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DSLPIDControl.py
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DSLPIDControl.py
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import math
import numpy as np
import pybullet as p
from scipy.spatial.transform import Rotation
from gym_pybullet_drones.control.BaseControl import BaseControl
from gym_pybullet_drones.envs.BaseAviary import DroneModel, BaseAviary
class DSLPIDControl(BaseControl):
"""PID control class for Crazyflies.
Based on work conducted at UTIAS' DSL by SiQi Zhou and James Xu.
"""
################################################################################
def __init__(self,
drone_model: DroneModel,
g: float=9.8
):
"""Common control classes __init__ method.
Parameters
----------
drone_model : DroneModel
The type of drone to control (detailed in an .urdf file in folder `assets`).
g : float, optional
The gravitational acceleration in m/s^2.
"""
super().__init__(drone_model=drone_model, g=g)
if self.DRONE_MODEL != DroneModel.CF2X and self.DRONE_MODEL != DroneModel.CF2P:
print("[ERROR] in DSLPIDControl.__init__(), DSLPIDControl requires DroneModel.CF2X or DroneModel.CF2P")
exit()
self.P_COEFF_FOR = np.array([.4, .4, 1.25])
self.I_COEFF_FOR = np.array([.05, .05, .05])
self.D_COEFF_FOR = np.array([.2, .2, .5])
self.P_COEFF_TOR = np.array([70000., 70000., 60000.])
self.I_COEFF_TOR = np.array([.0, .0, 500.])
self.D_COEFF_TOR = np.array([20000., 20000., 12000.])
self.PWM2RPM_SCALE = 0.2685
self.PWM2RPM_CONST = 4070.3
self.MIN_PWM = 20000
self.MAX_PWM = 65535
if self.DRONE_MODEL == DroneModel.CF2X:
self.MIXER_MATRIX = np.array([ [.5, -.5, -1], [.5, .5, 1], [-.5, .5, -1], [-.5, -.5, 1] ])
elif self.DRONE_MODEL == DroneModel.CF2P:
self.MIXER_MATRIX = np.array([ [0, -1, -1], [+1, 0, 1], [0, 1, -1], [-1, 0, 1] ])
self.reset()
################################################################################
def reset(self):
"""Resets the control classes.
The previous step's and integral errors for both position and attitude are set to zero.
"""
super().reset()
#### Store the last roll, pitch, and yaw ###################
self.last_rpy = np.zeros(3)
#### Initialized PID control variables #####################
self.last_pos_e = np.zeros(3)
self.integral_pos_e = np.zeros(3)
self.last_rpy_e = np.zeros(3)
self.integral_rpy_e = np.zeros(3)
################################################################################
def computeControl(self,
control_timestep,
cur_pos,
cur_quat,
cur_vel,
cur_ang_vel,
target_pos,
target_rpy=np.zeros(3),
target_vel=np.zeros(3),
target_rpy_rates=np.zeros(3)
):
"""Computes the PID control action (as RPMs) for a single drone.
This methods sequentially calls `_dslPIDPositionControl()` and `_dslPIDAttitudeControl()`.
Parameter `cur_ang_vel` is unused.
Parameters
----------
control_timestep : float
The time step at which control is computed.
cur_pos : ndarray
(3,1)-shaped array of floats containing the current position.
cur_quat : ndarray
(4,1)-shaped array of floats containing the current orientation as a quaternion.
cur_vel : ndarray
(3,1)-shaped array of floats containing the current velocity.
cur_ang_vel : ndarray
(3,1)-shaped array of floats containing the current angular velocity.
target_pos : ndarray
(3,1)-shaped array of floats containing the desired position.
target_rpy : ndarray, optional
(3,1)-shaped array of floats containing the desired orientation as roll, pitch, yaw.
target_vel : ndarray, optional
(3,1)-shaped array of floats containing the desired velocity.
target_rpy_rates : ndarray, optional
(3,1)-shaped array of floats containing the desired roll, pitch, and yaw rates.
Returns
-------
ndarray
(4,1)-shaped array of integers containing the RPMs to apply to each of the 4 motors.
ndarray
(3,1)-shaped array of floats containing the current XYZ position error.
float
The current yaw error.
"""
self.control_counter += 1
thrust, computed_target_rpy, pos_e = self._dslPIDPositionControl(control_timestep,
cur_pos,
cur_quat,
cur_vel,
target_pos,
target_rpy,
target_vel
)
rpm = self._dslPIDAttitudeControl(control_timestep,
thrust,
cur_quat,
computed_target_rpy,
target_rpy_rates
)
cur_rpy = p.getEulerFromQuaternion(cur_quat)
return rpm, pos_e, computed_target_rpy[2] - cur_rpy[2]
################################################################################
def _dslPIDPositionControl(self,
control_timestep,
cur_pos,
cur_quat,
cur_vel,
target_pos,
target_rpy,
target_vel
):
"""DSL's CF2.x PID position control.
Parameters
----------
control_timestep : float
The time step at which control is computed.
cur_pos : ndarray
(3,1)-shaped array of floats containing the current position.
cur_quat : ndarray
(4,1)-shaped array of floats containing the current orientation as a quaternion.
cur_vel : ndarray
(3,1)-shaped array of floats containing the current velocity.
target_pos : ndarray
(3,1)-shaped array of floats containing the desired position.
target_rpy : ndarray
(3,1)-shaped array of floats containing the desired orientation as roll, pitch, yaw.
target_vel : ndarray
(3,1)-shaped array of floats containing the desired velocity.
