Mapping and Exploring Autonomous Robot

Team Members:

Andy Chacon, Carmen Arroyo, Luis Macias

 

Objective

M.E.A.R. is an undergraduate project at the University of Texas at El Paso focused on developing a six-legged, autonomous walking robot that combines the benefits of sophisticated motion and adaptive control in a single platform with many practical applications.  The purpose of this project is to build an autonomous robot that will have the capability of exploring an unknown area and map key points of interest.

Abstract

Robots have recently been used to search areas where humans and animals cannot explore.  One application of robots involves removing the human risk factor from a hostile or uninviting situation.  A potential use for this design would be in planetary exploration.  Using data taken by robots, scientists can command the unit to go to rock and soil targets of interest. Initial targets may be close to the landing sites, but later targets can be further away.  The use of robots in planetary exploration will expand our knowledge of regions otherwise unapproachable by humans. 

Project Description and Operation

          A six-legged autonomous walking robot was built in order to map and explore unknown areas.  Mapping the area consists of marking the positions of obstacles so the robot can distinguish between accessible and inaccessible points.  Various sensors are used to determine these obstacles.  The microcontroller accepts inputs from the sensors in order to recognize land formations and make note of their existence and location.  The environment was needed in order to simulate the obstacle the robot could possibly encounter. 

 

 

Method of Completion

The objective of the robot is to map an entire area of a predetermined size.  Mapping the area consists of marking the position of obstacles so that the robot can distinguish between accessible and inaccessible points.  Various sensors such as sonar and pyroelectric sensors are used to determine these points.  For the objective, the microcontroller must accept inputs from sensors to recognize land formations and make note of their existence and location.  It must also keep track of the terrain it has covered in order to precede.

 

The following block diagram depicts the path of operation that is being followed.

 

Modular Description of Block Diagram

 

Environment

The environment was needed in order to simulate the kinds of obstacles and points of interest that the robot could possibly encounter.  The environment itself consisted of two eight foot by four foot by half-inch plywood.  The two boards were placed next to each other in order to create a total area of sixty-four square feet.  Since the hazardous obstacles needed to be powered by a 120-volt AC power supply wiring needed to be run. Since we did not want to deal with the problem of having the robot trip over the wires, a groove was cut so that the wire could run smoothly under the main area without causing any problems. Then a small hole was cut in the board allowing the wire to come up and power the light bulbs that are used.

Points of Interest and Hazardous Obstacles

Points of Interest were made out of plastic. The only requirement was that they be flat. This allows the ultrasonic sensor to detect them more easily. Hazardous Obstacles consisted of a light bulb with enough wattage to create enough heat for the pyroelectric sensor to detect. After some testing it was found that a standard sixty-watt light bulb created enough heat for the sensor to detect.

Sensors

At the beginning of the project the original design called for four different types of sensors to be used. After the implementation of the ultrasonic sensor it was found that the other sensors were not needed. But after some testing and in an effort to correct the inaccuracies in positioning the compass module was added to the design.

The Devantech Ultrasonic Sensor is the primary sensing unit on the robot. It uses ultrasonic sound to locate objects in front of it. It has a capability of detecting objects from three inches to thirty inches in front of it. In our case we implemented it so that it would wait until an object was five inches in front. Once it was set off, it then turned on the pyroelectric sensor.

The Eltec Pyroelectric sensor senses differences in the surface temperature of an object in comparison to the background temperature.  It has a window of difference that can be adjusted using the code in order to make it more or less sensitive.

The Devantech compass module was used in order to better define position.  It uses the magnetic field of the earth to create a three hundred and sixty degree representation of the standard compass that we use. We defined zero degrees as north and a clock wise increment was used to represent each pole. East being approximately ninety degrees, etc.    

Microcontroller

The OOPic provides an Object-oriented language model designed to interact with the electrical hardware components that you attach to the OOPic. We designed our hardware interface in software by creating Objects and setting their properties to define their behavior and interaction with hardware. These Objects also can be interconnected to form a Virtual Circuit. It can be programmed using Basic, C, or Java syntax.

Servo Controller

 

Two Scott Edwards Servo Controllers were used to control the twelve servos needed for leg movement.  Controlling servos from a microcontroller is not difficult, but as the number of servos that need to be controlled increases, the microcontroller can become bogged down servicing the servos, leaving no time for monitoring sensors or other I/O. The Serial Servo Controller takes care of the timing and leaves the microcontroller free to deal with other issues.

 

Servos

 

          The HS-422 servos were used for the robot.  They are made up of a DC motor, gear reduction, output shaft with position feedback, and a control PC board all built into a small rectangular enclosure. The output shaft is limited to approximately 180 degrees of rotation, but is normally used in a 90 degree range. The system is proportional, so the output shaft can be moved quickly or slowly to any position.  These servos are strong, light weight, reliable, yet easy to setup and control.

 

LCD

 

            The Scott Edwards LCD was used in order to display messages which corresponds to the robots actions.  The LCD was also used to display the positions of the obstacles as they are encountered.

 

Division of Tasks

Issues

The project has many issues dealing with the accuracy of the robot.  This means that the robot will not always be in the position that it is supposed to be in so this leads to many other errors. These errors include mapping errors and final position errors. In the mapping errors it is found that since the positioning of the robot is off, the places where the obstacles and points of interest should have been mapped are incorrect. Secondly, the final position is also not correct, but in most cases it is found to be within our specified amount of error, which is one foot. This means that the robot has to be within one foot of the proposed final position.

Conclusion

 

Although some problems were encountered throughout the year, the team worked together and pulled through.  At this point, this prototype is able to identify objects in front of it, distinguish between points of interest and hazardous obstacles, and complete the path.  This project will be improved over the years and also used as a motivational tool for upcoming future engineers.

Sponsor

This project was sponsored by Benjamin C. Flores Ph.D, Associate Professor of Electrical and Computer Engineering at the University of Texas at El Paso. At the request of Dr. Flores this project was pursued in order to develop a physical attraction that could allure younger students to the fields of engineering and science. It is also a project that can be enhanced and developed in the future by other senior project teams.