For the full article please see the Winter 2007 issue of Robot Magazine.
Using a CMUcam2+ Huey can seek out, track, and chase color. He is also equipped with a thermal sensor that allows him track heat. By combining or alternating between color and heat, Huey can be used to create all sorts of interesting applications. Like his heat seeking predecessor the Follow-Me Rover, Huey is currently programmed to follow people. By simply having a piece of colored paper showing out of your back pocket or wearing a colored wrist band Huey will follow you around like a loyal pet. But unlike his predecessor Huey can use his color sensing ability to locate objects, follow his fellow robots, navigate using colored signs, sense and track motion, and, of course, chase cats.
Huey uses my Module Robot System (MRS).
The primary base for Huey is the A4WD1 Rover from Lynxmotion. This rover sports four 5 inch RC tires each with a 7.2 volt motor. For this base, two standard 3300mah 7.2 volt batteries were mounted in the interior of the rover. One is used to provide power for all the electronics and the other for the motors. The motors are wired in left/right pairs and are driven by two Parallax HB-25 motor controllers. The base processor is a Propeller Proto Board which was mounted externally on the rear of the rover.
Huey’s intelligence is divided between two Parallax Propeller Proto Boards. One Propeller is used for sensor processing. It’s called the Robot Sensor Array (RSA). The other Propeller (called the Mission Controller) is used to coordinate and execute Huey’s mission.
The Robot Sensor Array controls three major sensor systems: collision avoidance, beacon navigation and color/thermal tracking. Collision avoidance is implemented using two IR and one ultrasonic sensor. The Sharp GP2D12 distance measuring sensors are used for left/right proximity detection. A Parallax Ping ultrasonic sensor is used to measure the distance of objects directly in front.
The RSA also supports infrared beacon-based navigation. This system uses an IR detector mounted at the end of a rectangular tube which restricts the detector’s field of view to a few degrees. The tube assembly is mounted on a standard servo. By scanning the sensor left and right it is possible to precisely detect and determine the bearing to a beacon.
The most important function that the RSA performs is color and thermal tracking. Like the beacon navigation function the RSA can provide a bearing to a color or heat source. It determines the bearing to the target using two sensors: the Devantech TPA81 Thermal Array and the Acroname CMUcam2+.
The Devantech TPA81 is used for thermal tracking. This sensor has an array of eight heat detectors (called pixels) mounted horizontally giving it a field of view of about 45 degrees. For color tracking Huey uses a version of the CMUcam2 from Acroname called the CMUcam2+. The CMUcam2+ is mounted in a Turret Assembly also available from Acroname. For stability the entire assembly is mounted on a Base Rotate Kit from Lynxmotion. The faceplate that comes with the turret was designed to hold various sensors including the TPA81. Unfortunately the mounting holes for the TPA81 are off center from the camera lens. This prevented the two sensors from having the same field of view. In order to fuse the data from both the CMUcam2+ and the TPA81, a custom faceplate was constructed from some 1/8 inch PVC panel stock and a couple of short aluminum square bars.
The Mission Controller is responsible for the coordination and execution of Huey’s mission. This part of Huey’s brain reads sensor data from the RSA and then sends the appropriate movement commands to the Base. By changing the code in the Controller you can create a variety of interesting missions that Huey can execute.
A detailed schematic and all the source code can be downloaded from the links on the right or from http://www.botmag.com/issue9.