forked from Archive/PX4-Autopilot
91 lines
3.1 KiB
Plaintext
91 lines
3.1 KiB
Plaintext
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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.
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A mixer begins with a line of the form
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M: <scaler count>
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If the scaler count is zero, the mixer is a placeholder and the device will not
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allocate a mixer for this position. Otherwise, this line is followed by scaler
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definitions matching the given count.
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A scaler definition is a line of the form:
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S: <group> <index> <-ve scale> <+ve scale> <offset> <lower limit> <upper limit>
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The first scaler definition following the M: line configures the output scaler.
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The <group> and <index> fields are ignored in this case.
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For the remaining scalers, the <group> value identifies the control group from
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which the scaler will read. Control group 0 is the vehicle attitude control
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group; other group numbers may be assigned for other purposes. The <index> value
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selects the control within the group that will be scaled.
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The remaining fields on the line represent the 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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