Development of Low Cost Printable Modular Robot

Development of Low Cost Printable Modular Robot

Saket M. Pardeshi

Prajakta P. Pachore

Pratibha Nalini R

Arockia Selvakumar A*

SMBS, VIT University,

Chennai, India *[email protected]

Abstract

Modular robotics is a new approach in the field of robotics. Modular robots are

autonomous and self-reconfigurable. It can change its shape by changing its topology. This

research gives a detailed of hardware design and development of control system for semi-self -

reconfigurable robotic system. Semi-self-reconfigurable robot is homogeneous type with 3D

printed modules. Research deals with change in configuration of existing modules, reproduction

of modules and equipment advancement, obscuring the edge between the computerized and

physical world. Control system is designed such that locomotion is optimized for power

consumption. This research also focuses on study of locomotion and the phase difference which

is a major factor for locomotion. Snake like locomotion is achieved by sinusoidal wave. Each

module consists of sinusoidal generator. Each sinusoidal generator acts as Central Pattern

Generator (CPG), which controls rotation angle of each module. Arduino is used as control unit.

Use of Arduino enables ease of programming and hardware development.

Keywords: Modular Robot; rapid prototyping; semi-reconfigurable robot; Locomotion;

Central Pattern Generator; Printable Modular Robot; Arduino

1 Introduction A robot is a mechanical or virtual specialists, more often than not an electro-mechanical machine

that is guided by a PC program or electronic hardware. Robots are of various types according to structure, function etc. Modular robotics is a type of robotics where each robot is composed of large number of repeated module. This modules are capable of rearranging themselves to form large variety of structures. Self- reconfigurable system is classified into two main categories; chain type and lattice type. In chain type, modules are connected in series forming tree or loop structure. Chain configuration is versatile but computationally difficult to present and analyze. In lattice configuration, modules are connected in space filling 3D pattern. Modular robotics promises versatility, robustness and low cost. Self-reconfiguration capability of modular robot allows it to adopt it to surroundings. It can change its shape according to the task to be performed i.e. one robot can perform various task. Modular robotic system leads to lower cost since mass production of identical modules has an economical advantage. Toshio Fukuda et al developed first modular robot in 1988 named ‘The Cellular Robotic System (CEBOT)’. CEBOT research developed a concept of cellular robotic system.

International Journal of Pure and Applied MathematicsVolume 114 No. 11 2017, 253-263ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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It is a new kind of robotic system which is able to reconfigure itself to optimal structure depending on purpose and environment. Each cell is able to communicate with each other. CEBOT has achieved automatic connection and separation. CEBOT was the first step towards modular robotics. Since then modular robotics is developing fast [1]. Mark Yim et al. developed PolyBot in 1998. PolyBot is a chain type modular robot. Each module has one degree of freedom and two connection plate. Further two generation of PolyBot has been developed. Low heterogeneity of system is design point for getting more functionality [2]. Satoshi Murata et al. developed M-Tran in 2002. Modular Transform is a hybrid type of modular robot. Research proposed Central Pattern Generation method for locomotion generation. This made modular robot to adapt to unknown terrain. Research took a huge leap in development of modular robotics [3]. Jens Liedke et al. developed CoSMO in 2013. This Collective Self-Reconfigurable Modular Organism i.e. CoSMO is new modular robotic platform. CoSMO has huge computational and communication capabilities. CoSMO use BLDC motor to actuate which results in high load carrying capacity. CoSMO is also capable of transmitting power among its modules. Modular robots developed so far are highly costly [4]. Denis Krupke et al. developed the Printable Modular Robot (PMR) in 2012 as shown in Figure 1. PMR developed by 3D printed mechanical structure and other components used as per standard. Use of 3D printed structure and standard parts reduce manufacturing cost remarkably [5].

