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mc_att_control: prepare yaw weight from gain ratio

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According to the paper the quaternion controller is built on
the yaw weight represents the ratio between the roll/pitch and
the yaw attitude control time constant. It also states that as a
thumb rule a value of ~0.4 works alright for most multicopter
platforms. The default attitude gains of PX4 which were determined
independent of the paper from experimental results have a ratio of
2.8/6.5 = 0.43 which matches.
This commit is contained in:
Matthias Grob 2018-03-03 20:57:32 +00:00
parent 6317d36ec9
commit c4fb2b26fd
1 changed files with 17 additions and 14 deletions
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31
src/modules/mc_att_control/mc_att_control_main.cpp
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@ -101,6 +101,8 @@ extern "C" __EXPORT int mc_att_control_main(int argc, char *argv[]);
#define MAX_GYRO_COUNT 3
using namespace matrix;
class MulticopterAttitudeControl
{
public:
@ -235,7 +237,7 @@ private:
} _params_handles; /**< handles for interesting parameters */
struct {
math::Vector<3> att_p; /**< P gain for angular error */
Vector3f attitude_p; /**< P gain for attitude control */
math::Vector<3> rate_p; /**< P gain for angular rate error */
math::Vector<3> rate_i; /**< I gain for angular rate error */
math::Vector<3> rate_int_lim; /**< integrator state limit for rate loop */
@ -388,7 +390,6 @@ _loop_update_rate_hz(initial_update_rate_hz)
_vehicle_status.is_rotary_wing = true;
_params.att_p.zero();
_params.rate_p.zero();
_params.rate_i.zero();
_params.rate_int_lim.zero();
@ -520,7 +521,7 @@ MulticopterAttitudeControl::parameters_update()
/* roll gains */
param_get(_params_handles.roll_p, &v);
_params.att_p(0) = v;
_params.attitude_p(0) = v;
param_get(_params_handles.roll_rate_p, &v);
_params.rate_p(0) = v;
param_get(_params_handles.roll_rate_i, &v);
@ -534,7 +535,7 @@ MulticopterAttitudeControl::parameters_update()
/* pitch gains */
param_get(_params_handles.pitch_p, &v);
_params.att_p(1) = v;
_params.attitude_p(1) = v;
param_get(_params_handles.pitch_rate_p, &v);
_params.rate_p(1) = v;
param_get(_params_handles.pitch_rate_i, &v);
@ -566,7 +567,7 @@ MulticopterAttitudeControl::parameters_update()
/* yaw gains */
param_get(_params_handles.yaw_p, &v);
_params.att_p(2) = v;
_params.attitude_p(2) = v;
param_get(_params_handles.yaw_rate_p, &v);
_params.rate_p(2) = v;
param_get(_params_handles.yaw_rate_i, &v);
@ -826,18 +827,20 @@ MulticopterAttitudeControl::control_attitude(float dt)
vehicle_attitude_setpoint_poll();
_thrust_sp = _v_att_sp.thrust;
using namespace matrix;
float yaw_w = .4f;
/* prepare yaw weight from the ratio between roll/pitch and yaw gains */
Vector3f attitude_gain = _params.attitude_p;
const float roll_pitch_gain = (attitude_gain(0) + attitude_gain(1)) / 2.f;
const float yaw_w = math::constrain(attitude_gain(2) / roll_pitch_gain, 0.f, 1.f);
attitude_gain(2) = roll_pitch_gain;
/* get estimated and desired vehicle attitude */
Quatf q(_v_att.q);
Quatf qd(_v_att_sp.q_d);
/* ensure quaternions are exactly normalized because acosf(1.00001) == NaN */
/* ensure input quaternions are exactly normalized because acosf(1.00001) == NaN */
q.normalize();
qd.normalize();
/* calculate reduced attitude which we would command if we about the vehicle's yaw */
Vector3f e_z = q.dcm_z();
Vector3f e_z_d = qd.dcm_z();
@ -849,22 +852,21 @@ MulticopterAttitudeControl::control_attitude(float dt)
q_mix *= math::sign(q_mix(0));
qd = qd_red * Quatf(cosf(yaw_w * acosf(q_mix(0))), 0, 0, sinf(yaw_w * asinf(q_mix(3))));
/* quaternion attitude control law, qe is rotation from q to qd */
Quatf qe = q.inversed() * qd;
/* using sin(alpha/2) scaled rotation axis as attitude error (see quaternion definition by axis angle)
* also taking care of the antipodal unit quaternion ambiguity */
Vector3f eq = 2.f * math::sign(qe(0)) * qe.imag();
math::Vector<3> e_R(eq.data());
/* calculate angular rates setpoint */
_rates_sp = _params.att_p.emult(e_R);
eq = eq.emult(attitude_gain);
_rates_sp = math::Vector<3>(eq.data());
/* Feed forward the yaw setpoint rate. We need to transform the yaw from world into body frame.
* The following is a simplification of:
* R.transposed() * math::Vector<3>(0.f, 0.f, _v_att_sp.yaw_sp_move_rate * _params.yaw_ff)
* R.transposed() * Vector3f(0.f, 0.f, _v_att_sp.yaw_sp_move_rate * _params.yaw_ff)
*/
Vector3f yaw_feedforward_rate = q.inversed().dcm_z();
yaw_feedforward_rate *= _v_att_sp.yaw_sp_move_rate * _params.yaw_ff;
@ -1148,7 +1150,8 @@ MulticopterAttitudeControl::task_main()
_thrust_sp = _v_att_sp.thrust;
math::Quaternion q(_v_att.q[0], _v_att.q[1], _v_att.q[2], _v_att.q[3]);
math::Quaternion q_sp(&_v_att_sp.q_d[0]);
_ts_opt_recovery->setAttGains(_params.att_p, _params.yaw_ff);
math::Vector<3> attitude_p(_params.attitude_p.data());
_ts_opt_recovery->setAttGains(attitude_p, _params.yaw_ff);
_ts_opt_recovery->calcOptimalRates(q, q_sp, _v_att_sp.yaw_sp_move_rate, _rates_sp);
/* limit rates */