PRACTICAL METHOD OF CONSTRUCTING MECHATRONICAL

PRODUCTS
Grujičić R.1, Bratić D. 1, Grubiša L. 1, Mijanović O. 1, Mijanović Markuš M. 1, Mijanović Z. 2,
Tomović R. 1
1
University of Montenegro, Faculty of Mechanical Engineering Podgorica
2
University of Montenegro, Faculty of Electrical Engineering Podgorica

Abstract: Construction of an autonomic mobile robot for collecting pucks of different color is
developed using the methodological procedure of constructing. This article describes steps
used in developing construction and shows the final design solution.

1. INTRODUCTION
A team of students was formed at the Faculty of Mechanical Engineering in Podgorica
with the task of developing its own solution for autonomous robot and presentation of the
robot at one of the worlds’ contests. Being that a robot is typical mechatronical device, in
order to develop such product, knowledge in the field of mechanical engineering, electrical
engineering and mechatronics was needed, so that was a motive for selecting students of
mechanical engineering, electrical engineering and mechatronics as a team members. This
team took part at the Robot Challenge competition, held in Vienna, Austria, on 29th and 30th
of March, 2014, competing in the Puck Collect discipline.

2. PUCK COLLECT DISCIPLINE

Robot Challenge is a competition that is being organized since 2004 and up until now
over 1500 different autonomous robots were presented since then. Puck Collect is one among
the several disciplines organized at this competition. This particular discipline requires the
robot to move around the field, collect the pucks of appropriate colour and dispose them in its
own base. During the competitive round two robots compete against each other. One of the
robots has the task of disposing blue pucks, while the other one should deliver red pucks for
the time period of 3 minutes. Each properly disposed puck counts for one point. If the
disposed puck is in inappropriate colour, team is counted for one negative point. Round
winner is the robot (and the team) which collects more points.
Court dimensions are 2500x2500 [mm]. Bases (one blue, and the other red) are placed
diagonally. Their dimensions are 700x700 [mm]. Ten red and ten blue pucks (with diameter
of 40 mm, and height of 20 mm) are randomly distributed on the court (Figure 1).

Figure 1. Court and the randomly distributed pucks

3. METHODOLOGICAL PROCEDURE OF CONSTRUCTING
Development of construction for the puck collecting mobile robot is based on
methodological procedure of constructing. Constructors’ experience and intuition have the
dominant role in conventional methods for constructing. Regarding this, engineer was often in
situation to choose the solution that seemed the most suitable at the moment, without
comprehensive analysis of all the possible solutions and factors that define technical and
economical validity of the product. Considering all mentioned, methodological approach
tends to develop the process of construction as a general method that could be applied for the
realisation of any constructors task, not only for individual cases. Methodological approach
tends to include logical thinking to a greater extent in the process of constructing, while
suppressing intuition, subjective decisions and “blind” following of a seemingly good idea, at
the same time. This approach does not neglect constructors’ talent and intuition, but improves
ones creativity and directs him/her on the development of new, better and more optimal
solutions, while simplifying and rationalising process, regarding time and resources
consumption.
Multiple methods in the field of methodological approach in constructing occurred with
the development of science of constructing. Methods differ from one another in terms of
complexity and approaches on problem solution. Method called “Practical method of product
construction” is being developed at the Faculty of Mechanical Engineering in Podgorica for
the past fifteen years. It can be used for development of new or modification of existing
products. This method focuses on finding more optimal and more creative solutions through
the realisation of appropriate physical effects. Procedure implies seven logically dependant
and mutually conditioned steps:
• task defining and change of properties,
• functional structure (logical model of construction),
• principles of solutions (physical model of construction),
• configuration of construction (objective model of construction),
• solution improvement (interference and fault analysis),
• selection of the most optimal solution and
• development of design details.