Figure 1: Printable Modular Robot (PMR)

Locomotion planning and control is major part of any modular robotic system. Houxiang Zhang et

al in his research explained how caterpillar are successful climbers and can manoeuvre in complex

environment. Research build Cube-M modular robot and successfully implemented caterpillar like

locomotion [6]. VojtechVonˇasek proposed a global motion planning for modular robot, in that the

central pattern generators produce periodic control signals, hence wide locomotion generation is

found to be possible and his research also presents the modification of ‘Rapidly exploring random

tree’ algorithm for modular robot [7]. Dennis Krupke introduced a smart locomotion generation based

on automatic orientation and topology detection of a reconfigurable modular robot. In that, two axis

accelerometer is integrated with Printable Modular Robot platform. Accelerometer gives orientation

and topology of modular robot. Based on the information of accelerometer, optimized locomotion of

PMR is generated [8]. Modular robotics holds key to future of robotics. The applications of modular

robotics are vast. Mark Yim gives the following applications of modular robotics a) Space exploration

b) Search and Rescue c) Bucket of Stuff. As space exploration has many constraints such as

unpredictable environment, mass and volume of equipment to carry to study such environment.

Modular robotics can give solution to these problems. ‘Bucket of Stuff’ is a futuristic idea where

customer will have container of full of modules. And as per need of customer modular robot will take

shape and perform desired task [9]. Craig Eldershaw et al developed war robot with PolyBot modular

robotic platform [10]. Andres Faina et al developed a modular robot to work under dynamic and

unstructured environment in industries. In that, the modular robot is developed for shipyard

application [11]. Modular robot is capable of work as Cartesian as well as spherical manipulators.

Robot have also achieved climber and walker locomotion.

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Based on the literature survey, the modular robotics found to be a costly approach. PMR promises

low cost modular robot. Locomotion planning is considered as a one of the major factor which affects

the performance of modular robot. Hence there is need of development of locomotion technique for

optimized locomotion for effective use of power source. This research aims to develop a low cost

printable modular robot and to design a low cost printable modular robot based on the availability of

standard components. Research also deals with static analysis of mechanical structure of printable

modular robot to check whether the design is safe or not and a control system has developed for

different locomotion to optimize the power consumption of PMR. This paper is organized in eight

sections. Section 2 describes problem with previous work. Section 3 is devoted to design of modular

robot, 3D printing and hardware development. Section 4 deals with analysis and material selection. In

section 5, we discuss locomotion techniques. In section 6, we carry out actual prototyping of

printable modular robot. Section 7 contains results of static analysis as well as locomotion study.

Section 8 summaries research carried out and a discussion on future scope.

2 Problem DefinItion A module of PMR must have enough space to contain all essential components, e.g.

microcontroller, actuators and connection mechanism. And robot should be small to fit in restricted space. Hence the research is focused on mechanical design of module and its optimization. The locomotion of snake like robot is like sinusoidal curve. Locomotion affects power consumption. As we set amplitude and phase difference in sinusoidal motion, if amplitude is high motion will be tall but displacement will be short or if amplitude is short motion will be short in height also short displacement. Similarly phase difference affects displacement of modular robot. Hence phase difference is important factor for locomotion. Research is focused on finding optimized phase difference and develop control system for modular robot for optimized power consumption.

3 Design Of Modular Robot Krupke et al. [5], 2012 developed design of modules which are optimized for 3D painting and

includes only standard components. The design of printable 3D modules is designed in solid works.

Now depending upon standard component availability and considering low cost as main criteria for

hardware design, we have improved existing design. As in existing Robot, the cost of power source

is high. Hence we are proposing low cost power supply to reduce cost. So depending upon power

source and availability of standard electronic components, we have modified the design. Figure 2

shows three iterations of the lower module. Note: increased wall thickness in second generation

depending upon available magnet slot specification and design optimization for improved magnet

slot in third generation.

Figure 2: Improvement in design of module

Figure 3 shows the development cycle of modular robot, the iteration in hardware design and

improvement can be verified against the simulation. The initial model can be tested and optimized

by using simulated environment in short iteration. When these virtual parts fulfil the required


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requirements, they can be materialized by the 3D printer. Now complete modules can be assembled

using standard components and evaluated in real world.

Figure 3: Iterative hardware development cycle of modular robot.

A. 3D printing

3D printing is additive manufacturing technology where 3D object is created by laying down

successive layer of material. The 3D printer utilized for this task is a custom designed gadget. The

configuration has been modified to support simultaneous printing with three extruders for an

extensive variety of extruder qualities and materials. ABS-Plastic material is used for 3D printing.

