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Hazards Detection

The Create® 3 robot is equipped with a variety of sensors that are capable to detect hazards in the environment.

In particular you will find:

  • Bumper sensor to detect front contacts.
  • Cliff sensors to detect holes and steps.
  • Wheel drop sensors to detect if a wheel is not touching the ground.

The hazard_detection topic

The Create® 3 robot will periodically publish on the hazard_detection ROS 21 topic a vector of all the currently detected hazards. If the vector is empty, this means that no hazards are currently being detected.

Each element of the vector will denote a different hazard detection. Look at the HazardDetection.msg definition in order to see how to differentiate different types of hazards. The header field of each indivdual detection will provide all the information required to localize it. In particular the timestamp will denote when the robot detected the hazard and the frame id will denote the location of the sensor that performed the detection.

Important

The hazard_detection topic will also contain a BACKUP_LIMIT hazard if the robot safety features are preventing it from safely moving further backwards. Look at the safety documentation for details and how to disable it.

Example

No hazards: 

header:
  stamp:
    sec: 1688673217
    nanosec: 973425138
  frame_id: base_link
detections: []

Many hazards: 

header:
  stamp:
    sec: 1688673239
    nanosec: 782492541
  frame_id: base_link
detections:
- header:
    stamp:
      sec: 1688673239
      nanosec: 782576914
    frame_id: cliff_side_left
  type: 2
- header:
    stamp:
      sec: 1688673239
      nanosec: 782576914
    frame_id: cliff_front_left
  type: 2
- header:
    stamp:
      sec: 1688673239
      nanosec: 782576914
    frame_id: cliff_front_right
  type: 2
- header:
    stamp:
      sec: 1688673239
      nanosec: 782576914
    frame_id: cliff_side_right
  type: 2
- header:
    stamp:
      sec: 1688673239
      nanosec: 781947051
    frame_id: left_wheel
  type: 3
- header:
    stamp:
      sec: 1688673239
      nanosec: 781947051
    frame_id: right_wheel
  type: 3
- header:
    stamp:
      sec: 1688673239
      nanosec: 782576914
    frame_id: base_link
  type: 0

The kidnap_status topic

By "kidnap" we denote the action of manually lifting the robot and, eventually, placing it back in a location which may be different from the original one.

The Create® 3 robot combines together different sensors data in order to determine when it's being kidnapped. A boolean status will be periodically published on the kidnap_status topic.

Example 
header:
  stamp:
    sec: 1688672489
    nanosec: 526097022
  frame_id: base_link
is_kidnapped: false

The ir_intensity topic

7 sets of IR emitters and receivers are available in the front bumper to detect objects at close range.

The Create® 3 robot will periodically publish on the ir_intensity topic the raw intensity readings obtained from these sensors. The message will be a vector where each element corresponds to a different sensor. The higher the intensity value is, the closer an obstacle is to the robot. The header field of each indivdual detection will provide all the information required to localize it. In particular the timestamp will denote when the robot detected the hazard and the frame id will denote the location of the sensor that performed the detection.

Example 
header:
  stamp:
    sec: 1688673736
    nanosec: 121692158
  frame_id: base_link
readings:
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_side_left
  value: 0
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_left
  value: 0
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_front_left
  value: 0
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_front_center_left
  value: 0
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_front_center_right
  value: 5
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_front_right
  value: 0
- header:
    stamp:
      sec: 1688673736
      nanosec: 121692158
    frame_id: ir_intensity_right
  value: 3

The cliff_intensity topic

4 sets of IR emitters and receivers are available in on the bottom of the robot just behind its front bumper to detect presence or absence of the floor.

The Create® 3 robot will periodically publish on the cliff_intensity topic the raw intensity readings obtained from these sensors. The message will be a vector where each element corresponds to a different sensor. The higher the intensity value is, the more intensely the floor is perceived. The header field of each indivdual detection will provide all the information required to localize it. In particular the timestamp will denote the time of the reading and the frame id will denote the location of the sensor that performed the detection.

Example 
header:
  stamp:
    sec: 1688672489
    nanosec: 986327471
  frame_id: base_link
readings:
- header:
  stamp:
    sec: 1688672489
    nanosec: 986327471
  frame_id: cliff_side_left
value: 2207
- header:
  stamp:
    sec: 1688672489
    nanosec: 986327471
  frame_id: cliff_front_left
value: 2235
- header:
  stamp:
    sec: 1688672489
    nanosec: 986327471
  frame_id: cliff_front_right
value: 2206
- header:
  stamp:
    sec: 1688672489
    nanosec: 986327471
  frame_id: cliff_side_right
value: 2187

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