DESIGN AND DEVELOPMENT OF AUTONOMOUS ROVER MOBILE ROBOT

Hazel M. Aboga-a, Armando D. Alvarez, Mark Chester M. Cuadra, Charlane T. Dagang and Ruvel J. Cuasito, Sr.

College of Industrial and Information TechnologyMindanao University of Science and Technology

Lapasan Highway, Cagayan de Oro City, 9000 Philippines

This paper describes an autonomous rover mobile robot that could navigate itself in known and partially known environments. The robot is consist of six wheels that are individually controlled by a servo motor for steering enabling the robot to turn in place. The rover uses the rocker bogie design with each rockers connected to a differential mechanism located inside the body. The differential mechanism is consist of three bevel gears meshed together to produce a counter rotating motion of the shafts. This maintains the traction force between the wheels and the ground hence enables the rover to climb on obstacles up to 1.5 times its wheel diameter. Obstacle detection was enabled by using an infrared proximity-collision sensor that detects object up to 25cm in range. The sensor is mounted on a servo in order to find a path whenever an obstacle is detected. The robot uses the Gizduino X microcontroller to control multiple subsystems of the design.

Keywords: microcontroller, autonomous mobile robot, rover, Rocker-Bogie, Differential Mechanism, infrared sensor

1. Introduction

The history of autonomous mobile robotics research has largely been a story of closely supervised, isolated experiments on platforms which do not last long beyond the end of the experiment. There are no

universally accepted definitions that encompass notion of mobility, programmability, and the use of sensory feedback in determining subsequent behavior.

The major challenge for autonomous mobile robots is navigation. Several approaches have been proposed to address the problem of motion planning of a mobile robot. It is often decomposed into path planning and trajectory planning. Path planning is to generate a collision free path in an environment with obstacles and optimize it with respect to some criterion. Trajectory planning is to schedule the movement of a mobile robot along the planned path. If the environment is a known static terrain and it generates a path in advance, it is said to be off-line algorithm. It is said to be on-line if it is capable of producing a new path in response to environmental changes.

The intelligent autonomous systems of motion planning problem has been studied thoroughly by the robotics research community over the last years. The basic feature of an autonomous mobile robot is its capability to operate independently in unknown or partially known environments. The autonomy implies that the robot is capable of reacting to static obstacles and unpredictable dynamic events that may impede the successful execution of a task.

To achieve this level of robustness, methods need to be developed to provide solutions to localization, map building, planning and control.

The robots are compelling not for reasons of mobility but because of their autonomy, and so their ability to maintain a sense of position and to navigate without human intervention is paramount [1].

Most of the applications require a robot to work in relatively unstructured and unknown environments. Navigational task of moving the robot from one location to another is usually operated by humans. One crucial drawback of this approach is the large energy requirement of high bandwidth communication which consumes most of the energy that the robot carries around. Moreover, employing qualified operating personnel is costly [2].

The design and development of this mobile robot will enhance learning concepts on autonomous mobile robot navigation and control algorithm. Moreover, it would portray a mobility system that is capable of obstacle climbing that could be used in the discussion of mechanical concepts in the academe, and lastly it would entice the community to engage in scientific and technological courses.

The general objective of the study was to develop an autonomous rover mobile robot that can navigate in partially known or unknown environment. Specifically, the study aimed to:

(a) Design an autonomous rover mobile robot with respect to the requirements and constraints of the system.

(b) Develop an autonomous rover mobile robot relative to the established design parameters used in the system.

(c) Implement the control algorithm developed for the rover mobile robot to navigate itself effectively in response to its environment.

(d) Evaluate the performance of the rover mobile robot according to the established test instruments.

2. Scope and Limitations

The premise of the study included the design, development, and evaluation of an autonomous rover mobile robot that could navigate itself in partially known or unknown environments. The fundamental control function was anchored on the ability of the robot to avoid obstacles. Infrared Proximity-Collision sensor was the primary sensor used in the rover mobile robot for obstacle detection and navigation. A camera was mounted on the rover to take pictures of the environment it traverse. Servo motors were used as the prime mover of the prototype and for steering system.

