Motors and propellers — transcript

00:00:00.500 --> 00:00:06.064 Motors, speed controllers and props: how battery power becomes thrust.

00:00:06.414 --> 00:00:11.789 Most drones use brushless motors: a permanent magnet turning near electromagnets.

00:00:11.789 --> 00:00:17.229 The speed controller energises them in turn, and each one pulls the magnet around.

00:00:17.914 --> 00:00:21.440 KV isn't kilovolts. It's RPM per volt.

00:00:21.440 --> 00:00:28.311 A 1000 KV motor on 10 volts turns at about 10,000 RPM. On 20 volts, 20,000.

00:00:29.914 --> 00:00:33.535 Each motor has an electronic speed controller, or ESC.

00:00:33.535 --> 00:00:39.527 It takes DC from the battery and turns it into the three-phase AC a brushless motor needs.

00:00:41.914 --> 00:00:46.286 Commands from the flight controller set how fast it fires that sequence.

00:00:46.286 --> 00:00:49.281 It can even act as a brake on the motor and prop.

00:00:52.414 --> 00:00:58.588 Props are sized like 10 by 4.5: 10 inches tip to tip, and 4.5 inches of pitch,

00:00:58.588 --> 00:01:02.106 the distance one turn would move it forward.

00:01:04.914 --> 00:01:10.460 Blade angle is measured from the plane of rotation, and it's fixed on a multirotor.

00:01:10.460 --> 00:01:15.677 The tip moves much faster than the root, so the blade twists to even out lift.

00:01:18.414 --> 00:01:22.063 Each prop's torque pushes the body the other way.

00:01:22.063 --> 00:01:28.047 Two props spin clockwise and two anticlockwise, so it cancels. Speed up one pair,

00:01:28.047 --> 00:01:29.725 and the aircraft yaws.

00:01:31.914 --> 00:01:36.968 Before each flight, check every prop is secure and undamaged. Nick or chip?

00:01:36.968 --> 00:01:37.766 Replace it.

00:01:41.414 --> 00:01:45.979 So: KV is RPM per volt, the ESC sets motor speed,

00:01:45.979 --> 00:01:50.452 and paired props cancel torque and give you yaw.

00:01:50.802 --> 00:01:54.042 Last one. How does a multirotor yaw?

00:01:55.002 --> 00:01:58.189 By changing the speeds of its clockwise and anticlockwise motors.