Planes using a traditional PWM controlled ESC (electronic speed controller) for motor output will likely need to be calibrated.
Remove the propeller from your aircraft before starting ESC calibration
Calibrating an ESC involves teaching the ESC what range of throttle inputs it should respond to. It needs to know what PWM value on the throttle channel corresponds with the commanding the motor to be off, and what PWM value corresponds with full throttle. These values are stored inside the ESC.
Typical ESC Calibration¶
The most common type of ESC calibration for small electric aircraft is the max-throttle/min-throttle method.
To perform this type of calibration you will need to be able to control power to your motor separately from power to the autopilot. If you don’t have separate power, then you can temporarily power your autopilot from a USB cable for the purposes of this calibration.
The steps for calibration are:
- start with the autopilot powered, but with the ESC unpowered and propeller removed
- switch to MANUAL flight mode
- disable the safety switch (if fitted) and arm the airplane
- move the throttle stick on your transmitter to maximum
- add power to the ESC
At this stage the ESC/motor should beep to indicate that it is in ESC calibration mode. Typically it will be 2 or 3 quick beeps, but the motor won’t turn.
- now lower the throttle stick rapidly to zero
- the ESC should beep to indicate it has accepted the new calibration range
- now slowly raise the throttle and check that the motor responds correctly
Alternative ESC Calibration¶
If the typical ESC calibration method above doesn’t work, instead adjust the SERVOx_MIN and SERVOx_MAX values on the appropriate servo channel (SERVOx) you had set as the Throttle channel in ref:servo setup <servo-functions> to match the existing range of your ESC.
To use this method slowly raise the SERVOx_MIN value until it is set to a value just below the point that the motor comes on. A value about 20 PWM points below the point where the motor starts turning is usually a good choice.
Next move the transmitter stick to full throttle and adjust SERVOx_MAX until maximum RPM is reached. You can use a tachometer, or just use the sound of the motor as a guide.
Reversing PWM based ESCs¶
If you are using a reversing ESC for reverse thrust ( see Automatic Landing section on Reverse Thrust Landing ), and its PWM based rather than CAN, OneShot, or DShot, then you may need to calibrate it. Usually, a button is provided for setting full forward, neutral, and full reverse. In this case, you will need to setup an RCx_OPTION on an RC channel to allow setting full reverse manually. Follow the manufacturers instructions for calibration.
Most brushed motor ESCs have a fixed calibration which will require manually setting the throttle output’s
SERVOx_MIN parameters to match the ESCs maximum points.
Other ESC Protocols¶
New ESC’s using protocols other than PWM often do not require calibration. Some examples include CAN, OneShot, and DShot. The digital signals replace the need for PWM calibration.