3. Methodology

3.1 Conceptual Design

The design of the robot was a rocker-bogie six wheel configuration as shown in Figure 1. Each wheel was driven independently by a servo motor. Each servo motor that is driving the wheels was connected to another servo motor for steering.

Figure 1. The Overall Design of the Prototype

The design was consists of two rockers hinged to the sides of the main body as shown in Figure 2. Each rocker was connected to a steering servo at one end and a smaller frame at the other end. Two servo motors were attached to the end of each of these small frames. The numbers 1 to 6 are used to identify the servo motors for programming and pin assignments.

Figure 2. Top View of the Prototype

The connection between symmetrical lateral mechanisms was provided by a differential mechanism which is located inside the body as shown in Figure 3. This mechanism provided an important mobility characteristic of the rover: one wheel can be lifted vertically while other wheels remain in contact with the ground. This feature

provides rock climbing capability for the rover. It can climb obstacle 1.5 times its wheel diameter in height.

The mechanism was consist of three bevel gears which were meshed together to create a counter rotating shaft so that when one side goes up, the other side goes down.

Figure 3. Differential Mechanism

3.2 Design Components

Figure 4 shows the dimensions of the body of the rover. The body was 200 millimeters long, 100 millimeters wide and 45 millimeters high. A 10 millimeter hole was drilled at the center of the sides of the body for the connection of the shafts.

Figure 4. The Body

Figure 5 shows the dimensions of the rocker. The rocker was bended at an angle of 151 degrees. Its horizontal distance was 215 millimeters. A shaft of 70 millimeters length was connected with the rocker. The height of the rocker with respect to the horizontal axis was 50 millimeters. A 10 millimeter hole was drilled in the rocker for the shaft. Another hole of the same dimension with the hole of the servo frame was incorporated for the connection of the rocker and the servo frame. Four 2 millimeter holes were included for the connection of front steering servo mounting frame.

Figure 5. The Rocker

Figure 6 shows the dimensions of the servo frame. The servo frame was 180 millimeters in length and 25 millimeters in width and height. Two steering servo motors were attached in the servo frame for steering. Each servo motor shell was 40 millimeters long. The servo motors were attached through the holes with 2 millimeters in diameter and center distance of 5 millimeters from the servo shell. A 6 millimeter hole was situated at the center of the servo frame for the connection with the rocker.

Figure 6. Servo Frame

Figure 7 shows the dimensions of the front steering servo mounting frame. The frame was 68 millimeters in length and 25 millimeters in width and height. A steering servo motor was attached in the frame for steering. The servo motor shell was 40 millimeters long. The servo motor was attached through the holes with 2 millimeters in diameter and center distance of 5 millimeters from the servo shell. Four 2 millimeter holes were included in the front steering servo mounting frame for the connection with the rocker.

Figure 7. Front Steering Servo Mounting Frame

Figure 8 shows the dimensions of the rotational servo mounting frame. The frame was 68 millimeters in length and 25 millimeters in width and height. A rotational servo motor was attached in the frame to drive the wheels. The servo motor shell was 40 millimeters long. The servo motor was attached through the holes with 2 millimeters in diameter and center distance of 5 millimeters from the servo shell. A 5 millimeter hole was situated at the top of the frame for the connection with the steering servo motor.

Figure 8. Rotational Servo Mounting Frame

Figure 9 shows the dimensions of the sensor protector. The component had a length of 50 millimeters, width of 60 millimeters and height of 25 millimeters. Four 2 millimeter holes were drilled at the top to attach the sensor of the robot. A hole of 5 millimeters in diameter was located at the bottom for the mounting of the sensor protector in a servo motor.

Figure 9. Sensor Protector

Figure 10 shows the dimensions of the sensor servo mounting frame. The frame was 55 millimeters long, 38 millimeters wide and 12 millimeters high. An area of 40mm x 18mm was cut at the middle for the mounting of servo motor. The frame was also cut at one end 7mm x 7mm for the attachment of the frame to the body of the rover. Four 2 millimeter holes were drilled for the attachment of the servo motor to the frame.

