Recently, I have been hearing a buzz word "phase delay" around the FPV community a lot. In plain words, phase delay is the delay between what the drone sees versus the reality, which could be several milliseconds behind. This causes a lot of issues, one very common analogy in real life is:

Two polite persons walking towards each other on the same lane and start to give way to each other, but only end up walking on the same lane again.

If one of the person knows the other person is going to give way to them, they could stop moving thus resolving the conflict.

This happens in the drone PID controller a lot too, especially on the D term, which is very senstive to such delays. However,

What does PID try to solve in general? Simply put, PID is a way to answer the question - how much “force” to apply to reach a target state from one state?

Some examples:

  1. Adjust the power of an AC to reach a temperature
  2. Apply throttle or brake to reach a speed
  3. Adjust the motor RPM of a drone, to reach certain rotation speed