3.1. Task defining and change of properties

This phase implies comprehensive analysis regarding possibility of realization and
market placement of the product, investors’ requirements, etc. Previous, similar, solutions are
observed and analyzed, good ideas are pointed out, adequate literature is collected as well as
all the important information. It is necessary to define all the requirements that derive from
comprehensive analysis and place them into the requirements list consisted of three
categories: fixed requirements, tolerated requirements and wishes.
All of these requirements derive from the investors’ requests, market analysis, customer
needs, etc., depending on for whom is product being developed and quantity of units that need
to be produced. Fixed requirements are those whose fulfilment is unconditional. Therefore, all
the solutions that are not up to those requirements are considered unsuitable and eliminated at
the beginning. Tolerated requirements are the requirements that have a breach, or interval
within whom the solution could be found. It would be good if wishes could be fulfilled, but it
is not obligatory. Wishes represent the main criteria for selection of optimal solution among
the solutions that fulfil previous two categories of requirements. Table 1 shows the list of
requirements for the puck collecting robot.
 Table 1. List of requirements for the puck collecting robot
LIST OF REQUIREMENTS
FIXED TOLERATED WISHES
Autonomous operation of
Robot dimensions: Minimal costs of production
robot
up to 500x500 [mm]
Minimal costs of materials
Time for task Simple design
realisation: Good mobility
up to 3 minutes Higher speed of robot

3.2. Functional structure (logical model of construction)

Overall function of the product should be defined in one sentence. In this particular
case, that sentence is: “It is necessary to create an autonomous mobile robot which will move
around the court, collect pucks in appropriate colour and dispose them to the defined
location.” Overall function needs to be disassembled in multiple partial and elementary
functions. Partial functions contain defined and existing solutions (i.e. gears, heat exchanger,
etc.), while elementary functions are based on application of appropriate physical effects. In
this particular case, overall function is disassembled into the following partial and elementary
functions: motion, collecting, (puck) colour identification, sorting, storing, detecting an
appropriate base, and disposal (of pucks). By combining partial and elementary functions,
various functional structures can be formed. Some of the possible functional structures are
shown in the Figure 2.
Randomly arranged Sorted and

pucks disposed pucks

1. motion 2. collecting 3. sorting 4. storing 5. disposal

signal 1

6. colour identification

signal 2
7. detecting an appropriate base

a)
7. detecting an appropriate base
1. motion
signal 2

2. collecting 3. sorting 4. storing 5. disposal

signal 1

6. colour identification
Sorted and
Randomly arranged
disposed pucks
pucks b)
Figure 2. Functional structures for the autonomous mobile puck collecting robot
 Next step is forming of a list for selection of an optimal functional structure. Each
functional structure is evaluated with the “+” or the “-“ sign based on the questions that derive
from the list of requests:
• is the functional structure appropriate for the technical task,
• are the requirements fulfilled,
• is realisation of the project possible,
• is the development of the construction simple,
• are the material, manufacturing and maintenance costs optimal, etc?
Only the functional structures evaluated with all the “+”’s are appropriate for the next
phase.

3.3. Principles of solution (physical model of construction)

It is necessary to define all the possible physical effects, which represent potential
solutions of partial functions, for the previously disassembled overall functional structure. It is
recommended to come up with as many solutions as possible during this phase, and write
them down – even the ones that are not entirely fulfilling tasks’ requirements. Each solution
needs to be numbered, sketched and (if possible) described with appropriate equation.
Principles of solutions for the partial function “sorting” are shown in the Table 2. All
the other partial and elementary functions should be treated in this manner.

