Mimebot: Sphere-shaped Mobile Robot
Imitating Rotational Movement
Shuhei Tsuchida

Tatsuya Takemori

GR. Sch. of Engineering,
Kobe University

GR. Sch. of Engineering,
Kyoto University

shuhei.t@stu.kobeu.ac.jp

takemori.tatsuya.23a@st.kyotou.ac.jp

Tsutomu Terada

Masahiko Tsukamoto

GR. Sch. of Engineering,
Kobe University
PRESTO, JST

GR. Sch. of Engineering,
Kobe University

tsutomu@eedept.kobeu.ac.jp
ABSTRACT
When designing a performance involving people and mobile
robots, we must consider the required functions and shapeof the robot. However, it can be diﬃcult to account for all of
the requirements. In this paper, we discuss a mobile robot
in the shape of a ball that is used in theatrical performances.
Such a spherical robot should be agile and be able to rolllike a ball. However, it is diﬃcult to create a robot withall of these characteristics. Instead, we propose a mobile
robot that can give the audience the optical illusion of theunique movements of a sphere by mounting a spherical LED
display on a high-agility wheeled robot. The results of anexperiment using a prototype indicate that this sort of robot
can broaden the range of possible performances by giving theoptical illusion of being a rolling sphere.

CCS Concepts•Human-centered computing → Human computer interaction (HCI);

Keywords
Mobile robot, Spherical robot, Optical illusion, Performance,LED

1. INTRODUCTION
As robotics technology progresses, there are more opportunities for performers to act together with mobile robot,
such as robots that act as “doubles” of actors oﬀ-stage [1],Permission to make digital or hard copies of all or part of this work for personal orclassroom use is granted without fee provided that copies are not made or distributedfor profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others thanACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission
and/or a fee. Request permissions from permissions@acm.org.

MoMM ’16, November 28-30, 2016, Singapore, Singapore
c 2016 ACM. ISBN 978-1-4503-4806-5/16/11. . . $15.00⃝
DOI: http://dx.doi.org/10.1145/3007120.3007128

