JSET: Journal of Science & Engineering Technology Vol. 3 Issue 2 (December) 2016 pp. 92 – 96

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Developing Spherical Robot at Universiti Kuala Lumpur

Murniwati Anwar1,a, Lukman Hakim Omar2,b, Yusof Mohd Ekhsan3,c Muhammad Nazwan Hafiz Mohd Nadzir4 Mohamad Sukri Mohamad Kasim5

Department of Industrial Automation, Universiti Kuala Lumpur Malaysia France Institute,

Section 14, Jalan Teras Jernang, 43650 Bandar Baru Bangi, Selangor, Malaysia E-mail: murniwati@unikl.edu.my a, lukmanhakim@unikl.edu.my b, yusofme@unikl.edu.my c

Abstract — The purpose of this paper is to share experiences in developing a spherical robot at Universiti Kuala Lumpur. There are two development phases; the first phase is designing several types of mechanical structure and the second is to develop the control algorithms and the third is to integrate with cameras and wireless equipment to make the robot more useful. The new mechanical structure improvised the robot movement with different types of terrain and the control algorithm is improving the system stability. The robot is controlled wirelessly and equipped with sensors and camera. It is also integrated with mobile android-based application.

Keywords—spherical robot; mechanical structure; control alogrihm

I. INTRODUCTION

Spherical robot or ball robot becomes an interest study under the Final Year Project Thesis in Universiti Kuala Lumpur Malaysia France Institute due to its shape. It is capable to roll faster in any terrain. Several design was made to make the robot stable and easy to control such as a pendulum design, where permanent shaft locate through the center of the spherical robot and with a pendulum around the shaft, hamster ball design and others [1]. The spherical robot design in UniKL was based on hamster ball design. The first robot design is successfully built but due to the thin robot casing, the robot casing crack during the testing. In order to overcome the problem in the robot structure, several development phase have been made including improving the stability of the robot and in order to make the robot more useful, added-value accessories such as camera for surveillance and android smartphone for wireless control are included in the package.

The first robot was built with a rotating shaft inside the spherical casing robot. A shaft is connected in the middle between the casing, controller and battery. It uses Arduino UNO (Atmega328P) as the controller. A DC motor is use to drive the prototype forward and reverse by rotating the outer

sphere case. Servomotor is use to steering the prototype to the right and to the left by moving the load (weight).

The center of gravity of the robot has been determined to improve the stability of the robot. Inertial Measurement Unit (IMU) 5DOF sensor with Gyro and accelerometer sensor embedded together was selected instead of encoder as the feedback signal to give the tilt angle and the acceleration rate to the controller.

II. MECHANICAL DESIGN

The first design of spherical robot prototype as shown in Figure 1 was built by hollow plastic sphere with join from two half hollow sphere and rotating shaft inside the spherical casing of robot. The advantages of spherical robot are easy to roll forward / backwards and turn left / right, reduce power consumption due to spherical shape and fully covered design will have the advantage to protect the inner part, electronic and mechanical from any disturbances. The disadvantage of this design is difficult to troubleshoot the internal parts due to outer cover and potentially to cause defect (crack or surface bend) to its spherical surface. The robot movement is controlled via wireless remote control using 49MHz frequency.

Figure 1: First design of sp

JSET: Journal of Science & Engineering Technology (Special Issue: August) No. 01 (2016) pp. 92 – 96

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herical robot prototype

The second phase of the project is to enhance the mechanical part. The 60cm diameter of sphere case made by aluminium plate is used to strengthen the robot structure. Most of the part that is used in this version is remain the same components. In addition, the spherical robot use android smartphone as a remote control to control the movement. Figure 2 shows the internal structure of the spherical robot

.

Figure 2: Spherical robot internal structure design

III. ELECTRICAL DESIGN Accelerometer sensor is used to senses the acceleration

forces due to robot movement while gyro sensor is used to sense the angular velocity. Combination of both sensors signal will get the angular position which is possible to measure acceleration and gravitational placement in X, Y and Z axis.

DC motor is use to move the prototype forward and

reverse direction by rotating the outer sphere case and at the same time, servo motor is use to steering the prototype to the right and left by moving the load (weight).

