Rescue Robot Design and Automation

12-6-2015 Rescue Robot
3rd Grade on Mechanical Engineering
Group 7
Izaro Aretxaga
Iñigo Bravo
Julen Egaña
Maider Etxagibel
Unai Suarez

7th
GROUP
Final Version
Arrasate-Mondragon, 12 June of 2015

ABSTRACT
POPBL VI Rescue robot I
The Basque Government has contacted with the Mondragon Unibertsitatea to
make a prototype of an autonomous rescue vehicle, which makes easier the rescue labor
to the operators. This task must be completed fulfilling some compulsory specifications,
such as go upstairs and downstairs. This document provides all the relevant information
about the design, manufacture and assembly of the prototype. The first part of the
project consisted of the design of a prototype which satisfied the specifications required.
This stage, however, is centered on the manufacture and assembly of the robot. In order
to make the vehicle go up and down the stairs in an autonomous way, the robot has been
automated. Finally, to ensure the robot withstands an overweight when it remains still,
static analyses of the critical elements have been carried out.

ABSTRACT
POPBL VI Rescue robot II
Eusko Jaurlaritza Mondragon Unibertsitatearekin jarri da kontaktuan
salbamendu lanetan gizakiari lana errazten duen ibilgailu autonomo baten
prototipoa burutzeko. Ibilgailu honek espezifikazio zehatz batzuk bete behar ditu,
hala nola, eskailerak igo eta jaitsi. Dokumentu honetan prototipo horren diseinu,
fabrikazio eta muntaiaren inguruko beharrezko informazioa aurkitzen da.
Proiektuaren lehenengo atala, beharrezko espezifikazio guztiak betetzen dituen
prototipoaren diseinuan oinarritu zen. Zati hau, aldiz, robotaren fabrikazio eta
muntaian zentratzen da. Bestalde, robota automatizatu egin da, eskailerak igo eta
jaitsi nahiz zirkuitu jakin bat burutzeko gai izateko. Robota geldi dagoela gainkarga
bat aplikatzerakoan jasango duela ziurtatzeko, pieza kritikoekin analisi estatiko bat
eraman da aurrera.

ABSTRACT
POPBL VI Rescue robot III
El Gobierno Vasco se ha puesto en contacto con la Universidad Mondragón
para el diseño del prototipo de un vehículo autónomo de salvamento que facilite las
labores de rescate al operario. Este vehículo debe de cumplir ciertas especificaciones,
como subir y bajar escaleras. En este documento se facilita toda la información
relevante sobre el diseño, fabricación y montaje del prototipo. La primera parte del
proyecto consistió en el diseño de un prototipo que cumpla las especificaciones
necesarias. La segunda parte, sin embargo, se centra en la fabricación y montaje del
vehículo. La automatización del robot se ha llevado a cabo para conseguir que este
sea capaz tanto de subir y bajar las escaleras como de completar un circuito
específico. Por otra parte, se han llevado a cabo análisis estáticos de las piezas
críticas del robot para asegurar que este es capaz de soportar una sobrecarga
cuando está quieto.

INDEX
POPBL VI Rescue robot IV
INDEX
1. INTRODUCTION................................................................................................................. 1
1.1. Project Frame......................................................................................................1
1.2. Approach to the problem ....................................................................................5
1.3. Objectives ...........................................................................................................5
1.4. Planification........................................................................................................6
2. DEVELOPMENT OF THE PROJECT.................................................................................. 8
2.1. Redesigning of the robot .....................................................................................8
2.2. Manufacturing process ......................................................................................10
2.3. Assembly of the robot .......................................................................................17
2.4. Verification of the robot....................................................................................23
2.5. Automation of the robot ....................................................................................48
2.5.1. Elements.................................................................................................................... 49
2.5.2. Electric circuits.......................................................................................................... 51
2.5.3. Programming of the PLC .......................................................................................... 54
2.6. Budget ...............................................................................................................57
3. RESULTS ........................................................................................................................... 66
4. CONCLUSIONS................................................................................................................. 69
5. FURTHER RESEARCH..................................................................................................... 72
6. REFERENCES.................................................................................................................... 73

INDEX
POPBL VI Rescue robot V
FIGURE’S INDEX
Figure 1 Different earth robots.....................................................................................................................1
Figure 2 First version design ........................................................................................................................3
Figure 3 Path geometry and dimensions.......................................................................................................6
Figure 4 Final design: Three-wheel system..................................................................................................8
Figure 5 Before and after star design............................................................................................................9
Figure 6 Structure of the final design ...........................................................................................................9
Figure 7 Before and after design of the gear shaft......................................................................................10
Figure 8 Process of copying holes..............................................................................................................16
Figure 9 Structure of the partial assembly..................................................................................................18
Figure 10 Chock and connection block assembled.....................................................................................18
Figure 11 Complete assembly of the structure ...........................................................................................19
Figure 12 Gears, wheels and bearing mounting .........................................................................................20
Figure 13 Transmission system design.......................................................................................................20
Figure 14 Motor and motor´s plate assembly .............................................................................................21
Figure 15 Three-wheel shaft's pinion .........................................................................................................21
Figure 16 Tensor design .............................................................................................................................22
Figure 17 Electronic components location .................................................................................................22
Figure 18 Finished assembly......................................................................................................................23
Figure 19 Model of the structure ................................................................................................................24
Figure 20 Stresses created due to the overweight.......................................................................................24
Figure 21 Stresses created bigger than 8 MPa............................................................................................25
Figure 22 Deformation appeared due to the overweigth ............................................................................26
Figure 23 Displacement formed because of the overweigth.......................................................................26
Figure 24 Motor´s placement in the structure.............................................................................................27
Figure 25 Stress concentrarion in the motor´s plate ...................................................................................27
Figure 26 Displacement created due to the motor´s weigth .......................................................................28
Figure 27 Three-wheel star model..............................................................................................................28
Figure 28 Forces produced in the clamping due to the overweight ............................................................29
Figure 29 Tension concentration of the three-wheel star ...........................................................................29
Figure 30 Tension concentration in the radious of the stars .......................................................................30
Figure 31 Tension values without radious..................................................................................................30
Figure 32 Tension values with radious.......................................................................................................31
Figure 33 Displacement suffered by the three-wheel star ..........................................................................31
Figure 34 Free body diagram going upstairs position ................................................................................33

INDEX
POPBL VI Rescue robot VI
Figure 35 Free body diagram going upstairs ..............................................................................................34
Figure 36 Working cycle of the robot ........................................................................................................36
Figure 37 S-N Diagram of the tube ............................................................................................................36
Figure 38 Haigh´s diagram.........................................................................................................................37
Figure 39 Equivalent strees calculation......................................................................................................38
Figure 40 Limit range of the stress.............................................................................................................40
Figure 41 Lifetime of the tube upstairs ......................................................................................................40
Figure 42 Free body diagram downstairs position .....................................................................................41
Figure 43 Free body diagram going downstairs .........................................................................................42
Figure 44 Lifetime of the tube downstairs..................................................................................................43
Figure 45 Position of the strain gage and indicator ....................................................................................45
Figure 46 Three element rosette gage.........................................................................................................45
Figure 47 Robot with the overweight of 70kg............................................................................................46
Figure 48 Position of the principal strains..................................................................................................47
Figure 49 Indicator above the sheet............................................................................................................48
Figure 50 Remote control...........................................................................................................................49
Figure 51 LDR electric circuit....................................................................................................................51
Figure 52 Power scheme ............................................................................................................................53
Figure 53 Order scheme .............................................................................................................................54
Figure 54 Programmed circuit....................................................................................................................55
Figure 55 First level automatic mode GRAFCET......................................................................................55
Figure 56 First level manual mode grafcet.................................................................................................56
Figure 57 First level automatic mode GRAFCET......................................................................................57
Figure 58 First level lights module GRAFCET..........................................................................................57
Figure 59 Distribution of the different costs [€].........................................................................................64
Figure 60 Distribution of the different costs [€] without some electric components..................................65
Figure 61 Robot’s final design ...................................................................................................................66