tuka@kobe-u.ac.jp

dancing humanoid robot [2], and those that imitate characters from the world of fantasy [3]. Some are bigger [4,5], and same are smaller [6, 7, 8] than the performers theyinteract with but their moves must match those of the performers. Manabe et al. [9] developed a system that helps
a performer recognize the object intuitively by using quadcopters controlled by the relationship between the body ofthe performer and the data the of movement in real space.
When designing a performance involving people and mobile
robots, we must consider the required functions and shapeof the robot. However, it can be diﬃcult to account for allof these requirements. For example, a performance involving objects flying in the air, which uses, set, quadcopters,
could be expensive and diﬃcult to control, whereas one using wires to lift quadcopters into the air would be more economical and possibly have the same eﬀect on the audience.
In this study, we chose a sphere-shaped mobile robot andconstructed a mechanism for it to ‘act’ like a rolling ball.
There are many forms of bodily expression that use spherical objects, including works of art, such as MOVEment [10],Moon Beams [11], Metamorphose(s) [12], Ballons de baudruche [13], La danse des ballons [14], sports, such as gymnastics and freestyle football, and mime, magic, and juggling. Presenting rotating spheres on stage usually means aball has to be used. Here, a self-propelled ‘rolling’ robot ofsome kind would be needed because a normal sphere cannot freely travel on a stage. Examples of spherical mobile
robots include Sphero2.0 [15] which actually rolls on surfaces. In our previous research [16], we developed a systemfor creating performances using mobile robots and used it in
actual performances. However, the dynamic performance ofour rotating mobile robots is inferior to that of a robot withwheels. The mechanism of moving the center of gravity of arolling robot makes it hard to change its acceleration. Moreover, a spherical shape under centrifugal force cannot dosudden turns. This means the robot’s agility cannot matchthat of human performer. Furthermore, rotational mobile
robots have diﬃculty self-positioning. The reason is thatthe sensors and moving parts must be inside the sphericalshell, and this makes it diﬃcult for the robot to sense theoutside world by using markers, etc. Even though a robot
covered with a non-transparent spherical shell can measure
its position by using a camera, etc., it is diﬃcult to measure
its posture. A large error in the measured posture wouldinterfere with the performance because the robot would not
move in the directions specified in the staging. Additionally, it is diﬃcult for a rotational mobile robot to represent
a glowing rolling ball. The robot itself inside the spherical shell does not roll. Here, the shell could have LEDs
attached to it. However, it is diﬃcult to attach LEDs, microcomputer, or batteries on the spherical shell because its
inner surface must also be spherical.Thus, spherical mobile
robots have many constraints on their performances thatpose problems on stage.
In this study, we built a mobile robot that can give theaudience the optical illusion of the unique movements ofspheres by mounting a spherical LED display on a highagility mobile wheeled robot. The robot does not roll. Instead, moves quickly and accurately by using omnidirectional wheels. Additionally, the robot’s capabilities can beeasily expanded by attaching various devices to parts of it
that are not covered by the spherical shell. The optical illusion of rotational movement is created by using lighting
patterns on the surface of the sphere created using the LED
system.
The contribution of this paper is threefold.
• We propose the concept of using pseudo-physical movements in performances with robots.
• We built a robot that visually reproduces the movements of a rolling sphere and is capable of faster movements and easier position estimations in comparison
with previous spherical robots.
• We created a performance that included the robot interacting with a professional performer. Commentsfrom the audience and the performer helped us to identify the challenges in regard to the reproducibility of
the rotational movement of a sphere, and means ofsupport for and implementation of the same.
In this study, we focused on productions using spherical mobile robots and did prototyping. Balls and other sphericalobjects are often used in performances and in ball sports.
However, there are challenges to expanding this ball motif into one with interactive motion capabilities. We foundthat movements that are diﬃcult to implement with existing mechanisms can nonetheless be visualized through theuse of light. The main goal in this study is to show thatrotational movement can be depicted in this way; it is not
to create an artistic performance.

2. RELATED WORK
Various driving mechanisms are used by sphercal mobile
robots. Bhattacharya [17] summarized the mechanisms thatmove the center of gravity by incorporating an actuatorinside the sphere. Many spherical mobile robots, such as
security monitor robots [18] and cleaning robots [19], embody these mechanisms. Crosseley [20] has summarized thedriving mechanisms that do not involve moving the centerof gravity, such as deforming the sphere, and wind power.
Bruce et al. [21] developed a radically diﬀerent rolling robot

based on a tensegrity structure. A strong, robust robot
can be created at low cost by using this sort of structure.
Urakubo [22] developed a spherical rolling robot that has adriving mechanism equipped with a gyro. The robot travels using the torque generated by high-speed rotation of amomentum wheel. Aoki [23] developed a robot that cantransform into a sphere. The robot rolls by creating torqueagainst the ground by making two of its legs produced fromthe internal sphere. The above driving methods make itharder for the robot to change its acceleration comparedwith a wheeled robot directly in contact with the ground.
In addition, the driving methods described above cannot
execute sudden turns because of centrifugal force. Anotherdriving method is to use two independent hemispheres as
wheels see Polaris [24] to accelerate. However, this method
does not provide enough agility to overcome centrifugal force
or produce a rolling motion characteristic of a sphere.
Certain lighting eﬀects can be helpful when a robot interacts with a user. Kobayashi [25] used a blinking lightand beeping sounds to create ‘‘artificial subtle expression’’(ASE) so that a robot can communicate fluently. Rea [26]researched how a robot can alter how people use or perceive
the environment. In this case, the robot’s display expresses
the current mood of the room. Baraka [27] studied how tobest express a robot’s state in relation to its tasks and theenvironment. Sakai [28] developed a small, interactive humanoid. They evaluated the arrangement and blinking patterns of LEDs that would reproduce the eﬀect of someone
nodding. The blinking LEDs could not duplicate the motionof the robot itself. The illusion of motion, however, would
improve the quality of communication. Here, our goal is tomake blinking LEDs reproduce the eﬀect of actual moving
objects.
Some researchers [29, 30] have used computer graphics tostudy human motion perception of objects moving under theforce of gravity. However, no one has yet attempted to use
a moving object that emits light to reproduce the motionof an actual sphere. In this study, a blinking light source
attached to a mobile robot causes the illusion of physicalmotion.
There have been previous attempts by stage directors andartists to expand the range of physical expressions aﬀordedby moving objects. CHUNKEY MOVE [31] created a performance called ‘‘CONNECTED’’, in which objects move inaccordance with a performer’s motions and look like they
are emotely being manipulated by the artist. Wurtzel [32]created a performance called ‘‘AMALUNA’rq, which combines a dancer and cloth soaring freely in the air. It uses
a fan mounted in the floor of the stage. Adding illusion effects with light to a performance involving moving objects
and performers can be a new dimension of entertainment.

