2008 IEEE/RSJ International Conference on Intelligent Robots and Systems
Acropolis Convention Center
Nice, France, Sept, 22-26, 2008
Mechanical Design of Odin, an Extendable Heterogeneous Deformable
Modular Robot
Andreas Lyder, Ricardo Franco Mendoza Garcia and Kasper Stoy
Abstract— Highly sophisticated animals consist of a set of
heterogenous modules decided by nature so that they can
survive in a complex environment. In this paper we present
a new modular robot inspired by biology called Odin. The
Odin robot is based on a deformable lattice and consists of
an extendable set of heterogeneous modules. We present the
design and implementation of a cubic closed-packed (CCP) joint
module, a telescoping link, and a flexible connection mechanism.
The developed robot is highly versatile and opens up for a wide
range of new research in modular robotics.
I. I NTRODUCTION
In biology a set of building blocks is combined to create
highly sophisticated animals with large variety of capabilities
and advantages for the specific environments in which they
exist. These building blocks provide different functionality
to an animal. For example, bones that create structures,
and muscles that create actuation for locomotion and manipulation, and they are all equipped with sophisticated
sensory systems. In this paper we present a concept that
applies the ideas of biology to developing a robotic set of
modules, which can be combined and reach a higher level
of sophistication. In addition we present the implementation
of some of the first modules.
Inspired by biology, the Odin robot consists of a hierarchy
of functionally differentiated modules. The hierarchical concept of the Odin robot was introduced in [1]. The individual
modules on the lowest level of the hierarchy have very simple
functionalities. The low-level modules can be combined to
create new and more sophisticated meta-modules in a higher
level of the hierarchy. This can be continued until the level
of sophistication is satisfied. For example, low-level modules
resembling bones, muscles and tendons can be combined to
form higher-level meta-modules like legs, arms and spines.
These meta-modules can again be combined and reused to
form a variety of animals.
Though, the hierarchical concept of Odin robot is inspired
by biology, it is named as after the chief god from the Norse
mythology, Odin. According to myth Odin is able to change
his shape into animal form. He is known to take on the shape
of a fish, a worm, a bird, or a beast.
One of the key motivations [2] of modular robotics is
versatility. The question is, how do we decide the optimal
set of low-level modules to achieve the highest level of
versatility? We propose a modular robot with an extendable
set of heterogeneous modules. In this case, the set of building
Andreas Lyder, Ricardo Franco Mendoza Garcia and Kasper Stoy are
with The Maersk Mc-Kinney Moller Institute, University of Southern
Denmark, 5230 Odense M, Denmark – E-mail: {lyder, franco,
kaspers}@mmmi.sdu.dk
978-1-4244-2058-2/08/$25.00 ©2008 IEEE.
Fig. 1. Odin robot with 21 modules in a closely packed lattice (cubic
closed-packed) configuration. The configuration consists of 8 telescoping
link modules (black links), 6 rigid passive link modules (white links), and 7
joint modules. The links are connected to the joints with a flexible connector.
blocks is not restricted to a limited set of modules. By having
this unrestricted set of building blocks the user can quickly
build a robot and if needed extend the functionality with a
new module. It is important here note that the aim of building
this robot is to have a robot which is not limited to one or
few applications, but can be used in many applications to
solve a variety of tasks.
Additionally, the Odin robot has a deformable structure.
Depending on its configuration it can passively deform and
adapt to external forces. Using actuators the robot can actively change the distribution of internal forces. The shape is
therefore a result of the internal forces and the external forces
applied to the system. This adds some new features to the
modular robot. Most modular robots adapt to an environment
by changing its configuration. The Odin robot, however,
is able to adapt to changing environments by deforming.
Analyzing the kinematic and dynamic characteristics is an
important aspect and work in progress, however, it is not the
focus of this paper. The focus of this paper is merely on the
concept and the realization of the robot.
The implementation of the Odin robot is based on a lattice
structure consisting of link and joint modules. Each link
connects to a joint at each end of its cylindrical body. The
arrangement of connections on the joints determines the
lattice structure of the robot. The modules presented in this
paper are a joint with a cubic closed-packed arrangement
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of connections and a telescoping link. We also describe the
implementation of a flexible connector connecting the link to
the joint. Fig. 1 shows a configuration of the Odin robot with
8 telescoping link modules, 6 passive rigid link modules, and
7 CCP joint modules.
II. R ELATED W ORK
Modular robots can be divided into two categories based
on their mechanical design: Homogeneous and heterogeneous systems. In homogeneous modular robots, all modules
are mechanically identical. One of the advantages of homogeneous systems is that all modules can be replaced by any
other module if they should fail. They may also be more
applicable to mass-production due to the higher number of
identical parts. Examples of homogeneous modular robots
are the M-TRAN [3] and the ATRON robot [4].
