Buzz on the Khepera IV

The Khepera IV is a commercial robot produced by K-Team.

A Buzz port for the Khepera IV is available at https://github.com/MISTLab/BuzzKH4. An ARGoS plugin to simulate the robot is available at https://github.com/ilpincy/argos3-kheperaiv.

• Wheels

• set_wheels(lws,rws) sets the speed of the wheels to lws (left wheel speed) and rws (right wheel speed). The speed is expressed in cm/sec. The maximum speed of the real Khepera is about 20 cm/sec. lws,rws must be floating point values.

• gotop(ls,as) sets the speed of the center of mass of the robot. The speed is expressed as a vector in polar coordinates, where ls is the linear speed (i.e., the forward speed, in cm/sec) and as is the angular speed (i.e., in rad/sec). The vector is internally transformed into wheel actuation. ls,as must be floating point values.

• gotoc(sx,sy) sets the speed of the center of mass of the robot. The speed is expressed as a vector in cartesian coordinate, where sx is the linear speed along the local x axis of the robot (i.e., the forward speed, in cm/sec) and sy is the linear speed along the local y axis of the robot (a vector pointing left, according to the right-hand rule). The vector is internally transformed into wheel actuation. sx,sy must be floating point values.

• To activate this actuator in ARGoS, use the differential_drive actuator.

• LEDs

• set_leds(r,g,b) sets the color of the three LEDs on top of the Khepera IV. The color is expressed with 0-255 integer values for each of the channels (red, green, blue).

• To activate this actuator in ARGoS, use the leds actuator.

• Proximity sensors
  • The Khepera IV proximity sensor is a set of 8 infrared emitter/receiver pairs distributed regularly in a ring around the robot. The sensors are numbered 0 to 7. Sensor 0 looks straight ahead, and the numbers increase counterclockwise when looking at the robot from above.
  • proximity is the Buzz table that contains the proximity readings. Each element of this table (e.g., proximity[0], proximity[1], …) is in turn a table that contains two elements:
    • angle, which corresponds to the angle (expressed in radians) at which the sensor is located on the body of the robot
    • value, which is the actual reading. Each individual sensor is saturated (value 1.0) by objects closer than 4 cm; the maximum range of the sensor is 12 cm. Between 4 and 12 cm, the readings follow an exponential law with the distance: 4.14*exp(-33.0*distance)-.085.
    • To activate this sensor in ARGoS, use the kheperaiv_proximity sensor.

• Light sensors
  • The Khepera IV light sensor is a set of 8 infrared emitter/receiver pairs distributed regularly in a ring around the robot. The sensors are numbered 0 to 7. Sensor 0 looks straight ahead, and the numbers increase counterclockwise when looking at the robot from above.
  • light is the Buzz table that contains the light readings. Each element of this table (e.g., light[0], light[1], …) is in turn a table that contains two elements:
    • angle, which corresponds to the angle (expressed in radians) at which the sensor is located on the body of the robot
    • value, which is the actual reading. The sensors all return a value

between 0 and 1, where 0 means nothing within range and 1 means the perceived light saturates the sensor. Values between 0 and 1 depend on the distance of the perceived light. In ARGoS, each reading R is calculated with R=(I/x)^2, where x is the distance between a sensor and the light, and I is the reference intensity of the perceived light. The reference intensity corresponds to the minimum distance at which the light saturates a sensor.

• To activate this sensor in ARGoS, use the kheperaiv_light sensor.

• Ultrasound sensors
  • The Khepera IV ultrasound sensor is a set of 5 emitter/receiver pairs distributed regularly in an arc in front of the robot. The sensors are numbered 0 to 4. Sensor 0 looks straight ahead, and the numbers increase counterclockwise when looking at the robot from above.
  • ultrasound is the Buzz table that contains the ultrasound readings. Each element of this table (e.g., ultrasound[0], ultrasound[1], …) is in turn a table that contains two elements:
    • angle, which corresponds to the angle (expressed in radians) at which the sensor is located on the body of the robot
    • value, which is the actual distance of the detected obstacle in cm. Each individual sensor is saturated by objects closer than 25 cm; the maximum range of the sensor is 200 cm.
    • To activate this sensor in ARGoS, use the kheperaiv_ultrasound sensor.

• LIDAR sensor
  • The Khepera IV LIDAR sensor returns 682 readings in a 270 degrees arc (if not configured to return less readings in the .argos file).
  • lidar is the Buzz table that contains the LIDAR readings. Each element of this table (e.g., lidar[0], lidar[1], …) is the distance of the object detected by a specific laser beam.
    • To activate this sensor in ARGoS, use the kheperaiv_lidar sensor.

• Battery sensor
  • This sensor returns the state of the battery.
  • battery is a table that contains two elements:
    • available_charge, a value between 0.0 and 1.0
    • time_left, the number of control steps before battery depletion
    • To activate this sensor in ARGoS, use the battery sensor.

• Positioning sensor (ARGoS only)
  • This sensor is a sort of GPS, only available in ARGoS. The positioning sensor returns the current pose of the robot.
  • pose is a table that contains two elements:
    • position, a 3D array {x, y, z}
    • orientation, an array {yaw, pitch, roll}
    • To activate this sensor in ARGoS, use the positioning sensor.