scripts/robo_explorer.py

   1 #!/usr/bin/env python
   2 import roslib; roslib.load_manifest('roboint')
   3 import rospy
   4 import tf
   5 from math import sin, cos, pi
   6 from geometry_msgs.msg import Twist, TransformStamped, Point32
   7 from sensor_msgs.msg import PointCloud
   8 from nav_msgs.msg import Odometry
   9 from roboint.msg import Motor
  10 from roboint.msg import Inputs
  11
  12
  13 class RoboExplorer:
  14         def __init__(self):
  15                 rospy.init_node('robo_explorer')
  16
  17                 rospy.Subscriber("cmd_vel", Twist, self.cmdVelReceived)
  18                 rospy.Subscriber("ft/get_inputs", Inputs, self.inputsReceived)
  19
  20                 self.pub_motor = rospy.Publisher("ft/set_motor", Motor)
  21                 self.pub_cloud = rospy.Publisher("point_cloud", PointCloud)
  22                 self.pub_odom = rospy.Publisher("odom", Odometry)
  23
  24                 self.wheel_dist = 0.188 # 18.8cm
  25                 self.wheel_size = 0.052*0.5 # 5.1cm gear ration=0.5
  26                 self.speed = (0, 0)
  27                 self.x = 0
  28                 self.y = 0
  29                 self.alpha = 0
  30                 self.last_in = [0, 0]
  31                 self.odom_broadcaster = tf.TransformBroadcaster()
  32                 self.last_time = rospy.Time.now()
  33
  34                 rospy.spin()
  35
  36         def inputsReceived(self, msg):
  37                 current_time = rospy.Time.now()
  38
  39                 self.send_odometry(msg, current_time)
  40                 self.send_point_cloud(msg, current_time)
  41
  42                 self.last_time = current_time
  43
  44         def send_odometry(self, msg, current_time):
  45                 dt = (current_time - self.last_time).to_sec();
  46                 in_now = msg.input[1:3]
  47                 in_diff = [abs(a - b) for a, b in zip(in_now, self.last_in)] # get changed inputs
  48                 if self.speed[0] < 0:
  49                         in_diff[0] = -in_diff[0]
  50                 if self.speed[1] < 0:
  51                         in_diff[1] = -in_diff[1]
  52
  53                 dist_dir = (in_diff[1] - in_diff[0])*self.wheel_size*pi/8 # steps_changed in different direction => m
  54                 delta_alpha = dist_dir/self.wheel_dist
  55
  56                 dist = (in_diff[0] + in_diff[1])/2.0*self.wheel_size*pi/8 # steps_changed same direction => m
  57
  58                 delta_x = cos(self.alpha + delta_alpha/2)*dist
  59                 delta_y = sin(self.alpha + delta_alpha/2)*dist
  60
  61                 self.alpha += delta_alpha
  62                 if self.alpha > 2*pi:
  63                         self.alpha -= 2*pi
  64                 elif self.alpha < -2*pi:
  65                         self.alpha += 2*pi
  66                 self.x += delta_x
  67                 self.y += delta_y
  68                 self.last_in = in_now
  69
  70                 # speeds
  71                 vx = delta_x / dt
  72                 vy = delta_y / dt
  73                 valpha = delta_alpha / dt
  74
  75                 # since all odometry is 6DOF we'll need a quaternion created from yaw
  76                 odom_quat = tf.transformations.quaternion_from_euler(0, 0, self.alpha)
  77
  78                 # first, we'll publish the transform over tf
  79                 self.odom_broadcaster.sendTransform((0.0, 0.0, 0.0), odom_quat, current_time, "odom", "base_link");
  80
  81                 # next, we'll publish the odometry message over ROS
  82                 odom = Odometry()
  83                 odom.header.stamp = current_time
  84                 odom.header.frame_id = "odom"
  85
  86                 # set the position
  87                 odom.pose.pose.position.x = self.x
  88                 odom.pose.pose.position.y = self.y
  89                 odom.pose.pose.position.z = 0.0
  90                 odom.pose.pose.orientation = odom_quat
  91
  92                 # set the velocity
  93                 odom.child_frame_id = "base_link";
  94                 odom.twist.twist.linear.x = vx
  95                 odom.twist.twist.linear.y = vy
  96                 odom.twist.twist.angular.z = valpha
  97
  98                 # publish the message
  99                 self.pub_odom.publish(odom)
 100
 101         def send_point_cloud(self, msg, current_time):
 102                 cloud = PointCloud()
 103                 cloud.header.stamp = current_time
 104                 cloud.header.frame_id = "sensor_frame"
 105                 cloud.points.append(Point32(msg.d1/10.0, 0, 0))
 106                 self.pub_cloud.publish(cloud)
 107
 108         # test with rostopic pub -1 cmd_vel geometry_msgs/Twist '[0, 0, 0]' '[0, 0, 0]'
 109         def cmdVelReceived(self, msg):
 110                 trans = msg.linear.x
 111                 rot = msg.angular.z # rad/s
 112
 113                 # handle rotation as offset to speeds
 114                 speed_offset = (rot * self.wheel_dist)/2.0 # m/s
 115
 116                 # handle translation
 117                 speed_l = 0
 118                 wish_speed_left = trans - speed_offset
 119                 if abs(wish_speed_left) > 1.7/64.3:
 120                         speed_l = 64.3*abs(wish_speed_left) - 1.7
 121                         if wish_speed_left < 0:
 122                                 speed_l*=-1
 123                 speed_r = 0
 124                 wish_speed_right = trans + speed_offset
 125                 if abs(wish_speed_right) > 1.7/64.3:
 126                         speed_r = 64.3*abs(wish_speed_right) - 1.7
 127                         if wish_speed_right < 0:
 128                                 speed_r*=-1
 129
 130                 # check limits
 131                 if speed_l < -7: speed_l = -7
 132                 elif speed_l > 7: speed_l = 7
 133                 if speed_r < -7: speed_r = -7
 134                 elif speed_r > 7: speed_r = 7
 135
 136                 outmsg = Motor()
 137                 outmsg.num = 1
 138                 outmsg.speed = round(speed_l)
 139                 self.pub_motor.publish(outmsg)
 140
 141                 outmsg = Motor()
 142                 outmsg.num = 2
 143                 outmsg.speed = round(speed_r)
 144                 self.pub_motor.publish(outmsg)
 145
 146                 self.speed = (speed_l, speed_r)
 147
 148 if __name__ == '__main__':
 149         RoboExplorer()