Instrumentation & Measurement Magazine 25-9 - 39

Table 1 - Comparison of the specifications of an ant walking at its spontaneously
chosen speed to those of an analogous hexapod robot
Indicator
Total mass
Middle leg segment length (mm)
Speed (cm/s)
Stride length (mm)
Stride frequency (Hz)
8.92 mg
Coxa-trochanter: 0.4
Femur: 1.6
Tibia: 3
0.4
5.7
0.7
multiply the ant's indicator value by the associated scale factor
to estimate the same indicator for the robot.
Numerous other parameters exist, not presented in Table
1, which characterize the walking performance of an insect or
a robot [10], either unrelated to both the robot and the animal
or which are hard to evaluate for one of the two. One example
of this is the cost of transport (CoT) [1], a typical estimation
of the energy needed to move an agent at a specific speed and
with a given load. For a robot it is defined as a dimensionless
value easily measurable at the power supply input. For hexapod
robots based on Dynamixel servomotors, the CoT values is
usually between 1.5 and 6.2 [1]. When it comes to biology, the
CoT is frequently defined in joules per kilogram-meter and
requires an estimation of the metabolic rate [11], which is difficult
to evaluate for an ant measuring only a few millimeters.
An ant's CoT is estimated at a value of 39 [1], but it depends on
the ant's weight and measurement conditions [11].
Table 1 ant's scaled parameters suggest that a robot is able
to exceed the parameters measured in our Messor barbarus ant
walking at its spontaneously chosen speed. Our robotic leg is
able to generate higher speeds of up to 38 cm/s, defined by the
chosen actuator specifications (ours has a maximum speed of
97 rpm and is one of the highest for a servomotor of this category).
However, the ant's speed can reach up to 86 cm/s [12],
leading to the conclusion that robot performance limits are still
below those of the animals.
As shown on Fig. 5b, the implemented leg tip path conserves
the continuity of speed and acceleration, inherited from
the ant's kinematics, despite the resizing. Nevertheless, the
contact of the robot's leg with the ground is highly disturbed
(Fig. 5c), and an increase in the error is observed after high
acceleration phases. These variations in the error value are primarily
caused by the high inertia of the robot leg, and secondly
by robot imperfections [1]: motor heating, friction, mechanical
backlash and leg stiffness.
Taking into account the limitations of bio-inspired robots,
are there any benefits to using robots, instead of simulated
insect multibody models? As shown by the hexapod robot
experiments of the last decade [1], the development of insect
inspired robots is mainly motivated by the study of real
insect locomotion, navigation, or visual sensory systems. It
December 2022
Ant
Scale factor
α = 1:58
α3
α
α1/2
α
α-1/2
Hexapod robot
(ant's values scaled
to the robot's size)
2 kg (1.7 kg)
Coxa-trochanter: 40 (23)
Tibia: 95 (93)
Femur: 178 (174)
21 (3)
265 (330)
0.8 (0.09)
is still rare to see dynamics hypotheses proven by hexapod
robot studies, due to drawbacks inherent in robot mechanical
systems. The development of new and more realistic
robots, closer to biological structures, should soon begin to
overcome these drawbacks. Currently, the dynamic properties
observed in insects, i.e., energy recovery during walking
[8], limb elasticity and compliance [8], are more likely to
be implemented in robots and constitute essential features
of insect legs that are rarely present in conventional
hexapod robot legs but which appear meaningful for walk
stabilization.
Conclusions
A bio-inspired robot usually takes a specific animal as a model,
so designing a bio-inspired hexapod robot whose size is about
58 times that of an ant (10 mm) could appear, at first glance,
inconsistent, even if mimicking observations at a larger scale
appears tempting. This study focuses on two data sets collected
from two test benches: the first used to characterize
the walk of an ant, and the other to test the performance of a
conventional artificial leg often used in bio-inspired robotics
research.
In addition to robotic applications, our test benches could
be used to deduce hypotheses about the dynamic behavior of
ants, such as the intra-leg coordination or the coordination of
its six legs during its locomotion. From a robotics point of view,
test benches are useful for extrapolating the energy consumption
of a legged robot from a single leg and therefore increasing
their navigation distance, a prerequisite for the implementation
of a navigation system based on bio-inspired visual
sensors. In conclusion, this study is a first step towards understanding
how biological data from ant locomotion can be used
in hexapod robotics.
Acknowledgment
This research was supported by the French Agence de
l'innovation de défense (AID), the CNRS (PEPS MiMiC-ANT
Program), and Aix Marseille University (AMU). The authors
would like to thank David Wood and Kristy Virostek for revising
the English and Camille Dégardin for providing her
illustration.
IEEE Instrumentation & Measurement Magazine
39