INDEX
POPBL VI Rescue robot VII
TABLE’S INDEX
Table 1 Decision matrix of different earth robots.........................................................................................2
Table 2 Motor chosen decision matrix .........................................................................................................4
Table 3 Manufacturing of the robot’s parts ................................................................................................11
Table 4 Parts needed to assembly the structure..........................................................................................17
Table 5 Parts needed to assembly the structure ..........................................................................................19
Table 6 Results of the upstairs static analysis ............................................................................................34
Table 7 Applied coefficient and the choosing criteria................................................................................39
Table 8 Results of the downstairs static analysis........................................................................................41
Table 9 Elements of power and order circuits ............................................................................................52
Table 10 Inputs and outputs of the PLC .....................................................................................................53
Table 11 Electrical component´s total price ...............................................................................................58
Table 12 Commercial element´s cost .........................................................................................................59
Table 13 Machine taxes..............................................................................................................................59
Table 14 Raw material and machining cost................................................................................................60
Table 15 Manual operations costs ..............................................................................................................61
Table 16 Preparation time cost ...................................................................................................................62
Table 17 Unexpected operations cost.........................................................................................................63
Table 18 Final budget of the manufacturing of the robot ...........................................................................63
Table 19 Results of the theoretical analysis ...............................................................................................66
Table 20 Comparison and error between the theoretical and practical results ...........................................67

INTRODUCTION
POPBL VI Rescue robot 1
1. INTRODUCTION
Dangerous situations, such as nuclear explosions, earthquakes, inundations... can
occur anywhere and is necessary to be prepared to cope with them. In order to be able to
work in those situations, different types of robots and drones are used. The most
important advantage of these vehicles is that they make possible not to put people’s life
at risk, arriving to places with a difficult orography, what could be dangerous to the
operator. Moreover, they are also used to carry on heavy objects or first aid kits.
That’s why the Basque Government asked Mondragon Unibertsitatea about the
possibility of manufacturing a new robot. The objective of this self-sufficient vehicle is
to make rescue group’s work easier, ensuring the security of the people and providing
new applications. Therefore, it was decided to design and manufacture a rescue robot.
With the aim of improving the design done in the first part of the project, on the
following report, all the information about the redesign, the manufacture and testing of
the robot can be found.
1.1. Project Frame
When the project was presented, the first task was to carry out a market research in
order to know which type of robots there were depending on different factors. One
example of those factors is the environment in which they were going to work, such as
air, water and earth. Taking into account the specifications needed to be accomplished,
the project was centered on the earth robots. Once having decided the type of robot,
three different vehicles were analyzed: zipper, three-wheel and caterpillar (Figure 1). If
more information is needed, see appendix A.
Figure 1 Different earth robots

INTRODUCTION
As the task needed to be carried out is to design, manufacture and test a
prototype, the first step was to consider different possible designs and movement types
of the robot and choose the most appropriate one. This work was accomplished by using
a decision matrix, shown in table 1, where it is possible to see that the design chosen
was the three-wheel system. The main characteristic of this type of robot is that the
three-wheel conjunct rolls free in its shaft in order to go up and down the stairs.
Table 1 Decision matrix of different earth robots
Importance Zipper Three-wheel Caterpillar
Ability to go upstairs 3 1 3 2 6 2 6
Efficiency 3 1 3 3 9 2 6
Ability to turn 3 2 6 2 6 2 6
Complexity of the
system
2 2 4 2 4 1 2
Stiffness 2 1 2 2 4 3 6
Price 2 2 4 2 4 2 4
Manufacturing and
assembly
3 3 9 2 6 2 6
Total 31 39 36
Step by step the design has been improved until reaching the first version
(Figure 2). After that, some redesigns have been developed until achieving the final
design. The details of the redesigning have been explained in the development of the
project.

INTRODUCTION
Figure 2 First version design
In what the dimensioning and the insurance of the good accomplishment of the
robot is concerned, the static analysis of three critical parts of the robot was carried out:
three-wheel shafts, can store and structure. In respect of the three-wheel shafts, it was
obtained that the most critical situation was when the robot remains still and must
withstand four times its weight. Taking this and the maximum allowed working
deformation into account, the dimensioning of the supports was made. In order to carry
it out, the working requirements were also taken into account. Furthermore, an analysis
of the comparison between different materials was carried out, reaching to the
conclusion that the most appropriate material was aluminum.
To prove the stability of the robot and ensure it was not going to rollover, the
maximum angle in which the robot will have to work was 77.89º.
In what the motors is concerned, three different types of motors were analyzed,
asynchronous motors, servo motors and direct current motors. A matrix was done in
order to know which the motor that complied, in the best way, the needed characteristics
was (Table 2). The conclusion reached was that the most appropriate type of motor for
this case was the direct current motor.

INTRODUCTION
Table 2 Motor chosen decision matrix
Importance Asynchronous Serbo
Direct
current
Size and
weight
5 2 10 3 15 4 20
Velocity
control
3 3 9 5 15 3 9
Price 4 4 16 2 8 3 12
Power 5 3 15 2 10 4 20
Maintenance 2 3 6 4 8 5 10
Noise 2 2 4 2 4 2 4
Consumption 3 2 6 4 12 3 9
Efficiency 3 3 9 4 12 2 6
Total 75 84 90
After having chosen the motor, it was proved that the one chosen was able to
give the torque necessary to work in an adequate way.
During the entire project, and in order to ensure the perfect quality of the robot, a
FMEA was carried out.

INTRODUCTION
1.2. Approach to the problem
After accepting the request of the public administration it has been decided to go
ahead with the project. The length of the project is one year, when the prototype will be
designed, manufactured and tested. This project consists of two stages. The first one
was focused on the design of the robot, as it is explained in the previous part. This
stage, however, consists of the manufacturing and testing of the robot designed, making
all the improvements necessary in order to obtain the best result.
1.3. Objectives
The main objective of this second part of the project is to redesign, manufacture,
assembly and test the robot. To reach this principal objective, some supporting
objectives must be completed:
 Design, develop and assembly an automation system for the robot in
order to be autonomous.
 Verify the critical parts of the robot in order to know if the robot is going
to work in a proper way even in the critical situation.
The robot must fulfill the following specifications:
 The budget of the project must be of 600€.
Movement
 The robot should be able to climb three stairs followed.
 The stairs dimensions: 17 mm high and 300 mm of horizontal part.
 Time to climb each stair: 30s.
Stiffness
 Load to be transported:
o When the robot is not moving (Steady state): Each project team
will have to set a unitary deformation range for the critical part of
the robot, taking into consideration that the robot must be able to
withstand a load of four times its own weight.

INTRODUCTION
o When the robot is moving it must be able to work in continuous
mode and move a load and a volume of six filled refreshment
cans.
Automation
 The robot should be controlled by an OMRON PLC.
 The remote control will be by cable.
 The robot should operate connected to a standard electric plug (the use of
batteries is not allowed).
 The robot must be able to perform automatically a previously defined
path. The dimensions of the path are shown in the figure below (Figure
3).
Figure 3 Path geometry and dimensions
 For safety reasons, the robot working slope is limited to 40. So, if the
robot finds in its way any obstacle that demands a higher slope, it must
stop.
 If your robot has some digital output free, you can consider installing:
automatic light control, add a buzzer to switch on whenever the robot is
moving.
1.4. Planification
To carry out the phases of the project in the correct way, a good planning of the
tasks is necessary. In order to be the most effective possible, the different activities that
are going to be performed during the project have been analyzed. A coordinate has been
assigned to each task, in addition to their length (Appendix B).

INTRODUCTION
This second part of the project is divided into different tasks. The first ones are
planned to center and limit the problem in order to make easier to carry out the project.
The rest of the tasks are divided into practical and theoretical ones, which are developed
simultaneously, in order to carry out the project in the best way possible. This planning
will have to be adjusted during the project, depending on the workload and it is follow
up.
In order to compare the planning done in the first stage of the project with the
one followed really, the real planning has been represented in another colour.

DEVELOPMENT OF THE PROJECT
2. DEVELOPMENT OF THE PROJECT
The development of this project is directly related with the previously explained
objectives and specifications. The following part contains all the necessary information
to understand the robot behavior under different situations, the automation, the
manufacturing and the assembly of the robot. Also, includes the budget calculus, to
have a real idea of the robot cost.
2.1. Redesigning of the robot
Before reaching the final version some changes have been done. This robot has
some critical parts that must work with high precision in order to get a perfect
movement. These parts have been optimized as much as possible since the first design
of the project. Mainly three parts have been modified: stars, wheel shafts and the
structure (Figure 4).
Figure 4 Final design: Three-wheel system
One of the most important parts is the star, in which the shafts of the gears are
introduced. In this case, the dimensions have been reduced as much as possible to
ensure the appropriate climbing of the stairs. The old and the new versions can be seen
in figure 5.

