After 2 long years of on-and-off work my coilgun project is finally completed. For anyone who doesn't know what a coilgun is, it's a gun that fires a projectile with magnetic force instead of gunpowder. The projectile from this gun won't kill a person, but the electrical energy stored in the capacitors is 78 times the lethal amount for human beings so this is no toy.
Some technical data:
- Action: single stage, bolt
- Weight: 7.75lbs or 3.52kg
- Power supply: 12V NiMH battery (needs recharge after ~15 shots)
- Charging: 40 watt regulated ZVS flyback driver (charge time ~30s)
- Capacitor bank: 4x 3900uF 400VDC
- Stored electrical energy: ~1.25kJ
- Switch: SCR
- Efficiency: unknown, probably 1-3%
- Body: lightweight ABS plastic pipe and sheets
***Answers to commonly asked questions***
Q: Will it kill a human?
A: The only ways it will kill is if someone were to touch the capacitors or high voltage charging circuit, which could easily cause electrocution. I suppose if you fired it straight into your stomach or face from point-blank range and refrained from seeking medical attention afterward, you could die that way as well. The muzzle energy of the coilgun is not comparable to regular firearms.
Q: You should shoot it into some meat!
A: That's a waste of a potential sandwich
Q: Will you sell it?
A: Nope, sorry!
Q: Will you post plans?
A: And deprive you of the fun of building your own? Of course not! But I'm willing to point you in the right direction. It's not that hard- I started this project with zero experience with electronics. It takes more patience than anything else.
Q: What are the songs in this video?
A: In order: Kick It, Rally, and Behemoths from Mechwarrior 4, Invaders by Excision and Datsik, Still Alive by Jonathan Coulton and GlaDOS
Q: What is the projectile speed/energy?
A: I don't know yet. I'll post what it is once I have the equipment to measure it (speed trap, scale).
Q: Will a smaller projectile result in better efficiency?
A: No, a smaller projectile won't be able to absorb as much magnetic flux as a larger projectile, due to a phenomenon known as magnetic saturation (Wikipedia it!)
Q: Will multiple coil stages improve power/efficiency?
A: Yes! I only have one stage on this design for the sake of simplicity.
Q: Will rifling in the barrel improve accuracy?
A: No- not at these projectile speeds. A projectile has to be moving at a certain speed before rifling is effective. Also, rifling depends on the bullet expanding within the barrel, which doesn't happen with a magnetically propelled projectile.
Q: How do you claim 1.25kJ of energy?
A: Some websites which feature my gun state that I am delivering as much energy to target as a .45ACP. They are incorrect, either because they didn't read my description or maybe they just didn't fully understand it. 1.25kJ is the ELECTRICAL energy stored in the capacitors, according to the equation E = 0.5*C*V^2. For this gun, C=15600uF and V=400V, thus E = 1248J. One of the main drawbacks for coilguns is EFFICIENCY, which, for single-stage hobbyist designs (like mine) is limited to about 3%. So if we assume a 3% efficiency (as stated in the video), the kinetic energy (delivered to target by projectile) is in the area of 37J, which is much more than a bb gun but much less than a real gun. I don't have the equipment to measure the exact kinetic energy, but as soon as I do I will report it. Thanks!
Q: You misspelled necessity! You suck!
A: I'm SO sorry. How can I possibly make up for for all the pain and distress I've brought into your life?