Returns
-------
float
The target thrust along the drone z-axis.
ndarray
(3,1)-shaped array of floats containing the target roll, pitch, and yaw.
float
The current position error.
"""
cur_rotation = np.array(p.getMatrixFromQuaternion(cur_quat)).reshape(3, 3)
pos_e = target_pos - cur_pos
vel_e = target_vel - cur_vel
self.integral_pos_e = self.integral_pos_e + pos_e*control_timestep
self.integral_pos_e = np.clip(self.integral_pos_e, -2., 2.)
self.integral_pos_e[2] = np.clip(self.integral_pos_e[2], -0.15, .15)
#### PID target thrust #####################################
target_thrust = np.multiply(self.P_COEFF_FOR, pos_e) \
+ np.multiply(self.I_COEFF_FOR, self.integral_pos_e) \
+ np.multiply(self.D_COEFF_FOR, vel_e) + np.array([0, 0, self.GRAVITY])
scalar_thrust = max(0., np.dot(target_thrust, cur_rotation[:,2]))
thrust = (math.sqrt(scalar_thrust / (4*self.KF)) - self.PWM2RPM_CONST) / self.PWM2RPM_SCALE
target_z_ax = target_thrust / np.linalg.norm(target_thrust)
target_x_c = np.array([math.cos(target_rpy[2]), math.sin(target_rpy[2]), 0])
target_y_ax = np.cross(target_z_ax, target_x_c) / np.linalg.norm(np.cross(target_z_ax, target_x_c))
target_x_ax = np.cross(target_y_ax, target_z_ax)
target_rotation = (np.vstack([target_x_ax, target_y_ax, target_z_ax])).transpose()
#### Target rotation #######################################
target_euler = (Rotation.from_matrix(target_rotation)).as_euler('XYZ', degrees=False)
if np.any(np.abs(target_euler) > math.pi):
print("\n[ERROR] ctrl it", self.control_counter, "in Control._dslPIDPositionControl(), values outside range [-pi,pi]")
return thrust, target_euler, pos_e
################################################################################
def _dslPIDAttitudeControl(self,
control_timestep,
thrust,
cur_quat,
target_euler,
target_rpy_rates
):
"""DSL's CF2.x PID attitude control.
Parameters
----------
control_timestep : float
The time step at which control is computed.
thrust : float
The target thrust along the drone z-axis.
cur_quat : ndarray
(4,1)-shaped array of floats containing the current orientation as a quaternion.
target_euler : ndarray
(3,1)-shaped array of floats containing the computed target Euler angles.
target_rpy_rates : ndarray
(3,1)-shaped array of floats containing the desired roll, pitch, and yaw rates.
Returns
-------
ndarray
(4,1)-shaped array of integers containing the RPMs to apply to each of the 4 motors.
"""
cur_rotation = np.array(p.getMatrixFromQuaternion(cur_quat)).reshape(3, 3)
cur_rpy = np.array(p.getEulerFromQuaternion(cur_quat))
target_quat = (Rotation.from_euler('XYZ', target_euler, degrees=False)).as_quat()
w,x,y,z = target_quat
target_rotation = (Rotation.from_quat([w, x, y, z])).as_matrix()
rot_matrix_e = np.dot((target_rotation.transpose()),cur_rotation) - np.dot(cur_rotation.transpose(),target_rotation)
rot_e = np.array([rot_matrix_e[2, 1], rot_matrix_e[0, 2], rot_matrix_e[1, 0]])
rpy_rates_e = target_rpy_rates - (cur_rpy - self.last_rpy)/control_timestep
self.last_rpy = cur_rpy
self.integral_rpy_e = self.integral_rpy_e - rot_e*control_timestep
self.integral_rpy_e = np.clip(self.integral_rpy_e, -1500., 1500.)
self.integral_rpy_e[0:2] = np.clip(self.integral_rpy_e[0:2], -1., 1.)
#### PID target torques ####################################
target_torques = - np.multiply(self.P_COEFF_TOR, rot_e) \
+ np.multiply(self.D_COEFF_TOR, rpy_rates_e) \
+ np.multiply(self.I_COEFF_TOR, self.integral_rpy_e)
target_torques = np.clip(target_torques, -3200, 3200)
pwm = thrust + np.dot(self.MIXER_MATRIX, target_torques)
pwm = np.clip(pwm, self.MIN_PWM, self.MAX_PWM)
return self.PWM2RPM_SCALE * pwm + self.PWM2RPM_CONST
################################################################################
def _one23DInterface(self,
thrust
):
"""Utility function interfacing 1, 2, or 3D thrust input use cases.
Parameters
----------
thrust : ndarray
Array of floats of length 1, 2, or 4 containing a desired thrust input.
Returns
-------
ndarray
(4,1)-shaped array of integers containing the PWM (not RPMs) to apply to each of the 4 motors.
"""
DIM = len(np.array(thrust))
pwm = np.clip((np.sqrt(np.array(thrust)/(self.KF*(4/DIM)))-self.PWM2RPM_CONST)/self.PWM2RPM_SCALE, self.MIN_PWM, self.MAX_PWM)
if DIM in [1, 4]:
return np.repeat(pwm, 4/DIM)
elif DIM==2:
return np.hstack([pwm, np.flip(pwm)])
else:
print("[ERROR] in DSLPIDControl._one23DInterface()")
exit()