3.

AWARENESS OF ISSUES

In our previous, we gave a number of performances using spherical mobile robots. The spherical robots of these
performances actually rolled in the direction of travel. In
particular we did a performance combining these robots andperformers at INTERACTION 2015, held at the National
Museum of Emerging Science and Innovation in Japan on
March 6th-8th, 2015. We were able to reliably repeat the
one-minute performance over the two-hour demonstration.
We performed the same demonstration at ACE 2015 (shownin Fig. 1), which was held at the White Box and BlackWĞƌĨŽƌŵĞƌ

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Box arts complex in the Medini Mall, Medini, Malaysia, on
November 6th-8th, 2015. However, our robots often deviated from their target positions. The error rate rose significantly as the performance time became longer. The reason was that the measurement error of the posture of therobots increased over time. It is diﬃcult to measure theposture of robots covered with a non-transparent sphericalshell from the outside. Therefore, it is diﬃcult to correct
posture through external means. Moreover, the limitations
on the movements of the mobile robots, such as poor acceleration and inability to make sharp turns, limited the rangeof expression.
Further, we collaborated with performers in various genres to create a performance involving them and our mobile
robot. These performances often required the performer tograb the robot. However, the driving parts mounted on theinside of the spherical shell made it hard for performers to
grasp the robot. Moreover, we found that any violent movements of the shell could damage the robot inside.
Attaching a marker for motion capture to the outer surface in this study and using a spherical LED display canresolve these problems. In fact, we believe that these mechanisms can have the same eﬀect on an audience that physicalmotion has amd can make robots and quadcopters more reliable stage elements. Here, we focus on stage eﬀects generated with spherical mobile robots and investigated the visualeﬀect of using alternative mechanisms to depict rotational
movement.

4. PRELIMINARY INVESTIGATION ON ROTATIONAL MOVEMENT EXPRESSION
OF A SPHERICAL LED DISPLAY
We studied how a changing pattern can make a ball appear to rotate. To do so, we built a mobile robot equippedwith a spherical LED display and evaluated its visual eﬀect.
A motion illusion using light requires continuous movement of light. To accomplish this, we devised the methodof mounting LEDs on the inside of a spherical surface withvery fine gaps separating the elements. Moreover, controlling the LEDs while showing a simulation of the light patterns improves the generation eﬃciency of visual eﬀects. We
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Figure 2: Combination of spherical LED display andmobile robot (TDSTO48-350).

and mounted it on top of a TDSTO48-350 robot [33] from
Tosadenshi Co. Fig. 2 illustrates the construction of thedisplay and the robot.

4.1

Proposed System

The appearance of the spherical LED display we createdis shown in Fig. 3. We attached Dotstar LEDs [34] from
Adafruit Co. to the inner surface of a transparent, spherical shell, that had a diameter of 120 mm. The completed
included 530 full-color LEDs controlled by twelve Arduinonano units [35]. The entire sphere was sprayed with whiteliquid rubber so that the LEDs would be invisible and thelight from them would be diﬀuse.

