atbetaflight/docs/Mixer.md

Mixer

Cleanflight supports a number of mixing configurations as well as custom mixing. Mixer configurations determine how the servos and motors work together to control the aircraft.

Configuration

To use a built-in mixing configuration, you can use the Chrome configuration GUI. It includes images of the various mixer types to assist in making the proper connections. See the Configuration section of the documentation for more information on the GUI.

You can also use the Command Line Interface (CLI) to set the mixer type:

1. Use mixer list to see a list of supported mixes
2. Select a mixer. For example, to select TRI, use mixer TRI
3. You must use save to preserve your changes

Supported Mixer Types

Name	Description	Motors	Servos
TRI	Tricopter	M1-M3	S1
QUADP	Quadcopter-Plus	M1-M4	None
QUADX	Quadcopter-X	M1-M4	None
BI	Bicopter (left/right)	M1-M2	S1, S2
GIMBAL	Gimbal control	N/A	S1, S2
Y6	Y6-copter	M1-M6	None
HEX6	Hexacopter-Plus	M1-M6	None
FLYING_WING	Fixed wing; elevons	M1	S1, S2
Y4	Y4-copter	M1-M4	None
HEX6X	Hexacopter-X	M1-M6	None
OCTOX8	Octocopter-X (over/under)	M1-M8	None
OCTOFLATP	Octocopter-FlatPlus	M1-M8	None
OCTOFLATX	Octocopter-FlatX	M1-M8	None
AIRPLANE	Fixed wing; Ax2, R, E	M1	S1, S2, S3, S4
HELI_120_CCPM
HELI_90_DEG
VTAIL4	Quadcopter with V-Tail	M1-M4	N/A
HEX6H	Hexacopter-H	M1-M6	None
PPM_TO_SERVO
DUALCOPTER	Dualcopter	M1-M2	S1, S2
SINGLECOPTER	Conventional helicopter	M1	S1
ATAIL4	Quadcopter with A-Tail	M1-M4	N/A
CUSTOM	User-defined

Servo filtering

A low-pass filter can be enabled for the servos. It may be useful for avoiding structural modes in the airframe, for example.

Configuration

Currently it can only be configured via the CLI:

1. Use set servo_lowpass_freq = nnn to select the cutoff frequency. Valid values range from 10 to 400. This is a fraction of the loop frequency in 1/1000ths. For example, 40 means 0.040.
2. Use set servo_lowpass_enable = 1 to enable filtering.

The cutoff frequency can be determined by the following formula: Frequency = 1000 * servo_lowpass_freq / looptime

For example, if servo_lowpass_freq is set to 40, and looptime is set to the default of 3500 us, the cutoff frequency will be 11.43 Hz.

Tuning

One method for tuning the filter cutoff is as follows:

1. Ensure your vehicle can move at least somewhat freely in the troublesome axis. For example, if you are having yaw oscillations on a tricopter, ensure that the copter is supported in a way that allows it to rotate left and right to at least some degree. Suspension near the CG is ideal. Alternatively, you can just fly the vehicle and trigger the problematic condition you are trying to eliminate, although tuning will be more tedious.

2. Tap the vehicle at its end in the axis under evaluation. Directly commanding the servo in question to move may also be used. In the tricopter example, tap the end of the tail boom from the side, or command a yaw using your transmitter.

3. If your vehicle oscillates for several seconds or even continues oscillating indefinitely, then the filter cutoff frequency should be reduced. Reduce the value of servo_lowpass_freq by half its current value and repeat the previous step.

4. If the oscillations are dampened within roughly a second or are no longer present, then you are done. Be sure to run save.