Heterogeneous modular robots have two or more mechanically different modules. Heterogeneous systems with two
different modules are the most common ones. In latticebased systems they most often consist of link and node
modules. This is the case with the Tetrobot [5] and SMAnet robot [6] where the node interconnects several links in
a specified lattice. In chain-based systems there is often an
additional passive module providing branching of chains of
active modules, like the PolyBot [7]. However, the CKBot
[8] is a heterogeneous chain-based system which has both
different active and passive modules and depending on the
functionality the modules also provide branching.
In this paper we propose an extendable heterogeneous
system that has an undefined number of different modules.
The very first proposal for a modular robot, the CEBOT [9],
presented in 1988, was a heterogeneous system which could
be extended by applying specific modules. Another example
is the I-Blocks [10] which are developed for educational
purposes.
Deformability has been introduced in a couple of examples. The SMA-Net robot cited above has a loose deformable
structure which enables it to adapt to the environment. The
Derformatron [11] is an example of a modular robot with
flexible bonds when its modules are expanded, however,
when contracted the bonds are rigid. A different approach
is presented using the Slimebot [12]. The Slimebot changes
shape by stochastic reconfiguration due to its sticky surface.
Connections are made spontaneously when two modules
make contact, and disconnection occurs if the disconnection
stress exceeds the yield stress.
In this paper, we present a novel proposal for an extendable
deformable modular robot. The Odin robot does not have a
limited set of modules and therefore it can be extended with
a large variety of functionality items such as sensors and
actuators. Additionally, the modules of the Odin robot can
be connected in a deformable lattice.
III. T HE O DIN C ONCEPT
The Odin robot is a manually reconfigurable robot. The
key features of the Odin robot is that it is extendable and
it is based on a deformable lattice. As pointed out in the
Fig. 2. Odin modules – A CCP joint and a telescoping link. The link
consists of two connectors with the body in between.
previous section, there has been quite a few proposals on how
to design a modular robot. The key feature of most of these
systems is their ability to self-reconfigure, and some have
showed very promising results. However, we have decided
to focus on some different and novel aspects in modular
robotics.
We want the robot to develop into a robotic set of building
blocks which can be brought to unknown environments and
configured within a reasonable amount of time to solve a
task that could not have been prepared for in advance. An
example application could be going to Mars where the tasks
can not be predicted. At ICRA’08 The Odin robot entered the
Planetary Contingency Challenge. Each team were limited to
bring 25 kg of equipment in a limited size container. Upon
arrival the teams were given 4 hours to solve a task, which
is not known beforehand, in a Mars environment. In these
cases it is important that the robot has a versatile selection
of functionality so that the robot will solve as many different
tasks as possible. All of this functionality cannot be put into
one module so we propose a system which is based on a
hierarchy of modules. Individually, the modules on the lowest
hierarchical level are very simple. By combining these simple
heterogeneous modules, their functionality adds up to create
a more sophisticated robot.
The low-level modules can be divided into four basic
categories based on their functionality:
• Structure module – passive module which adds structural features.
• Actuated module – active module which enables the
robot to perform locomotion and manipulation.
• Sensor module – provides sensory inputs about the
environment.
• Power module – provides energy to the robot.
New features can always be added to the robot, there
is no complete set of low-level modules which makes it
extendable. It is, therefore, easy for a user, who does not
want to develop a completely new robot, but just want to
add a smaller feature, e.g. a specific sensor input, to embed
this feature by only developing the specific sensor module.
We also wanted the structure of the robot to have some
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Fig. 4. Flexible connector. Section view. The centre of rotation of the balland-socket joint is coincident with the surface of the joint module. (5) Body
mount. (6) Body control PCB. (7) Spring. (8) Locks the ball in the socket.
(9) Ball-and-socket joint. (10) Key for locking connector in joint module.
(11) Spring contacts in PCB with a six-redundant connection layout for four
electrical connections.
Fig. 3. Joint module with 12 connections in a CCP lattice arrangement.
