Introduction
This example demonstrates ability to move Baxter's head by nodding and panning its head to random angles for 10 seconds.The code consists of a main() function that initializes the ros node and creates an instance of the Wobbler class. In the __init__() function, an instance of the head interface is created. The wobble() function is then called, which performs a single head nod before panning the head to random angles for 10 seconds.
Interfaces -
- Head.set_pan(<double>)
- Head.command_nod()
- Head.pan()
Code Walkthrough
Now, let's break down the code.
30 import argparse
31 import random
32
33 import rospy
34
35 import baxter_interface
36
37 from baxter_interface import CHECK_VERSION
This imports the baxter interface for accessing the Head class. The CHECK_VERSION is imported to check if the software running on the robot would be compatible with this local version. It is not necessary to check the version in custom programs.
40 class Wobbler(object):
41 def __init__(self):
42 """
43 'Wobbles' the head
44 """
45 self._done = False
46 self._head = baxter_interface.Head()
The _head is an object of the Head class within the baxter_interface. This creates a subscriber to the topic robot/head/head_state and publishers to the topics robot/head/command_head_pan, robot/head/command_head_nod. The object _head, would be used to control the head nodding and panning.
49 # verify robot is enabled
50 print("Getting robot state... ")
51 self._rs = baxter_interface.RobotEnable(CHECK_VERSION)
52 self._init_state = self._rs.state().enabled
53 print("Enabling robot... ")
54 self._rs.enable()
55 print("Running. Ctrl-c to quit")
baxter_interface.RobotEnable(CHECK_VERSION) checks if the sdk version updated in the settings is compatible with the sdk version loaded on the param server of the Robot and creates an object _rs of the RobotEnable class. The next line sets the _init_state of the robot to its current state. The enable() performs the actual enabling of the robot. It is important to note that the robot should be in enabled state before attempting to move its joints.
57 def clean_shutdown(self):
58 """
59 Exits example cleanly by moving head to neutral position and
60 maintaining start state
61 """
62 print("\nExiting example...")
63 if self._done:
64 self.set_neutral()
65 if not self._init_state and self._rs.state().enabled:
66 print("Disabling robot...")
67 self._rs.disable()
This function performs a clean shutdown of the program. The _done variable gets updated once the head finishes its wobbling. Then, the head is moved to its neutral position and checks if the _init_state was in disabled state and the current state is enabled. If so, it resets the robot to the disable state.
69 def set_neutral(self):
70 """
71 Sets the head back into a neutral pose
72 """
73 self._head.set_pan(0.0)
The set_pan function moves the head to the desired joint position. It employs a PID position controller to move the head joint to that position. In order to move the head to the neutral position, the pan is set to 0.
75 def wobble(self):
76 self.set_neutral()
77 """
78 Performs the wobbling
79 """
80 self._head.command_nod()
81 command_rate = rospy.Rate(1)
82 control_rate = rospy.Rate(100)
83 start = rospy.get_time()
This is where the actual wobbling happens. Before the robot starts to wobble its head, it moves its head to the neutral position. The command_nod() performs a single nod of the head by publishing on the robot/head/command_head_nod topic.
86 while not rospy.is_shutdown() and (rospy.get_time() - start < 10.0):
87 angle = random.uniform(-1.5, 1.5)
This retrieves a random floating point number between -1.5 and 1.5. These random angles are generated for 10 seconds.
84 while (not rospy.is_shutdown() and
85 not (abs(self._head.pan() - angle) <=
86 baxter_interface.HEAD_PAN_ANGLE_TOLERANCE)):
This ensures that it loops till the current head pan position and the random angle generated above is within the HEAD_PAN_ANGLE_TOLERANCE
89 self._head.set_pan(angle, speed=30, timeout=0)
90 control_rate.sleep()
91 command_rate.sleep()
This publishes the corresponding position and the speed to the robot/head/command_head_pan
93 self._done = True
94 rospy.signal_shutdown("Example finished.")
Once the wobbling is completed, the _done variable is updated as True and a shutdown signal is sent.
97 def main():
98 """RSDK Head Example: Wobbler
99
100 Nods the head and pans side-to-side towards random angles.
101 Demonstrates the use of the baxter_interface.Head class.
102 """
103 arg_fmt = argparse.RawDescriptionHelpFormatter
104 parser = argparse.ArgumentParser(formatter_class=arg_fmt,
105 description=main.__doc__)
106 parser.parse_args(rospy.myargv()[1:])
107
108 print("Initializing node... ")
109 rospy.init_node("rsdk_head_wobbler")
110
111 wobbler = Wobbler()
An object of the Wobbler class is generated and this initializes the head interface, checks for the appropriate version and enables the robot.
112 rospy.on_shutdown(wobbler.clean_shutdown)
113 print("Wobbling... ")
114 wobbler.wobble()
115 print("Done.")
116
117 if __name__ == '__main__':
118 main()
The actual nodding and panning happens when the wobble() function is called.
