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Lock, Stock, and Three Smoking Coils: The Electric Musket
Ryan EderDavid Grothe
Jason KamudaThomas Minor
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Introduction
Gauss Rifle
Features: Charge status/readiness Three stages Store previous shot records and statistics
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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
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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.
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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)
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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
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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
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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.
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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
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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
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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?