Figure 5 Before and after star design
Another essential part, which has been redesigned, is the structure of the robot. It
must support the weight of all the electric components and the cans without deforming
more than a certain value, so a stronger design has been done assembling some nerves
to the structure. The new structure is shown in figure 6.
Figure 6 Structure of the final design
The last critical parts are the shafts of the stars. As the aim of those parts is to
transmit the movement from the gears to the wheels, this transmission must be as
precise as possible. To achieve it, the design of that transmission has been changed. The
connection between the shafts and the gear has been done by pins, not allowing the gear
slide in the shaft. Both designs are shown in figure 7.

Figure 7 Before and after design of the gear shaft
2.2. Manufacturing process
One of the main objectives of this part of the project is to manufacture the rescue
robot. To achieve an optimum manufacturing some important details must be taken into
account. All the manufacturing process has been summarized in the table 3.

Table 3 Manufacturing of the robot’s parts
Part
Name of the
part
Reference in
plans
Used
machines
Processes
Long square
tube
EI_G07_001
Mechanical
saw
Cut all the
square tubes
with the
adequate length
Drill
Make all the
holes. To make
the keyholes,
make a hole in
each corner and
join them with a
rasp
Short square
tube
EI_G07_002
Mechanical
saw
Cut all the
square tubes
with the
adequate length
Drill
Make all the
holes
Auxiliary shaft
EI_G07_003
Mechanical
saw
Cut all the
cylinders longer
than the final
size to be able to
mechanize them
Lathe
Mechanize all
the parts in the
conventional
lathe
Drill
Make all the
holes

Handmade Thread one hole
Three wheel
shaft
EI_G07_006 -
This part will be
manufactured in
a company out
of the university
Framing
square
EI_G07_005
Mechanical
saw
Cut all the parts
with the correct
dimensions
Drill Make all the
holes
Main shaft
EI_G07_004
Mechanical
saw
Cut all the shafts
longer than the
final size to be
able to
mechanize them
Lathe
Mechanize all
the pieces in the
conventional
lathe
Drill Make all the
holes
Handmade Thread one hole
Three wheel
tube
EI_G07_007
Mechanical
saw
Cut all the parts
longer than the
final size to be
able to
mechanize them

Chock
EI_G07_008
Mechanical
saw
Cut all the
square tubes
with the correct
dimensions
Drill
Make all the
holes
Connection
block
EI_G07_009
Mechanical
saw
Cut all the parts
longer than the
final size to be
able to
mechanize them
Milling
Make the
internal hole
Drill
Make all the
holes
Handmade
Thread all the
holes
Base sheet
EI_G07_010
Shears
Cut the sheet
with the correct
dimensions
Drill
Make all the
holes

Motor plate
EI_G07_011
Shears Cut the plate
with the correct
dimensions
Milling
Make all the
holes and the
keyholes
Nerve
EI_G07_012
Shears
Cut the plate
with the correct
dimensions
Drill
Make all the
holes
Tensor plate
EI_G07_013
Shears
Cut the plate
with the correct
dimensions
Milling
Make all the
holes and the
keyholes
Tensor shaft
EI_G07_014
Mechanical
saw
Cut all the shafts
longer than the
final size to be
able to
mechanize them
Lathe
Mechanize all
the parts
Drill
Make all the
holes

Sheets shaft
EI_G07_015
Manual
saw
Cut all the parts
with the correct
length
Holes sheet
EI_G07_016
Shears
Cut the sheet
with the correct
dimensions
Drill
Make all the
holes
Star
EI_G07_017
-
This part will be
manufactured in
a company out
of the university
Wheel
EI_G07_018
Lathe
Cut all the
wheels,
mechanize then
and make the
central hole
Drill
Make all the
holes

Handmade
Stick the
external rubber
with super glue.
In what the structure is concerned, all the elements are tied with screws, that’s
why all the holes between the parts must be concentric. To achieve it, the holes of some
elements have been copied on others, that is to say, the holes of the part are going above
others are the ones that have been copied (Figure 8):
 Framing squares on long and short tubes
 Nerves on long tubes
 Chocks and connection blocks on long tubes
 Base sheet on long tubes
Figure 8 Process of copying holes
With regard to the main and auxiliary shafts, they have to move at the same time
as the gears and in the case of the main shafts, with the wheels too. That is why both
elements have been assembled to the shaft using pins. To achieve that union the
common holes of the shafts with the other two elements have been done with those
assembled. After that, the pins have been introduced immediately because the hole tends
to close.

Therefore, the holes of the gears and the shafts must be in the center. To ensure a
proper functioning those holes have been done in the lathe.
2.3. Assembly of the robot
Once all the parts have been manufactured, the next step is to assembly the
robot. This process will be done in three parts: the structure, the three-wheel stars and
the transmission.
Structure
The structure is a square frame stiffened with some nerves assembled above four
blocks. The parts needed are shown in the table 4.
Table 4 Parts needed to assembly the structure
Part Quantity Dimensions[mm]
Long square tube 2 25x25x3x500
Short square tube 2 25x25x3x300
Framing square 4 30x30x2x25
Nerves 2 30x5x300
Chock 4 25x25x3x50
Connection block 4 40x40x30
First of all, a square frame has been mounted using the long and short tubes and
fixing them to the framing squares and screws. After that, the nerves have been added to
the structure between the two long tubes using screws. This will give the stiffness
needed to the structure (Figure 9).

Figure 9 Structure of the partial assembly
Finally, the square frame has been assembled to the connection blocks. Between
the two elements some chocks have been added in order to give height to the structure
with the aim not to hit the stairs. This connection has been done with screws too (Figure
10).
Figure 10 Chock and connection block assembled
The complete assembly of the structure is the next one (Figure 11). The only
thing missing is to add the can collector that will be done at the end. The next step will
be the assembly of the three-wheel star.

Figure 11 Complete assembly of the structure
Three-wheel stars
The robot is composed by four three-wheel stars, which are made by two parts
with star form and some shafts introduced between those. The entire conjunct has been
assembled above circular tubes where he three-wheel shaft have been introduced. The
parts needed are shown in the table 5.
Table 5 Parts needed to assembly the structure
Part Quantity Dimensions[mm]
Star 8 Not home manufacturing
Main shaft 12 Ø12x73.5
Auxiliary shaft 12 Ø12x73.5
Three-wheel shaft 4 Ø18x160
Circular tube 4 Ø25xØ20x120
Wheel 12 Ø70x31
First of all, friction bearings have been introduced in the stars and in the circular
tube. As the shafts have to roll inside the stars, those elements are indispensable. After
that, the wheels have been assembled to the main shafts using pins and main and
auxiliary shafts have been introduced in the stars. At that point, the shafts have been
fixed axially using threaded pins. Therefore, the gears have been mounted in all the
shafts using pins (Figure 12).

Figure 12 Gears, wheels and bearing mounting
Finally, the circular tubes have been introduced in the center hole of the star and
the three-wheel shaft inside the tube.
Transmission
A transmission system has been used to bring the movement from the two
motors to the wheels. The composition of that system has been made by three pinions
and two chains for each motor (Figure 13).
Figure 13 Transmission system design
The first step to mount the transmission has been to assemble the motor´s plates.
The fixing of those parts has been made by screws. Once the plats have been mounted,
the motors have been fixed there by screws (Figure 14).

Figure 14 Motor and motor´s plate assembly
The next step has been to introduce the three-wheel shafts in the tubes. Those
shafts have the gears assembled already, so the pinions have been mounted in the
opposite end of the shafts using keys and fixing them with thread pins. At that point the
four three-wheel shafts have been completely assembled (Figure 15).
Figure 15 Three-wheel shaft's pinion
For the optimum functioning of the transmission is essential to have the chain
tensed. That is why a tensor system has been assembled in the structure and each tensor
is made by two plates, the tensor shaft and the pinion (Figure 16).

