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

Ryan EderDavid Grothe

Jason KamudaThomas 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 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

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 (PUITM) needs GPIO

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

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?