Authors: Juan Pablo Carbajal, Dorit Assaf, Emanuel Benker
📝 Abstract
This article describes an exemplary robot exercise which was conducted in a class for mechatronics students. The goal of this exercise was to engage students in scientific thinking and reasoning, activities which do not always play an important role in their curriculum. The robotic platform presented here is simple in its construction and is customizable to the needs of the teacher. Therefore, it can be used for exercises in many different fields of science, not necessarily related to robotics. Here we present a situation where the robot is used like an alien creature from which we want to understand its behavior, resembling an ethological research activity. This robot exercise is suited for a wide range of courses, from general introduction to science, to hardware oriented lectures.
💡 Deep Analysis
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A simple self-made robotic platform built by the authors was used for the activity. The robot had two wheels, each one actuated by a DC motor. Two light sensors [1] were attached to the robot. The robot was controlled by a simple onboard program that defined a relation between inputs coming from the sensors and output signals sent to each motor.
We provided the robot with the behavior of Valentino Braitenberg’s vehicle number 3 [2]. The light sensors of the robot commanded the rotational speed of the two motors. The connection was inhibitory, meaning that when the sensor measured light, the speed of the motor connected to it was reduced proportionally to the sensor’s output. This sensor-motor configuration generates a light following behavior (Figure 1). More details about the robot, the control program and how to reproduce this exercise are explained in later sections.
Next we describe how we used the robot to engage students in scientific thinking. This exercise was part of a class on modeling mechatronics systems that took place at the Baden-Wuerttemberg Cooperative State University Loerrach, Germany. The students were mainly 3rd year bachelor students. The objective of the activity was to let students find out the sensor-motor relationship by means of hands-on experimentation and free exploration. The students had to create a hypothesis about the controller implemented in the robot and later verify it through experiments. Introducing the robot. The activity started with the presentation of the robot and a demonstration of its behavior when a light was placed in front of it. The robot moved by default in a straight line, and when it passed close to the light it turned towards it. The robot was even able to track the light (this depends on the sensor gain and motor speed, therefore it requires calibration prior to demonstration). This light loving behavior, though simple, always captivates the audience as well as the teachers.
The assignment. After several playful tests with the light, the students were asked to give explanations, in the simplest possible way, about the controller implemented in the robot such that it shows this behavior. Additionally, they were asked to propose an experiment that tests their explanation. In other words, they were asked to develop a model of the internal works of the robot and to produce a hypothesis verifiable through experimentation. The robot allowed us to create a complete and interesting research situation. At this point, to avoid diverging explanations, we suggested to the students to focus on the role of the sensors.
Hands on. The production of models and tests was done in small groups (3-4 people) and we let the students form the groups by themselves. During this phase, we visited each group and discussed their ideas to assure the experiments will help deciding whether a given model should be discarded or not. It is important to remark that we did not correct the models, since any model is just an approximation. Thus, we just suggested changes in the model to simplify the verification process. After several minutes of group discussion, the groups presented their models, the experiment to be conducted on the robot and what they expected to observe. Since the number of available robots was enough, the students were able to perform their experiments. Otherwise the teacher could select a few experiments and try them in the robot.
The closure. The conclusion of the activity is left to the criteria of the teacher. In our case, due to the lack of time, we explained the controller and introduced Braitenberg’s ideas. In other circumstances, we would have requested the students to produce a short report of the experience and postpone the explanation to the next class.
The custom robotic platform is shown in Figure 2. Next, we describe the hardware that is needed to reproduce the robot exercise just described.
As mentioned above, the robot has two motors that can rotate individually at different speeds. Light sensors are placed at the right and left front side of the robot. These sensors can detect a light source within a range of about 10 cm and were previously calibrated by the students by measuring the output voltage as a function of the distance to a light source. The robot control program was implemented such that each light sensor is connected (via the controller) to one motor and influences its speed directly. Whenever a light sensor measures light the speed of the motor is reduced proportionally to the sensor’s measurement. The less light a sensor detects, the faster the motor rotates and vice versa.
A commercial Arduino control board (http://www.arduino.cc
) was used to control the robot. Figure 2 shows the components of the robot. Six rechargeable batteries are used for power supply. An USB communication unit is used for programming and monitoring the control board. Two light sensors provide sensory input to the control board which controls the two motors an
