Jun 19 2012

Part 1: Dotty


If you have read the “Building a swarm robot” post, you already know that we at DoBots are aiming to develop a cheap platform for swarming experiments. The Dotty is the result of our first attempts. As mentioned before, we are interested in equipping our small bots with machine learning algorithms to assist the swarm in fulfilling the given task and providing the robot with a better understanding of its location and its characteristics.

The physical frame which we selected for the Dotty is the AREXX frame, which contains 2 motors, some experiment space in the form of two breadboard-like areas for electroniccomponents, and a battery compartment. The motors drive two wheels, the third is a passive turning wheel.

One of our wishes is to attach a number of different sensors to the robot that are not optimized individually, but which will be used as a composite by the algorithms, trying to catch one sensor’s weaknesses with the other one’s strengths.

The same applies to the actors, also aiming to enable both communication between bots as communication with human observers.

We have used an Arduino board as the brain of our little robot and added different circuits and sensors to empower the AREXX frame and alter it to a smarter robot.

The actual design of the electronics and circuits has already gone through a number of revisions. As we could not find solutions readily available for all of our wishes, electronics design became a necessity, and revisiting the knowledge required essential.

At the end we aim to have a Dotty equipped with sensors and electronics like: IR sensor, Microphone, Speaker, Light sensor, Motor sensor, Battery sensor and Gas sensor.

Light-power- collision avoidance

One of our first experiments was a “Light-power- obstacle avoidance” scenario in which the Dotty is equipped with a light sensor and an IR sensor. The IR- sensor is responsible for the obstacle avoidance task and the light sensor data is used for adjusting the robot’s speed. As the light level sensed by the bot is higher, it moves faster.

Below, you will find the hardware characteristics, a short video and a link to the code.

Microcontroller and additional electronics

For this project we used a LilyPad Arduino board as microcontroller for the Dotty. We also added a motor controller to the AREXX frame, in order to control two DC motors, for moving forward or backward. The speed of the motors can be adjusted by the Arduino PWM output.

The Infrared sensor

The Infrared sensor can be bought easily; we got it through iprototype.nl. It has 3 connections, ground, supply voltage and sensor out. It produces a voltage proportional to the measured obstacle distance.

The Light sensor

A challenge frequently addressed in Artificial Intelligence is the extraction of periodicity in a series of observations. Figuring out which frequency fits the observed data, enabling an accurate forecast, is far from trivial, especially if multiple modulation sources with each their own repeat cycle are involved. The choice for the light sensor is motivated by this question, as the cycle of daylight (modulated by season and weather) is an excellent example of the type of data central to this problem.

The circuit we use is very simple and very cheap. It contains a single transistor, a Light Dependent Resistor (LDR) and two additional resistors.

Schematic of Light sensor circuit for the DoBots Bot One

Below, you can see a short video, recorded during the experiment.

You also can download the code written for this experiments from our SVN repository.

Looking for the light source

Using the same hardware, electronics and sensors (mentioned above), we tried out another experiment to see if the Dotty can find a source of light by comparing the received data from the light sensor. Using a simple feedback algorithm, the received light levels are compared every 0.5 seconds. If the sensor data indicates that the Dotty is receiving less light than before, it turns with a random angle and moves in a different direction, searching for a light source. If the Dotty receives a higher light level than before, it continues moving forward with the same direction.

Below you can see how Dotty succeeds in finding the light source (in this case a desk lamp).

The piece of code wiritten for this experiment can also be found in our SVN repository.

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