Total time required for 3D printing is 4 hrs. For water solvent structures, PVA is utilized.

B. Hardware Development

Modules of robot is a consolidation of a 3D printed mechanical parts, one smaller scale servo for

motion, and one Arduino Nano V3 board as a control framework. The Arduino Nano V3

microcontroller was decided at its moderate cost, little shape variable, and also broad gathering of

open programming and drivers. One Arduino board and one micro servo are needed for each

module. Past work [5] utilized LiPo battery as a force supply. But considering the cost as a major

factor we have replaced it with Li-ion battery. Two Nokia BL5C batteries are used to power Arduino

and micro servo. Two batteries are connected in series to get 7.4 volt as each battery is of 3.7 volt

1020mAh. Neodymium magnets are used for mechanical interconnections and electric connections.

Figure 4: Standard components of one module.

Due to change in power supply that is use of Li-ion battery instead of LiPo battery, cost of

modular robot drastically decreases. Li-ion battery has low maintenance, low cost to energy ratio,

less expensive to manufacture and less cost than LiPo battery. Hence we proposed to use Li-ion

battery instead of LiPo battery.

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Figure 5: Mechanical assembly of three modules in Solid works

Control board Arduino Nano V3 (AT mega 328p, 16 MHz, 32 KB

flash memory, USB, I2C.)

Micro servo motor Micro servo (Tower Pro MG90, 2kg/cm torque at 4.8V)

Power supply Low cost two cell Li-ion batteries (3.7V, 1050mAh)

Magnets Neodymium Magnets(NdFeB) (6mm*3mm Disc-10)

TABLE I. HARDWARE DEVELOPMENT

4 Static Analysis Of Pmr To balance between strength, weight, durability and manufacturability, the utilization of

Computer Aided Design (CAD) displaying and Finite Element Analysis (FEA) systems are helpful in examination. It covers the outline requirements, material choice, and auxiliary examination and configuration adjustments. It will at last cover the consequences of the actual real world usage of the design.

A. Material selection

Material selection is very important factor while designing and manufacturing of modular robot. The main criteria taken into consideration while choosing the material for the module are strength, cost, density, availabity and Feasibility for 3D printing. The materials feasible for 3D printing are ABS, PLA and PVA plastic. ABS plastic has chosen for manufacturing of 3D components because it is having higher melting pointed and it is stronger and harder than other two plastic. ABS plastic is mainly used for warm application such as extruder. By considering all these factors, ABS Plastic is used as material for fabrication of modules. The table 2 shows properties of isotropic ABS plastic.

Tensile Modulus 2140 MPa (N/mm2)

Yield Strength 42 MPa (N/mm2)

Poisson’s ratio 0.35

TABLE II. MATERIAL PROPERTIES OF ABS PLASTIC


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5 Locomotion Technique Basically locomotion is of two types, one type is sending a module from tail to head of structure.

Other way of locomotion is whole body locomotion. First method is useful to overcome large obstacles. Whereas other method is for fast locomotion. For snake like structure second method is useful. Locomotion generation for snake like modular robot is based on whole body locomotion. This approach in locomotion is fast as there is no reconfiguration of modular robot. Each module have independent control unit on it. The motion commands can be sent to each module by sending it to particular module or broadcasting it to all. A master module sends commands to other modules which acts as slave module. Any module is capable to act as master. Figure 6 shows master slave communication. The movement information of every walk can be put away in every module distributively. At start of certain stride master module will send a synchronization charge ceaselessly with certain recurrence. All module will waver rhythmically and independently. This reduces workload on master and negotiate locomotion.

Figure 6: Master Slave Communication

The control of snake like robot is based on rhythmic motion produced by sinusoidal generators. Each sinusoidal generator acts as Central Pattern Generator (CPG), which controls rotation angle of each module. Very smooth movements can be achieved by sinusoidal generators. Control is much easier with sinusoidal generators. The motion generated by sinusoidal is given by following equation.