Figure 16 Tensor design
First of all, the tensor plates have been mounted in the keyholes of the structure.
Those keyholes have been machined in order to adjust the tension of the chain, so the
plates have been mounted in order to have the most margins to tense the chain.
Therefore, the shaft has been introduced into the two plates having mounted some
bearings there and finally the pinions have been assembled in the shafts using some
pins.
Finally, the chains have been assembled in the pinions and tensed with the
tensor. The can collector has been mounted after the transmission system assembly.
Regarding the electric components, they have been mounted in the backside of
the robot in a standardized DIN rail (Figure 17).
Figure 17 Electronic components location

The finished assembly is shown in the figure 18.
Figure 18 Finished assembly
2.4. Verification of the robot
To verify that the robot is working in a proper way is necessary to know how the
different parts behave in the specify process. That work have been done carrying out a
structural analysis using finite elements method calculating the displacements, stresses
and unitary deformations and a fatigue analysis of the critical parts of the robot to
approach the lifetime. The results of the structural analysis have been compared with the
ones calculated using strain gages and an indicator. As only one of the critical parts
suffer fatigue that is the part have been analyzed.
Theoretical structural analysis
First of all, the critical parts have been chosen. In the first part of the project the
chosen elements as the most critical ones were the next ones: the structure, the bolts of
the cans and three-wheel shafts. Nevertheless, when the redesigning has been done, it
has been realized that the shafts weren’t the elements which suffer the most, but the
three-wheel tube. Besides, the can´s bolts have been neglected because they only have
to support the can’s weight, apart from being over dimensioned, so another part has
been chosen such as the motor plate.
As it has said in the specifications, the robot must withstand an overweight of
four times its weight. It has been decided to make all the analysis in that condition,

because is the most critical one. The materials used to manufacture the robot are
aluminum (6063 T6) and steel (F-1045).
The first part analyzed have been the structure. Figure 19 shows the model of the
structure of the system in order to do the theoretical analysis.
Figure 19 Model of the structure
It has been decided that the overweight (70 kg), which is four times the weight
of the robot, will be placed on the bottom plate. Figure 20 shows the stresses created by
the applied overweight.
Figure 20 Stresses created due to the overweight
The tension concentration in the structure is not very big, despite the applied
overweight of 70kg. The maximum tension concentration will be in the corners of sheet
and in the joint with the structure. With the aim of concreting more the critical zones, it
has been set a value of 8 MPa shown in the figure 21. In this way it can be seen that the
tension concentration is in the position told before, which will be the best to attach the
strain gage that have been explained later.

Figure 21 Stresses created bigger than 8 MPa
It can be seen that there is a high tension concentration in each connection block
which are clamped. This phenomenon happens because the software used needs a
clamping in order to carry out the simulation. Those clamping suffer a crushing because
of the overweight, but this tension concentration is neglected for the theoretical analysis
because physically this is not happening.
Apart from that, the maximum deformation of the system has been estimated. A
strain gage is a device used to measure deformation on an object. The gage is attached
to the object by a suitable adhesive and as the object is deformed, the foil is deformed,
causing its electrical resistance to change. This resistance changes, usually measured
using a Wheatstone bridge, is related to the strain. Figure 22 shows the deformation
suffered by the system as a result of the overweight applied. Besides, the maximum
unitary deformation appears where the maximum tension is situated, that will be
6
105.189 
 mm.

Figure 22 Deformation appeared due to the overweigth
Therefore, the bottom plate will deform as figure 23 shows. It can be said that the
system is stiff enough taking into account that the maximum displacement established
was just one millimeter. In appendix C can be seen more detailed the aspect that the
structure will have after applying the overweight.
Figure 23 Displacement formed because of the overweigth
The next part that has been analyzed are the motor plates. Those parts have been
chosen because they must withstand the weight of the motor while it is moving. This
part will be fixed to the structure with screws, figure 24.

Figure 24 Motor´s placement in the structure
If this part breaks down, the robot will not be able to move because the
transmission will be lost. Figure 25 shows the tension concentration in the plate of
steel, in consequence of the motor’s weight (1.5kg) that will be of 112 MPa. That will
be very concentrated in edges of the hole. In addition, the unitary deformations will be
in the same place, as it can be seen in appendix C.
Figure 25 Stress concentrarion in the motor´s plate
The weight of the motor apart from creating internal tensions, also creates a
deformation as it is shown in figure 26. A big deformation will not be appropriate and if
it happens, it will be necessary to find a solution. In this case, the plate will deform 0.1
mm so the motors will work correctly.

Figure 26 Displacement created due to the motor´s weigth
Finally, as it has been said before, the tubes are going to suffer when the
overweight is placed on the system. Figure 27 shows the three-wheel star model, where
the tube is placed. The tube is the most critical element in the system, because if it
breaks down when the overweight is placed, the robot will not be able to complete its
function. This would happen because the structure will uphold in the shaft, which is
inside the tube, and it wouldn´t rotate because of the force produced by the weight.
Figure 27 Three-wheel star model
Before doing the theoretical verification of the maximum tensions and
displacements, the force in each joint of the structure with the three-wheel star model
must be known. In order to obtain it, figure 28 shows the forces created by the
overweight in each clamping.

Figure 28 Forces produced in the clamping due to the overweight
Once the forces are known, the verification of the three-wheel star model has
been done, exactly the tube verification. For this analysis 271 N force is going to be
used, because is the most critical one. However, it can be seen in the appendix C a
comparison between the three-wheel stars, depending on the force that corresponds to
each one.
The maximum punctual tension is shown in figure 29 with the aim of proving
that the tube endures the overweight. The tube suffers a maximum stress of 29 MPa.
Figure 29 Tension concentration of the three-wheel star

Another important detail is what happens in the stars. As it can be seen in the
figure 30 there is a big tension concentration in the edges of the stars. This happens
because they do not have the needed radius and the tension concentration in that point is
bigger.
Figure 30 Tension concentration in the radious of the stars
The tube is the first element which is going to suffer the force created by the
overweight. This is logical, because is the element of the three-wheel star which is in
contact with the structure. After the tube, the star will start suffering in its edges. Figure
31 shows the tension in the edges of the star and it can be seen that the lower edge is
which suffers more with 24 MPa. This happens because when a weight is applied, the
legs tend to open.
Figure 31 Tension values without radious

Taking these tensions into account, it has been decided that a radius is necessary
in the three edges of the stars in order to decrease the tension concentration in those
edges. In this way, the star will be more secure against the force created by the
overweight (Figure 32).
Figure 32 Tension values with radious
Therefore, figure 33 shows the displacement of the assembly taking into account
the forces that produces the overweight in the structure.
Figure 33 Displacement suffered by the three-wheel star
Once the verification of the overweight has been completed, the robot will be
able to complete its cycle correctly. As it has been said before, while the robot is
transporting the cans upstairs and downstairs it will suffer from fatigue. This fatigue

will only affect to the tubes, because those are the only ones which suffers a changing
force.
The tubes are going to suffer highest force when the robot is going downstairs,
because the shafts will incur impact.
Fatigue analysis
The three wheel tube is one of the critical elements of the robot. In order to
know which is going to be its lifetime, the calculus of the fatigue has been carried out.
The fatigue determines the lifetime of an element that suffers from repetitive forces. The
limit lifetime the robot must endure is a million of cycles, taking into account that a
cycle is a stair going up or down.
The forces the tube suffers vary depending on the robots working position.
That’s why the three situations in which the robot will work are going to be analyzed,
doing the circuit in a plane surface and going up and down the stairs.
There are three methods to perform the fatigue analysis, and as in this project
what it is wanted to obtain is the lifetime of the component knowing its nominal stress,
the one used is the S-N model. The S-N diagram makes possible to obtain the number of
cycles a component can work depending on the stress at which it is submitted.
The first situation that has been analyzed is when the robot is doing the circuit in
a plane surface. As the tube does not work turning on itself and it does not suffer any
impact, it will not suffer from fatigue when it is in a plane surface, given that in that
situation the force supported by the tube will be constant.
The second situation in which this analysis has been used is when the robot is
climbing the stairs. As the back wheel's tube and the ones of the front do not suffer the
same magnitude of force, the most critical ones have been analyzed. In this case, the
back wheel’s tubes are the ones that suffer the most. This happens because in this case,
they have to withstand almost all the weight of the robot when this is going up the stairs
(motors and electronic components).
The tubes suffer from bending stress, which will be caused by the strength of the
weight of the three-wheel stars situated in one side of the tubes while the other part is

built in the connection block. In order to calculate the stress originated, this formula is
used.
 
I
rrM io 
 (1)
When,
 
 
 
 
 4
o
i
mmInertia:
mmtubetheofradiousOuter:
mmtubetheofradiousInner:
NmtorqueBending:
MPastressBending:
I
r
r
M

In order to calculate the torque produced in bending while climbing the stairs, it
is necessary to know which the load that causes it is, which is obtained from static
analysis (Figure 34).
Figure 34 Free body diagram going upstairs position
When,
W1: Weight of the robot
W2: Weight of the cans
F1: Force suffered by the backside tubes
F2: Force suffered by the front tubes

After doing all the calculus that are necessary, it is obtained that the force
suffered by each tube is the next that is shown in the table 6.
Table 6 Results of the upstairs static analysis
1W [kg] 2W [kg] 1F [N] 2F [N]
17.5
2.5 62.86 35.14
Once having calculated the strength suffered by the tube, the bending stress have
been calculated. This stress calculated is the one the tube suffers in the least critical
situation, given that.
 
