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MultirotorMixer: Apply thrust gain independently from other axes 

Align the way motor output is computed with the model used in the mixer generation script.
previous:
`out = (roll_gain*roll + pitch_gain*pitch + yaw_gain*yaw + thrust)*out_gain`
new:
`out = roll_gain*roll + pitch_gain*pitch + yaw_gain*yaw + thrust_gain*thrust`
which is the standard matrix*vector multiplication.

This commit has 0 effect on symmetric platforms (i.e. most) as thrust_gain==1 on these platforms.
On asymmetric platform --where some thrust_gain are lower than 1-- the previous formulation resulted in coupling between thrust and other axes.

fixes #8628
This commit is contained in:
Julien Lecoeur 2018-01-09 08:10:36 +01:00 committed by Daniel Agar
parent 0e3574c44f
commit 262d9c790b
2 changed files with 11 additions and 10 deletions
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6
src/lib/mixer/mixer.h
View File

@ -546,10 +546,10 @@ public:
* Precalculated rotor mix.
*/
struct Rotor {
float roll_scale; /**< scales roll for this rotor */
float roll_scale; /**< scales roll for this rotor */
float pitch_scale; /**< scales pitch for this rotor */
float yaw_scale; /**< scales yaw for this rotor */
float out_scale; /**< scales total out for this rotor */
float yaw_scale; /**< scales yaw for this rotor */
float thrust_scale; /**< scales thrust for this rotor */
};
/**

15
src/lib/mixer/mixer_multirotor.cpp
View File

@ -187,9 +187,7 @@ MultirotorMixer::mix(float *outputs, unsigned space)
for (unsigned i = 0; i < _rotor_count; i++) {
float out = roll * _rotors[i].roll_scale +
pitch * _rotors[i].pitch_scale +
thrust;
out *= _rotors[i].out_scale;
thrust * _rotors[i].thrust_scale;
/* calculate min and max output values */
if (out < min_out) {
@ -206,6 +204,11 @@ MultirotorMixer::mix(float *outputs, unsigned space)
float boost = 0.0f; // value added to demanded thrust (can also be negative)
float roll_pitch_scale = 1.0f; // scale for demanded roll and pitch
// Note: thrust boost is computed assuming thrust_gain==1 for all motors.
// On asymmetric platforms, some motors have thrust_gain<1,
// which may result in motor saturation after thrust boost is applied
// TODO: revise the saturation/boosting strategy
if (min_out < 0.0f && max_out < 1.0f && -min_out <= 1.0f - max_out) {
float max_thrust_diff = thrust * thrust_increase_factor - thrust;
@ -262,9 +265,7 @@ MultirotorMixer::mix(float *outputs, unsigned space)
float out = (roll * _rotors[i].roll_scale +
pitch * _rotors[i].pitch_scale) * roll_pitch_scale +
yaw * _rotors[i].yaw_scale +
thrust + boost;
out *= _rotors[i].out_scale;
(thrust + boost) * _rotors[i].thrust_scale;
// scale yaw if it violates limits. inform about yaw limit reached
if (out < 0.0f) {
@ -300,7 +301,7 @@ MultirotorMixer::mix(float *outputs, unsigned space)
outputs[i] = (roll * _rotors[i].roll_scale +
pitch * _rotors[i].pitch_scale) * roll_pitch_scale +
yaw * _rotors[i].yaw_scale +
thrust + boost;
(thrust + boost) * _rotors[i].thrust_scale;
/*
implement simple model for static relationship between applied motor pwm and motor thrust