4.2

Experiment Procedure

We investigated the influence of visual eﬀects using light.
The two items we surveyed were as follows.
1. Relationship between lighting patterns and optical illusions.
2. Relationship between the distance between the sphereand audience and the level of optical illusion.
We recruited nine male and two female participants withan average age of 23.8 and asked them to look at six performances including the moving robot with the spherical LED
display. The observation points (see Fig. 4) were as follows.
• Observation point A
P1: Rolling motion depicted with one light ring.
P2: Rolling motion depicted with two rings.
P3: Rolling motion depicted with six rings.

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P5: Rolling motion depicted with two rings.
P6: Rolling motion depicted with six rings.
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The lighting patterns are shown in Fig. 5.
At observation point A, the participants watched the spherethrough a mirror from a distance of 10 m. At observation
point B, the participants watched the sphere from a distanceof 5.5 m.
The performer danced for about 30 seconds. The songthat was used was 110 bpm. The participants watched theperformances from a height of approximately 110 cm above
the floor, so that they could not see the mobile robot mounting the sphere on stage. The lights of the room were turned
oﬀ to highlight the light from the LEDs. Only the performer
was highlighted by a spotlight. If the lighting pattern rotated in the advancing direction, the rotational speed of themobile robot was 0.3 m/s. The participants were asked after
they had watched all the performances.
Q1 Did the sphere appear to be rolling?
We asked these questions in order to determine the reason
for any breaking of the optical illusion, to suggest possible
improvements to the optical illusion, and to identify aspects
that the participants noticed, such as the size, shape, andchange in movement velocity.

4.3 Results and Considerations
The results for Q1 are shown in Fig. 6. The verticalaxis indicates the average value for the performances givenby the eleven participants calculated on a five-point scale.
The vertical bar indicates the standard deviation, and thehorizontal axis indicates each individual performance.
Two of the participants responded that “If I was awayfrom the light, it looked beautiful,” and “it would be likely

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Figure 5: Lighting patterns.

to be fully utilized on a big stage.” It is possible that theappearance of the light changed with distance.
When more rings were shown in the lighting pattern, theparticipants gave a higher evaluation. Two of the participants responded that “the lighting needs to have a surface
area that can be recognized as a sphere,” and “the morepatterns there are, the more it seems as if it is rotating."
Nine out of the eleven participants noticed that the velocity of the sphere and the rotational speed of the lights
were not the same and commented on it. This indicatedthat we needed to find a way to assure that the velocity androtational speeds are the same.

5.

DEVELOPMENT AND EXPERIMENTSSPHERE-SHAPED MOBILE ROBOT

5.1 Improvement of the system
The findings of the preliminary study showed that it isnecessary to synchronize the rotation of the lights of thespherical LED display with the distance moved by the robot.

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Table 1: Comparison of TDSTO48-350 and createdmobile robot.
Mobile robot created
TDSTO48-350
in this study
Diameter
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200 mmWeight3500 g
600 g
CPU
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STM32F405
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30 minutes
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Figure 7: Comparison of system configurations.

accelerated faster than the other.
In an actual stage performance, to facilitate the optical illusion of a rolling sphere, the driving part, i.e., the mobile
robot should be as low and as small as possible.
Fig. 7 compares the system configurations before and after we made improvements to the system, while Fig. 8 shows
the robot we created and Table 1 compares the TDSTO48350 and the mobile robot we created.
The driving part is hidden by covering the entire mobile
robot with a plastic cover. When the sphere is on stage, it
is diﬃcult to see that there is a robot directly under it, andthis probably makes it easier to create an optical illusionof a rolling sphere. In addition the diameter of the mobile
robot is only 0.67 times that of the TDSTO48-350. In orderto accommodate all of the mechanisms within the plastic
cover, The controlling microcomputer was swapped with anmbed unit [36] from ARM Co. and 12 Arduino nano units.
The mobile robot sends out the velocity information andthe angle information to he mbed in real time. The mbed
uses this real-time information to control the LED lighting
patterns and texture of the display. In this way, the distancetraveled by the mobile robot can be synchronized with therotating pattern of the LED lights. Moreover, to generate alighting pattern in the mbed, the application doesn’t have togenerate the lighting pattern for controlling the light used in
the investigation of visual eﬀects. In this way, the amountof information to be transmitted to the mobile robot wasable to be reduced.
We compared the traveling performance of Sphero2.0 andthat of the mobile robot we created （Fig. 9）. To examine
the acceleration capability, the arrival times for a distanceof 1.0 m were compared. Here, Sphero2.0 took 1.39 second,and our robot took 1.00 second. Thus, our mobile robot

