Journal of Computer and Communications, 2014, 2, 8-16
Published Online May 2014 in SciRes.
How to cite this paper: Wu, F. and Williams, J. (2014) Design and Implementation of a Multi-Sensor Based Object Detecting
and Removing Autonomous Robot Exploration System. Journal of Computer and Communications, 2, 8-16.
Design and Implementation of a
Multi-Sensor Based Object Detecting
and Removing Autonomous Robot
Exploration System
Fan Wu1, Johnathan Williams2
1Computer Science Department, Tuskegee University, Tuskegee, AL, USA
2Electrical Engineering Department, Tuskegee University, Tuskegee, AL, USA
Email:, jwilliams6312@mytu.tuskegee. edu
Received March 2014
Copyright © 2014 by authors and Scientific Research Publishing Inc.
This work is licensed under the Creative Commons Attribution International License (CC BY).
Developing autonomous mobile robot system has been a hot topic in AI area. With recent advances
in technology, autonomous robots are attracting more and more attention worldwide, and there
are a lot of ongoing research and development activities in both industry and academia. In com-
plex ground environment, obstacles positions are uncertain. Path finding for robots in such envi-
ronment is very hot issues currently. In this paper, we present the design and implementation of a
multi-sensor based object detecting and moving autonomous robot exploration system, 4RE, with
the VEX robotics design system. With the goals of object detecting and removing in complex
ground environment with different obstacles, a novel object detecting and removing algorithms is
proposed and implemented. Experimental results indicate that our robot system with our object
detecting and removing algorithm can effectively detect the obstacles on the path and remove
them in complex ground environment and avoid collision with the obstacles.
Autonomous Robot Exploration System, Object Detecting and Removing Algo rithm, Multiple
1. Introduction
Developing autonomous mobile robot system has been a hot topic in AI area [1]. Many ideas have been pro-
F. Wu, J. Williams
posed and applied to autonomous robots. For example, Stanford Research Institute International AI Center de-
veloped Saphira [2]; Carnegie Mellon University Robot Institute developed Teambots [3]. Today autonomous
robots are attracting more and more attention worldwide in both academia and industry. The study of robotics
has increased considerably in the last decades and thanks to ongoing research both in the industry and education,
robots have become commercially available to the general public. Contests of football robotic teams [4], and
similar, are held annually and autonomous robots, as pets and home devices, such as dogs and vacuum cleaners,
are already available commercially. Some companies like Lego or VEX Robotics have commercial robotics kits
that contain everything you need to create your own robotic system.
Designing a robot’s behavior is a challenging task that researchers have been working for a long time. The
behavior-based approach to robot control has been the basis for many implemented robotics systems [5]-[7]. A
simple task such as moving an object from one point to another implies the intervention of a set of abilities that a
robot must be provided with in order to successfully achieve its goals. Some of these are: ability to perceive its
environment, ability to make decisions when planning the task, ability to navigate through the environment and
to avoid obstacles during the navigation, ability to execute the planned actions, and ability to recover from fail-
ure, among others. Clearly, the complexity of each individual’s ability, and therefore the overall robot’s beha-
vior design, is related to the complexity of the environment where the robot carries out the task. The higher the
complexity of the environment, the more challenging results the robot’s behavior design. Besides, the robot fea-
tures also play an important role in the robot’s performance of the task.
Path finding is an important issue and one of the most fundamental problems in mobile robotics [8] [9]. It is to
find a most reasonable collision-free path for a mobile robot to move from a start location to a destination in an
environment with obstacles. This path is generally optimal in some aspects, such as distance or time. However,
different regions usually have different road conditions, such as sandlot, grassplot and so on. How to find a rea-
sonable path meeting the need of above criterions and escaping from obstacles in such complex ground envi-
ronment is an open problem.
In this paper, we describe our experience on designing and implementing a multi-sensor based object detect-
ing and removing autonomous robot exploration system. The robot system described in this paper, 4RE, was de-
signed and implemented with the VEX Robotics Design System [10]. The VEX Robotics Design System is di-
vided into seven different “subsystems” where each one of the subsystems plays an important role in the design.
Once designed, all the systems were implemented together to create 4RE exploration robotic system. The pro-
gramming software used to program the robot was easyC. EasyC is a drag and drop application with predefined
functions in the C language.
The rest of the paper is organized as follow: Section 2 describes the VEX robotics design system briefly; Sec-
tion 3 presents our hardware architecture and the system design process; Algorithm design is presented in Sec-
tion 4 and our experimental results are discussed in Section 5. Finally section 6 concludes this paper with our
future directions.
