Citation: Roscia, F.; Cumerlotti, A.;
Del Prete, A.; Semini, C.; Focchi, M.
Orientation Control System:
Enhancing Aerial Maneuvers for
Quadruped Robots. Sensors 2023, 23,
1234. https://doi.org/10.3390/
s23031234
Academic Editor: Emanuele Lindo
Secco
Received: 6 December 2022
Revised: 6 January 2023
Accepted: 16 January 2023
Published: 20 January 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
Orientation Control System: Enhancing Aerial Maneuvers for
Quadruped Robots
Francesco Roscia
1
, Andrea Cumerlotti
1,2
, Andrea Del Prete
2
, Claudio Semini
1
and Michele Focchi
1,3,
*
1
Dynamic Legged Systems (DLS) Lab, Istituto Italiano di Tecnologia (IIT), 16163 Genova, Italy
2
Industrial Engineering Department (DII), University of Trento, 38123 Trento, Italy
3
Department of Information Engineering and Computer Science (DISI), University of Trento, 38123 Trento, Italy
* Correspondence: michele.focchi@unitn.it
Abstract:
For legged robots, aerial motions are the only option to overpass obstacles that cannot
be circumvented with standard locomotion gaits. In these cases, the robot must perform a leap
to either jump onto the obstacle or fly over it. However, these movements represent a challenge,
because, during the flight phase, the Center of Mass (CoM) cannot be controlled, and there is limited
controllability over the orientation of the robot. This paper focuses on the latter issue and proposes
an Orientation Control System (OCS), consisting of two rotating and actuated masses (flywheels or
reaction wheels), to gain control authority on the orientation of the robot. Due to the conservation of
angular momentum, the rotational velocity if the robot can be adjusted to steer the robot’s orientation,
even when the robot has no contact with the ground. The axes of rotation of the flywheels are
designed to be incident, leading to a compact orientation control system that is capable of controlling
both roll and pitch angles, considering the different moments of inertia in the two directions. The
concept was tested by means of simulations on the robot Solo12.
Keywords: legged robot; orientation control; articulated multi-body system
1. Introduction
Legged robots are designed for traversing rough terrain. Different types of gaits, such
as trot [
1
] or crawl [
2
], have been developed for quadrupedal robots. Thanks to progress
over the last two decades, robots have become lighter and stronger, which has enabled them
to perform with agile locomotion. However, sometimes it is not possible for the robot to
move around or over an obstacle with the gaits mentioned above, and jumps
are required.
When the robot is in the air, the CoM moves on a ballistic trajectory, and this is com-
pletely defined by the lift-off position and velocity. On the other hand, the base orientation
can be changed so as to exploit the conservation of the system’s angular momentum. This
means that it is possible to control the base angular velocity by changing the inertia of
the robot, e.g., changing the configuration of the joints. Nevertheless, the majority of
quadrupeds are designed with light legs, resulting in limbs that have little influence on the
total angular momentum.
Quadrupedal animals, like cats, can rearrange their tails and trunks to correct their
orientations during a fall [
3
]. Much work in the field of robotics has made use of an
additional link, such as a tail, as in [
4
,
5
]. This link rotates around an axis that does not pass
through the robot’s CoM. The distances between the axis of rotation and the CoM of both
trunk and tail have a large effect on the total inertia, even with a small tail mass. However,
the placement of the additional link makes the resulting robot asymmetric. Moreover, due
to its limited range of motion, a tail can be used only for a single jump, not for a repeated
sequence [
6
]. To circumvent these drawbacks, in [
7
–
9
] the authors attached a morphable
inertial tail with 3 Degrees of Freedom (DoFs) (pitch, yaw, and telescoping) on a monopod,
a biped and a quadruped, respectively, to enhance the agility of locomotion and to improve
safety in landing.
Sensors 2023, 23, 1234. https://doi.org/10.3390/s23031234 https://www.mdpi.com/journal/sensors
