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diff --git a/ROMFS/px4fmu_common/mixers/README b/ROMFS/px4fmu_common/mixers/README new file mode 100644 index 000000000..60311232e --- /dev/null +++ b/ROMFS/px4fmu_common/mixers/README @@ -0,0 +1,154 @@ +PX4 mixer definitions +===================== + +Files in this directory implement example mixers that can be used as a basis +for customisation, or for general testing purposes. + +Mixer basics +------------ + +Mixers combine control values from various sources (control tasks, user inputs, +etc.) and produce output values suitable for controlling actuators; servos, +motors, switches and so on. + +An actuator derives its value from the combination of one or more control +values. Each of the control values is scaled according to the actuator's +configuration and then combined to produce the actuator value, which may then be +further scaled to suit the specific output type. + +Internally, all scaling is performed using floating point values. Inputs and +outputs are clamped to the range -1.0 to 1.0. + +control control control + | | | + v v v + scale scale scale + | | | + | v | + +-------> mix <------+ + | + scale + | + v + out + +Scaling +------- + +Basic scalers provide linear scaling of the input to the output. + +Each scaler allows the input value to be scaled independently for inputs +greater/less than zero. An offset can be applied to the output, and lower and +upper boundary constraints can be applied. Negative scaling factors cause the +output to be inverted (negative input produces positive output). + +Scaler pseudocode: + +if (input < 0) + output = (input * NEGATIVE_SCALE) + OFFSET +else + output = (input * POSITIVE_SCALE) + OFFSET + +if (output < LOWER_LIMIT) + output = LOWER_LIMIT +if (output > UPPER_LIMIT) + output = UPPER_LIMIT + +Syntax +------ + +Mixer definitions are text files; lines beginning with a single capital letter +followed by a colon are significant. All other lines are ignored, meaning that +explanatory text can be freely mixed with the definitions. + +Each file may define more than one mixer; the allocation of mixers to actuators +is specific to the device reading the mixer definition, and the number of +actuator outputs generated by a mixer is specific to the mixer. + +A mixer begins with a line of the form + + <tag>: <mixer arguments> + +The tag selects the mixer type; 'M' for a simple summing mixer, 'R' for a +multirotor mixer, etc. + +Null Mixer +.......... + +A null mixer consumes no controls and generates a single actuator output whose +value is always zero. Typically a null mixer is used as a placeholder in a +collection of mixers in order to achieve a specific pattern of actuator outputs. + +The null mixer definition has the form: + + Z: + +Simple Mixer +............ + +A simple mixer combines zero or more control inputs into a single actuator +output. Inputs are scaled, and the mixing function sums the result before +applying an output scaler. + +A simple mixer definition begins with: + + M: <control count> + O: <-ve scale> <+ve scale> <offset> <lower limit> <upper limit> + +If <control count> is zero, the sum is effectively zero and the mixer will +output a fixed value that is <offset> constrained by <lower limit> and <upper +limit>. + +The second line defines the output scaler with scaler parameters as discussed +above. Whilst the calculations are performed as floating-point operations, the +values stored in the definition file are scaled by a factor of 10000; i.e. an +offset of -0.5 is encoded as -5000. + +The definition continues with <control count> entries describing the control +inputs and their scaling, in the form: + + S: <group> <index> <-ve scale> <+ve scale> <offset> <lower limit> <upper limit> + +The <group> value identifies the control group from which the scaler will read, +and the <index> value an offset within that group. These values are specific to +the device reading the mixer definition. + +When used to mix vehicle controls, mixer group zero is the vehicle attitude +control group, and index values zero through three are normally roll, pitch, +yaw and thrust respectively. + +The remaining fields on the line configure the control scaler with parameters as +discussed above. Whilst the calculations are performed as floating-point +operations, the values stored in the definition file are scaled by a factor of +10000; i.e. an offset of -0.5 is encoded as -5000. + +Multirotor Mixer +................ + +The multirotor mixer combines four control inputs (roll, pitch, yaw, thrust) +into a set of actuator outputs intended to drive motor speed controllers. + +The mixer definition is a single line of the form: + +R: <geometry> <roll scale> <pitch scale> <yaw scale> <deadband> + +The supported geometries include: + + 4x - quadrotor in X configuration + 4+ - quadrotor in + configuration + 6x - hexcopter in X configuration + 6+ - hexcopter in + configuration + 8x - octocopter in X configuration + 8+ - octocopter in + configuration + +Each of the roll, pitch and yaw scale values determine scaling of the roll, +pitch and yaw controls relative to the thrust control. Whilst the calculations +are performed as floating-point operations, the values stored in the definition +file are scaled by a factor of 10000; i.e. an factor of 0.5 is encoded as 5000. + +Roll, pitch and yaw inputs are expected to range from -1.0 to 1.0, whilst the +thrust input ranges from 0.0 to 1.0. Output for each actuator is in the +range -1.0 to 1.0. + +In the case where an actuator saturates, all actuator values are rescaled so that +the saturating actuator is limited to 1.0.
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