5.2

Experiment Procedure

We investigated the rotational speed of the lights and themoving speed of the mobile robot. The three items we surveyed were as follows.
1. The question of whether participants who could not
see the movements of the spherical mobile robot experience the optical illusion of a rolling spheres.
2. The relationship between the velocity of the robot andthe perception of the optical illusion.
3. Influence of the deviation between the amount of ‘‘rotation’’ and the moving distance on the illusion.
Regarding item (1), we assumed a situation in which therobot would be used in a real performance. We asked participants watching the spherical LED display for the firsttime if they thought that the sphere itself was physicallyrolling, rather than LED lights turning on and oﬀ. If theparticipants believed the optical illusion that the sphere wasrolling, robots such as this one can probably be used in real
performances. Regarding items (2) and (3), the allowable
ranges of each item can be determined by investigating theinfluences of each item on the optical illusion. Regarding(3) in particular, the sphere sometimes slipped dependingon the texture of the floor, for example, as in bowling. If it
is possible to give the optical illusion of a special rotation,for example when a mime pretends the floor is made of ice,
this could potentially widen the range of expressions andstage eﬀects.
Twelve males with an average age of 22.7 participated in
the experiment. The procedure was as follows.

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Step 1 A participant enters the room. He/She watches aperformance involving the mobile robot equipped witha spherical LED display and has no knowledge about
how it operates. He/She answers verbally the questionof whether or not the sphere appears to be rolling.
Step 2 The participant receives an explanation of the function of the spherical LED display and gets to know how
it works.

Figure 9: Acceleration comparison test of sphericalmobile robots.

0.5 times, 1.5 times, 2.0 times (moving speed of 0.6
m/s).

Step 3 The participant watches an actual rolling LED ball.
Step 4 The participant watches the visual eﬀects of thespherical LED display and evaluates it by comparing itwith the actual rolling LED ball that he/she watched
it in Step 3.
The floor plan is the same as that of Fig. 4. The lightsof the room were turned oﬀ to highlight the light from theLEDs. The performer was highlighted by the spotlight. The
performance used the same as choreography as the one described in Section 4.2. In Step 1, a spherical LED display
presents the rotation, and the participant observes it fromobservation point B of Fig. 4. Each participant watches aperformance only one time in Step 1. After the presentation, an experimenter orally asks the participant two questions: ‘‘Did the sphere appear to be rolling?’’ and ‘‘What
mechanism do you think makes the sphere moves?’’ In Step
2, the experimenter explains the mechanism of the mobile
robot and orally confirms whether or not the participant
recognized the mechanism. In Step 3, the position that theparticipant observes from is the same as in Step 1. The LEDball is actually rolling, and the presented lighting pattern is
as shown Fig. 10. The participant watches the actual rolling
LED ball only one time in Step 3. The performer does notgive a performance. In Step 4, the observation point is thesame as in Step 3. The performer does not perform. The
LED display shows showed the following visual eﬀect patterns, i.e., combinations velocity and rotation.
• Velocity
0.3 m/s，0.6 m/s，0.9 m/s，1.2 m/s．
• Amount of rotation of lights with respect to themoving distance

The performance involved a person with a mobile robot.
We suppose the performer’s moving speed is within 1.3 m/s,
which is the average walking speed, and we set the speedof the robot in its range. We asked the participants immediately after they had watched each of the visual eﬀect
patterns.
Q1 Did the sphere appear to be rolling?
The participant evaluated Q1 where in the reference evaluation of the rolling of an actual sphere was as 5, i.e., thelargest value. In addition, we let participants to freely comment on what they saw.