MPa1.318
11320.77
10)-(12.59562.86io
min 




I
rrM
S (2)
In the case of the inertia, is the one regarding to the axis perpendicular to the
axis of the tube.
  4
444
i
4
o
mm7711320
64
)20-(25π
64
π





dd
I (3)
The most critical situation is when the collision occurs. This phenomenon
appears due to the impact that the wheels have with the stairs when the three wheel
system is rotating (Figure 35).
Figure 35 Free body diagram going upstairs

In order to calculate the force suffered by the tube in that situation, the crash
equation has been used.
N85.183
050
40cos6.020cosm 11
T 




.t
θv
F (4)
When,
[s]crashofTime
s
m
hcratheofVelocity
[Kg]robottheofMassm
[N]crashtheinForce
1
1
T








t
sv
F
Knowing that the force just obtained is the one that suffer both back tubes, the
force suffered by each tube will be 91.925 N.
Both, the time of crash and the velocity of the robot before the crash, have been
obtained by making assumptions. In what the time of crash is concerned, the hypothesis
made is that the time of crash is really brief, assuming it is nearly zero. The velocity of
the robot before the crash, however, has been decided taking into account the maximum
velocity which is 1.137 m/s, that is to say the velocity of the crash must be lower than
this.
 
MPa928.1
11320.77
10)-(12.59591.925io
max 




I
rrM
S (5)
Once having calculated the maximum and the minimum stresses, it is possible to
calculate the medium and alternate stresses of the component, which are necessary to
know which the lifetime of the tube is. After that, the working cycle of the robot have
been concreted (Figure 36).
1.623MPa
2
m
minmax
m 

 S
SS
S (6)
0.305MPa
2
a
minmax
a 

 S
SS
S (7)

Figure 36 Working cycle of the robot
Once the medium and the alternate stresses have been calculated, the next step
will be to make the S-N diagram of the material before characterizing the component.
However, this will be in a process where the material’s lifetime would be infinite
without exceeded a certain force. This is the case, for example, of the steels. But in this
case the material is aluminum, a material that in any case its lifetime will be finite. The
stress calculated at 107
cycles (S7) is shown in the next figure (Figure 35). This stress
has been obtained from the program CES.
Figure 37 S-N Diagram of the tube
It is possible to see that the more cycles the component supports, its lifetime
decreases. As it can be seen, the previous S-N diagram is the one that corresponds to a
stress ratio of -1. The stress ratio is the ratio of the minimum stress experienced during a

cycle to the maximum stress experienced during a cycle. The stress ratio is obtained
with the next equation:
max
min
ratioStress
S
S
 (8)
The most common values for the stress ratio are 0 and -1, that is to say, when the
Smin is zero or when Smin and Smax have the same value, but one been negative. As in this
case the component does not accomplish any of these characteristics, the stress ratio has
been calculated.
68.0
max
min

S
S
(9)
As the only two regulated S-N diagrams are the ones that correspond to the
stress ratios 0 and -1, it is necessary to use the Haigh’s diagram in order to obtain the
stress value that will have a stress ratio of -1 and the same lifetime. To achieve that, the
first step is to locate the point A which is obtained joining the medium and alternate
stresses of the tube. After that, the equivalent stress has been calculated which will has
the same lifetime and a ratio of -1 (Figure 38). That is because is located in the same
line of the stress calculated previously and in the vertical axis, where Sm is zero so the
Smax and the Smin will be same in value but contrary in signs.
Figure 38 Haigh´s diagram
The equivalent stress is the value which is going to be used in the S-N diagram.
The next figure has been used to obtain the equivalent stress of the tube (Figure 39).

Figure 39 Equivalent strees calculation
After doing the necessary calculations, the equivalent stress has been obtained.
MPa306.0eq S
As it has been said before, the stress calculated is the one that corresponds to the
material, so, in order to calculate the stress of the component, some coefficients must be
applied (Table 7) [1]. As the stress value of the material corresponds to 107
cycles, the
coefficients have been also applied to this value. As it is a very difficult job to obtain
the coefficients that correspond to the aluminum, the ones used with steels have been
used. This is because it has been supposed that it is better to apply a no very exact
coefficients better than not applying any.
In order to obtain the stress of the component the next equation has been used.
f
vmftds
k
Scccccc
S
7'
7

 (10)

Table 7 Applied coefficient and the choosing criteria
Name of coefficient
Choosing criteria Value
Surface finish
cs
Machined and break
resistance 565 MPa
0.84
Dimensions and geometry
cd
Medium 0.85
Working way
ct
Testing and working in
bending
1
Reliability
cf
The stress considered is the
one of the limit of the
range, so the reliability is
maximum
(1)
1
Surface treatments
cm
Any surface treatment 1
Multiple effects
cv
Fretting, impacts, corrosion 0.75, 0.7, 0.8
Notch effect
kf
Any sensibility to notches 1
(1) The stresses of the stress range of the S-N diagram vary depending on the reliability of the component.
As in this case the stress used has been the one that corresponds to the line below, the one that has a reliability of
100%, the value of the reliability coefficient is 1.
After obtaining all the coefficients, the previous equation has been applied in
order to calculate stress of the component.
MPa89.24
7'
7 


f
vmftds
k
Scccccc
S (11)

In the next figure it is possible to see which the limit of the stress range of the
component is (Figure 40).
Figure 40 Limit range of the stress
Once the limit of the stress value has been calculated, the last part is to introduce
the equivalent stress in the S-N diagram in order to know where does it join with the
limit of the stress range and in that way calculate the lifetime of the tube (Figure 41).
Figure 41 Lifetime of the tube upstairs

As it is possible to see in the previous figure, the tube will last 7
102N 
cycles.
The third situation that has been analyzed is when the robot is going down the
stairs. The process that must be carried out in order to obtain the lifetime of the tube is
exactly the same to the one used when going up the stairs.
The first task is to calculate the force that causes the torque in bending. To do so,
the next free body diagram has been used (Figure 42).
Figure 42 Free body diagram downstairs position
After doing all the calculus that are necessary, it is obtained that the force
suffered by each tube is the next that is shown in the table 8.
Table 8 Results of the downstairs static analysis
1W [kg] 2W [kg] 1F [N] 2F [N]
17.5
2.5 62.86 35.14
Knowing this force, is possible to calculate the minimum stress suffered by the
tube, which is the one that suffered when going down the stairs. This minimum stress is
the same to the one calculated when going up the stairs.
 
1.318MPa
11320.77
10)-(12.52562.86r io
min 




I
rM
S (12)

As in the previous case, the maximum stress is the one obtained from the force
the tube suffer when the collision occurs.
Figure 43 Free body diagram going downstairs
The force is calculated with the next equation.
N76.275
0.05
40cos9.020cosm 21
T 




t
θv
F (13)
Knowing that the force just obtained is the one that suffer both back tubes, the
force suffered by each tube will be 137.88 N.
Once having obtained collision force, the maximum stress has been calculated.
 
MPa785.5
11320.7
10)-(12.525137.88r io
max 




I
rM
S (14)
The next step is to calculate the alternate and the medium stresses.
MPa55.3
2
m
minmax
m 

 S
SS
S (15)
MPa23.2
2
a
minmax
a 

 S
SS
S (16)
In order to obtain the lifetime of the tube when going down the stairs, it is
necessary to calculate the stress ratio of the component.
22.0
max
min

S
S
(17)
As in this situation the stress ratio is not 0 or -1, the Haigh’s diagram has been
used, in order to obtain, in this case also, the equivalent stress value that will have the
same lifetime that the tube.

