For my project I decided to use an IR Beacon to locate the Leader and track it. I have found on an US web-shop located in Las Vegas (Nevada) selling a cheap pair of IR Transceiver Beacons. This device is equipped by 6 IR LEDs emitting a pulse signal at an high frequency, and by 4 IR sensors located at the North, East, South and West of the device to determine the other beacon’s direction. This sensor is available online here for 50$.

Pololu Beacon pinciple

Pololu IR Beacon

Follower Robot

The RF used for this experiment will be the robot designed and developped by a previous MSc student. The IR beacon will be located upside of the robot and plugged on the battery.

Robot Follower

Leader Robot

As we don’t have RL available for the experiment, the idea is to buy a cheap Radio Controlled car where will be implemented an IR beacon. The follower will detect the beacon located on the RC car and follow the signal. The only requirements for the leader are a low price and the possibility to implement the IR beacon.

One of the main feature of this project is the Leader Path Following. There is many way to track an object or a leader, more or less complicated, efficient, computationally expensive, cost expensive, etc. Each specific case has an optimal solution, for our project we decided to Track the leader and consider it as a target. Therefore we can use a camera to have a visual contact with the leader or attach a beacon to the leader to be seen by the follower.

Visual Tracking

The aim of the Visual Tracking is to implement a Camera or any other CCD Sensor to the Follower and to capture a picture from the “Environment”. Then we have to process to the Perception Phase to get the Leader recognition and to the Action Phase to get the Distance and Bearing from the Leader. A lot of algorithm are available to track a white line on the ground, a colored object or a specific shape.

Nowadays it is really cheap to buy a webcam, the real problem is the computational cost of the image processing and it is not always possible to process it on-board.

Coloured ball tracking

Beacon Tracking

The principle of this solution is to equip the leader of a Beacon to send a signal all around the Robot Leader. The Robot Follower has to receive this signal and evaluate the Distance/Bearing from the Leader, then the Path Following Controller has to make the Follower tracking the Leader.

One of the technology for the Beacon Navigation is the Infra-Red Transceiver: The beacon located on the leader is made by several IR LEDs located all-around the device in order to cover the 360°.

The main problem of this technology is the low range of the IR transmitter for outdoors conditions. For information the maximum range of a standard IR transmitter in optimum condition (indoors) is about 20 ft (6 m) and can be reduce to 3ft (1 m) in very lightly conditions.

IR Beacon from a Senior year project

IR Beacon for research purpose

1. Sensor package for leader localization

• GPS
• Inertial Navigation System ( 1 compass / 3 gyros / 3 accelerometers)

Data fusion by Kalman filtering.

Data fusion

2. Data communication between robots

We have to find a way to insure the communication between the different robot, we can choose between 3 protocols:

• Bluetooth
• Zigbee
• Wifi
  

3. Algorithms for path tracking and following

Those algorithms will have to insure 3 different tasks:

• Path tracking (From the localization of the leader, waypoints)
  
• Path following
  
• Formation control