Inertial Measurement Unit (IMU) with 5 Degree of

Freedom (DOF) is used to measure the rate of change of X-axis, Y-axis and Z-axis, acceleration for X-axis and acceleration for Z-axis. Kalman Filter method is applied to estimate the measured value.

The second design of the spherical robot is improved to achieve the project objective in terms of durability and stability. The wide diameter of that spherical case will create better space for internal casing design.

Figure 3: Second design of spherical robot

Material selection comparison

Table 2 shows the comparison of few materials to be used. The cover that protects the spherical robot must use a strong material type with light in mass. The material selection of parts for the prototype is made due to mechanical properties of prototype such as the strength, stress and weight of the part. Therefore, in the third phase development, the suitable material used for the mechanical structure is aluminium.

Table 2: Comparison of materials

Materials Advantage Disadvantage

Acrylic •Light •Hard •No corrosion

•Cannot be deform •Difficult to cut

Aluminium (Alloy)

•Light (low density of materials) •Easy to deform •High melting point •Strong

•Difficult to cut using hacksaw •Less stronger than stainless steel

Stainless

steel

•Strong •Corrosion resist

•Mass weight •Difficult to cut •Difficult to deform

Zinc plates

•Strong •High melting point

•Easy to bend and change in shape. •Mass weight •High cost •Difficult to fabricate.

Driving and steering design Driving principles is important criteria that should be added

for all types of mobile robot. Since the spherical robot can be considered as a part of mobile robot, the driving principles is selected based on the most common application.

The steering was design to overcome the problem in

turning the spherical robot either left or right. In addition, the idea to create this steering principle comes when the situation happen if spherical robot faced the obstacles during its operation. During that time, the robot must have the ability to encounter the obstacles rather than collide with it. The

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INTERNAL COMPONENT

DRIVING

OPERATION: foward/backwards

ACTUATOR : DC motor

STEERING

OPERATION: Turn left / right

ACTUATOR : Servo motor

descriptions summary for driving and steering for this project is presented in Figure 4.

Figure 4: Driving and steering descriptions

To drive the rolling shaft, DC motor is used and the position of DC motor is located at the center of ball robot and connected with driving shaft via V-belt. In the same time, each end of driving shaft is connected to a disk joint. To drive the spherical robot, the gear and belt is used to create the desired design as shown in Figure 5.

Figure 5: Driving design

The servo motor is used to drive the steering shaft. Figure 6 shows the design of steering concept for this project. The servo motor will rotates with certain rotation that may result of angles γ values. In this case, batteries as pendulum is act to shift the robot either left or right with certain value of angle γ. However, in this situation, the maximum rotation angle of servo motor is based on the command that programmed on microcontroller. Figure 7 shows the tilt position left and right of spherical robot.

Figure 6: Steering design

Figure 7: Tilt position of spherical robot

Electrical design

The controller circuit layout in Figure 8 shows the connection of controller and input output devices that control the spherical robot. Arduino UNO ATmega328P is the controller that have 14 digital inputs / outputs (where the project uses discrete input for signal from wireless joystick controller and discrete output for DC and servo motor). The robot movement either forward / reverse or right / left will be controlled from joystick. Gyro sensor will determine the error angle and automatically respond to the position of the robot. The objective using this gyro sensor is to balance the movement of robot. Signal from joystick controller to the controller is using discrete signal and it will be process to produce discrete output and generate servo motor to tilt the load (weight) according to signal.

Figure 8: The controller circuit layout

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IV. RESULT

The spherical robot is tested to move on several type of

terrain. The results from the testing are reviewed by referring the combination of driving and steering principle.

A. Speed motion test of spherical robot i) Floor (Flat surface)

Table 3: Speed motion test at floor (Flat surface)

Distance/m Time/s Speed/(ms-1) 3 5.8 0.517 3 6 0.5 3 5.9 0.508

Average 0.508

Figure 9: Spherical robot at flat surface floor Table 3 shows the speed motion of spherical robot on the flat surface floor in 3-meter distance movement with different time taken to move. Figure 9 shows the actual view of floor (flat Surface).

ii) Grass (Flat surface)

Table 4 shows the speed motion of the spherical robot on the flat surface grass in 3-meter distance with different time taken to move. Figure 10 shows the actual view of grass (flat Surface).

