Circuit diagrams of a drone copter with an explanation..
Honestly, the work is all in the software.
In each of the 4 corners is a motor. These are almost always brushless, because they are most efficient and precisely controllable, and in drone efficiency matters. Inside, the blue squares, is a speed controller / driver. A brushless motor can’t work off of straight battery power. It has to be pulsed in the correct pattern at the correct speed. This speed controller senses load variation as the motor spins and figures out how to get it started. Once it’s spinning, the speed controller maintains or adjusts the speed based on the signal from the flight controller (in this diagram, and arduino). Each of these speed controllers runs software responsible for controlling one motor.
A flight controller really consists of two parts at a minimum. A processor and an accelerometer. The accelerometer is the tiny dark blue board out to the right. It indicates which way is down, as well as any other forces acting on it such as a sudden gust of wind. Many flight controllers also contain GPS, or a barameter (for determining altitude).
The CPU of the flight controller takes the data from the accelerometer and processes it using a lot of math that takes into account variation over time. It then processes this to figure out which motor needs to speed up or slow down to maintain perfectly level hovering. It does this thousands of times per second, and updates the signal to each speed control. If the front left corner starts to tip down, the accelerometer notices, the CPU is informed, and tells the speed controller to speed up that motor to maintain balance.
The last step is the receiver, which is any normal RC receiver. It feeds direction to the CPU of which direction the pilot wants it to go, and then with the information from the accelerometer, figures out how to tweak the signal to each speed control. For instance, up and down are easy, simply increase or decrease the speed to all 4 speed controllers. Forward means you increase the signal to the back 2 speed controllers, and decrease the signal to the front, and the motors react accordingly and create a tilt that is maintained until the forward signal is no longer received.
To turn to the right, it’s important to know that a quadcopter has 2 blades rotating each direction. The front left and back right will rotate one direction, and the front right and back left will rotate the other. To turn, the CPU simply increases the speed to the two that rotate the opposite directly, and decreases the speed of the others. This maintains the same amount of lift, but changes the rotational torque of the propellors to favor one direction over another, causing the copter to rotate.
Humans don’t fly quadcopters. Computers do. We just tell the computer what we want to happen.
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