02_JAER_V5N1

Journal of Advanced Engineering Research 
ISSN: 2393-8447 
 Volume 5, Issue 1, 2018, pp.6-11 
Research Article  6  www.jaeronline.com 
Design, Analysis and Fabrication of Walking Assistant for physically  
challenged people 
S. Sakthi Sundharam1,*, V. Sathish Kumar2 
1Department of Mechanical Engineering, Adhiparasakthi Engineering College, Melmaruvathur, India. 
2Department of Mechanical Engineering, Alagappa Polytechnic College, Karaikudi, India. 
*Corresponding author email: [EMAIL] 
 
  
ABSTRACT 
In recent years, exoskeletons have become one of the key areas in research. Even though many successful design of 
exoskeleton have done by many companies and research scholars, walking assistance for children are less and infrequent 
and expensive. This paper aims at design of walking assistant device for physically challenged children ages at 6 to 15 
years old in an economical price. It can be used for two purposes: as walking practice and walking assistive device. The 
key feature of project is use of Arduino board as microcontroller to control stepper motor (NEMA34) linked to joints and 
links, which swings to make leg movements. It can be used with both SMPS and battery according to the convenience of 
the user. 
Keywords: Exoskeleton, Walking Assistant, Robotics, Electric motor. 
1. INTRODUCTION 
Exoskeletons have got huge attention now a days. It has 
been used in military [1], rehabilitati on [2] and medical 
assistance [3]. In military [4] it has been used to lift 
weight and to carry large weapons and as a guard. On 
the other hand, these are used medically for assisting 
the patients [5], who are injured during accidents in 
their spinal cord and to the old people [6] [7]. The graph 
represents the rise in number of people above 60 years 
[8]. From graph, it is evident that number of people in 
2050 would be more than one billion. Hence, there will 
be great need for exoskeletons, which would help them 
to walk independently without anyone’s help.  
 
Fig. 1 Percentage of the population aged 60 years or 
over, estimated for 1950- 2050 [1] 
There are many commercially available exoskeleton 
such as MIT exoskeleton, BLEEX and HAL. BLEEX 
has seven degree of  freedom, one at knee, 3 DOF’s at 
the hip and 3 at ankle. It follows sensitivity 
amplification controller strategy. Design is based on 75 
kg human and clinical gait analysis data [9]  but, wearer 
have to hold the weight of back pack that has controller 
and power unit.  
MIT exoskeleton has followed pelvic harness technique 
[10], which will reduce the weight of back bag by 
transferring it to the ground due to linkages in the pelvic 
area. It has springs to add power to the joints [11]. HAL 
comes in different mo dels and many purposes such as 
rescue support rehabilitation, labor support and 
entertainment [12]. It is based on electro myography 
signals from electrodes attached to the skin [13], which 
uses power and controller in its backpack to operate.  
Following this there are other walking assistive devices 
such as re -walk [14], e -legs [15] commercially 
available.  
Major drawback of these devices is, it is not economical 
and some have problem of weight laid on the wearer. 
Hence, our design scope is to make a cost e ffective and 
economical exoskeleton with less weight carried by the 
wearer. First, the paper undergoes design stage of 
exoskeleton, then it follows selection of motor and 
analysis. Finally results are discussed.