2. VEX Robotics Design System
The VEX Robotics Design System is divided in to seven different subsystems that interact with each other to
create a robotic system. In order to design and implement a robot, some knowledge about each subsystem is re-
quired, which are presented in the following subsections [11].
2.1. Structure
The structure subsystem is very important because it forms the base structure of the robot. It can be considered
to be the skeleton of the robot, where the other subsystems are attached.
The structural components that form this subsystem include metal sheets, frames, nuts, screws, standoffs, and
more building parts. The VEX Robotics Design System comes with pieces of different shapes and sizes. How-
ever, it follows a standard hole-spacing system that expands the user’s options to create whatever shape is
The design of this subsystem has to be strong and firm but the weight of the robot always has to be kept in
mind depending on the robot’s tasks and challenges. Another important thing to consider is that the other sub-
systems will be added to the structure; therefore space has to be measured to successfully implement the re-
maining parts.
F. Wu, J. Williams
2.2. Motion
The motion subsystem is in charge of making the robot move, in other words it is like the muscles in our body.
Motion includes the motors that generate power as well as the wheels and gears that move the robot around,
transforming the power into work to help the robot achieve its goals. Just like with the Structure Subsystem,
wheels, gears, motors, and servomotors come with standardized holes that make the assembling process easier
and faster. This property is called openness and it gives the user the ability to add hardware without having to
make changes, or as less change as possible.
The design of this subsystem will vary depending on the needs of the robot and it will be strongly incorpo-
rated with the components of the Structure Subsystem. The number of wheels used on the base to move the ro-
bot and the number of motors to power the wheels will depend on how heavy or how big the structure of the ro-
bot is. Depending on the robot’s tasks; motors and gears need to be considered to create arms or other moving
parts on the robot’s structure.
2.3. Sensors
The Sensor Subsystem is what helps the robot detect different things in its environment. It is the eyes and ears of
the robot. Without this subsystem it would be impossible for a robot to operate autonomously. The VEX Robot-
ics Design System includes some sensors in the kit but different types are available online. The sensors included
are bumper sensors, limit-switch sensors, light sensors, ultrasonic sensors, and infrared light sensors.
The design of this subsystem starts with the structure because there are some sensors that require a specific
placement. Once the sensors have been installed, they will draw the power indirectly from the batteries through
the Microcontroller. Finally, The Microcontroller will receive the information from the sensors making the robot
behave depending on the code being executed.
2.4. Logic
The Logic Subsystem is the major component of the VEX Robotics Design System. The Microcontroller is the
only part that forms this subsystem but it is in charge of coordinating and controlling all the other subsystems. In
other words, it is the brain of the robot.
The Microcontroller interacts directly with the other subsystems. When designing the structure, a safe place
for the Microcontroller has to be considered because most of the other subsystems need to be connected to it.
The power from the batteries is drawn directly from the Microcontroller and it is then distributed among the
other subsystems. Once powered, the Microcontroller will control all the motors directly and process the infor-
mation gathered by the sensors.
2.5. Programming
The Programming Subsystem is not a physical system of VEX. It is the software application that tells the robot
how to behave. The programming software included in the VEX Robotics Design System is easyC. EasyC is a
drag -and -drop application with predefined functions in the C language, as shown in Figure 1. The functions are
“dropped” in a programming window and depending on the function, a window prompts asking the user to enter
the desired arguments. EasyC is a very easy to use tool but it seems to be designed for users with basic pro-
gramming skills.
3. Hardware Architecture
3.1. System Architecture
Define abbreviations and acronyms the first time they are the VEX Robotics vehicle is composed of several dif-
ferent components that interact with one another in recognizing an object in front of the vehicle, picking it up,
and setting it back down again. All of these subsystem components of the robot consist of the wheel and motor
system that moves the machine, the gear system that controls the movement of the arm, the robot arm itself, and
the attached claw device the can extend, grab, pick up, and set down objects. Each individual subsystem can be
further broken down into smaller details further in this report. In Figure 2, a visual representation of the robot is
shown. VEX Robotic tools and machinery, including metal frames, gears, nuts, screws, plastic wheels, motors,
F. Wu, J. Williams
Figure 1. Some predefined functions
in EasyC.