Figure 10. Sensor Servo Mounting Frame

Figure 11 shows the dimensions of the circuit protector. The circuit protector was used to cover the circuitry of the robot. The protector is 130 millimeters in length, 100

millimeters in width and 45 millimeters in height.

Figure 11. Circuit Protector

Figure 12 shows the dimensions of the servo spacer. The servo spacer was used to make a vertical clearance between the steering servo motor and the rotational servo motor. The spacer had a diameter of 10 millimeters and a height of 15 millimeters. The component was hollowed at the center 2.5 millimeters in radius. Two holes of radius 0.5 millimeters are included for the attachment of the spacer to the steering servo motor.

Figure 12. Servo Spacer

3.3 Control Algorithm

The sensor was used to detect obstacle. When an obstacle is detected, the computer system of the rover will give execution task

to the actuators in order to avoid the obstacle and move the robot to a collision free path. The operation of the robot was to stop if the sensor detects an object or obstacle. The robot will then look left and right to check which path is free from obstacle. The robot then moves to the selected path.

3.4 Evaluation

Evaluation was done in order to measure the performance of the prototype. The performace was evaluated by the following parameters:physical appearance, overall performance, mobility, automation complexity and marketability.

The parameters was evaluated through a survey on some engineering and technology students and experts by means of a survey questionaire. Likert scale was used as the statistical tool for measurement of the parameters. The following responses will be used: very poor, poor, fair, very good, excellent. Likert scale responses are to be treated as ordinal data.

4. Results and Findings

4.1 The Developed Rover Mobile Robot

Figure 13 shows the finished prototype of the study. It involved the interconnection of all the design components that includes the differential mechanism, servo motors, frames, sensors and camera.

Figure 13. The Finished Prototype

Figure 14 shows the Rocker Bogie mechanism of the prototype. The rocker was attached to the side of the body with one end connected to the front wheel steering servo and the other end connected to the servo frame.

Figure 14. The Rocker Bogie Mechanism

Figure 15 shows the differential mechanism of the rover mobile robot inside the body. The mechanism was consist of three bevel gears meshed together in order to produce a counter rotating motion of the shafts.

Figure 15. The Differential Mechanism

4.2 Evaluation

The respondents for the evaluation are selected students from the Electro-Mechanical Technology, Computer Engineering and Faculties of the related courses. There are fifteen (15) respondents, five (5) Electro-Mechanical students, five

(5) Computer Engineering students and five (5) faculties of related courses. The rover mobile robot was evaluated according to the rates indicated below.

Table 1 shows the average mean responses of the respondents on the evaluation parameters used in the study. The mobility has the highest average mean response of 4.133. Aesthetics has the lowest average mean response of 3.900 which was mainly contributed by the harnessing of the wires in the system. Performance, Automation Complexity and Marketability had average means of 3.925, 3.967 and 3.960 respectively.

Table 1. Summary of the Average Mean Responses of the Evaluation Parameters

Parameters Average Mean

Adjectival Rating

Aesthetics 3.900 Very Good

Performance 3.925 Very Good

Mobility 4.133 Very Good

Automation

Complexity

3.967 Very Good

Marketability 3.960 Very Good

Each of the average mean of the evaluation parameters is within the range of the 3.5 – 4.4 which has an adjectival description of very good. Figure 16 shows graphical representation of the average mean responses of the respondents on the evaluation parameters used in the study.

Figure 16. Graphical representation of mean responses

5. Conclusions and Recommendations

The robot was perceived to be very good in all design aspects. Therefore, the robot was functional and met the desired objectives of the study based on the evaluation conducted on the autonomous rover mobile robot.

The researchers recommended the following based on the evaluation results of the study:

a. The harnessing of the wires of the robot is needed to be improved since it has the lowest rating in the evaluation.

b. The programming concept is needed to be improved since the researchers used basic programming.

c. The materials used in the prototype must be economical in order to reduce the total cost in developing the project.