04. Implement P Controller
Implement P Controller - Artificial Intelligence for Robotics
In the following quiz you'll implement a P controller.
Note that in all of the following programming quizzes the
run
function has been changed to return the x and y coordinates, or trajectory of the robot instead of printing the values. These will then be plotted against the reference line which should give you a better intuition for what the controller is doing. Thus, the code will look slightly different than in the videos but the general controller algorithms remain the same.
Start Quiz:
# -----------
# User Instructions
#
# Implement a P controller by running 100 iterations
# of robot motion. The desired trajectory for the
# robot is the x-axis. The steering angle should be set
# by the parameter tau so that:
#
# steering = -tau * crosstrack_error
#
# You'll only need to modify the `run` function at the bottom.
# ------------
import random
import numpy as np
import matplotlib.pyplot as plt
# ------------------------------------------------
#
# this is the Robot class
#
class Robot(object):
def __init__(self, length=20.0):
"""
Creates robot and initializes location/orientation to 0, 0, 0.
"""
self.x = 0.0
self.y = 0.0
self.orientation = 0.0
self.length = length
self.steering_noise = 0.0
self.distance_noise = 0.0
self.steering_drift = 0.0
def set(self, x, y, orientation):
"""
Sets a robot coordinate.
"""
self.x = x
self.y = y
self.orientation = orientation % (2.0 * np.pi)
def set_noise(self, steering_noise, distance_noise):
"""
Sets the noise parameters.
"""
# makes it possible to change the noise parameters
# this is often useful in particle filters
self.steering_noise = steering_noise
self.distance_noise = distance_noise
def set_steering_drift(self, drift):
"""
Sets the systematical steering drift parameter
"""
self.steering_drift = drift
def move(self, steering, distance, tolerance=0.001, max_steering_angle=np.pi / 4.0):
"""
steering = front wheel steering angle, limited by max_steering_angle
distance = total distance driven, most be non-negative
"""
if steering > max_steering_angle:
steering = max_steering_angle
if steering < -max_steering_angle:
steering = -max_steering_angle
if distance < 0.0:
distance = 0.0
# apply noise
steering2 = random.gauss(steering, self.steering_noise)
distance2 = random.gauss(distance, self.distance_noise)
# apply steering drift
steering2 += self.steering_drift
# Execute motion
turn = np.tan(steering2) * distance2 / self.length
if abs(turn) < tolerance:
# approximate by straight line motion
self.x += distance2 * np.cos(self.orientation)
self.y += distance2 * np.sin(self.orientation)
self.orientation = (self.orientation + turn) % (2.0 * np.pi)
else:
# approximate bicycle model for motion
radius = distance2 / turn
cx = self.x - (np.sin(self.orientation) * radius)
cy = self.y + (np.cos(self.orientation) * radius)
self.orientation = (self.orientation + turn) % (2.0 * np.pi)
self.x = cx + (np.sin(self.orientation) * radius)
self.y = cy - (np.cos(self.orientation) * radius)
def __repr__(self):
return '[x=%.5f y=%.5f orient=%.5f]' % (self.x, self.y, self.orientation)
############## ADD / MODIFY CODE BELOW ####################
# ------------------------------------------------------------------------
#
# run - does a single control run
robot = Robot()
robot.set(0, 1, 0)
def run(robot, tau, n=100, speed=1.0):
x_trajectory = []
y_trajectory = []
# TODO: your code here
return x_trajectory, y_trajectory
x_trajectory, y_trajectory = run(robot, 0.1)
n = len(x_trajectory)
fig, (ax1, ax2) = plt.subplots(2, 1, figsize=(8, 8))
ax1.plot(x_trajectory, y_trajectory, 'g', label='P controller')
ax1.plot(x_trajectory, np.zeros(n), 'r', label='reference')