(1)

Where, y = rotation angle of corresponding module, A = amplitude, T = control period, t = time, = phase, O = initial offset, i = module no., = phase difference between two adjacent modules

Figure 7: Parameters of sinusoidal wave generator

As shown in figure parameters of sinusoidal wave generator varies. The rotation angle ‘y’ varies from +90° to -90°. Angle of rotation always follows . As maximum

rotation range for actuator 180°, following restriction is also met | °. Let’s consider robot has M modules, hence M sinusoidal wave generators are there. Each generator has four independent variables . To obtain the solution space for locomotion equation or sinusoidal wave generation equation following assumptions are done, 1) All generators have same Amplitude (A) and Period (T) 2) All generators have no offset 3) The phase difference in each consecutive generator is always same (∆ ) 4) Generator located at one end i.e. master module is taken as phase reference

Applying assumptions locomotion equation becomes

(2)


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6 Experimental Prototype Robot mainly consist of 3D printed mechanical structure, Li-Ion battery, Micro Servo motor

and Arduino. Arduino Nano V3 is controlling element and micro servo motor is actuating element of robot. Figure 9 shows modular robot developed.

Figure 9: Module of Developed Robot

The controlling signal to micro servo motor is given by Arduino Nano V3 through pin D9. Power to micro servo motor and Arduino is given by Li-Ion battery which is connected to pin

Vin and Gnd. The connections of control system of modular robot are as per shown in figure 10.

Figure 10: Connection Diagram

7 Results And Discussion

The force is applied on rib which connects battery mount to servo mount. Total 20N acts on

each rib considering the following factors, 1) Weight of all components and modules 2) After

lifting of one module, it should sustain the weight of other modules 3) During locomotion

such as step climbing, where modules are perpendicular to each other. Hence force acting on

pivot connection of Arduino mount and servo mount is maximum 4) Considering worst

condition – in this case forces acting on modules is unpredictable.Hence to avoid all these

problems, modules are designed by considering maximum force as main criteria for designing,

hence that the module can withstand in worst condition.

A. Battery ad-on Analysis-

Forces are applied on rib connecting battery ad-on to servo mount because stress

concentration is maximum at rib. Figure 11 shows boundary conditions and forces applied on

battery ad-on. As per static analysis, figure 12 shows maximum deformation of 0.014 mm at

connecting rib. As shown in figure13, stress induced in battery ad on is 1.201N/mm2 which is

less than yield stress of material. Hence design is found to be safe and robust in working

environment.


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Figure 11: Boundary Condition Figure 12: Meshed Battery Ad-on

Figure 13: Deformation Figure 14: Induced Stresses

B. Servo mount analysis

Forces are applied on pin connection between servo mount and Arduino mount because

stress concentration is maximum. Figure 15 shows boundary conditions and forces applied

on servo mount. As per static analysis, figure 17 shows maximum deformation of 0.4629 mm

at pin connection. As shown in figure18, stress induced in servo mount is 7.010 N/mm2

which is less than yield stress of material. Hence design is safe and robust for work in any

environment.

Figure 15: Boundary Condition Figure 16: Meshed Servo module

Figure 17: Deformation Figure 18: Induced Stresses


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C. Locomotion analysis

MATLAB is used to plot graphs. MATLAB code is generated for single cycle of sinusoidal

wave. While experimenting following constraints are also applied to setup. The amplitude is

varied from 10° to 90° with step of 10°. The phase difference is changed from 0° to 175° with

step of 25°. Figure 19 shows graph of amplitude vs. Displacement per cycle. The displacement

for same phase difference increases as amplitude increases. The displacement is tiny and

negligible as phase difference approaches 0° to 180°. It is interesting that when phase difference

is in between 75° to 100° we get maximum displacement for given amplitude.

Figure 19: Locomotion and Amplitude Figure 20: Locomotion and Phase

Relationship Difference Relationship

Figure 20 shows relationship of displacement and phase difference. Various color lines

indicate phase difference variation with same amplitude. As seen in graph amplitude increases

till 75° and decreases after 100°. Hence displacement is most efficient for phase difference from

75° to 100°. It is observed that displacement is negligible for phase difference of 00 and 180

0.