Table 2. Principles of solutions for the partial function “Sorting”

3. Partial function: SORTING

Field of Solution
Physical effect Principle solution
physics no.
Sorting is done by a single septum
that would be in a right or left
position depending on the colour
of the upcoming puck
Rotational motion of the septum
Mechanics 3.1

௣ 
௜   ∙ 

௣

Sorting is done by rotating element

with barriers (septum)
Rotational motion of the rotating
element
Mechanics
௣ 
௜  ௧௥ ∙ 3.2

௣   ∙   ௣௔௞ ∙ ∙

௣
 Table 2. Principles of solutions for the partial function “Sorting” (SEQUEL)
3. Partial function: SORTING

Field of Solution
Physical effect Principle solution
physics no.
Sorting is done by a channel with a
Effect of free fall (free fall of the gape at its bottom which would
open and close if necessary
puck through the gape)
௣௔௞  ∙
Mechanics ௣௔௞  2 ∙ ∙ 3.3

Rotational motion of gapes’ door

௣ 
௜   ∙ 
௣௔௞

Sorting is done by two doors. One

door is being opened for the pucks
of one colour, and the other door is
being opened for the pucks of a
different colour.
Rotational motion of the door
Mechanics
௣ 
௜   ∙ 
3.4

௣
௣

Sorting is done by element which

would divert the direction of
Impact force of the element (slider) pucks’ motion
Mechanics into the puck – action force
3.5
(mechanisms)
 ∙

Sorting is done by element which

would divert the direction of
pucks’ motion

Impact force of the element (piston)

into the puck – action force
Hydraulics 3.6
 ∙
 Table 2. Principles of solutions for the partial function “Sorting” (SEQUEL)
3. Partial function: SORTING

Field of Solution
Physical effect Principle solution
physics no.
Sorting is done by element which
would divert the direction of
pucks’ motion

Impact force of the element (piston)

into the puck – action force
Pneumatics 3.7
‫ܽ∙݉= ܨ‬

Sorting is done by air flow which

would divert the direction of
pucks’ motion

Fluid Air flow 3.8

mechanics

Sorting is done by suction of

elements of an appropriate colour

Fluid Suction force 3.9

mechanics

All the proposed principles of solutions are evaluated in the same manner as the
functional structures in the previous phase. So called morphological box is being created out
of the positively evaluated solutions. Afterwards, basing on the principle of compatibility,
solutions are combined and various conceptual variants are formed in that manner.
Conceptual variants need to be evaluated in reference to the criteria formed according to the
list of requirements. Each criterion, based on its significance, has its own weight factor. Each
criterion for conceptual variant can be evaluated with a degree from 0 to 4. That depends on a
degree of fulfilment of conceptual variant in reference to a criterion based on list of
requirements. Total value obtained by multiplication of weight factor and degree of fulfilment
for each criterion represents the basis used for further evaluation of optimal solutions.
3.4. Configuration of construction (objective model of construction)
It is necessary to form a three-dimensional
three dimensional model of construction which will be capable
of reproducing the previously defined physical effects in the previous phase, based on the
optimal conceptual variant. This phase implies certain calculations and estimates that will
enable quality synthesis of individual elements of construction. First step is forming of a basic
dispositional sketch for the principle solution. BasingBas on the dispositional sketch,
constructional variants are formed. They are all based on the same physical effects, but differ
from one another regarding form, quantity, dimensions and position of working bodies and
surfaces. List of conceptual variants for the adopted and optimal solution for partial function
“Sorting” is shown in the Table 3.. List of conceptual variants for other partial functions is
also formed in this manner.

Table 3. Variation matrix for the principle solution 3.2

3.2.1

Basic
disposition

3.2.2 3.2.3 3.2.4

Shape variation
of the working
surfaces

3.2.5 3.2.6 3.2.7 3.2.8

Quantity and
shape variation
of the working 3.2.9 3.2.10 3.2.11 3.2.12
surfaces

3.5. Solution improvement (interference and fault analysis)

Each individual variant is considered and checked separately to determine if it could
perform without interferences. If any interference or fault causing the non-functionality
non functionality of the
construction is determined, it is necessary to propose the countermeasures
countermeasures for its removal or
reduction of its effects. Interference and fault analysis for individual variants is shown in the
Table 4.
 Table 4. Interference and fault analysis for puck collecting robot
Partial
INTERFERENCES AND FAULTS COUNTERMEASURES
solutions
Calculation of the relevant properties of
1.8.1
Insufficient motor power for robots’ the motor is needed. Number and
to
motion placement of drive motors should be
1.8.6
determined basing on the calculations
Right side of the conic element should be
Possible jam of the pucks in the conic moved forward in reference to the left side
element constriction (or vice versa)

