Difference between revisions of "HamsterPython"

Revision as of 15:12, 19 March 2019

Python setup

• Note you are connected to the hamster_net (wifi / router)

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$ export ROS_IP=<your IP>

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$ export ROS_MASTER_URI=http://10.0.2.<HAMSTER AGENT Number>:11311

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• If the Hamster is powered and your terminal is well configured you should be able to

See all data streams <syntaxhighlight lang="bash" line='line'>

$ rostopic list

</syntaxhighlight> See imagery from the robot <syntaxhighlight lang="bash" line='line'>

$ rqt_image_view

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Python Example 1

• Receive laser scan from robot to decide if free

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1. !/usr/bin/env python

import rospy from sensor_msgs.msg import Imu

def is_free(ranges ,start_index, end_index ,min_distance): #sub array from angle to angle s_ranges = ranges[start_index:end_index] #filter the array b_ranges = filter(lambda x: x <= min_distance, s_ranges) return len(b_ranges) == 0

def callback(msg): if is_free(msg.ranges,160,200,0.2): print "FREE" else: print "BLOCKED"

rospy.init_node('scan_values')

1. Put your Hamster number instead of agent<number>
2. The agent number is printed on the Hamster cover

sub = rospy.Subscriber('/agent14/scan', LaserScan, callback)

rospy.spin()

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Python Example 2

Detect right/left turn from IMU

• IMU angles are represented in Quaternions [[1]] hence translated to RPY (roll pitch yaw)
• RPY are in radians, translated to degrees

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1. !/usr/bin/env python

import rospy import math from sensor_msgs.msg import Imu from tf.transformations import euler_from_quaternion, quaternion_from_euler

def calculate_robot_angle(orientation): quaternion = ( orientation.x, orientation.y, orientation.z, orientation.w) euler = euler_from_quaternion(quaternion) roll = euler[0] pitch = euler[1] yaw = euler[2] return math.degrees(yaw)

prev_angle = 0 def callback(msg): global prev_angle curr_angle = calculate_robot_angle(msg.orientation) if curr_angle > prev_angle : print "TURINING LEFT" else: print "TURINIGN RIGHT" prev_angle = curr_angle

rospy.init_node('imu_values') last_angle = 0

1. Put your Hamster number instead of agent<number>
2. The agent number is printed on the Hamster cover

sub = rospy.Subscriber('/agent14/imu', Imu, callback)

rospy.spin() </syntaxhighlight>

Python Example 3

• Drives the robot forwards until senses from the Lidar that there is less than a meter free ahead of it

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1. !/usr/bin/env python

import rospy from sensor_msgs.msg import LaserScan from ackermann_msgs.msg import AckermannDriveStamped

pub = rospy.Publisher('/agent14/ackermann_cmd',AckermannDriveStamped, queue_size=1)

def is_free(ranges ,start_index, end_index ,min_distance): #sub array from angle to angle s_ranges = ranges[start_index:end_index] #filter the array b_ranges = filter(lambda x: x <= min_distance, s_ranges) return len(b_ranges) == 0

def callback(msg): global pub if is_free(msg.ranges,160,200,1): ack_msg = AckermannDriveStamped() ack_msg.header.stamp = rospy.Time.now() ack_msg.header.frame_id = 'your_frame_here' ack_msg.drive.steering_angle = 0 ack_msg.drive.speed = 1 pub.publish(ack_msg)

rospy.init_node('driving_hamster')

1. Put your Hamster number instead of agent<number>
2. The agent number is printed on the Hamster cover

sub = rospy.Subscriber('/agent14/scan', LaserScan, callback)

rospy.spin()

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