Hi everyone, I've been building a quad rotor drone using an Arduino Uno and 4 brushed DC motors. Logic level N-channel MOSFETs provide the speed control.
Problem is my mosfets keep shorting out and sending full power to the motors (which is kinda terrifying when it happens and results in having to replace the mosfet). Also my capacitors and freewheel diodes soldered onto the motor terminals keep exploding. Looks like I could use some help setting up my speed control circuit to the motors, and the back EMF protection circuit. And I would like to rule out the possibility that my programming is causing these meltdowns. I will describe my setup in as much detail as possible below.
Arduino Uno interprets signal from RC reciever, uses signal to output 4 independent PWM signals.
The PWM outputs range from 0 to 255 and trigger 4 mosfets (IRLB8743). There are no resistors between the arduino output and the mosfet gate. Each mosfet has a 10k ohm resistor between the gate and source.
The motors are brushed DC salvaged from airsoft guns, have been seen drawing > 10amps each, and 2 of the 4 are wired to reverse polarity so they spin in the required directions. There was a (IN4004) diode soldered across each of the motor terminals with the marked stripe facing the positive side of the power to the motor. A capacitor (H414) 100uf, 50v, was also soldered to each of the motor terminals, to the correct polarity (+ on cap to +input power to motor).
The battery pack is 14.8v @ 9ah (Li-Ion). Battery voltage drops to approx 11v while powering all 4 motors on high, voltage returns to approx 16v when load is removed.
The entire system worked great and consistently during months of testing. Then I changed 2 things and stuff began to melt down and explode.
1) I added a large variety of functions to the arduino's sketch (arguments for steering and tilt and whatnot). However I believe the arduino is still outputting PWMs of 4.4v on a 0-255 duty cycle to the mosfets at all times.
2) I added larger propellers to the motors, causing them to draw more amperage.
My mosfets generate a lot of heat even when I'm only applying a small duty cycle to them, they short out after a certain point too. Ive tried heavier freewheel diodes which seem to be holding now. Various sizes and types of capacitors keep exploding, some just melt the leads off. Note the mosfets seem to run cooler with larger capacitors on the motors.
So...any ideas on how to stop this circuit from melting would be much appreciated, thanks in advance :)