2.6.1
to
2.6.5

Set up an additional barrier between the

Possible disposition of puck in an
compartments which will direct puck in
inappropriate disposal compartment
the appropriate compartment for disposal

3.2.1
to
3.2.12

3.6. Selection of the most optimal variant

Main goal of the evaluation of variants is a selection of a single conceptual variant for
each partial function. Overall optimal variant is obtained by combining those conceptual
variants. Due to numerous possible solutions, evaluation procedure is performed in two steps.
First step implies the selection of the optimal variants obtained after the interference and
fault analysis (in the same manner that optimal conceptual variants were evaluated and
selected).
Second step implies forming of the morphological box out of optimal conceptual
variants, combining them in all the compatible ways and selecting the most optimal one after
the process of evaluation.
The result of all the previous phases of methodological approach is the first assembly
technical drawing, shown in Figure 3.
 Figure 3. Final model for construction of puck collecting robot (disassembled)
1) cover, 2) electrical components support, 3) base Plexiglas plate, 4) the drive motor
support, 5) drive motor, 6) driving wheel, 7) free wheel, 8) conic element, 9) storage
compartments’ door motors, 10) storage compartments’ door motors’ support

3.7. Development of design details

This phase refers to a fine design improvements. Up until this phase, the assembly
technical drawing and first three-dimensional model of the construction are obtained. Basing
on that information, each individual part of the construction is considered and analysed. Final
dimensions and shape of each element are defined and then the workshop drawing is being
made. Final calculations and estimates are being done for defining tolerances, surface quality
and similar, if needed. Result of this phase is completion of the technical documentation.
Manufacturing of each element should be done at the end according to the workshop
drawings.

4. CONCLUSION
Originally, the idea was for robot to suck pucks and sort them in the suction channel.
Application of the methodological approach for the design development pointed out to a much
realistic and simplier solution.
Comprehensive analysis determined the weaknesses of the construction and proposed
measures for the improvement.
The result is a very simple, but effective design which can be improved in the future,
also using the methodological procedure approach. Participation at the competition provided
an opportunity to see other teams’ solutions for this particular task, good ideas, but also the
weaknesses other robots have. This could be valuable experience for further adaptation and
improvement of our robot.
Team work and application of methodological approach of the design development led
to a simple conceptual solution. However, robot design should be improved in the upcoming
phases. Suggestions for the improvement are following:
• supporting wheels should be substituted with the so called “Bull's-eye caster”
wheels, considering that supporting “standard caster” wheels affect the predicted
path of the robot;
• by using the “Omni” wheels as the driving ones, mobility and agility of the robot
would be greatly improved, which is very important for the successful task
realisation;
• one directional door which would open only on the inside of the robot should be set
up at the entry area of the conical element (this door would prevent the collected
pucks to leave the conical area during the backward motion of the robot);
• number of the ultrasonic sensors should be reduced due to Doppler Effect which
may occur when there are many ultrasonic sensors operating on different
frequencies in the limited area. Ultrasonic sensors could be replaced with the
bumper sensors;
• colour detection sensor is based on the SMD technology, so for a precise reading
and determination of the colour object must be very close to the sensor (about
2mm). Due to this fact, usage of the more powerful sensor should be considered;
• finally, instead of the DC motor, modified servo motor should be used for the
sorting operation. Servo motor can provide valuable information regarding position
and rotation speed.

REMARK
This paper is supported through the Project of multifunctional service robot “MNE-
ROBECO” (2012-2015) which is funded by Ministry of Science of Montenegro, and whose
representative is Faculty of Mechanical Engineering in Podgorica, at the University of
Montenegro.

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