

  7. How do we store the energy in the first place? • Use a DC-DC converter • 9V battery input (really only 4.8V), 990V output • @1A draw, provides 700mAh, or 42 minutes of continuous charging • Won’t actually need continuous charging except for boot-up • Need PWM to drive transformer

  8. 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.

  9. 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 (PUITM) needs GPIO

  10. Microprocessors • Freescale MCF51QE128 Series • 50.33MHz @ 2.4-3.6V • 32-bit • 1 6-channel, 2 3-channel Input Capture/PWM, SPI • 24-channel 12-bit ADC • 71 GPIO • FPU

  11. Microprocessors • Microchip PIC32MX Family • 80MHz @ 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?

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