5.3

Results and Discussion

Eleven out of the twelve participants believed the illusion that the sphere was rolling during at the performance.
When participants received an explanation on the functionof the spherical LED display and got to know the rotational
movement of the lights in Step 2, the participants answered“I thought that the sphere was just rolling”, “I thought that
the LED ball was rolling by running on electric rails.” and“I thought there was a driving part inside the LED ball andthat the LED ball was rolling because its center of gravity was moving.” These answers confirmed that the participants perceived the sphere to be physically rolling. However,one participant recognized that the rotation was due to thelights. The participant commented that the lights he saw
were not discrete but continuous. Accordingly, we considered that the participant possibly recognized some aspectof the lights, or that the sensitivity of the participants eyes
was aﬀected by the experimental conditions.
The results of the questionnaire in relation to item (2)of the previous section are shown in Fig. 11. The verti-

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cal axis indicates the average value of the answers to Q1
that the twelve participants gave. The vertical bars indicate
standard deviation. The horizontal axis represents the velocity of the robot when the visual eﬀects were presented.
We assessed the diﬀerence between the velocities by using
ANOVA. There was no significant diﬀerence; however, as thefigure indicates, the slowest speed of 0.3 m/s and the fastest
1.2 m/s received low evaluations. When the rotational speedof the light pattern was slow, the participants commented
that they “found that the lights of the spherical LED display
did change not smoothly”, “felt discomfort when watching
it closely (i.e., carefully)”, and “found that the LEDs lookedpebbly”. These problems can be avoided by covering thesphere with smaller LEDs. On the other hand, when the rotational speed of the lights was fast, we got comments suchas “the flicker of the light patterns impaired the appearanceof the sphere” and “the sphere appeared to be moving while
the lights randomly flickered.” We supposed these problems
could be overcome by raising the frame rate of the display
above its current 30 fps.
The results of the questionnaire on the amount of rotationof the light pattern with respect to the moving distance wereused to investigate item (3) of the previous section. They
are shown in Fig. 12. The vertical axis indicates the averagevalue of answers to Q2 from the twelve participants. The
vertical bars indicate standard deviation. The horizontal
axis represents the amount of rotation of the light patternwith respect to the moving distance. We assessed the difference between the amount of rotation of the light patternwith respect to the moving distance by using ANOVA. There
was a significant diﬀerence（F(2,22) = 5.01, p < .05）. Moreover, we assessed the diﬀerence by using a Bonferroni test.
Here, as well, there was a significant diﬀerence between therolling-to-movement ratios of 1.5 and 2.0（p < 0.05） the
optical illusion diminishes when the rotation increases toomuch relative to the distance moved. The optical illusion
tends to be maintained when the rotation is reduced rather
than increased. We received comments such as, “the robot
seemed to be rotating much more when the rotation waslarger than the distance moved," and “I felt the optical illusion happening when the rotation was synchronized with the
movement." Regarding the rotation, the eﬀect on the optical
illusion seemed to be small even when there was noise due
to slipping and sensor errors. Moreover, the evaluation waspoor when the rotation was reduced. We received comments
such as, “the rotation was as if a bowling ball was slippingon the lane" and “the lighting method was interesting".
In summary, eleven out of twelve participants believed theillusion that the sphere was rolling when they watched theperformance, which is surprising. Our system visually reproduced the movements of a rolling sphere. There is strong
possibility that it can be used to give the optical illusion of arolling sphere in real performances. Moreover, the improved
hardware and software made the illusion possible even whenthe LED ball moved too slowly or too quickly. Furthermore,
we found that attention needs to be paid to the relationshipbetween rotation and moving distance when setting up a
performance.