Table 4: Speed motion test at Grass (Flat surface) Distance/m Time/s Speed/(ms-1)

3 6.7 0.448 3 6.5 0.462 3 6.9 0.435

Average 0.448

Figure 10: Spherical robot at flat surface grass

iii) Uneven surface

Table 5 shows the speed motion of spherical robot on uneven surface grass in 3-meter distance with different time taken to move. Figure 11 shows the actual view of uneven surface grass.

Table 5: Speed motion test at uneven surface Distance/m Time/s Speed/(ms-1)

3 8.2 0.366 3 8 0.375 3 8.3 0.361

Average 0.367

Figure 11: Spherical robot on uneven surface grass

B. Movement Test of spherical robot

Table 6: Stability movement observation Surface type Description/Observation

Forward / Backward Movement

Left / Right Turn

Floor (Flat surface)

Good. The spherical robot move with better

movement.

Good. The spherical robot turn with better

movement.

Grass (Flat surface)

Moderate. The spherical robot move

with moderate movement.

Moderate. The spherical robot turn

with moderate movement.

Uneven surface

Moderate. The spherical robot move

with difficult movement.

Moderate. The spherical robot turn

with difficult movement.

From Table 6 shows the observation of stability movement of spherical robot. The spherical robot most effective on floor (flat surface) compared to moving on grass and uneven surface.

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C. Mechanical Structure Observation Result

From the observation, the structure of mechanical is able to maintain their durability. Table 7 shows some problem that happen during testing the spherical robot:

Table 7 : Problems observation Problems Causes of problem

Camera cables stuck at shaft

• Limitation of the space in the robot cause the cable to stuck at the shaft during its rotation.

Steering gear slipped

• Too much of torque produce by servo motor caused the gear to slip regularly.

• The a l i g n m e n t o f s h a f t w a s s l i p d u e t o h i g h vibration to internal casing.

• The shaft gear and servo gear i s not properly attached.

Belt often slip • Too much of torque produce by DC motor caused the belt to s l i p . This w i l l reduce the power transmission for driving shaft.

• The belt connection between dc motor gear and rolling shaft gear not properly tighten during installation

D. Limitation Of The Project

The objective of this project is to design a suitable

mechanical structure and algorithm for the robot. For mechanical structure, the design of prototype dimensions must be precise and accurate because it will influenced the movement of the prototype. In example, the spherical shape of outer case. It is difficult to find something that is suitable for spherical shape material from hard plastic. In the end, the spherical hard plastic is used as the casing although the accuracy has to be sacrificed a bit

The limitation of the prototype also found in the

movement. The prototype is not turning or tilts to the left or right accordingly. The angle of the load in prototype in order to tilt left or right is small and not enough to turn the prototype during movement. The outer case of prototype can be improved by add studs or rubber skin for more grip, dampens variation and provides traction.

The other problem is about the cable from camera to power source. Base of the camera need to be static when the prototype move but because of the cables, it only can move for a limited distance only

V. CONCLUSION

In conclusion, project of spherical robot is focused on developing of mechanical aspects. These design are taken by considering the aspect of stability in the movement of the spherical robot. The mechanical part of this spherical robot should be design with certain materials that fulfil the desired criteria for stability motion. At the same time, the design must consider on its application whereas the prototype must have the ability to turn with better motion either at different applications. In this project, the spherical robot have managed to be design with suitable mechanical structure with combination of steering and driving principle.

We are able to achieve the objective of project that need to

improve locomotion of spherical robot, to improve mechanical structure and several terrain or surface and purpose of spherical wireless communication for surveillance and monitoring. Unfortunately, there are still limitations in the project.

Generally, we still achieved the objective of spherical

robot.

VI. REFERENCES

[1] A Richard Chase,; and Abhilash Pandya,; Review of

Active Mechanical Driving Principles of Spherical Robots.

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