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Dwa failed to produce path in free space

asked 2018-01-23 20:54:36 -0600

scopus gravatar image

updated 2018-02-22 19:46:51 -0600

Hi, all. I found a bug for dwa local planner. When the goal is in the -x and -y direction with respect to robot's current pose, the robot moves really slowly, even stop.

It outputs "The dwa local planner failed to find a valid plan, cost functions discarded all candidates. This can mean there is an obstacle too close to the robot". This information is generated from here when the cost of computed path is smaller than zero.

Obviously, we can see that there is no obstacle around the robot at that time. This case can be repeated as long as we want. toal_cost

The parameters are listed as follows:

DWAPlannerROS:

# Robot Configuration Parameters - Kobuki
  max_vel_x: 0.3  # 0.55
  min_vel_x: 0.0 

  max_vel_y: 0.0  # diff drive robot
  min_vel_y: 0.0  # diff drive robot

  max_trans_vel: 0.3 # choose slightly less than the base's capability
  min_trans_vel: 0.04  # this is the min trans velocity when there is negligible rotational velocity
  trans_stopped_vel: 0.1

  max_rot_vel: 1.57 # default 5.0  # choose slightly less than the base's capability
  min_rot_vel: 0.4  # this is the min angular velocity when there is negligible translational velocity
  rot_stopped_vel: 0.4

  acc_lim_x: 1.0 # maximum is theoretically 2.0, but we 
  acc_lim_theta: 2.0
  acc_lim_y: 0.0      # diff drive robot

 # Goal Tolerance Parameters


 yaw_goal_tolerance: 0.05  # 0.05
  xy_goal_tolerance: 0.05 # 0.10
  # latch_xy_goal_tolerance: false

# Forward Simulation Parameters
  sim_time: 1.7  #1.5       # 1.7
  vx_samples: 20      # 3
  vy_samples: 1   #1       # diff drive robot, there is only one sample
  vtheta_samples: 40  # 20

# Trajectory Scoring Parameters
  path_distance_bias: 32.0      # 32.0   - weighting for how much it should stick to the global path plan
  goal_distance_bias: 12.0      # 24.0   - wighting for how much it should attempt to reach its goal
  occdist_scale: 0.02           # 0.01   - weighting for how much the controller should avoid obstacles
  forward_point_distance: 0.325 #0.325 # 0.325  - how far along to place an additional scoring point
  stop_time_buffer: 0.2         # 0.2    - amount of time a robot must stop in before colliding for a valid traj.
  scaling_speed: 0.25           # 0.25   - absolute velocity at which to start scaling the robot's footprint
  max_scaling_factor: 0.2       # 0.2    - how much to scale the robot's footprint when at speed.

# Oscillation Prevention Parameters
  oscillation_reset_dist: 0.05  # 0.05   - how far to travel before resetting oscillation flags

# Debugging
  publish_traj_pc : true
  publish_cost_grid_pc: true
  global_frame_id: odom
# Differential-drive robot configuration - necessary?
  holonomic_robot: false

Very looking forward anyone can give me any advice to solve this problem! Thank you!

EDIT1:

Thank you! @David Lu I have updated the image with colored cost cloud. The trajectory cloud is not displayed because its topic output nothing suddenly. The topic of trajectory cloud output colored fan-shaped cloud in front of robot normally. However, as the robot cannot move forward, the fan-shaped cloud disappeared. I am not sure that the topic of cost cloud output normally because it has persistence in rviz. It is not updated until a new message arrives.

EDIT2: Thanks again! @David ... (more)

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Comments

Is the screenshot showing the local or global costmap?

David Lu gravatar imageDavid Lu ( 2018-01-30 11:25:50 -0600 )edit

Thank you for your attention! It's global costmap. The local costmap is not being shown there. But I don't think this problem is relative to the costmap.

scopus gravatar imagescopus ( 2018-01-30 18:35:23 -0600 )edit

If there was an obstacle, it would be on the local costmap.

David Lu gravatar imageDavid Lu ( 2018-01-30 19:10:48 -0600 )edit

Thank you! The environment of this experiment is in control, we are sure that there is no obstacle around the robot at that time.

scopus gravatar imagescopus ( 2018-01-30 19:28:55 -0600 )edit

We found that the path.cost_ is smaller than zero which makes the dwa planner can't generate controlling velocity .

scopus gravatar imagescopus ( 2018-01-31 18:40:56 -0600 )edit

I would show the local costmap anyway. The most probable reasons for a negative score are obstacles and being off the costmap. It may also help to visualize the cost and trajectory clouds.

David Lu gravatar imageDavid Lu ( 2018-02-05 12:36:38 -0600 )edit

2 Answers

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answered 2018-02-08 12:34:45 -0600

David Lu gravatar image

Try systematically setting the weights (path_distance_bias, goal_distance_bias, occdist_scale) to zero to see which Cost Function is creating the negative score.

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Comments

Hi, I updated the question with "EDIT2". Please give me help again.Thanks!

scopus gravatar imagescopus ( 2018-02-12 00:08:43 -0600 )edit

Hi, @David Lu, Even though the robot can move by aduusting the parameters at that position, the robot may not move normally at other positions with same parameters. So would you like to tell us how to make the robot always move normally with same parameter setting. Thanks!

scopus gravatar imagescopus ( 2018-02-13 20:55:18 -0600 )edit

With all of the parameters non-zero (i.e. their original values) can you visualize the cost cloud and post screenshots of the different channels of that visualization?

David Lu gravatar imageDavid Lu ( 2018-02-14 09:37:32 -0600 )edit

There's something wrong with the goal_cost, but then I noticed that the goal seems to be inside an obstacle. Does navigation work if the goal is in free space?

David Lu gravatar imageDavid Lu ( 2018-03-02 12:54:29 -0600 )edit
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answered 2018-05-16 09:38:16 -0600

lvilelap gravatar image

Hi guys, i would really appreciate if someone could help me with this one.

I had the same problem, my cost value is always negative, but in my case it's -6 and it's the cost function number 1 that discards it. I made the same tests of setting to zero one parameter at a time, but i haven't got to any conclusion. - When the 3 parameters are zero : No velocity discarded message but robot doesnt move. - When the 3 parameters are not zero : Velocity 0.405, -0.089, 1.000 discarded by cost function 1 with cost: -6.000000 - When i set only path_distance_bias to zero : Velocity 0.405, -0.089, 1.000 discarded by cost function 1 with cost: -6.000000 - When i set only occdist to zero : Velocity 0.405, -0.089, 1.000 discarded by cost function 3 with cost: -3.000000 - When i set only goal distance bias to zero : Velocity 0.405, -0.089, 1.000 discarded by cost function 1 with cost: -6.000000

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Asked: 2018-01-23 20:54:36 -0600

Seen: 1,201 times

Last updated: Feb 22 '18