Exploded view. (1) North half. (2) Female connector PCB with a sixredundant connection layout. (3) PCB support base. (4) South half.
level of substance. It may also be more difficult to create a
hierarchy of modules using a chain-based structure. The Odin
robot is, therefore, based on a lattice structure. However, how
do we make a manually reconfigurable lattice-based modular
robot move in and adapt to a given environment? The lattice
must somehow be able to change shape. This shape change
must be actively controlled by actuators within the system to
make the robot move. The simplest imaginable type of actuation in a lattice is linear changes of the distances between
the joints. In a lattice based on links and joints, where the
links are not able to rotate around the joints, a synchronized
actuation must be closely coordinated to change the shape of
the structure. For example, in a tetrahedron, the length of all
6 links must be actuated at the same time in order to maintain
all angles in the system. If we allow the links to rotate around
the joints, the structure becomes more flexible, and we can
change the distances between the joints individually. This
also enables a more versatile shape change.
When the links are able to rotate freely around the joints
of the structure, only a closely packed triangular lattice will
be stable and rigid. Other lattices, like the simple cubic or
lattices which are not closely packed, will have an unstable
and wobbly structure. To make these structures stable and
also to induce new structural properties we add springiness
to the links’ three-dimensional rotation around the centre of
joint. The structure will now try to stabilize the links at zero
angle of rotation depending on the external forces acting on
the structure. We call this structure a deformable lattice since
the shape is affected by the external forces.
IV. D ESIGN AND I MPLEMENTATION
As presented in the previous section, the Odin robot has
two key features. It has an extendable set of heterogeneous
modules and is based on a deformable lattice. Also, the modules were divided into four different categories depending on
their functionality. In this section we introduce three basic
mechanical parts that is required to assemble an Odin robot.
The Odin robot is based on a link-and-joint structure,
where the joint connects the links in a specified lattice. The
joint is a mechanical part in itself, however, the link consist
of two different parts, a body and two connectors, one at each
end of the body. Therefore we divide the mechanical design
of the Odin robot into three basic parts: Joints, connectors,
and bodies.
In this section we also give a short description of the
integrated electronics embedded in the robot.
A. Joint - CCP
The joint module specifies the lattice in which the robot
can be configured and it is, therefore, the most important
structural module. In this paper we will present a joint
which enables the robot to be configured in a CCP structure,
however, it is easy to develop other joints with a different
lattice. The CCP structure was chosen because of its high
stability and strength due to its triangular substructures. It
is also known to be the most dense packing of spheres. A
configuration of modules in a closely packed CCP structure
will be rigid. However, by leaving out modules, so that the
configuration is not closely packed, is also possible to create
flexible structures. The ability to create both rigid and flexible
substructures increases the versatility of the robot.
A CAD model of the joint module assembly can be seen
on Fig. 3. It consists of 12 female connection slots. Each
connection slot is six redundant, which means that a link can
be connected in six different orientations. This may come in
handy if the link has an actuator or a sensor that operates
around a specific axis perpendicular to the link, e.g. bending.
The arrangement of surface pads on the female connector
PCB provides the same four electrical connections in any
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Fig. 5. Telescoping body. Section view. A brushless DC-motor drives the middle shell through the gears. The outer and the inner shells are aligned with
respect to each other, and due to the opposite threads the body is able to contract and expand. The aligning shell has a gradient strip inside detectable by
the reflective sensor, and since the aligning shell moves linearly with the middle shell it is possible to read the absolute extension of the body. (12) Gear
27T. (13) Motor housing. (14) Gear 8T. (15) Outer shell. (16) Reflective sensor. (17) Gear 43T. (18) Middle shell. (19) Aligning shell. (20) Inner shell.
angle the link is connected. These electrical connections
include power sharing and a communication bus between all
connected links. The joint is made in ABS material printed
on a 3D printer based on Fuse Deposit Modeling (FDM).
B. Connector - Flexible
Optimally, the links would share the same centre of
rotation through the joint, however, mechanically it is very
difficult to develop a connection mechanism that is both
easy to connect and disconnect and provides the electrical
connections. Instead, we have connected the links to the
surface of the joint and developed a flexible connector.
The flexible connector has a ball-and-socket joint with a
centre of rotation on the surface of the joint. Around the
ball-and-socket joint we have placed a spring which sets
the springiness of the connector. We can create connector
modules and experiment with different springs from very
soft to rigid.
Fig. 4 shows a CAD model of a flexible connector cut in
half. The socket fits into the six-redundant connection slot of
the joint and holds four spring contacts to create electrical
connections. It places the ball-stud with its centre on the
surface of the joint, exactly 25mm from the centre of the
joint. The ball is locked in place by a spring around the
ball-stud. The spring also provides the springiness of the
connector, not only around the ball’s centre of rotation, but
also around the vertical axis of the connector. Four extra
flexible wires (not illustrated) passes through the ball-stud
from the spring contacts to the control PCB inside the body
mount. The socket is machined in POM (Polyacetal) and the
key and ball-lock is machined in aluminum. The spring and
the ball-stud are modified of-the-shelf products. Finally the
mount is produced using FDM.