MPa26.2eq S
The last step is to introduce the equivalent stress in the S-N diagram in order to
obtain the lifetime of the tube.
Figure 44 Lifetime of the tube downstairs
As it can be seen in the previous diagram, the lifetime of the tube when going
down the stairs is of 7
101N  cycles.
Damage
Fatigue damage of a component increases with the applied cycles in a
cumulative manner which can lead to the fracture of the part. In order to know how
much the three-wheel tube suffers in each cycle, the damage of the three-wheel tube has
been calculated. [2]
The damage of a component refers to how much the component suffers in each
cycle. It is measured in percentages, where the maximum damage, the fracture of the
part, corresponds to hundred per cent.
100
i
i
i 
N
n
D (18)

When,
force.asufferinglifecomponentsThe:
cycles.ofnumberActing:
[%].cycleeachinsuffereddamageofPercentage:
i
i
i
N
n
D
The acting number of cycles depends on the magnitude in which is wanted to
calculate the damage. As one of the specifications of this project is that the robot must
go up and down three stairs, the damage is going to be calculated taking into account
those two parameters.
In order to calculate the total damage the tube suffers when carrying out the
whole work, first of all is necessary to calculate the damage caused in each cycle in both
situations, when going up and down the stairs.
With the next equation, the damage suffered by the tube when going up the three
stairs has been calculated.
%105.1100
102
3
100 5
7
1
1
1




N
n
D (19)
In order to calculate the damage suffered when the robot is going down the three
stairs, the equation used is the same.
%103100
101
3
100 5
7
2
2
2




N
n
D (20)
Once the damages of the both situations have been calculated, in order to obtain
the total damage the tube will suffer when completing the whole working cycle, both
damages must be summed.
%105.4 5
21T

 DDD (21)
Even the damage of the tube calculated has a very low percentage, it is a logic
answer, taking into account the comparison between the lifetime of the component and
the working cycle that must perform.
Strain gages
After analyzing theoretically the behavior of the structure, a real analysis has
been done. In the theoretical part, it was concluded that the gage should be collocated in
the longitudinal tube and the indicator below the bottom plate, figure 45. The two
different analyses have been done in the same time and with the same weight.

Figure 45 Position of the strain gage and indicator
First of all, to start with the real analysis, the strain gage was set to the
mentioned tube. The used strain gage is a three-element rosette one, a strain gage which
can measure out in three different ways. This peculiar gage, figure 46, is used when the
direction of the tension is unknown and as the theoretical analysis doesn´t inform, this
strain gage is exemplary.
Figure 46 Three element rosette gage
Once strain gages have been chosen and assembly has started, it is important to
have in mind the specifications of the company in order to do a correct measurement
while the structure is supporting the overweight, figure 47. [3]

Figure 47 Robot with the overweight of 70kg
After the analysis has been realized, those are the results of the unitary
deformation of the strain gages. The three strain gages have those unitary deformations
and taking into account the figure 46, the maximum (εmax) and minimum (εmin) principal
strains will be calculated apart from the maximum shearing strain (γmax).
 
 
  6
3
6
2
6
1
1072gageGreen
10173gageWhite
1052gageRed









The red gage will be in traction but the other two strain gages, white and green,
will be in compression. The white strain gage is in the longitudinal direction of the tube
and when the weight is applied in the sheet it will have a vertical displacement. In the
same way, it will produce a compressive force in the tube, that´s why the white strain
gage has the bigger unitary deformation.
     52
32
2
3121max 10259,52
2
1 



  
(22)
     42
32
2
3121min 10736,12
2
1 



   (23)
     42
32
2
31max 10261725005,22 
 
(23)

On the other hand, as ε1 is bigger than ε2, the angle to the maximum strain is
rotated ϕP clockwise from the first axis, and the minimum principal strain is located at
ϕP+90º.
  º918.2
2
tan
2
1
21
2131
P 







 


 (24)
The maximum strain will be 2.918º counterclockwise from the first axis (red
gage) and the minimum principal strain will be located at the angle but from the second
axis (white axis), as it can be appreciate in figure 48.
Figure 48 Position of the principal strains
Once the directions of the maximum and minimum principal strains are known,
it´s possible to calculate the principal stresses that are going to have each strain and it
will be possible to calculate the maximum sharing stress too. First of all, it´s necessary
to know the properties of the aluminum to get a result and thus [4]:
33.0
MPa69000E



  MPa364.0
1
E
minmax2max 

 

 (25)
  MPa097.12
1
E
maxmin2min 

 

 (26)
 
MPa867.5
12
E
maxmax 

 

 (27)
The maximum principal stress will be in the maximum principal strain, while the
minimum principal stress will be in the minimum principal strain. Apart from that, the
maximum shearing stress created by the overweight in the longitudinal tube will be of

5.867 MPa. Those stresses are the ones that will be produced in the principal strains, as
it had been said before.
At the same time that the strain gage is measuring the unitary deformations, the
indicator is measuring the maximum displacement of the sheet, where the overweight is
applied. This indicator, figure 49, has measured that the sheet will deform less than 1
mm.
Figure 49 Indicator above the sheet
2.5. Automation of the robot
As the robot designed has to be autonomous, is necessary to develop an
automation system architecture. In this case, it has been decided to use programmable
logic system instead of electrical wired system controller. The reasons of that decision
are the next ones:
 The robot has to move in manual and automatic modes so is necessary to
have a programmable logic controller.
 It requires less space to the components.
 Simpler connections than electrical wiring.
After choosing the automation system it can be said that the automation level of
our robot is machine level. The controller that will be used is a PLC.
The main components of the automation system are the remote control, the
controller (PLC) and the electric motors. Apart of that, some sensors (inclinometer and
LDR), a lights module and a buzzer are used too.

2.5.1. Elements
Remote control
The remote control is the element that allows the operator control the robot. The
remote is made up with different elements that are necessary for the correct
functionality of the robot:
 Joystick
 Two position switches
o Manual/Auto modes
o High/Low velocities
 Start button
The remote control allows two modes of moving, such as manual and automatic.
In manual mode, the robot is able to move in any direction in two different velocities.
Besides, it includes a start button that will be used to begin or finish the automatic
cycle.
As you can see in the next image, the remote control is composed by the
following elements (Figure 50).
Figure 50 Remote control
Joystick
One of the most important ability of the robot is to move in any direction such
as, forward, backward, left and right. To achieve that, a joystick has been added to the

remote control. This device will be the one will allow the operator control the four
directions of the robot.
Two position switch
This element allows the operator to change the robot modes from automatic to
manual mode and the velocities from low to high velocity.
Start button
The start button is the element that allows the operator to start or finish the
automatic mode, sending the signal to start or finish the circuit.
PLC
As it has said before, the controller that will be use is a PLC. That component
will receive the signal of the inputs and, after interpreting that, will send the order to the
outputs. To do that process, is necessary to upload a program to the controller to know
which orders have to send to each output. The connections between the inputs and the
outputs with the controller will be point to point [5].
The characteristics of the PLC are the next ones:
 12 digital inputs.
 2 analog inputs.
 8 outputs.
 24V Power supply needed.
Others
Lights control
A LED module has been installed in the robot to illuminate it in dark places. To
control that a LDR sensor has been added, is an electric component whose resistance
varies depending on the light received. This sensor switches on the lights when the
ambience starts to get dark [6].
To program the LDR is necessary to add a resistance to the circuit, in order to be
able to measure the resistance of the detector and make the PLC know if the lights must
be switched on or not. This is due to the fact that the PLC is only able to read the

voltage, not the resistance. If another resistance is not added, even if the resistance of
the LDR changes with the change on the light intensity, the voltage received by the PLC
will be of 24V, a constant value. With the other resistance, however, with the change on
resistances, being the current of the circuit constant, the value of the voltage will
change, sending to the PLC different values of voltage. The voltage sent to the PLC will
be the one of the second resistance and depending on that value the one of the LDR will
be different. After some calculus, appendix D, the value of the second resistant will be
150 Ω. This element is going to be connected to the analogue input of the PLC (Figure
51).
Figure 51 LDR electric circuit
Inclinometer
This sensor is part of the security system of the robot. One of the restrictions of
the robot is that it cannot be inclined more than the maximum angle established in the
specifications (40º). So, the inclinometer ensures that the robot will work always with
an angle less than 40º.
Buzzer
The buzzer is an emergency element that provides security to the people that are
around the robot, that is to say, any time that the robot is going to start to turn the buzzer
warns people.
2.5.2. Electric circuits
The automation system is made by two electrical circuits: Power and order
circuits. The first will be used to supply the different components of the circuit and the
second, using the PLC, will be to control all the components.

