The goal for this kind of robots is to follow a black line over a white floor as quick as possible. The track has also branches which should be taken properly by the robot. It should be able to read some little strips located at both sides of the track which shows the robot the right direction to take in the next branch. In almost all the competitions, taking the wrong side of the branch makes the robot to travel a longer distance and, sometimes involves a 10-15 seconds penalty over the total time achieved.
The tracks usually have many turns and 90 degrees corners so DIEZ has been designed to be lightweight and small in order to achieve these movements as fast as possible with the less moment of inertia.
Prior to the final assembly of the robot, a CAD design was performed when all the decisions about the design were made. Here you can see a GIF showing the first steps from CAD to assembly phases:
Sensors, Control Board and Algorithm:
The main board is an LPC2138-01 based on a 32-bit LPC2138 microcontroller at 60 MIPS.
The sensor board's got 10 tiny SMD reflective sensors which are read by the microcontroller with one of its A/D converters. Due to the different light conditions in the contests and sometimes, the camera flashes and the reflection ratios of the track surfaces, DIEZ performs an ambient light cancelation by reading the sensors with the IR led switched off. Besides, the IR led light is modulated to achieve an even more reliable reading from the sensors.
The control algorithm used by DIEZ is a PD controller. The input of the controller is the position of the center of the line, which is estimated using an interpolation function of the values read from the sensor board. A C# application's been developed to test and debug the algorithm before coding it into the microcontroller. Here you can see an screenshot of this program which allowed us to monitor in Real Time what the robot saw in every moment. Also, thanks to the SD socket of the LPC2138-01 board, the robot was recording all the data and parameters on it for a later study with this program. This was specially useful to detect some of the problems of the algorithm because we had all the telemetry. This recording was quite feasible using the Embedded File System Library since the robot just had to create a new telemetry file on a FAT32 filesystem which was perefctly readable from any computer.
Weight and Dimensions
The total weight of DIEZ is less than 400 gr (about 14 oz) with two Li-Po batteries (1450 mAh).
Its size is 15 x 15 x 7 cm (5.9 x 5.9 x 2.7 inches).
Here you can see a video with DIEZ in action. Those 'ugly' pink thingies on its wheels are stripes of a water balloon which we had handy to increase the adherence and, thus, the maximum speed to reach a corner. Due to its light weight, these rubbers were necessary to avoid the skids.
Again, hope you liked the article.