The electronics of the cheQuadX was supposed to run off this 3.7volt Lithium battery ( ion / polymer ?).

However, the IRFZ44n would not turn ON with the 3.7 volt PWM output created by the Arduino Pro mini. As per the datasheets of IRFZ44n the Vgs is typically in the range of 2-4 volts. When IRFZ44n turns ON, the Rds reduces to about 17.5 mΩ and the circuit has the motor in series with Rds; As soon as the Rds drops, the motor starts to draw large currents from the battery, propellers/blades rotate and thrust is created.

Alaaas, IRFZ44n did not work( no turn ON) with the ~3.7volt output of arduino. It required a higher voltage at the Gate. I tried experimenting with different voltage settings until I got it working. In the working case I kept Vds at 3.7v and applied 5v across Gate-Source, the motors ran crazy( at full speed ).

Initially, I planned to run only the BT and GY-51 module with 5v. For producing 5v out of 3v I used the 3v to 5v voltage booster module. These modules have a limited current sourcing capability and hence I tested running the three viz arduino, GY-51 and BT simultaneously with the voltage booster module. All three, the arduino, GY-51 and BT ran happily and I fixed the circuit in place. Now, the circuit is all set up for flying and PID control is to be written. I am referring to AVR221 application note for PID implementation cue. And it just crossed my mind if I will be able to achieve a good PID implementation with the limited throughput( 16 MIPS on pro mini at 16MHz). Only time will tell. :)