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Why does the DWA Local Planner need an acceleration value of >= 1.0?

asked 2014-08-14 08:21:27 -0600

Chrissi gravatar image

updated 2014-08-14 09:21:08 -0600

Sometimes, in cluttered environments, our (differential wheeled) robot seems to accelerate too fast and navigates itself into places it cannot escape from. Just to test if a lower acceleration would do any good I tried reconfiguring it but it seems that setting the parameter /move_base/DWAPlannerROS/acc_lim_x lower than 1.0 causes move_base to not do anything any more. Since the parameter is a float value, I expect that the reason is not just an int cast somewhere. Does anyone know why an acceleration lower than 1.0 m/s^2 might not be supported?

Edit: Just to give some more info, these are the other parameters we use:

  acc_lim_x: 1.0

  acc_lim_y: 0.0

  acc_lim_th: 2.0

  min_vel_y: 0.0
  max_vel_y: 0.0
  max_rot_vel: 1.0
  min_rot_vel: 0.4

  yaw_goal_tolerance: 0.1

  xy_goal_tolerance: 0.3

  latch_xy_goal_tolerance: true
  sim_time: 1.7

  path_distance_bias: 5.0 #default:32
  goal_distance_bias: 9.0 #default:24
  occdist_scale: 0.01 #default:0.01

  oscillation_reset_dist: 0.05

  prune_plan: true

  holonomic_robot: false

Not listed parameters use the default values.

Edit2: To answere David's comment: These are the parameters we use for the local costmap:

  update_frequency: 5.0
  publish_frequency: 2.0
  static_map: false
  rolling_window: true
  width: 4.0
  height: 4.0
  resolution: 0.05
    - {name: obstacle_layer, type: "costmap_2d::VoxelLayer"}
    - {name: inflation_layer, type: "costmap_2d::InflationLayer"}

So the resolution is 0.05 which is the default value if I'm not mistaken.

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What is the resolution of your local costmap?

David Lu gravatar image David Lu  ( 2014-08-14 08:58:33 -0600 )edit

What ROS Distro are you on? Also, are you using the binaries for navigation, or are you compiling the code yourself?

David Lu gravatar image David Lu  ( 2014-08-18 11:58:52 -0600 )edit

Also, check two things: 1) What are the cmd_vels that are being published (if any) 2) If you set the parameter publish_traj_pc to true, what does the point cloud look like in rviz?

David Lu gravatar image David Lu  ( 2014-08-18 12:11:27 -0600 )edit

We are on Hydro and use the binaries. I will check the other things asap.

Chrissi gravatar image Chrissi  ( 2014-08-20 05:51:26 -0600 )edit

There is only 0 s published in /cmd_vel and I don't have the publish_traj_pc parameter in my set-up and under /move_base/DWAPlannerROS/trajectory_cloud there is nothing published.

Chrissi gravatar image Chrissi  ( 2014-08-22 06:32:10 -0600 )edit

Tested it with the stage simulator, turtlebot on ros indigo. Had no problems, maybe updating helps.

AReimann gravatar image AReimann  ( 2014-10-01 03:30:15 -0600 )edit

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answered 2014-08-14 15:30:56 -0600

David Lu gravatar image

This wouldn't be a permanent solution, but what happens when you set your resolution to .01?

The measure of progress that DWA uses is how many grid cells closer to the goal did you get on this move. That means you're occasionally at the mercy of the resolution. If you're not moving fast enough to get out of the cell, there will be no viable trajectories that go anywhere.

This is a bad implementation and I'm working on fixing it, but for now try the resolution change to see if that gets you anywhere.

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Thank you very much for the tip! I'll try that and report back.

Chrissi gravatar image Chrissi  ( 2014-08-15 06:32:09 -0600 )edit

Today I finally had time to test it. Sadly, setting the resolution to .01 does not have any effect. As soon as I set the acc_lim_x below 1.0 (e.g. .9) move_base is not able to find a path any more.

Chrissi gravatar image Chrissi  ( 2014-08-18 03:59:28 -0600 )edit

@Chrissi Are you still having issues with this?

surfertas gravatar image surfertas  ( 2017-05-08 01:00:46 -0600 )edit

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Asked: 2014-08-14 08:21:27 -0600

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Last updated: Aug 14 '14