S. Sakthi Sundharam and V. Sathish Kumar / Journal of Advanced Engineering Research, 2018, 5 (1), 6-11 
Research Article                  7 www.jaeronline.com 
2. DESIGN OF THE EXOSKELETON 
Previous works reg arding the  successful design of 
lower limb exoskeleton [16] [17] were taken into 
account, while designing our lower limb exoskeleton 
and some of the basic concepts of design is derived 
from these examples, parameters such as, length of link 
,motor range, joints, gear and harness.  
Initially selection of motor is done and design of 
walking assistant followed concurrent steps of 
designing structure, joints and mounting clamps.  Some 
basic requirements such as height adjustments, angle 
and speed limit are taken into account. 
1.1 Selection of Motor 
Selection of motor is one the crucial situation in 
exoskeleton process because whole exoskeleton is 
depend on the motor and drive. Hence, different motors 
available in market are explained and selected motor for 
our exoskeleton is justified. 
1.1.1. Servo Motor Vs Stepper Motor 
Basic difference between these motor is number of 
poles available, stepper has 50 to 100 poles without 
encoder attachment and servo has 4 to 12 poles with 
encoder attachment. Encoder is used to know exact 
position due to less number of poles in servo motor. 
In our case, angle should be precise and holding torque 
should be more and weight should be less. So, stepper 
motor has precise angle control and less weight than its 
servo counterpart. It has added advant age of producing 
high torque in less speed . Hence bipolar stepper motor 
have been selected for this application. 
1.1.2. Motor Rating and Torque 
Table 1, shows different children of different ages, their 
weight, height of hip to knee and knee to ankle  from a 
sample of 30 children. Children are grouped due to 
similar measurements in the intermittent ages and  
average result from each  group are taken into account. 
In order to specify the torque requirement for our each 
joint, we have taken results of Royer TD el al. ( 2005) 
and Kerrigan et al. (2000) work in derivation of torque.  
For instance, the 80 kg and 1.80 m height man would 
require 45 Nm to walk but, we require torque for people 
with weight below 40 kg. Hence , NEMA bipolar motor 
of rating 34 kg cm torque and cur rent ratings of 4 amps 
is selected , which will produce 3.4 Nm in order to 
amplify torque,  an attachment of planetary gear box of 
ratio 10:1 is added to it, which will provide the required 
torque. The planetary gear box have different varieties 
like 3:1,5: 1,10:1 or 20:1 , we selected 10:1,which is 
appropriate for the application. It will increase torque 
by reducing speed  
Table 1 Categorization of children with different age 
group 
Age group 
(average) 
Hip to 
knee 
(average) 
(mm) 
Knee to 
ankle 
(average) 
(mm) 
Foot 
(average) 
(mm) 
5-8 267 318 152 
9-12 350 330 178 
12-15 410 380 203 
 
1.2. Design of Structure 
Initially, weight of motor, driver , battery , and 
transformer for power supply, were taken into account. 
Each motor weighted about 185 kg and driver weighted 
0.3 kg for each set  and transformer weights about 3kg . 
Whereas, there are four sets of motors and drivers . 
Hence by t aking these into consideration, we have 
designed a base structure with square iron tube of the 
thickness 2mm as shown in figure 2. Several suppo rts 
are given at the joints and welded in order to hold the 
whole weight and wheels are provided at the bottom for 
movement. We have avoided cross triangulation 
instead, we made short triangulation which serve the 
purpose. 
 
Fig. 2 Design of main frame 
1.3. Design of Links and Joints 
Links are the important parts that transfer power from 
motor to the leg of human, hence it should designed in a 
manner to transfer whole power produced by the motor 
without any loss.  During walking action links have to 
move adjust slightly in vertical direction for convenient 
movement of legs  due to change of angle during 
movement. The link material used is aluminum 6025.

S. Sakthi Sundharam and V. Sathish Kumar / Journal of Advanced Engineering Research, 2018, 5 (1), 6-11 
Research Article                  8 www.jaeronline.com 
 
Fig. 3 Links attached with one another with aluminum rivet 
Table 2 Length of links 1, 2 and 3 
LINK LENGTH OF LINK (mm) 
LINK 1 275 
LINK 2 170 
LINK 3 100 
 