Figure 2. Hardware Architecture of VEX Robot. 1. Black
Motors; 2. Green—4 inch Wheels; 3. YellowGear System;
4. WhiteGear Rods/Axes; 5. GreyRobot Arm; 6. Orange
Robot Claw with Elbow Joint in Rest Position.
and the Cortex microcontroller. The claw itself came in a separate kit already assembled with its own motor and
simply needed to be attached to the arm.
The machine itself utilizes four large 4 inch plastic wheels that provide a strong base and balance for the robot
during movement. Eight motors are used in total with two of them being used to control the wheels.
Two pairs of the smaller gears are used to drive the four large gears on the robot arm with the last two gears
controlling the up and down movement of the robot arm.
For the sensors, three are used in total with two of them being the limit switches to control the range of mo-
tion of the arm and the third being an ultrasonic range finder that is attached on the claw component.
All of these various parts are wired to a single VEX Robotic Cortex microcontroller that acts as the “brain” of
the robot where it processes the code downloaded into its memory and follows the programming instructions.
3.2. System Design and Implementations
The robot is composed of various simple subsystems that when programmed as one, is able to accomplish dif-
ferent tasks, in this case being the simple objective of lifting and setting down an object in its path.
F. Wu, J. Williams
1) Base
Obviously one of the most important aspects of designing and building an object is constructing its frame or
base in which it will support the entire weight of the machine itself. A good strong base is necessary in robotics
as it provides structural integrity and durability when it’s out in the field accomplishing its assigned objectives.
The material used to create the base was several near foot long metal frames or beams that form a square shape.
The parts are screwed tightly together, ensuring that it can handle the stress and load of the other VEX parts that
would later be built on top along.
2) Wheels and Motors
The next stage of the building process was the appropriate selection and positioning of the wheels and motors.
As mentioned before four 4 inch plastic wheels were implemented in this design as they provided the robot with
enough structural support and weight when it is traveling over various surfaces. Other wheel types were at-
tempted before this and failed poorly as they simply were not big enough to hold the robot’s weight required,
resulting in the vehicle tipping over whenever it attempted to move. Also instead of four motors being used on
the wheels individually, two were decided to be adequate as they would rotate the back wheels, and providing
the necessary amount of force required to move the entire machine while the front two wheels give additional
stability for the robot’s frame and as well as aiding its movements whether forwards or backwards as well.
3) Gear System
A four pair gear system is necessary in controlling the up and down motion of the robot arm. Two pairs of
smaller gears are “driver” gears as they provide the initial torque or turning force, courtesy of the motors at-
tached to them, to rotate the two pairs of larger gears that are connected to the arm component. At first only a
two and later three pair gear system was used in this design, however it was quickly shown that the given torque
would not be sufficient in raising and lowering the robot as the total weight of the arm component and the po-
tential load it might carry was simply too heavy. However when a fourth pair of smaller type gears were pro-
vided, the gear system was successfully able to lift the arm up and down smoothly. Also, in conjunction with the
gear system, three motors were used to provide the torque, with a primary motor and two backups, a secondary
and tertiary motor. The primary and secondary motors were attached to the last row of gears as they could give
the system the most turning force when working together. The third motor was connected to the third row of
gears as any extra torque it gave would simply be insurance in case the load the arm was carrying was on the
heavy side.
4) Arm
Attached to the gear system was the robot arm itself. This section of the robot might have been the most com-
plicated and difficult area of the robot to design, build, and program as it consisted of the three smaller subsys-
tems that worked as one to provide the robot with a range of motion and abilities.
a) Arm bar
The “arm bar” of the robot was the heaviest part of the entire arm subsystem. It was directly attached to the
last pair of the gear system as it would be needed to raise or lower the whole arm component itself. In essence
one can liken it to the upper arm that is connected to the shoulder joint of the human body.
b) Elbow Joint
The second subsystem of the arm would be the “elbow joint” as similar to a human body it would bend like an
elbow to raise or lower the forearm. When the arm bar is raised, the elbow joint can adjust the number of de-
grees it bends downwards to aim the VEX robotic claw. In its rest position it lies flush on top of the arm bar.
c) Arm Extender/Claw
The final part of the robot arm is the arm extender and claw device that is attached to the elbow joint of the
robot. After the arm bar has either risen or lowered and the elbow joint has moved the appropriate amount of
degrees, the arm extender simply stretches outwards from the elbow joint with the claw attached at its front al-
ready open and ready to grab the object in the robot’s way. Once the item is in ensnared, the arm can simply be
pulled back into the elbow joint, where it then soon returns to its rest position. This process can easily draw
comparisons with the claw game machines that one utilizes to grab prizes in a box.