In the next table (Table 9) all the components of each circuit is shown:
Table 9 Elements of power and order circuits
Component Function
Power circuit
KA1 Relay
Change power
supply
KA2 Relay Forward or stop the
M1 motor
KA3 Relay Backward or stop
the M1 motor
KA4 Relay Forward or stop the
M2 motor
KA5 Relay Backward or stop
the M2 motor
M1 Motor
Movement of one
side of the robot
M2 Motor
Movement of one
side of the robot
Order circuit
Joystick
Control the
movement of the
robot
PLC
Control the output
elements
Two position
switch
Select manual/auto
mode
Two position
switch
Select high/low
velocities
NO Start button
Start/finish auto
cycle
Other elements
NC Inclinometer
Limit the angle of
the robot
Lights module and
LDR
Switch on/off the
lights

The power circuit contains four relays to supply the motors and one to change
the power supply. The relays will be activated by the PLC. In every moment a power
supply will be connected such as the 24V or 12V. When a signal arrives to the
controller, it will send a specific signal previously programmed, which will activate the
different relays to supply the adequate motor with a certain current. The power circuit is
shown in the next image (Figure 52).
Figure 52 Power scheme
In what the order circuit is concerned, all the control will be done through the
PLC. The inputs are the components that will send the signal to the controller. After
that, the controller will interpret that signal and will actuate the output that corresponds.
The order circuit and the different inputs and outputs are shown in the figure 53 and
table 10.
Table 10 Inputs and outputs of the PLC
Digital inputs Analog inputs Digital Outputs
Joystick
Manual/Auto switch
Velocity switch
Start button
Inclinometer
LDR
KA1 relay coil
KA2 relay coil
KA3 relay coil
KA4 relay coil
KA5 relay coil
Lights module
Buzzer

Figure 53 Order scheme
2.5.3. Programming of the PLC
As the PLC is a programmable controller is needed a program that fix all the
actions of the cycle in the PLC. The programming language used is ladder type. Before
starting programming the controller, a previous work has been done. Some GRAFCETs
have been developed to represent the program. In this case two types of GRAFCET
have been done: First level and second level.
A GRAFCET is a model of graphic representation which gives the possibility to
do a model to automate processes, taking into account entrances, actions to be carried
out and the processes caused by these actions.
In first level diagrams the steps and the actions of the program are shown.
However, in the second level ones apart of the actions and the steps the inputs and the
outputs are taking account. The first level diagrams are shown in the figures 55, 56, 57
and 58. For more detail the second level diagrams and the program are attached in the
appendix E.
In this project, as the robot must work in both an automatic and manual mode,
at least two different GRAFCETs will be necessary. Apart from those, as an
inclinometer and lights are included in the circuit, each of the elements will be
represented in its own GRAFCET.

As far as the automatic mode is concerned, this one is activated with a two
position switch, which can be switched on in any moment of the circuit. When the
automatic program is activated, the robot remains still until the start button is pressed,
when the robot starts its path. The circuit programmed is the next one: forward in the
beginning, turn left, short forward, turn left and long forward, which is show in the
figure 54. Once this circuit has been completed, a loop is entered into and it is started
from the first turn left. Each of these movements is controlled by a timer, giving to the
robot certain time to do the different movements.
Figure 54 Programmed circuit
Figure 55 First level automatic mode GRAFCET

In the case of the manual mode, as the previous one, can be activated in any
moment, even when the automatic mode is been executed, by activating it with the
switch. The main difference with the automatic mode is how the robot is controlled. In
this case, if any movement is wanted to be maintained continuously, the joystick must
be maintained pushed. That is to say, if any moment is pushed in the joystick, the robot
will stop immediately. In this mode, unlike in the other one, the robot can work in two
possible velocities, a fast one when climbing the stars and a slower one when going
down. To activate any velocity, the manual mode must be activated. The image below,
figure 56, shows the GRAFCET of the manual mode.
Figure 56 First level manual mode grafcet
In respect of the inclinometer, it is a normally closed detector which is only in
the manual mode, given that the automatic mode is carried out in a plane surface. When
the robots inclination increases more than 40º, this detector activates stopping the robot
and letting only the backward movement, till the inclination of the robot decreases the
40º. The next image, figure 57, shows the grafcet of the inclinometer’s program.

Figure 57 First level automatic mode GRAFCET
Regarding the lights module, they are switched on when the light received by the
sensor is less than the 30% of the maximum. The lights module program is shown in the
next image, figure 58.
Figure 58 First level lights module GRAFCET
Finally, as regards the buzzer, is activated every time the robot turns left or right.
2.6. Budget
To know the economic value of the prototype, a budget has been calculated. The
different costs have been divided in three groups and one of these groups has been
divided in other four subgroups:
 Electrical components
 Commercial elements

 Parts of the robot
o Costs of the mechanizing of the parts
o Costs of the manual operations
o Costs of the preparation operations
o Costs of the unexpected operations
The electrical components have been the first costs calculated, taking into
account the list of the elements ordered and the price of each one. The total price has
been obtained summing the final price of each component. All that information is
shown in the table 11, where some elements appear without VAT because the supplier
gives directly with it.
Table 11 Electrical component´s total price
In the next step the price of the commercial elements needed in the robot have
been calculated. The prices have been taken from the catalogues of the suppliers, and
knowing the quantity of each element, the final price has been obtained, as it can be
seen in the table 12.

Table 12 Commercial element´s cost
Finally, the cost of the manufacturing has been calculated in three different
parts, as it has been said before.
First of all, apart from the cost of the raw material of each part the
manufacturing operation costs have been calculated. In order to know how much does
each operation costs, the tax of each machine has been specified, that is to say, how
much each machine costs per hour. These taxes are shown in table 13.
Table 13 Machine taxes
Once that these taxes are known, the manufacturing time has been calculated for
each part and multiplying those factors the total value has been calculated. The process
to calculate the time of each part is attached in the appendix E the results obtained is
shown in the table 14. The three wheel shafts and stars have been manufactured in a
company outside the university, so they have not been taken into account the price of
the machine. Their entire price has been taken inside price of the raw material.

Table 14 Raw material and machining cost
However, apart from the machining cost other ones have been also taken into
account, such as manual operation, preparation time and unexpected operation costs.
The manual operations represent the 20% of the machining time, the preparation time
the 15% and the unexpected operations the 10%. The results have been shown in the
next tables, respectively (15, 16 and 17).

Table 15 Manual operations costs

Table 16 Preparation time cost

Table 17 Unexpected operations cost
Summing all the different points, the final budget obtained for manufacture the
robot is the next one (Table 18):
Table 18 Final budget of the manufacturing of the robot

So, the necessary money to manufacture the robot will be 1677.74€. The
transporting taxes have not been taken into account because they differ depending on
the place where the company is.
As it can be seen in the figure 59, most of the money needed is divided between
the electrical elements, the commercial elements and the mechanizing of the parts. The
rest of the groups have not got much economic importance.
Figure 59 Distribution of the different costs [€]
To compare the budget obtained with the estimated by the university, an analysis
has been done, seen that there are some important differences between both costs. The
value of the budget that the Mondragon Unibertsitatea has provided is of 850.93€, and
the one calculated of 1677.74€.
There is a significant difference of 826.81€ between the two budgets. After
analyzing all the elements bought, it has been concluded that this difference occurs
because in the one obtained by Mondragon Unibertsitatea, the two motors, the power
supply, the relays, the inclinometer, the LDR, the LEDs, the buzzer and one of the
position switch have not been taking into account. After adding this elements to the
budget of the university, the difference is 293.81€ between the two budgets.
The remaining difference can occur due to these reasons:
 The commercial elements ordered on the budget and the ones that the
university has provided are different and it can suppose a little difference
in the prices.

 In the budget given by the university, the price of the machine due to the
manufacture of each part have not been taking into account.
 In the budget given by the university, the unexpected operations and the
preparation time have not been taking into account.
Once having analyzed these differences, and not having taken into account the
price of the motors and the power supply, the results obtained are shown in the figure
60.
Figure 60 Distribution of the different costs [€] without some electric components
Now the value of the electrical parts is much lower, and the more expensive
group will be the one formed by the commercial elements. They are expensive because
the possible discounts have not been taking into account buying a concrete number of
pieces.
Supposing that the discount exists, the most expensive things will be the ones
related with the manufacturing of the robot. In all the cases, the preparing time, the
manual operations and the unexpected operations represent a very low percent of the
final price.

