Aerial-Biped: a new physical expression by the biped robot
using a quadrotor
Azumi Maekawa

Ryuma Niiyama

Shunji Yamanaka

The University of Tokyoazumi@star.rcast.u-tokyo.
ac.jp

The University of Tokyoniiyama@isi.imi.i.u-tokyo.
ac.jp

The University of Tokyo
yam@iis.u-tokyo.ac.jp

Figure 1: Aerial-Biped generating a gait in real time.

ABSTRACT

1 INTRODUCTION

We present a biped robot which can move agiler than conventional
robots. Our robot can generate bipedal walking motion automatically using the proposed method. By using a quadrotor for balance
and movement it is possible to make an agiler movement, and generate a gait interactively and in real time according to the motionof the quadrotor using the optimized control policy of the legs. Our
system takes the velocity of the quadrotor as an input and legs motions are produced so that the velocity of the foot in contact withthe ground to zero, and bipedal walking motion is generated. The
control policy is optimized using reinforcement learning with aphysics engine.

There has been a desire to make robot creatures like living things
since ancient times. Progress in modern robot technology is remarkable, but there are still many difficulties and problems in orderto realize a robot that has flexible thinking and can deal with thevarious environment, such as appears in science fiction movies.
We focused on a bipedal walking robot which is one of suchdifficulty. Bipedal robots currently have various problems, such as
heavy motion, costs, and risk of falling. Realising a bipedal robot
like a living thing is one of the biggest challenges so far and manystudies have been conducted. We developed a biped robot for entertainment which can move agiler than ever before. We used thelegs of the robot in order to realize the appearance features seen
in bipedal walking, and we used a quadrotor as a means of movement. As a close approach, there is a biped walking robot using
the buoyancy of a balloon[Ghassemi and Hong 2016]. Our robot
uses quadrotor to enhance maneuverability, enabling a richer physical expression. In addition, motions of the legs are automaticallygenerated according to the motion of the quadrotor using the proposed method As methods for realizing the appearance of walking motion of a robot for entertainment, there are using link structures[Coros et al. 2013; Thomaszewski et al. 2014]. In these methods, although an arbitrary motion trajectory can be installed in arobot, it is limited to a cyclic and static motion. We propose themethod that allows the biped robot to move more dynamic andgenerate a gait interactively in real time.

CCS CONCEPTS• Computer systems organization → Robotics;

KEYWORDS
robotics, entertainment, biped robot, unmanned aerial vehicle, gait
generation
ACM Reference format:
Azumi Maekawa, Ryuma Niiyama, and Shunji Yamanaka. 2018. Aerial-Biped:
a new physical expression by the biped robot using a quadrotor. In Proceedings of SIGGRAPH ’18 Emerging Technologies, Vancouver, BC, Canada,
August 12-16, 2018, 2 pages.
https://doi.org/10.1145/3214907.3214928
Permission to make digital or hard copies of part or all 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 citationon the first page. Copyrights for third-party components of this work must be honored.
For all other uses, contact the owner/author(s).
SIGGRAPH ’18 Emerging Technologies, August 12-16, 2018, Vancouver, BC, Canada© 2018 Copyright held by the owner/author(s).
ACM ISBN 978-1-4503-5810-1/18/08.
https://doi.org/10.1145/3214907.3214928

2 METHOD
we focused on the velocity of the foot in contact with the ground.
Our method is designed considering that the appearance of gait
can be realized by generating the motion of the legs that makes
the velocity of the foot in contact with the ground to zero. TheSIGGRAPH ’18 Emerging Technologies, August 12-16, 2018, Vancouver, BC, CanadaA. Maekawa et al.

Figure 3: The robot foot trajectory generation system in thehardware
generation system by controlling the input interactively. In addition, they can control the quadrotor with the remote, and makethe biped robot walk and experience choreography of the robot.

4 CONCLUSIONS AND FUTURE WORK

Figure 2: (a) (b) The robot model used to learn the control
policy of the legs. (c) The control system in the real robot

control policy used for a gait generation is optimized by reinforcement learning with a physics engine. We define the robot model asshown in Fig. 2 and learning the policy is executed under following
conditions.
(1) the body has one degree of translation freedom.
(2) each leg has two degrees of rotation freedom.
(3) the velocity of the body changes randomly.
(4) the robot gets a better reward as the velocity of the foot in
contact with the ground is closer to zeroThis our method can generate the robot foot trajectory automatically that realize the appearance of bipedal walking according tothe body movement.
In the real robot, the velocity of the quadrotor is estimated by
the motion capture data, and the input of the servomotors of eachjoint is generated using the optimized control policy. Several methods have been developed can interactively generate gaits of bipedal
walking characters in computer animation[Holden et al. 2017; Penget al. 2017]. Our method can generate a gait of the biped robot in
the real world.

3

USER EXPERIENCEAt SIGGRAPH 2018 Emerging Technology exhibition, we will demonstrate the proposed gait generation system (Figure 3) and the realrobot implemented using this system, Aerial-Biped. Attendees cansee how the robot work and experience the robot foot trajectory

We propose a biped robot for entertainment using a quadrotor. This
robot can move agiler than conventional robots and generate a gaitin real time using the control policy which makes the velocity of
the foot in contact with the ground to zero, as the velocity of thequadrotor is input.
In this study, assuming movement of the quadrotor, that is, movement of the body of the robot is 1 dimensional, the gait is generated.
As the next plan, we are going to increase the degree of freedomof the body and legs. There is a possibility that various motions
can be generated by this and it will become possible to imitate themotion of the character in the animation.

ACKNOWLEDGMENTS
I would like to thank M. Inami for useful advice. This work wassupported by JST ERATO Grant Number JPMJER1501, Japan.

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