5) Sensors
For this project only three sensors were needed. There were two limit switches and an ultrasonic range finder.
The limit switches, were sensors that made a slight clicking nose when their bar is pressed at the right angle.
These are extremely useful in telling the robot the arm when to stop moving. One limit switch was attached on a
base bar just under the arm bar part to halt its movement with the second connected below the elbow joint when
F. Wu, J. Williams
it was in its rest position. The ultrasonic sensor contains two speakers in which one sends out a frequency pulse
and the second retrieves it. There is also a timer installed as it notes the time required for the sound travel back
to the sensor, and later takes that information and calculates the distance the frequency traveled. With this at-
tached to the claw, the robot was able to easily detect whenever an item stood in its way.
6) Microcontroller and Battery
The VEX Cortex Microcontroller is the device that makes all of the robots actions possible. As mentioned
before it “computes” or processes the commands it downloads, via USB cable, from the Easy CV4 language. It
along with the 7.2 V battery is attached to an empty space in the back of the robot. The motors are wired in mo-
tor ports 1 - 10 while the sensors are wired in digital input/output ports 1 - 12.
4. Obstacle Detecting and Removing Algorithm
The programming itself was somewhat simple and not really complicated although the lines of code was exten-
sive. The code basically instructed the robot to begin traveling in a straight line. However as soon as the ultra-
sonic range finder detects an object in its direction, the robot will immediately stop, back up slightly. The next
stage is critical as the robot will soon start to grab the object as it uses all three motors to raise the arm bar itself
to an appropriate angle. Next the program has the robot bend its elbow joint downwards where it will then open
the law to its maximum width and extend the arm downward where it will stop and the claw will close shut with
the object in its grasp. The elbow joint will then rise upwards until it hits the limit switch, signifying its “rest”
position. The arm extension will then immediately return to its shortened position with the object still in the hold
of the claw. At this stage there are several options one can make in the programming for the robot. The pro-
grammer can either change the last bit of code where it has the machine lower the arm and set the object back
down and move away or simply spin in other direction and then set the object down in a different spot. Either
one is acceptable as the robot demonstrates the ability to identify an obstacle, grab, and lift it. The code that will
be shown later in this report will be the former, where it simply sets the object back down and moves away.
Figure 3 shows the data flow of our object detecting and removing algorithm.
Move Forward
Check Ultrasonic Sensor
Distance < 10
Raise Arm, Lower Elbow
Joint, and Open Claw
Extend Claw
Close Claw, and Grab Object
Raise Arm/Elbow Joint
Retract Claw
Rotate Robot, and Release Object
Finished, and keep moving forward
Figure 3. The flowchart of the
F. Wu, J. Williams
The algorithm 1 labeled “Grab Obstacle Code” shows the pseudo code of our obstacle detecting and removing
Alg. 1: Grab Obstacle Code
1. SetMotor (3, 30)
2. SetMotor (6, 35)
3. while (1) //condition is always true
4. while (1)
5. Start Ultrasonic (1, 11)
6. sound = GetUltrasonic (1, 11)
7. if(sound > 10) //object is far away
8. printToScreen(“go\n”)
9. SetMotor (3, 30)
10. SetMotor (6, 35)
11. else (
12. SetMotor (3, 0)
13. SetMotor (6, 0)
14. bre ak //jump to next while loop
15. while (1)
16. printToScreen (“pickup\up”)
17. SetMotor (3, 0)
18. SetMotor (6,0)
19. SetMotor (3, 40)
20. SetMotor (6, 45)
21. wait (400) //wait for .4 seconds
22. SetMotor (3, 0)
23. SetMotor (6, 0)
24. SetMotor (1, 127) //raise arm
25. Wait (500)
26. SetMotor (9, 80) //raise arm
27. Wait (100)
28. Break
29. While(1)
30. SetMotor (7, 70) //lower elbow joint
31. Wait (550)
32. SetMotor (7, 0)
33. SetMotor (2, 0)
34. SetMotor (9, 0)
35. SetMotor (4, 60) //open claw
36. Wait (1000)
37. SetMotor (4, 0)
38. SetMotor (8, 80) //extend arm
39. Wait (750)
40. SetMotor (8, 0)
41. SetMotor (4, 60) //close claw
42. Wait (1000)
43. SetMotor (4,0)
