This document describes the design and development of a modular humanoid arm based on RC servo motors. The arm has 6 degrees of freedom from shoulder to wrist using RC servo motors at each joint. A PIC18F4520 microcontroller controls the servo motors through a controller board. The arm is able to perform motions mimicking human arm movement like pick and place tasks. The modular design allows replacing the pneumatic suction gripper with a multi-finger gripper for increased dexterity.

1. International Journal of Advanced Research in Engineering RESEARCH IN ENGINEERING
INTERNATIONAL JOURNAL OF ADVANCED and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME
AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 7, November - December 2013, pp. 156-160
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IJARET
©IAEME
DESIGN AND DEVELOPMENT OF MODULAR HUMANOID ARM BASED
ON RC SERVO MOTOR
Kapse S. S.1,
Dr. S. S. Ohol2
1
2
Department of Production Engineering, College of Engineering Pune, India
Department of Mechanical Engineering, College of Engineering Pune, India
ABSTRACT
This paper presents a modular humanoid arm based on RC servo motor, it consist of
mechanical design part and control part. The modular humanoid arm has 6 Degree of Freedom (DoF)
from shoulder to wrist and uses RC servo motor at each joint to perform motions that mimic human
arm motions. The efficient movement of humanoid robot arm depends on the servo controller that
control servo motors at wrist, elbow, shoulder and multi finger gripper. Use of RC servo motor
makes design compact and includes low power dissipation, high power density, and high control
precision. Modularity comes in design, if the multi finger gripper replaced by pneumatic suction
gripper. PIC18F4520 microcontroller is used with MICROC for PIC compiler.
KEYWORDS: Anthropomorphic, Modular arm, MICROC for PIC, RC servomotor.
I. INTRODUCTION
Humanoids are robots that are designed for social and interactive operations. Humanoid
robots have been developed by many research groups to perform motions that mimic human motions
for assisting human activities. In order to behave in anthropomorphic manner, the humanoid arm
should have enough Degree of Freedom. For arm, 6Dof from shoulder to wrist and for multi finger
gripper it varies from 5 to 24 depending on type of motion required. The design of Humanoid Robot
is shown in Fig 1.
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2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME
Figure 1: Design of Humanoid Robot
The Robotic Research Company has developed an industrial robotic arm with modular joint and
compact mechanical design [1]. Its 7 DoF are used to mimic human movement in human oriented
environment. The Robotic hand from the University of Tokyo has a high control bandwidth for
grasping objects using vision sensing [5]. The German Aerospace center’s (DLR’s) Light weight
Robot is composed of safety brakes with modular joints are connected via carbon fiber structure [24]. NASA’s Robonaut DLR II and ARMAR III hands are latest that shows closer design
concentration on mimicking human hands [6-8].
II. MECHANICAL DESIGN
The mechanical design consist of 6Dof, 2 Dof for shoulder, 1 Dof for elbow and 3 Dof for
wrist to perform motions similar to actual human arm. Pneumatic Suction gripper gives it modularity
if it is replaced by multi finger gripper having 14 Dof. The developed modular arm is shown in fig 2.
Figure 2: Six Dof modular humanoid arm with pneumatic suction gripper
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3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME
At each joint RC servo motor provide high control bandwidth and compact design. RC servo
motor connected with angle plate in such way that, it gives high torque and less vibration as shown
in fig 3. All mechanical parts of modular arm made of aluminum alloy, so that the weight of arm
reduced. The arm can perform motions such as pick and place of delicate materials like glass. The
weight of each RC servo motor is 70 gram with size of 60X30X54 mm, stall torque of 1.9 Nm at 6V.
The wrist attachment plate is connected in such way that pneumatic suction gripper or multi finger
gripper can be easily attached to it.
Figure 3: Assembly of Angle plate with RC servo motor
III. CONTROL STRATEGY
For selection of motor, it is very important to know how much torque is required for
application. The extreme case analysis of shoulder motor is done using solid works motion analysis
and required torque comes to 1.6 Nm as shown in fig 4.
M o to r T o rqu e 2 (n e w to n -m m )
1600
1205
811
416
22
0.00
0.10
0.20
0.30
0.40
0.50
Time (sec)
0.60
0.70
0.80
0.90
1.00
Figure 4: Extreme case analysis for torque calculation of shoulder motor
The PCB board of the controller is shown in fig 5, the microcontroller is PIC18F4520. The
controller consist of : 1) Under voltage protection circuit which resets board when the power supply
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4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME
is below 6V and protecting voltage can be adjustable. 2) USB interface circuit which has “CTS”
judging bit and can output TTL voltage. 3) The hand held control device connected via USB with
main controller to send and receive control signal. 4) I/O interface circuit which has 32 I/O ports for
connecting RC servo motor. 5) Programming interface circuit which adopts standard serial port ISP
protocol of STC and is used to receive and data from or to MICRO C for PIC software.
Figure 5: PCB of main controller
A RC servo motor includes a DC motor, gear, potentiometer and control circuit. A DC motor
connected with gear which gives feedback to potentiometer. The potentiometer changes its position
according to current motor position. Pulse width modulation signal is required to control motor is
shown in fig 6.
Figure 6: Variation in Pulse width to control motor
Each RC motor is controlled to get required motion. The suction generator of capacity 3
lt/min gives vital amount of air to grasp object using suction cup.
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5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME
IV. CONCLUSION
The design, manufacturing of mechanical part and assembly has been successfully finished.
Total 6 RC servo motor along with pneumatic gripper has controlled using hand held device. PIC
18F4520 microcontroller along with MICROC for PIC implemented successfully. The signal from
hand held device has sent or receive using USB interface to main controller. By adding visual
algorithm, environmental information can be acquired and obstacle avoidance can be added.
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