What the ESC is actually timing #
A brushless motor turns because the ESC energizes its windings in sequence, creating a magnetic field that pulls the rotor around.
To know where the rotor is, a sensorless ESC watches the back-EMF: the voltage generated by the spinning motor in the phase that isn’t currently being driven.
From that signal, the ESC works out when the rotor has reached the correct position and when it should move to the next electrical step. Each of those changes is called a commutation.
The complication is that the motor doesn’t react instantly.
The windings are inductors, so current takes time to rise and fall. At the same time, the faster the motor spins, the less time the ESC has available for each electrical step.
At low RPM, that delay is a relatively small part of the commutation period. At very high RPM, it becomes significant.
Timing advance compensates for this by moving the commutation point slightly earlier, keeping the stator’s magnetic field in a useful position relative to the rotor as speed increases.
More vs less #
More timing advance can produce more torque and RPM at the top end, particularly at high electrical speed. The trade-off is that excessive advance increases current and heat and reduces efficiency.
Less timing advance generally favors efficiency and lower temperatures and can make difficult motors more forgiving at lower speeds. Too little advance, however, can limit performance at very high RPM and can eventually make commutation less reliable.
There isn’t one perfect timing value for every operating condition.
The useful amount changes with motor speed, load, winding characteristics, voltage, and current. That’s why a fixed timing value is always a compromise.
What AUTO does #
That’s why Gen2 FW defaults to AUTO, with a maximum advance of 18 degrees.
Instead of forcing the motor to use the same timing everywhere, AUTO adjusts the amount of advance according to the operating condition.
For most builds, AUTO is the right answer, and you never need to touch it.
When to change AUTO #
Motors or ESC unusually hot after normal flights.
Try a fixed lower value. If temperatures drop without losing performance you care about, the motor may simply prefer less advance.
Desyncs at very high RPM or during hard punches.
A little more advance can sometimes help if the motor is running out of commutation margin at the top end.
But don’t automatically assume every punch-out desync needs more timing. Excessive current, voltage drop, motor saturation, ramp settings, or a damaged motor can produce very similar symptoms.
Problems mainly at low RPM or during acceleration from low throttle.
Trying less advance can make some motor combinations more forgiving.
Racing or speed builds.
A higher fixed value can be tested when maximum top-end performance matters more than efficiency, but motor and ESC temperatures should be checked after every change.
Troubleshooting.
Using a fixed value can remove one changing variable while diagnosing another problem.
What timing won’t fix #
Timing isn’t a general-purpose flight-tuning control.
It won’t fix:
- oscillation,
- prop wash,
- jello,
- bad filtering,
- excessive PID gains,
- bent or damaged propellers,
- mechanical vibration.
Those problems belong primarily to the flight controller tune or the hardware.
If the motors are healthy, temperatures are normal, and the ESC isn’t losing synchronization, timing probably isn’t the setting you need to change.
How to test a change #
- Write down the original setting.
- Change one step at a time.
- Fly the same battery type and roughly the same kind of flight.
- Land and check the motors and ESC immediately.
- Compare the result with your notes or logs, not with how you remember the previous flight.
As a simple field check, something that becomes uncomfortable to keep your finger on for more than a few seconds is getting hot enough to deserve attention.
If a timing change creates more heat without giving you a useful improvement, undo it.
And don’t change timing, PWM frequency, ramp settings, and PID tuning at the same time. Otherwise, even if the quad gets better, you won’t know why.
