Hardware-specific
This note may only apply to specific hardware. The internet suggests Pixracer is such hardware; I experienced it on a Pixhawk Cube Orange+.
When using the following servo outputs:
| Channel | Purpose | Type |
|---|---|---|
| 1 | Motor1 | ESC |
| 2 | Motor2 | ESC |
| 3 | Motor4 | ESC |
| 4 | TiltMotorFrontLeft | Servo |
| 5 | TiltMotorFrontRight | Servo |
| 6 | VTailLeft | Servo |
| 7 | VTailRight | Servo |
Channels 1-4 will be in PWM rate group 1, and channels 5-6 will be in rate group 2. Group 1 runs at 400Hz refresh rate, while group 2 runs at SERVO_RATE rate (default 50Hz).
When in an all-channels-neutral output, this looks like the following:
However, this may not work correctly with some / all servos. Instead, disable channel 4 and move the four servo groups up a channel:
| Channel | Purpose | Type |
|---|---|---|
| 1 | Motor1 | ESC |
| 2 | Motor2 | ESC |
| 3 | Motor4 | ESC |
| 4 | Disabled | NA |
| 5 | TiltMotorFrontLeft | Servo |
| 6 | TiltMotorFrontRight | Servo |
| 7 | VTailLeft | Servo |
| 8 | VTailRight | Servo |
to see the following:
The logic analyzer in use here does not have its channels offset to match the ch4-skip on ArduPilot. Channel 4 in the scope corresponds to channel 6 in ArduPilot.
This seems to be a holdover from Copter firmware, but apparently also applies in QuadPlane / tiltrotor quads.
See also