steering.py
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```00001 """
00002 *
00003 *  Description:  common steering constants and calculations
00004 *
00005 *  Copyright (C) 2005, 2007, 2009 Austin Robot Technology
00006 *
00008 *
00009 *  \$Id: steering.h 2 2010-01-17 01:54:03Z jack.oquin \$
00010 *"""
00011
00012 # This code originally imported angles.h
00013 # Angles.h has no python equivalent in ROS, but the math library
00014 # has the functions this file needs to do its job.
00015
00016 import math
00017 from art_msgs.msg import ArtVehicle
00018
00019 ## @brief
00020 #
00021 # Common steering constants and calculations.
00022 #
00023
00024 # Constants: #
00025 steer_speed_min = 3.8               # minimum speed for calculation #
00026                                     # (experimentally verified) #
00027
00028 # Determine steering angle (in degrees) for a given speed and yawrate.
00029 #
00030 #   This computation is based on a simplified "bicycle model" of
00031 #   vehicle steering geometery.  We ignore the slightly different
00032 #   angles of the two front wheels, abstracting them into a single
00033 #   wheel at the midline of the vehicle (like a bicycle or tricycle).
00034 #
00035 #   Consider a radius from the center of the vehicle's turning circle
00036 #   to the midpoint of the rear axle.  The vehicle's wheelbase is at
00037 #   a right angle to this radius, since the rear wheels do not pivot.
00038 #   The hypotenuse of this right triangle is the slightly longer
00039 #   distance from the midpoint of the front axle back to the center
00040 #   of the circle.  As long as the wheels do not slip, the acute
00041 #   angle between the radius and the hypotenuse will be equal to the
00042 #   angle of the front wheel relative to the midline of the vehicle.
00043 #
00044 #   Thus, the tangent of the steering angle is the wheelbase (w)
00045 #   divided by the radius (r).  We estimate r from the desired
00046 #   yawspeed (y), assuming a constant velocity (v):
00047 #
00048 #      y = (2*pi radians) / (2*pi*r/v seconds)
00049 #      y = v/r radians/second
00050 #      r = v/y
00051 #
00052 def steering_angle(v, y) :
00053     steer_radians = math.atan(ArtVehicle.wheelbase * y,v)
00055
00056     steer_degrees = min(steer_degrees, ArtVehicle.max_steer_degrees)
00057     steer_degrees = max(steer_degrees, -ArtVehicle.max_steer_degrees)
00058
00059     return steer_degrees
00060
00061 # Determine yaw rate (in radians/second) for a given speed and
00062 #  steering angle (in degrees).  Inverse of steering_angle().
00063 #
00064
00065 def angle_to_yaw(v, angle) :
00066     return v * math.tan(math.radians(angle)) / ArtVehicle.wheelbase
00067
00068 maximum_yaw = angle_to_yaw(steer_speed_min, ArtVehicle.max_steer_degrees)
```

art_common
Author(s): Austin Robot Technology
autogenerated on Fri Jan 3 2014 11:08:22