[mcguyver]

OK, a motor is basically an electromagnetic coil with another magnet system to offer repulsion/attraction to the coil. In the case of airsoft guns, their motors are a permanent magnet motor. This means that the only source of current draw inside the motor is the coil. Now, when a motor first starts, it will be drawing it's highest amperage. The industry term used to describe this is inrush current. As the motor starts to turn, it generates current as the magnetic poles of the motor coil cut through the magnetic lines of force of the magnets permanently attached to casing of the motor. This creates current inside the coils, current that is exactly opposite (180 degress out-of-phase) with the current used to start the motor. This is called counter electromotive force, or c-emf for short.

You have to remember that nearly all motors in nearly all types can also be generators. If you were to turn your motor fast enough, like clamp the shaft in a drill and spin it, it will generate voltage and current to a supplied load. So, as the motor is spinning to drive your gearbox, it also is generating voltage and current. And this current is high, almost as high as the current used to start the motor, but not quite. For example, the motor might draw 30 amps at inrush, and the c-emf could be 24 amps. The math looks like this:

30 amps (inrush) - 24 amps (c-emf) = 6 amps.

The above formula describes what is actually happening. The motor draws 30 amps (and always does while running, no matter what), but then generates 24 amps back to the battery. So, the net draw from the battery is actually 6 amps.

Now, when you talk about the capacity of a battery to discharge current, you must also take into acccount it's capacity to take that current back. The formula above describes the very basic operation, and does not take into account the pulses of current occurring in both directions due to pole reversal frequency. Even though this is a DC (direct current) system, there is a frequency and phase element present in the motor's cycle that makes it resemble an AC system, albeit with a more square-wave look to it.

Now, on to wiring and fuses. Just because your motor draws 30 amps at inrush does not mean you need wiring rated for 30 amps. This would be #10 AWG wire, and not very installation-friendly. Nor does it mean you need a 30 amp fuse. The Canadian Electric Code (which is law BTW) requires that wiring for AC and DC motors be rated in ampacity (current capacity) for 125% of the full load amps (rated running current as supplied by the manufacturer). For a motor rated for 6 amps FLA, this means 8 amps rated, or #16 wire. The maximum fuse would be 300% of the FLA or 3 x 6 = 18 amps. Now, airsoft guns hardly fall under the enforcement of the CSA, so this is not a legal issue, but the theory behind ratings is quite evident here. You can instal a 20 amp fuse and still protect the motor and wiring, but there may be the case of a blown fuse if you increase the load. Increasing the load will increase the FLA of the motor. The motor should be able to handle 125% load increase with no ill effects. An EG700 motor in a stock Marui is capable of handling 200% load increase to give you an example.

Are you lost and confused yet? You should try 3 phase motor theory and throw in a good helping of power-factor correction.

So, to sum it all up. Use a battery that is capable of large discharge currents (25+ amps at least). A fuse is your friend and is there to protect your wiring and motor. It IS NOT a source of resistance and DOES NOT reduce ROF or current flow to your motor (unless you use a current-limiting fuse, but that's not very common at all in the real world). #16 guage wire is sufficient even for the most upgraded of guns, and #18 is fine for stock or modestly upgraded guns. If a fuse blows, it has done it's job and saved you $$$ and time for repairs. If wire burns or melts, it's not a capacity issue for feeding your motor, but a short-circuit that needs to be repaired.