Especially, this 6000 series aluminum is selected due to 
the economic cost and easy machining . The weight of 
aluminum 4000, 5000 series would have weighed less 
due to its low density but, it is not economica l and 
availability in market is less. The mounting of motor to 
link is also made with same metal as used for links. The 
density of the metal comes around 2.8 g/cm3 and elastic 
modulus comes with 70 Gpa , Which is the appropriate 
range for the application. A luminum rivets are used to 
joint different links and motor to one another. In the 
final link there is cavity given for the harness, which 
will stick the link to the thigh and the calf muscle. All 
the links were designed in Creo and sent to CNC for 
machining. 
3. CONTROLLER FOR THE 
    EXOSKELETON 
3.1 Motor Drive 
Since, motor with 4 amps is selected, driver must be 4 
amps or above. Hence 4.5 amps driver is selected  as 
shown in figure (4), which would control the amount of 
current passing through motor. It has variou s micro 
stepping options ranges from 2 to 250. There are eight 
switches are provided in the drive in which first three 
switches are used to regulate current, fourth and fifth 
switches are used according to half and full current and 
other three switches are  used to attain micro stepping. 
There are fourteen micro stepping options are available 
in the drive. By making switch on and off, we can 
change pulse per revolution, which eventually changes 
stepping of motor.     
 
Fig. 4 12V and 4.5 amp motor drive 
3.2 Arduino 
The Arduino is used as microcontroller for the 
exoskeleton, we  have options for microcontroller such 
as PLC, Raspberry Pi etc. but, we selected Arduino due 
to its accuracy ,simple programming method and wide 
number of add on attachments like sensors a nd joystick 
that may rooted in the future. It can be coded with both 
c and  c++ program. The Arduino is connected to the 
drive which controls the motor angle and rpm. The 
change of angle, while walking is measured manually , 
and also with potentiometer using  Arduino. Finally 
angle is derived and programmed to Arduino, which 
sends signal to the drive makes motors to rotate 
clockwise and anticlockwise that makes links attached 
to thigh and cough muscle to move, eventually makes 
man to walk.

S. Sakthi Sundharam and V. Sathish Kumar / Journal of Advanced Engineering Research, 2018, 5 (1), 6-11 
Research Article                  9 www.jaeronline.com 
4. ANALYSIS 
Analysis o f different links and joints are done with 
HYPERMESH. The models that are designed in Cero 
are imported to the HYPERMESH and maximum 
forces are applied in the each ends of the joints, links 
and to the structure , their stress and strain reports are 
analyzed using HYPERMESH.  
Hence figure (5 -9) shows that all the links are in the 
safe zone. Initially , links with different thickness are 
analyzed, which showed maximum amount of stress  
region in the link. Every time thickness of the link is 
raised slightly and o bserved various results  in 
HYPERMESH. Finally, link of 100mm thickness is 
derived, which showed safe zone in the entire link and 
the design is subjected to manufacturing. In structural 
analysis, more stress is seen in the edges due to load of 
motor and wei ght of wearer. Hence triangulation is 
given at the each edge of the frame. After application of 
support, stress distribution is through out the frame and 
passes to the ground that makes it to be in safer zone as 
shown in figure (5) . As a result, there is no  over 
stressed areas and all parts of exoskeleton are in safe 
zone, which is ready to operate at full load. 
 
Fig. 5 Stress analysis of frame setup 
 
Fig. 6 Stress analysis of motor link 
 
Fig. 7 Stress analysis of Frame 1 
 
Fig. 8 Stress analysis of Frame 2 
 
Fig. 9 Stress analysis of Frame 3 
5. CONCLUSION 
Thus, the required movement of the leg has  been 
formulated. Use of NEMA motor with planetary gears 
along with drive and Arduino as micro controller has 
highly reduced cost of the exoskeleton.  Angle of motor 
and speed of motor can changed easily by changing the 
value in Arduino program. The whole setup along with 
transformer as power supply has come around 80k INR, 
which is negligible compared to other exoskeletons 
such as HAL, Re -Walk etc. Mounting of links,  drivers 
and motor to the frame makes fewer burdens  to the 
wearer, which is an added advantage of this design. 
Final setup is as shown in figure 10.

S. Sakthi Sundharam and V. Sathish Kumar / Journal of Advanced Engineering Research, 2018, 5 (1), 6-11 
Research Article                  10 www.jaeronline.com 
6. FUTURE WORK 
Mounting of sensor to the motor to know the exact 
angle of motor and joystick fo r the manual co ntrol of 
motor are some of the future works. 
 
Fig. 10 Final setup after assembly 
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