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I am currently working on building a quadcopter with brushless motors. I decided to try to build the ESCs by myself with some MOSFETs. I am using an Uno as the main controller on the receiving end. Before I started building I want to verify that I will not destroy my motors. What I am thinking on doing is sending a PWM signal to the MOSFETs which would turn each motor on and off in a fashion that would rotate the motor fully. Would this work without destroying the motors? I am using an 11.1v LiPo so there is a fair amount of current flowing. Also, would I need any current limiting resistors or can I just have a dead short through the windings?

Thanks

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    \$\begingroup\$ Have you researched how to drive a Brushless DC motor? "... sending a PWM signal to the MOSFETs which would turn each motor on and off in a fashion that would rotate the motor fully" doesn't read clearly as the right algorithm. The motors either need to be spinning under some load to generate enough back-EMF to ensure they don't get too hot, or the ESC needs to control PWM to ensure they don't get too much power. \$\endgroup\$ – gbulmer Sep 20 '14 at 1:54
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    \$\begingroup\$ You will get a quivering mess. A major function of an ESC is to detect when the motor position is such that a given switch (MOSFET) should be turned on to reinforce rotation. Without such a detection scheme you may fluke some sort of rotatin but are as likely to just make the motor vibrate. \$\endgroup\$ – Russell McMahon Sep 20 '14 at 11:09
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Yes, it is possible to do this and many people have done it. No current limiting is necessary, although it is good to use a current shunt to measure current through the windings (only one is enough).

Another thing that is essential is the BEMF sensing circuitry for rotor position estimation, commonly done with analog comparator of the MCU.

And the main and most important thing to implement is the control algorithm, which maintains constant load angle as the speed and load varies.

Edit: The MOSFETs need to be switched with two independent frequencies: The PWM which is something above 20 kHz and sets motor torque, and commutation frequency which is several hundred Hz and sets motor speed.

Edit: For development, 12V automotive bulb in series with battery provides reasonable short circuit protection.

Edit: Using just some MOSFETs is not enough. They have to be very good MOSFETs with \$R_{DSon}\$ in single-digit figures and low thermal resistance.

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  • \$\begingroup\$ There is no slip with a brushless motor. \$\endgroup\$ – Eric Sep 20 '14 at 2:27
  • \$\begingroup\$ @Brad Thanks, load angle was the word I was looking for. \$\endgroup\$ – venny Sep 20 '14 at 2:51

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