6.

TESTING THE ABILITIES OF THE
SPHERE-SHAPED MOBILE ROBOT

6.1 Improvement of the system
We improved the system to create a more convincing optical illusion, by incorporating all the experimental results
described in the previous section. Some improvements were
aimed at transporting the performance to a live stage. The
resulting LED display is shown in Fig. 13. We covered awhite, spherical shell having a diameter of 170 mm with
999 Dotstar LEDs. These full-color LEDs were controlled
by one mbed. The results described in the previous section

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Figure 13: Appearance of Spherical LED Displays.
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Figure 15:
robot.

to the robot so that it would not fall oﬀ, the inside of thesphere and the mobile robot were equipped with magnets.

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6.2

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Performance using spherical mobile

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Figure 14: Combination of mobile robot and spherical LED display.

indicated that the lights needed to be dimmed in order forthe display to change its lighting smoothly. Therefore, we
positioned the LEDs 7 mm from the sphere’s shell. Since
the spherical surface area illuminated by each LED became
wider as a result, it was more diﬃcult to distinguish eachindividual LED. Furthermore, in order for the light to be biased, all LEDs face a normal vector out of the sphere. Moreover, the intensity of the light needed to show the lighting
pattern was discussed in the previous section. The lights are
switched on and oﬀ in a binary pattern. In order to makerotating light patterns flow more smoothly, we used medium
intensity light, which is thought to create a stronger optical illusion of a sphere rolling. In addition, to increase thevisibility of the display, we attached a mechanism to it thatallowed it to move up and down.
The appearance of the new robot is shown in Fig. 14. A
spherical robot that moves by using its own center of gravity
can be held by a performer. On the other hand, the robotthat we described in the previous section cannot be held bya performer. Therefore, there is a possibility that it would
limit rather than expand the range of expressions. To widen
the range of expressions, we made it possible to detach thespherical LED display from drive section (i.e., the mobile
robot). The robot and display had a wireless connection via
Xbee. In order to safely attach the spherical LED display

Performance using optical illusions

By using the ability of the spherical LED display to mimica real sphere, it is possible to project optical illusions on thesurrounding environment. For example, by creating a large
diﬀerence between the rotational speed of the sphere andits velocity, it would be possible to make the floor appear
slippery (as if it were covered in ice) in the minds of spectators. Similarly, it is possible to make the sphere appear
be pushed, as if acted upon by an invisible force (such aswind), or to create the appearance of an invisible wall bymaking the sphere slam to a halt. As in mime, in creating
the appearance of an icy floor, strong winds, or the presenceof an invisible wall, the addition of environmental eﬀects canenhance a performer’s show. Additionally, the robot freely
controls its own rotational speed and can represent its timeaxis. Therefore, it ‘‘collaborates’’ with a mime in creating
optical illusions in the surrounding environment.
Here, we collaborated with Mr. Naoki Iimuro, a mime.
Fig. 15 shows him in a n actual performance with the robots
we created.
We recorded his performance and exhibited it at Robotics
x Future 2016 (there were 1460 attendees at the 18th team
exhibition, which included our team). The attendees had
the following reactions: “until being told how the mechanism worked, I was convinced that the sphere was physically rotating on its own", “it looked as if the sphere wasspinning on its own", “it looked as if the sphere was attachedto the wall, and rolling on it", “it seemed that the camera
angle was changing, which was very interesting", “it looked
as if the robot was surprised", “it looked as if the video’s
playback speed was changing", “in one scene the robot was
gentlemanlike" and “if the sphere could go up and down the
man’s waist, the amount of situations it could be used inwould increase."
Although the audience got their impressions from a recording and not a live performance, many of them believe theoptical illusion that the sphere was rotating, and thought
the whole thing very mysterious. From these impressions,
we can assume that the optical illusion is conveyed just as
eﬀectively in this format.

