Source code for morse.actuators.v_omega_diff_drive
import logging; logger = logging.getLogger("morse." + __name__)
from morse.core.services import service
import morse.core.actuator
from morse.helpers.components import add_data
[docs]class MotionVWDiff(morse.core.actuator.Actuator):
"""
This actuator reads the values of linear and angular speed and
applies them to the robot as speeds for the wheels. It only works
with robots of the type ``WheeledRobot``, such as the :doc:`Segway
RMP 400 <../robots/segwayrmp400>` and the :doc:`Pioneer 3-DX
<../robots/pioneer3dx>`. The movement of the robot is more
realistic, but also depends on more factors, such as the friction
between the wheels and the surface.
The speeds for the left and right wheels are calculated as:
left_speed = (v - e w) / R
right_speed = (v + e w) / R
where:
- **v** is the linear velocity given as parameter
- **w** is the angular velocity given as parameter
- **e** is half of the distance between the left and
right wheels
- **R** is the radius of the wheels
"""
_name = 'Differential Driver Actuator: \
Linear and angular speed (V, W) actuator'
add_data('v', 0.0, 'float',
'linear velocity in x direction (forward movement) (m/s)')
add_data('w', 0.0, 'float', 'angular velocity (rad/s)')
def __init__(self, obj, parent=None):
logger.info('%s initialization' % obj.name)
# Call the constructor of the parent class
super(self.__class__, self).__init__(obj, parent)
self.local_data['v'] = 0.0
self.local_data['w'] = 0.0
self._stopped = True
# get track width for calculating wheel speeds from yaw rate
parent = self.robot_parent
self._trackWidth = parent._trackWidth
self._radius = parent._wheel_radius
logger.info('Component initialized')
@service
[docs] def set_speed(self, v, w):
"""
Modifies v and w according to the parameters
:param v: desired linear velocity (meter by second)
:param w: desired angular velocity (radian by second)
"""
self.local_data['v'] = v
self.local_data['w'] = w
@service
[docs] def stop(self):
"""
Stop the robot
Internally, it sets (v, w) to (0.0, 0.0)
"""
self.local_data['v'] = 0.0
self.local_data['w'] = 0.0
[docs] def default_action(self):
""" Apply (v, w) to the parent robot. """
# calculate desired wheel speeds and set them
if (abs(self.local_data['v']) < 0.001) and \
(abs(self.local_data['w']) < 0.001):
# stop the wheel when velocity is below a given threshold
for index in self.robot_parent._wheels.keys():
self.robot_parent._wheel_joints[index].setParam(9, 0, 100.0)
self._stopped = True
else:
# this is need to "wake up" the physic objects if they have
# gone to sleep apply a tiny impulse straight down on the
# object
if (self._stopped):
self.robot_parent.bge_object.applyImpulse(
self.robot_parent.bge_object.position, (0.0, 0.1, -0.000001))
# no longer stopped
self._stopped = False
# Another formula for computing left and right wheel speeds:
# http://arri.uta.edu/acs/jmireles/Robotics/KinematicsMobileRobots.pdf
v_ws_l = self.local_data['v'] - \
(self._trackWidth / 2.0) * self.local_data['w']
v_ws_r = self.local_data['v'] + \
(self._trackWidth / 2.0) * self.local_data['w']
# convert to angular speeds
w_ws_l = v_ws_l / self._radius
w_ws_r = v_ws_r / self._radius
# set wheel speeds - front and rear wheels have the same speed
# Left side wheels
self.robot_parent._wheel_joints['FL'].setParam(9, w_ws_l, 100.0)
if 'RL' in self.robot_parent._wheels:
self.robot_parent._wheel_joints['RL'].setParam(9, w_ws_l, 100.0)
# Right side wheels
self.robot_parent._wheel_joints['FR'].setParam(9, w_ws_r, 100.0)
if 'RR' in self.robot_parent._wheels:
self.robot_parent._wheel_joints['RR'].setParam(9, w_ws_r, 100.0)
logger.debug("New speeds set: left=%.4f, right=%.4f" %
(w_ws_l, w_ws_r))