RESULTS
3. RESULTS
 A redesign of the robot has been carried out, modifying three elements of
the first design: the stars, the structure of the robot and the shafts of the
stars. The achieved final design is shown in the figure 61.
Figure 61 Robot’s final design
 Also a can collector has been manufactured and assembled.
 The most critical elements of the robot have been analyzed theoretically.
The deformation, displacement and stresses suffered by each part with
the overload applied are shown in the next table, table 19.
Table 19 Results of the theoretical analysis
Element
Unitary
deformation
Displacement
[mm]
Stress [MPa]
Structure 4
10895.1 
 1
10366.5 
 15
Motor plate 4
10229.3 
 1
10045.1 
 2.112
Three-wheel star
model
4
10772.8 
 1
1039.4 
 29.6

RESULTS
 The structure of the robot has been analyzed with the strain gage and the
indicator. The results obtained are the next ones:
o Transversal unitary deformation:
6
1 1052 

o Longitudinal unitary deformation:
6
2 10173 

o Diagonal unitary deformation:
6
3 1072 

o Maximum principal stress: MPa364.0max 
o Minimum principal stress: MPa097.12min 
o Maximum shearing stress: MPa867.5max 
o Maximum displacement of the sheet: mm95.0max 
 The next table shows a comparison between the theoretical and practical
results (table 20).
Table 20 Comparison and error between the theoretical and practical results
Theoretical
result
Practical
result
Error [%]
Structure
Unitary
deformation
6
105.189 
 6
10173 

4.55
Displacement
[mm]
0.5366 0.99
29.7
Stress [MPa] 15 12.097
10.71
 The robot is able to withstand
7
102 cycles going upstairs and
7
101
going downstairs.
 The damage suffered by the robot during the whole working cycle (three
stairs up and down) is of %105.4 5
 .
 An automation system has been designed that achieves the next actions:
o The vehicle moves in autonomous way using a remote control
o The robot stops if finds an obstacle that demands a higher slope
than 40º, and can only move backward. The device used to
achieve that is an inclinometer
o The robot is able to make the defined path automatically.
 As some outputs of the PLC were free, the extra components added in
order to take advantage of them were the next ones:

RESULTS
o Light control module
o Buzzer
 The budget of the project has been 1677.74 €.
o The most expensive elements are the two motors, the relays, the
power supply and the parts manufactured outside the university.

CONCLUSIONS
4. CONCLUSIONS
This stage of the project has been based, mainly, on the redesign, manufacture
and test of the robot’s prototype.
In what the redesign is concerned, three have been the parts modified. Regarding
the stars, once redesigned, the weight of the robot has diminished, apart from ensuring
that it will not hit the stairs when going up and down. In respect of the structure of the
robot, modifying it a stronger design has been obtained, making the robot able to
support in a more secure way the weight of the electric components and cans. Moreover,
the robot is able to withstand four times its weight. The last element redesigned, have
been the shafts of the stars, which modifying them transmit the movement in a more
efficient way.
In what the manufacturing and assembly is respected a robot which contains the
characteristics to completed the path and going upstairs and downstairs have been
achieved.
In order to improve the design, the possibility to machine three of the parts of
the robot in an external supplier have been given in one specification. However, the
quantity of those parts has been exceeded to secure the functioning of the gears not
achieving the specification named.
Generally, the assembly of the robot have been quite simple. Nevertheless, in the
three-wheel stars some difficulties have been appeared. The alignment of the three-
wheel shafts have not been completely achieved due to the non-perfect manufacturing
of the holes to introduce the screws, that is to say, the concentricity between parts have
not been achieved in all. Consequently, as the three-wheel stars have been introduced in
the shaft named before, the same problem has been appeared in those conjuncts.
Finally, it has been seen that the transmission between the gears consumes a part
of the power of the motors, reducing the velocity of the robot. This problem has been
appeared due to the material of the gears, which is nylon.

CONCLUSIONS
Taking into account the parameter imposed in the first part of the project, the
sheet where the overweight will be situated cannot be deformed more than 1mm when
the overweight is applied, and this has been respected.
In the redesign it has been concluded that the shafts are not the ones that suffer a
part of the weight of the robot, but the tube.
In the case of the motors plate, this will permit the correct functioning of the
motor, because is stiff enough.
The errors produced in the comparison between the theoretical and practical
results, is because the elements analyzed in the software have been very simplified, due
to the fact that the model has been modified in the workshop during the assembly and
because the overweight installed in the sheet is not uniform at all.
The comparison between the theoretical and practical results have been
satisfactory in what unitary deformation and tension are concerned, but not in the case
of the displacement.
Comparing the results obtained in the fatigue analysis and the limit previously
imposed, it can be seen that the robot will actually work in a proper way in the lifetime
estimated.
As the lifetime of the tube is so long, it has also been proved that the damage
suffered by the tube in each working cycle, three stairs up and down, will be minimum.
The robot has the ability to complete the path specified in a correct and
automatic way due to the correct programming of the PLC and the wiring system. Apart
from that, the vehicle is also able to move in a manual way thanks to the same reason.
In the case of the inclinometer, it accomplishes its function but it does not work
in a very precise way. Apart from that, when the robot vibrates due to the unevenness of
the ground, the inclinometer detects it stopping the robot. In order to solve this problem,
the program of the inclinometer has been modified with the aim of neglecting the effects
of the vibrations.
Another drawback of the inclinometer is that, as it is very sensitive to the
movement, when the robot vibrates due to the unevenness of the ground, the
inclinometer detects it stopping the robot. In order to solve this problem, the

CONCLUSIONS
inclinometer has been programmed to stop the robot only if the sensor maintains
deactivated more than a second.
Thanks to the light control module the robot is able to switch on the lights when
it is getting dark. The other component added has been a buzzer that beeps every time
the robot turns in order to warn the people that are around.
In what the budget of the manufacturing and assembly of the robot is respected,
the maximum value for the budget imposed by the university has been overtaken.
As the difference between the obtained and the ordered budget is the double, a
deep analysis has been made with the intention of reducing the price of the robot. After
finishing the analysis of the budget, it has been determined that is impossible to remove
any element because all of them are vital for the correct functioning of the robot. The
unique solution will be to negotiate the prices of the different elements with the
suppliers.
In what the planning of the project is concerned, it is possible to say that it has
been followed in a quite adequate way. The length and distribution of the tasks have
been accomplished, respecting the workload during the whole project. However, the
aspect that hasn’t been followed is the beginning date of some tasks, even it hasn’t been
a problem in the development of the project.

FURTHER RESEARCH
5. FURTHER RESEARCH
After the manufacturing and testing of the robot, it has reached to the conclusion
that some aspects need a redesign.
First of all, the most important aspect to be improved is design of the
transmission system. In the case of the gears, in order to enhance the power
transmission the material of these elements could be changed. Due to this modification
the contact between the gears will improve significantly the operating of the robot.
Apart from that, the dimensions of the pinions that tensile the chain could be diminished
to reduce their weight. This makes the chain able to assembly in an easier way, apart
from improving the functioning of the chain. With these changes the robot will move
with a faster velocity.
Another aspect of the design that could be modified are the wheels, which
having greater dimensions the robot will climb the stairs easily.
In what the mobility of robot is concerned, two are the aspects that could be
improved. In the case of the inclinometer, as it does not accomplish the specifications in
the best way possible a more precise one could be used. In this way the problem of the
vibrations will be solved. Besides, the power supply could also be changed by batteries,
providing in that way more autonomy to the robot.
Finally, in order to improve the aesthetic of the robot, the wiring could be picked
up in a more covered way.

REFERENCES
6. REFERENCES
[1] Universidad Carlos III de Madrid. Diseño de componentes mecánicos en base a
resistencia a la fatiga. [Online] [Consult: 04-06-2015] [http://ocw.uc3m.es/ingenieria-
mecanica/diseno-de-maquinas/material-de-estudio/fatiga_transparencias.pdf ]
[2] Imac. Fatiga estructural. [Online] [Consult: 01-06-2015]
[http://www.imem.unavarra.es/EMyV/pdfdoc/elemaq/em-transparencias_fatiga.pdf ]
[3] Tokio Sokki Kenkyujo Co. Catalogue Strain Gauges. [Consult: 10-06-2015]
[4] Universidad de Chile. Módulo de Young y coeficiente de Poisson para distintos
materiales. [Online] [Consult: 10-06-2015]
[5] Omron. CP1 CPU Unit. Operation manual. August 2008. [Consult: 20-05-2015]
[6] MORENO, Glenis., MARTINEZ, Fernando. Mediciones industriales. [Online]
[Consult:15-05-2015]
[http://martinezmorenomedicionesind.blogspot.com.es/2007/06/fotoresistencia-
ldr_16.html ]

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