With that said, your velocity and acceleration limits are different enough from the defaults that it required tuning some parameters to get things to run smoothly. With the parameters you provided, the robot wouldn't go much of anywhere. I made a few modifications, which I'll include below to get things working in a reasonable manner. First, I upped the sim_time parameter to 2.0 seconds from the default of 1.0 second. I did this because you have a very low maximum linear velocity and trajectories are scored from their endpoints, so simulating them a bit further helps to differentiate between paths. Also, since you have a really low maximum for your angular velocity, I felt like it might be helpful for the robot to attempt to follow the global plan more closely. To this end, I upped the path_distance_bias weight and dropped the goal_distance_bias weight. I only spent about 2 minutes tuning the parameters, so I'm sure that you'd be able to get even better behavior by playing around some more (upping the sim_time even more, or the trade off between following the path and moving towards the goal... see:�http://www.ros.org/wiki/base_local_planner�for parameter descriptions), but this at least exhibits reasonable results for me in simulation. My changes can be found below:

On Mon, Sep 27, 2010 at 7:44 AM, Patrick Goebel <patrick@casbs.stanford.edu> wrote:

Hello,

For the past month I have been going through the ROS tutorials and
trying everything out on my robot (http://www.pirobot.org) which uses a
Serializer PID controller for the drive wheels and seems to work well
outside of ROS for moving the robot particular distances at specified
speeds.

I am now trying to get the navigation stack up and running and I think I
am 95% of the way there. �The one glitch seems to be similar to what was
reported by Christian Verbeek on this thread. �Namely, the
base_local_planner appears to be issuing velocity commands that exceed
the maximums I have set. �For example, I have max_vel_x set to 0.2, yet
I am seeing numbers as high as 0.84 on /cmd_vel while simply trying to
move 1 meter forward. �Similarly, I have max_rotational_vel set to 0.15,
but I have seen greater values there too. �This is not a rare occurrence
but happens on almost every nav goal I set in rviz or publish from the
command line. �Hopefully I am just making a beginner's mistake but I
have played around with the parameters for two days now and I can't make
the problem go away.

Here are some of my config files:

base_local_planner_params.yaml:
TrajectoryPlannerROS:
� � max_vel_x: 0.2
� � min_vel_x: 0.05
� � max_rotational_vel: 0.15
� � min_in_place_rotational_vel: 0.1
� � acc_lim_th: 2.0
� � acc_lim_x: 1.0
� � acc_lim_y: 1.0
� � yaw_goal_tolerance: 0.2
� � xy_goal_tolerance: 0.2
� � controller_frequency: 5.0
� � holonomic_robot: false

cost_common_params.yaml:
obstacle_range: 2.5
raytrace_range: 3.0
footprint: [[-0.13, 0.16], [0.13, 0.16], [0.13, -0.16], [-0.13, -0.16]]
#robot_radius: ir_of_robot
inflation_radius: 0.55
transform_tolerance: 1.0
observation_sources: base_scan
base_scan: {sensor_frame: base_link, data_type: LaserScan, topic:
base_scan, marking: true, clearing: true

global_costmap_params.yaml:
global_costmap:
� � global_frame: map
� � robot_base_frame: base_link
� � update_frequency: 5.0
� � static_map: true
� � rolling_window: false

local_costmap_params.yaml:
local_costmap:
� � global_frame: odom
� � robot_base_frame: base_link
� � update_frequency: 5.0
� � publish_frequency: 0
� � static_map: false
� � rolling_window: true
� � width: 3.0
� � height: 3.0
� � resolution: 0.10

My map is simply a white square 500x500 pix at 0.10 resolution.

My move_base.launch file looks like this:
<launch>
<master auto="start"/>

<param name="robot_description" command="cat $(find
pi_robot)/urdf/pi_robot_urdf.xml" />


<node name="map_server" pkg="map_server" type="map_server" args="$(find
pi_robot)/blank_map.yaml"/>


<node pkg="fake_localization" type="fake_localization"
name="fake_localization" output="screen" />


<node pkg="tf" type="static_transform_publisher"
name="odom_map_broadcaster" args="0 0 0 0 0 0 /odom /map 100" />

<node pkg="move_base" type="move_base" respawn="false" name="move_base"
output="screen">
<param name="controller_frequency" value="5.0" />
<rosparam file="$(find pi_robot)/costmap_common_params.yaml"
command="load" ns="global_costmap" />
<rosparam file="$(find pi_robot)/costmap_common_params.yaml"
command="load" ns="local_costmap" />
<rosparam file="$(find pi_robot)/local_costmap_params.yaml"
command="load" />
<rosparam file="$(find pi_robot)/global_costmap_params.yaml"
command="load" />
<rosparam file="$(find pi_robot)/base_local_planner_params.yaml"
command="load" />
</node>
</launch>

I won't have a laser scanner until next month, so I am faking it with
the following node:

import roslib; roslib.load_manifest('pi_robot')
import rospy
from sensor_msgs.msg import LaserScan
from tf.broadcaster import TransformBroadcaster

rospy.init_node("base_scan")
scanPub = rospy.Publisher('base_scan', LaserScan)
scanBroadcaster = TransformBroadcaster()

scan_rate = 10
rate = rospy.Rate(scan_rate)

rospy.loginfo("Started base scan at " + str(scan_rate) + " Hz")

while not rospy.is_shutdown():

� � ranges = list()

� � for i in range(30):
� � � � ranges.append(3)

� � scan = LaserScan()
� � scan.header.stamp = rospy.Time.now()
� � scan.header.frame_id = "base_link"
� � scan.angle_min = -1.57
� � scan.angle_max = 1.57
� � scan.angle_increment = 0.108275862
� � scan.scan_time = scan_rate
� � scan.range_min = 0.5
� � scan.range_max = 6.0
� � scan.ranges = ranges
� � scanPub.publish(scan)

� � rate.sleep()

Thanks for your time!

Patrick Goebel

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