8 Summary And Future Scope

In this paper, a variety of Reconfigurable robots has been surveyed. On the basis of literature

review, we proposed a design of homogeneous self-Reconfigurable modular robot in which

modules are optimized for 3D printing and include only standard components. Design

modification is done as per availability of standard component. From static analysis result we

can conclude that the mechanical design can withstand at maximum loading condition also.

With design modification 10% material reduction is achieved. From MATLAB coding, it is

observed that for locomotion to be optimized for power consumption, phase difference is kept

between 75° to 100°. As power source of modular robot used is Li-ion battery performance and

battery life is increased. The cost of Li-ion battery is very less. The introduced result is

exceptionally adaptable and ease robot stage because of progress in the power source i.e. by

utilizing Li-ion battery rather than LiPo battery and by utilizing standard components and 3D

printed mechanical structure. Hence Modular robot was developed successfully with low cost.

The future work should focus on design modification based on availability of standard

components. Factor of safety achieved is greater than 3. Hence design can be further optimized

to reduce factor of safety. The communication between modules can be developed further more.


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The communication protocol can be updated to RS-422. The locomotion is developed for 1D

motion, further study can develop for 2D and 3D locomotion.

References [1] Toshio Fukuda, Tsuyoshi Ueyama, Yoshio Kawauchi and Fumihito Arai, “Concept Of Cellular

Robotic System (Cebot) And Basic Strategies For Its Realization,” ComputersElect.Engng Vol. 18, No. 1, pp. 11-39, (1992).

[2] Mark Yim, David G. Duff and Kimon D. Roufas, “PolyBot: a Modular Reconfigurable Robot” InternationalConferenceon Robotics& Automation, San Francisco, April (2000).

[3] Satoshi Murata, Eiichi Yoshida, Akiya Kamimura, Haruhisa Kurokawa,

Kohji Tomita, and Shigeru Kokaji, “M-TRAN: Self-Reconfigurable Modular Robotic System” IEEE/ASME Transactions On Mechatronics, Vol. 7, No. 4, December (2002).

[4] Jens Liedke, Rene Matthias, Lutz Winkler and Heinz Worn, “The Collective Self-Reconfigurable Modular Organism (CoSMO)” 2013 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM) Wollongong, Australia, July 9-12, (2013).

[5] Dennis Krupke, Florens Wasserfall, Norman Hendrich and Jianwei Zhang, “Printable Modular Robot: An Application of Rapid Prototyping for Flexible Robot Design” Unpublished.

[6] Houxiang Zhang, Juan Gonzalez-Gomer, and Jianwei Zhang, “A New Application of Modular Robots on Analysis of Caterpillar-like Locomotion” 2009 IEEE International Conference on Mechatronics. Malaga, Spain, April (2009).

[7] Vojtech Von asek, Martin Saska, Karel Ko snar and Libor P reucil, “Global motion planning for modular robots with local motion primitives” 2013 IEEE International Conference on Robotics and Automation (ICRA)Karlsruhe, Germany, May 6-10, (2013).

[8] Dennis Krupke, Martin Noeske, Florens Wasserfall, and Jianwei Zhang, “Smart Locomotion Generation Based On AutomaticOrientation And Topology Detection Of AReconfigurable Modular Robot” Unpublished.

[9] Mark Yim, Paul White, Michael Park, and Jimmy Sastra, “Modular Self-Reconfigurable Robots”, Unpublished

[10] Mark Yim, Wei-Min Shen, Behnam Salemi, Daniela Rus, Mark Moll, Hod Lipson, Eric

Klavins, and Gregory S. Chirikjian, “Modular Self-Reconfigurable Robot Systems Challenges and Opportunitiesfor the Future” IEEE Robotics & Automation Magazine, March (2007).

[11] Andrés Faíña, Félix Orjales, Daniel Souto, Francisco Bellas and Richard J. Duro, “Designing a Modular Robotic Architecture forIndustrial Applications” The 7th IEEE International Conference on Intelligent Data Acquisition and Advanced Computing Systems: Technology and Applications, 12-14 September (2013), Berlin, Germany


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Development of Low Cost Printable Modular Robot