C. Body - Telescoping
The body part of the link provides the functionality of the
Odin modular robot. By changing the body, any functionality
can be put into a link. The joint is a structural module,
but the link can be any type of module. A link can be a
structural module, e.g. a rigid rod filling out the lattice, or a
spring adding interesting structural features. A link can also
be an actuated module, e.g. a linear or a bending actuator. A
GPS link providing knowledge about the robot’s location or
a camera module adding vision to the robot are examples of
sensor modules. And finally, a link can hold power sources
such as batteries, solar energy panels or maybe even fuel
cells. The body enables the robot to be extended with a large
variety of functionalities.
In this paper we present a telescoping body which provides
linear actuation to change the distances between the joints.
Fig. 5 shows a CAD model of the telescoping body cut in
half. The telescoping body is inspired by the zoom lens of
a compact camera. It has four main cylindrical shells, the
outer, middle, inner, and align shell. The inside of the outer
shell has a counter-clockwise thread. The outside of the leftmost end of the middle shell has one revolution of thread
that fits the inside of the outer shell. Likewise, the middle
shell has an inside thread, however, clockwise, and the inner
shell has one revolution of thread matching the middle shell.
When the middle shell is rotated, it creates linear extension
and contraction, though only if the outer and inner shells are
not able to rotate with respect to each other. To make this
happen an align shell is moving linearly with the middle
shell which aligns the outer and inner shell. To be able to
read the absolute extension of the linear actuator, we have
placed an optical sensor which detects the reflection of a
grayscale gradient strip inside the align shell.
Since the middle shell moves linearly as it rotates, its
internal gear is driven by a long gear. The long gear is driven
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CCP Joint
- Diameter
- Max. # connected links
- Weight
Flexible Connector
- Max. angle of rotation from ball-joint centre
- Diameter
- Distance from centre of rotation to body
- Weight (without PCB)
Telescoping body
- Diameter
- Min. length
- Max. length
- Max. speed
- Strength
- Weight
by a brushless DC-motor (not illustrated) mounted in the
motor housing in the centre of the body with a gear attached
to its shaft. The gearing ratio is a reduction of 27/43. The
long gear is machined in brass and the two others in POM.
The rest of the parts are produced on a PolyJet prototyping
machine.
The body is 60mm long when contracted and extends to
132mm, a ratio of 2.20. The distance from the body to the
centre of the joint adds up to 50mm. This means that we are
able to change the distance between the centre of the joints
from 160 to 232mm, a ratio of 1.45.
D. Integrated electronics
Since the Odin robot is a fully heterogeneous modular
robot, the electronics in the modules are also different.
The joint provides power sharing and a terminated RS484 communication bus between all links connected to the
joint. Each link has two PCBs with electronics, a general
and a specific board. The general board is placed in the
connector at one end of the link, and the specific board in
the other connector at the other end of the link. The general
board is designed with a microcontroller and an interface to
connect specific electronics. The interface includes power,
communication and 8 digital input/output lines which can
be multiplexed with up to 4 PWM signals, an SPI bus or 4
analog input lines. The specific board is designed to hold the
specific electronics needed to make a specific link functional
and controllable by the microcontroller on the general board.
In the case of the telescoping link module, we have placed
a controller for a brushless-DC-motor and power electronics
to provide the current needed to drive the motor.
We have developed a hybrid communication system [13]
which provides both local and global communication between the modules in the modular robot. By means of software the links can choose to communicate locally through
each joint independently or to connect the communication
busses of both joints together and create a global bus. This
means that we can control the organization of the communication network. We can have a pure locally-connected system
or a pure globally-connected system, or we can set up a
hybrid system with both local and global communication.
V. S PECIFICATIONS
Table I summarizes the specifications of the currently implemented parts of the Odin robot. Some of the specifications
are presented in the previous section dealing with the design
of the modular robot. In this section, we present some additional specifications based on the following measurements.
The maximum speed of the telescoping link is measured
to approximately 50mm/s. The maximum linear strength
of a telescoping link has been measured to approximately
17.2N at a speed of 10mm/s. A connector weighs 20g,
and a telescoping body weighs 84g. The total weight of a
telescoping link module adds up to 104g. As a joint weighs
36g, a telescoping link can lift a linear configuration of up
to 13 telescoping links with joints in between.