44. SetMotor (8, 85) //shorten arm
45. Wait (1200)
46. SetMotor (8, 0)
47. Break
48. While(1)
49. Click = GetDigitalInput (3)
50. If (click == 1)
F. Wu, J. Williams
51. SetMotor (7, 120) //go to rest position
52. Else (
53. Break)
54. While(1)
55. SetMotor (3, 45) //rotate robot
56. SetMotor (6, 40) //rotate robot
57. Wait (500)
58. Break
59. While (1)
60. Hit = GetDigitalInput (2)
61. If (hit == 1)
62. SetMotor (1, 100) //lower arm
63. Else (
64. SetMotor (4, 60) //open claw
65. Wait (1000)
66. SetMotor (4, 0)
67. SetMotor (3, 40) //reverse
68. SetMotor (6, 45) //reverse
69. Wait (400)
70. SetMotor (4, 60) //close claw
71. Wait (400)
72. Break
73. While (1)
74. SetMotor (3, 45) //rotate robot
75. SetMotor (6, 40) //rotate robot
76. Wait (1000)
77. SetMotor (3, 0)
78. SetMotor (6, 0)
79. Break
80. While (1)
81. SetMotor (7, 0) //end program
82. SetMotor (2, 0) //end program
83. SetMotor (9, 0) //end program
5. Experimental Results
We constructed an environment to test our algorithm. The first environment consists of an open space sur-
rounded by four walls and a line on the ground, as Figure 4 shows. This environment is designed to test our ob-
stacle detecting and removing algorithm we designed above. Many trials and tests were ran to figure out the ap-
propriate rotating speeds, measured distances to objects, and correct arm movement to grab and pick up the de-
sired object. The robot is best suited to accomplish this task on an even and flat surface where it can easily
detect and get to an object. As of right now the robot will only sense objects that are in the path of the ultrasonic
sensor. As of now it does not sense obstacles on its flanks. Also the code is easily adjustable when one is trying
to make the robot grab objects of various heights, and lengths. The experimental results show that our robot can
detect the obstacles on the path precisely and remove the obstacles automatically with our algorithm.
The 4RE robot system is shown in Figure 5.
6. Conclusion and Future Work
In this paper we have designed, created, and programmed a robot using a wide array of sensors and motors to
detect foreign objects in its path of direction and move the offending item out of the way. It was a struggle first,
but the robot was successful in grabbing and setting the object out of its way. It should have no problem accom-
plishing this task with several types of different items provided they are light of weight and not to large or small.
However, this may present future problems in a real world situation. Since not all will be so easily removed
F. Wu, J. Williams
Figure 4. Test Environment for the algorithm.
Figure 5. The 4RE robot system.
from their positions as they may come in various shapes, weights, and sizes that would make it difficult for the
robot as its sensors would need to be adjusted to distinguish various objects and the best way to move them.
Future work will involve adding more types of resistors to overcome these limits along with improvements to
the current robot’s design so that any perceived flaws or hindrances to its ability will be immediately corrected.
[1] Fernandez, J.A. and Gonzalez, J. (1999) The NEXUS Open System for Integrating Robotics Software. Robotics and
Computer-Integrated Manufacturing, 15, 431-440.
[2] Konolige, K. and Myers, K. (1998) The Saphira Architecture for Autonomous Mobile Robots, SRI International.
[3] T. Balch, TeamBots, 2000.
[4] Lenser, S., Bruce, J. and Veloso, M. (2001) CMPack: A Complete Software System for Autonomous Legged Soccer
Robots. Proceedings of AGENTS’01, ACM Press, 204-211.
[5] Balch, T. andArkin, R.C. (2002) Behavior-Based Formation Control for Multi-Robot Teams. IEEE Transactions on
Robotics and Automation, 14, 926-939.
[6] Mataric, M. (1997) Behavior-Based Control: Example from Navigation, Learning, and Group Behaviors. Journal of
Experimental and Theoretical AI, 9, 323-336.
[7] de Leeuw, J.R. and Livingston, K.R. (2009) A Self -Organizing Autonomous Prediction System for Controlling Mobile
Robots. International Conference on Automation, Robotics and Control System, 123-129.
[8] Cox, I.J. and Wilfong, G.T. (1990) Autonomous Robot Vehicles, Springer Verlag.
[9] Borenstein, J., Everett, B. and Feng, L. (1996) Navigating Mobile Robots: Systems and Techniques, A. K. Peters, Ltd.,
[10] VEX Robotics Design Systems.
[11] VEX Inventor’s Guide.