6.3 Considerations
We asked Mr. Naoki Iimuro, who created the choreography for this performance, for his personal impressions, which
are reported below.
“A spherical robot on a moving stand demonstrated higher
power output and mobility than expected. It was able tomove very naturally during scenes such as when it pushed
against a wall without appearing too burdened. A trick
where an item was loaded, unloaded and the robot’s ‘reaction bar’s’ width expanded to show the robot’s character
was also well received. The idea to have the spherical robot
itself glow as an LED and give the illusion that it was moving was very interesting. However, the balance between theintensity of the spherical robot’s glow with the display of aperson led to a visual problem. In the first place, users ‘want
to see a person not a stand’. How that visual problem can beovercome will be an important topic in designing the next
performance. There is a potential for a simple separationof the spherical robot’s body and the stand, but regardlessunpredictable responses can be expected. If the robot werea bit lighter and easier to use and could fit comfortably in
one’s hand, it would lead to an especially good collaboration between robots and pantomime. We can expect moreprogress in the future."
At present, the robot is much more noticeable than theperformer is in the main part of the performance, so it is difficult to say that the highlight of expressions is good. This
problem may be able to be resolved by always illuminating
the performer on the robots side, or by shining a spotlighton the performer’s side, having the performer wear something shiny device, and using a combination of black lightand a fluorescent substance. Moreover, in the current performance, the spherical LED display did not have an interactive mechanism to react in real time to the motions of
performer.
The high-agility mobile wheeled robot has improved performance compared with a conventional spherical robot. However, taking the influence on the stage performance into account, it is diﬃcult to use it in ways that have the possibility of breaking the device, such as throwing the spherelike a ball, trying to bounce it, or rolling it on the surface ofsome other body. In the current mechanism, the diameterof the lower mobile robot is bigger than the upper sphere.
Therefore, an audience might see the lower part, which may
worsen the quality of the performance. In the future, weneed to make the lower part small enough to hide below theupper part.

7. CONCLUSION
This study described the creation of a mobile robot withhigh agility and simple self-localization features that is equippedwith a spherical LED display capable of producing the illusion of motion unique to its shape, i.e., rolling in any direction. The system was built and preliminary investigations
were conducted on optical illusions produced by its lighting
eﬀects. The results of the preliminary experiments were incorporated into improvements to the system. The improved
system allows for lighting patterns of the spherical LED display to be produced and controlled in real time based on thevelocity of the robot. In this way, the moving distance ofthe mobile robot can be synchronized with the rotation of
the lighting pattern of the spherical LED display. Further

tests conducted on the optical illusions it could produce indicted that 11 out of 12 test participants saw the robot as
a rolling sphere. These experiments demonstrated that thelarger the diﬀerence is between the distance traveled by the
robot and its rotation, the weaker the eﬀect of the optical
illusion. We created a performance featuring the robot witha professional performer and were impressed by its eﬀect on
audience.
As for future challenges, our work has possible applications in sports. The LED lights would be visible, in a poorlylit environment in which it would be hard to see. The resulting eﬀect might lead to the creation of various digital sports.
Moreover, children and the elderly, who cannot move theirbodies as well as adults, could easily participate in games
that involve rolling a heavy ball, like bowling. They could
also play games like soccer that involving accurately passing
a ball around. The robot can easily incorporate information
related to education and sports; for example, its movements
can be improved through programming.

8.

ACKOWLEDGMENTS

This research is supported financially by IPA Exploratory
IT Human Resources Project 2014 (The MITOH Program2014)，the Japan Science and Technology Agency (JST) Super Cluster Program (Kyoto Area, Construction of HighlyEﬃcient Energy to Achieve a Clean and Low Environmental Impact Society)，Grant-in-Aid for Scientific Research(A)(23240010) from the Japanese Ministry of Education, Culture, Sports, Science and Technology, and Program for Creating STart-ups from Advanced Research and Technology
from Japan Science and Technology Agency, JST.

9.

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