Instrumentation & Measurement Magazine 25-9

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 25-9

Instrumentation & Measurement Magazine 25-9 - Cover1
Instrumentation & Measurement Magazine 25-9 - Cover2
Instrumentation & Measurement Magazine 25-9 - 1
Instrumentation & Measurement Magazine 25-9 - 2
Instrumentation & Measurement Magazine 25-9 - 3
Instrumentation & Measurement Magazine 25-9 - 4
Instrumentation & Measurement Magazine 25-9 - 5
Instrumentation & Measurement Magazine 25-9 - 6
Instrumentation & Measurement Magazine 25-9 - 7
Instrumentation & Measurement Magazine 25-9 - 8
Instrumentation & Measurement Magazine 25-9 - 9
Instrumentation & Measurement Magazine 25-9 - 10
Instrumentation & Measurement Magazine 25-9 - 11
Instrumentation & Measurement Magazine 25-9 - 12
Instrumentation & Measurement Magazine 25-9 - 13
Instrumentation & Measurement Magazine 25-9 - 14
Instrumentation & Measurement Magazine 25-9 - 15
Instrumentation & Measurement Magazine 25-9 - 16
Instrumentation & Measurement Magazine 25-9 - 17
Instrumentation & Measurement Magazine 25-9 - 18
Instrumentation & Measurement Magazine 25-9 - 19
Instrumentation & Measurement Magazine 25-9 - 20
Instrumentation & Measurement Magazine 25-9 - 21
Instrumentation & Measurement Magazine 25-9 - 22
Instrumentation & Measurement Magazine 25-9 - 23
Instrumentation & Measurement Magazine 25-9 - 24
Instrumentation & Measurement Magazine 25-9 - 25
Instrumentation & Measurement Magazine 25-9 - 26
Instrumentation & Measurement Magazine 25-9 - 27
Instrumentation & Measurement Magazine 25-9 - 28
Instrumentation & Measurement Magazine 25-9 - 29
Instrumentation & Measurement Magazine 25-9 - 30
Instrumentation & Measurement Magazine 25-9 - 31
Instrumentation & Measurement Magazine 25-9 - 32
Instrumentation & Measurement Magazine 25-9 - 33
Instrumentation & Measurement Magazine 25-9 - 34
Instrumentation & Measurement Magazine 25-9 - 35
Instrumentation & Measurement Magazine 25-9 - 36
Instrumentation & Measurement Magazine 25-9 - 37
Instrumentation & Measurement Magazine 25-9 - 38
Instrumentation & Measurement Magazine 25-9 - 39
Instrumentation & Measurement Magazine 25-9 - 40
Instrumentation & Measurement Magazine 25-9 - 41
Instrumentation & Measurement Magazine 25-9 - 42
Instrumentation & Measurement Magazine 25-9 - 43
Instrumentation & Measurement Magazine 25-9 - 44
Instrumentation & Measurement Magazine 25-9 - 45
Instrumentation & Measurement Magazine 25-9 - 46
Instrumentation & Measurement Magazine 25-9 - 47
Instrumentation & Measurement Magazine 25-9 - 48
Instrumentation & Measurement Magazine 25-9 - 49
Instrumentation & Measurement Magazine 25-9 - 50
Instrumentation & Measurement Magazine 25-9 - 51
Instrumentation & Measurement Magazine 25-9 - 52
Instrumentation & Measurement Magazine 25-9 - 53
Instrumentation & Measurement Magazine 25-9 - 54
Instrumentation & Measurement Magazine 25-9 - 55
Instrumentation & Measurement Magazine 25-9 - 56
Instrumentation & Measurement Magazine 25-9 - 57
Instrumentation & Measurement Magazine 25-9 - 58
Instrumentation & Measurement Magazine 25-9 - 59
Instrumentation & Measurement Magazine 25-9 - 60
Instrumentation & Measurement Magazine 25-9 - 61
Instrumentation & Measurement Magazine 25-9 - 62
Instrumentation & Measurement Magazine 25-9 - 63
Instrumentation & Measurement Magazine 25-9 - 64
Instrumentation & Measurement Magazine 25-9 - 65
Instrumentation & Measurement Magazine 25-9 - 66
Instrumentation & Measurement Magazine 25-9 - 67
Instrumentation & Measurement Magazine 25-9 - 68
Instrumentation & Measurement Magazine 25-9 - 69
Instrumentation & Measurement Magazine 25-9 - Cover3
Instrumentation & Measurement Magazine 25-9 - Cover4
https://www.nxtbook.com/allen/iamm/26-6
https://www.nxtbook.com/allen/iamm/26-5
https://www.nxtbook.com/allen/iamm/26-4
https://www.nxtbook.com/allen/iamm/26-3
https://www.nxtbook.com/allen/iamm/26-2
https://www.nxtbook.com/allen/iamm/26-1
https://www.nxtbook.com/allen/iamm/25-9
https://www.nxtbook.com/allen/iamm/25-8
https://www.nxtbook.com/allen/iamm/25-7
https://www.nxtbook.com/allen/iamm/25-6
https://www.nxtbook.com/allen/iamm/25-5
https://www.nxtbook.com/allen/iamm/25-4
https://www.nxtbook.com/allen/iamm/25-3
https://www.nxtbook.com/allen/iamm/instrumentation-measurement-magazine-25-2
https://www.nxtbook.com/allen/iamm/25-1
https://www.nxtbook.com/allen/iamm/24-9
https://www.nxtbook.com/allen/iamm/24-7
https://www.nxtbook.com/allen/iamm/24-8
https://www.nxtbook.com/allen/iamm/24-6
https://www.nxtbook.com/allen/iamm/24-5
https://www.nxtbook.com/allen/iamm/24-4
https://www.nxtbook.com/allen/iamm/24-3
https://www.nxtbook.com/allen/iamm/24-2
https://www.nxtbook.com/allen/iamm/24-1
https://www.nxtbook.com/allen/iamm/23-9
https://www.nxtbook.com/allen/iamm/23-8
https://www.nxtbook.com/allen/iamm/23-6
https://www.nxtbook.com/allen/iamm/23-5
https://www.nxtbook.com/allen/iamm/23-2
https://www.nxtbook.com/allen/iamm/23-3
https://www.nxtbook.com/allen/iamm/23-4
https://www.nxtbookmedia.com