Documented Gains

 

Using the AEG Audio Analysis method, we measure rate of fire of the AEG mechbox before and after installation of the MOSFET. Using solid state switching should in theory improve the rate of fire by reducing the resistance of the system, since the contact switches are no longer part of the main conduction path. The gain should be particularly evident in heavy current drain applications.

The Test Platform
To test the possible gains of installing a MOSFET, we used our test platform G3 SG1 mechbox with the following mechbox modifications.

The mechbox configuration with M120 spring and high-speed gears presents a large torque demand for the motor, which in turn places a large current drain on the system, as discussed in Gearbox Science I. The use of a MOSFET in this configuration showed a 9.1% increase in measured rate of fire, which is relatively significant. During operation, the MOSFET began to heat up significantly, but did not fail.

As a side experiment, a more efficient DC-DC converter MOSFET made by STMicroelectronics was soldered into the circuit replacing the IRF3707. The STD50NH02 MOSFET was able to achieve a larger 14.2% gain in rate of fire, but due to its small package size and low power dissipation rating of only 60 watts, could not handle the heat generated by the system. The MOSFET failed after several tests, internally shorting the gate and source pins.