mirror of https://github.com/ArduPilot/ardupilot
155 lines
5.3 KiB
Plaintext
155 lines
5.3 KiB
Plaintext
PX4 mixer definitions
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=====================
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Files in this directory implement example mixers that can be used as a basis
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for customisation, or for general testing purposes.
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Mixer basics
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------------
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Mixers combine control values from various sources (control tasks, user inputs,
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etc.) and produce output values suitable for controlling actuators; servos,
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motors, switches and so on.
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An actuator derives its value from the combination of one or more control
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values. Each of the control values is scaled according to the actuator's
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configuration and then combined to produce the actuator value, which may then be
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further scaled to suit the specific output type.
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Internally, all scaling is performed using floating point values. Inputs and
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outputs are clamped to the range -1.0 to 1.0.
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control control control
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v v v
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scale scale scale
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+-------> mix <------+
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scale
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v
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out
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Scaling
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-------
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Basic scalers provide linear scaling of the input to the output.
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Each scaler allows the input value to be scaled independently for inputs
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greater/less than zero. An offset can be applied to the output, and lower and
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upper boundary constraints can be applied. Negative scaling factors cause the
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output to be inverted (negative input produces positive output).
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Scaler pseudocode:
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if (input < 0)
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output = (input * NEGATIVE_SCALE) + OFFSET
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else
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output = (input * POSITIVE_SCALE) + OFFSET
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if (output < LOWER_LIMIT)
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output = LOWER_LIMIT
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if (output > UPPER_LIMIT)
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output = UPPER_LIMIT
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Syntax
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------
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Mixer definitions are text files; lines beginning with a single capital letter
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followed by a colon are significant. All other lines are ignored, meaning that
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explanatory text can be freely mixed with the definitions.
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Each file may define more than one mixer; the allocation of mixers to actuators
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is specific to the device reading the mixer definition, and the number of
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actuator outputs generated by a mixer is specific to the mixer.
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A mixer begins with a line of the form
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<tag>: <mixer arguments>
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The tag selects the mixer type; 'M' for a simple summing mixer, 'R' for a
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multirotor mixer, etc.
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Null Mixer
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..........
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A null mixer consumes no controls and generates a single actuator output whose
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value is always zero. Typically a null mixer is used as a placeholder in a
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collection of mixers in order to achieve a specific pattern of actuator outputs.
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The null mixer definition has the form:
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Z:
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Simple Mixer
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............
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A simple mixer combines zero or more control inputs into a single actuator
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output. Inputs are scaled, and the mixing function sums the result before
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applying an output scaler.
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A simple mixer definition begins with:
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M: <control count>
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O: <-ve scale> <+ve scale> <offset> <lower limit> <upper limit>
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If <control count> is zero, the sum is effectively zero and the mixer will
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output a fixed value that is <offset> constrained by <lower limit> and <upper
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limit>.
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The second line defines the output scaler with scaler parameters as discussed
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above. Whilst the calculations are performed as floating-point operations, the
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values stored in the definition file are scaled by a factor of 10000; i.e. an
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offset of -0.5 is encoded as -5000.
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The definition continues with <control count> entries describing the control
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inputs and their scaling, in the form:
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S: <group> <index> <-ve scale> <+ve scale> <offset> <lower limit> <upper limit>
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The <group> value identifies the control group from which the scaler will read,
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and the <index> value an offset within that group. These values are specific to
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the device reading the mixer definition.
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When used to mix vehicle controls, mixer group zero is the vehicle attitude
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control group, and index values zero through three are normally roll, pitch,
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yaw and thrust respectively.
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The remaining fields on the line configure the control scaler with parameters as
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discussed above. Whilst the calculations are performed as floating-point
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operations, the values stored in the definition file are scaled by a factor of
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10000; i.e. an offset of -0.5 is encoded as -5000.
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Multirotor Mixer
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................
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The multirotor mixer combines four control inputs (roll, pitch, yaw, thrust)
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into a set of actuator outputs intended to drive motor speed controllers.
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The mixer definition is a single line of the form:
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R: <geometry> <roll scale> <pitch scale> <yaw scale> <deadband>
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The supported geometries include:
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4x - quadrotor in X configuration
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4+ - quadrotor in + configuration
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6x - hexcopter in X configuration
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6+ - hexcopter in + configuration
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8x - octocopter in X configuration
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8+ - octocopter in + configuration
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Each of the roll, pitch and yaw scale values determine scaling of the roll,
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pitch and yaw controls relative to the thrust control. Whilst the calculations
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are performed as floating-point operations, the values stored in the definition
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file are scaled by a factor of 10000; i.e. an factor of 0.5 is encoded as 5000.
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Roll, pitch and yaw inputs are expected to range from -1.0 to 1.0, whilst the
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thrust input ranges from 0.0 to 1.0. Output for each actuator is in the
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range -1.0 to 1.0.
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In the case where an actuator saturates, all actuator values are rescaled so that
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the saturating actuator is limited to 1.0.
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