50mm
12
36g
23◦
35mm
25mm
20g
35mm
60mm
132mm
50mm/s
17.2N
84g
TABLE I
S PECIFICATIONS OF THE IMPLEMENTED PARTS FOR O DIN .
The spring in the flexible connecter creates a torque when
the link is forced off centre. By measuring the torque τ at
several angles a we get the following polynomial relation
τ = 0.15a + 2.1a2 N · m
(1)
Fig. 6(a) shows the maximum rotation of the links, measured to 23◦ , around the centre of the ball joint. If we
consider three contracted telescoping modules configured
in a equilateral triangle, the links are rotated exactly 0◦
due to the arrangement of connections on the CCP joint.
Now, we allow the telescoping links to expand independently
of each other. Since the maximum angle, which the the
links can rotate, was measured to 23◦ the maximum ratio
of extension of the telescoping links can be calculated to
1.57. The telescoping links presented in this paper are able
to extend a ratio of 1.45 between the centre of the joints,
which means that all three telescoping links in the triangle
configuration can actuate freely. This is of course not the
case for any configuration, but the flexibility will still allow
the modules to create considerable changes of shape if
coordinated correctly. Ideally, the telescoping links would
be able to actuate freely in any configuration, however, due
to the mechanical constraints of the flexible connector this
is not possible.
The triangle is a closely packed substructure of the CCP
lattice and therefore the shape of the robot in this configuration can only be changed by internal actuation. The
hexagon is a substructure of the CCP lattice that is not closely
packed and therefore the shape of the robot can be changed
by outside forces. Fig. 6(b) shows a deformable hexagon
configuration of the robot with 6 telescoping links connected
through 6 joints. If the telescoping links are all contracted,
the distance between the joints is 160mm, and the height
of the hexagon is 277.13mm when all angles are retained.
Due to the flexibility of the joints the minimum height of
the hexagon configuration is 192.58mm and the maximum
height is 317.61mm. By measuring the actual configuration
we see that this is true. The linear strain of the hexagon
configuration can therefore be calculated to 0.65.
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higher number of smaller modules may make the robot more
adaptable within the same volume. Within the CCP lattice
structure actuated modules can be connected both in parallel
and in series. Parallel actuation can increase the exerted force
and serial actuation can increase the speed.
VII. C ONCLUSION
In this paper we have presented the concept of a new
modular robot called Odin inspired by biology. Unlike any
other known modular robots the Odin robots is based on a
deformable lattice and designed to be extendable with an
open set of heterogeneous modules. We have described the
implementation of a joint module with a CCP arrangement,
a telescoping link, and the flexible connection mechanism
which allows for the lattice to deform.
We have developed a very versatile modular robot which
opens up for a lot of new research in modular robotics.
VIII. ACKNOWLEDGEMENTS
(a) Angle of rotation
(b)
Deformation
hexagon shape.
of
This work is partly funded by Intel Cooperation.
Fig. 6. Deformability - The flexible connectors allow the joints to rotate 46◦
around the centre of the ball-joint. This enables a hexagon shape to deform.
The hexagon is a small example of a configuration where the lattice is not
closely packed and therefore not rigid.
VI. D ISCUSSION AND F UTURE W ORK
The Odin robot allows for a lot of parameters to be
optimized for different situations. In this paper we presented
an implementation of a joint with a CCP arrangement and
a telescoping module. We are currently working on a power
module with a Lithium-Polymer battery and a camera module
adding vision. However, the modules we have chosen to
implement may not be optimal for all applications. The
extendable heterogeneous concept allows any user to expand
the set of modules with new functionality. By making additional joints with other arrangements of connectors, the basic
structure of the robot can be optimized. The springiness of
the structure can also be altered by changing the spring of
the flexible connector, or a new type of connector can be
applied.
One of the very interesting research questions we will
be looking at with this robot is: how can we optimize the
distribution of different modules for specific tasks. Imagine
that a set of links with 50 actuators, 50 sensors and 50 battery
modules are available. However, there are only a limited
number of joint modules available and not all link modules
can be used. How are the modules configured and how are
they weighed in order to solve and optimize the solution of
a given task? If we want the robot to move fast, the number
of actuators may be weighed high. If accurate and versatile
sensor readings are preferable, the number of sensors may
be weighed high. Or, finally, if the robot should run for a
long time, battery modules are weighed high.
Another interesting research question is collective actuation. In modular robots there is always a tradeoff between
size and force. Smaller modules exert less forces, however, a
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