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I have a trouble whe modify this with Quad copter configuration, so I have 4 motor. When I say the command, 4 motor can't spin. But, when I removed the fourth motor PWM pin, It can spin after I have said "Start", and again, but when it reached its maximum PWM value (255), 3 motors suddenly stopped.I use 2N2222 and 100 ohm resistor just like you. Is there anything wrong with Arduino power supply?P.S. 2N2222 became so hot and then broken while the motor was spinning