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._wheelRadius 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))