The Swiss Federal Institute of Technology Lausanne in Switzerland (EPFL) has researchers utilizing Robots and AI to learn how animals operate and function. At EPFL’s BioRobotics Laboratory, Roboticists have developed a smart Eel that uses sensory feedback to swim.

AgnathaX Swimming Robot

This Robotic Eel leverages the power of its skin sensors to swim rather than depending on centralized programming. AgnathaX, the Robotic Eel, manages to coordinate its movement while swimming without central control; this makes it a pretty robust Robot.

Suppose you are familiar with what work the researchers and Roboticists at EPFL’s BioRobotics Laboratory specialize in and prioritize. In that case, you must have come across the existence of an AmphiBot quite a few times.

The AmphiBot is another Robotic invention, and AgnathaX is somewhat like its descendant. While the AmphiBot depends on central pattern generators to locomote in the water elegantly, AgnathaX doesn’t depend on CPGs for the same. Let’s read further for a better understanding of how AgnathaX can swim without CPGs.

AgnathaX uses skin sensors

Central pattern generators, commonly referred to as CPGs, are a chain of neural circuits used to create the rhythmic movements made by animals like Eels since they depend on oscillations to swim in the water.


With the help of newfangled electronic circuits alongside software, researchers and developers can replicate such neural circuits. To put it in simple words, experts can very likely copy central pattern generators to curate an Eel-like motion. The AmphiBot is a live example of this.

Even though the Robotic Eel portrays similar motions, like that of the AmphiBot, it can do so without needing to depend on centralized programming. Centralized programming is considered equal to a biological CPG.

Rather than CPG, AgnathaX employs its skin sensors to sense any changes in the water’s pressure. We can notice similar features in an Eel as well.

By incorporating such pressure sensors into the Robotic Eel’s motorized segments, AgnathaX can execute swimming motions. Also, AgnathaX can do so without having its segments connected in the absence of a centralized nervous system. Disconnected moving elements spontaneously syncing is generally referred to as entertainment.

AgnathaX body segments

For example, suppose you take four metronomes, place them a little apart from one another, and start each of their oscillations one by one, eventually, after a few minutes. In that case, all of the metronomes will oscillate in a synchronized manner.

Entertainment is quite handy for Robots because it offers another approach to control. It means that in case anything happens to the Robotic Eel’s centralized control system, it will be able to depend on its water pressure-mediated regular control to swim.

AgnathaX body segments

While developing AgnathaX, developers included rigid segments connected by actuated joints placed on the left and right side of the antagonistic muscles and two lateral force sensors. Each of these segments tends to retain its circuits which further incorporate oscillators and couplings.

AgnathaX Waterproof Arrangement

AgnathaX core consists of about ten servo motors, a Linux computer, a tail module, and some batteries. The exterior of the swimming Robot portrays its assembly sequence.

AgnathaX core incorporates a swimsuit as well that is waterproof, and the force plate module is fixed in place using magnets. It means that the load cells that consist of corresponding amplifiers, the communication circuit, and a few carbon fiber plates are set in place from the outside itself with the help of magnets. Each of these modules is connected via communication and power. The entire module is then connected to the Robotic Eel’s head.

AgnathaX further comprises a floating element that includes an LED to track motion, and it is placed at every module’s top.

AgnathaX Swimming Robot’s unique specs and features

As mentioned earlier, the AgnathaX Robotic Eel is an undulatory Swimming Robot that encompasses ten body modules, each of which is active. These modules are easily integrated with the lamprey-like Robot’s passive tail, exteroceptive sensors, and head unit.

AgnathaX Body Modules

AgnathaX uses three lithium polymer batteries, two of which are kept on the head unit’s sides and one battery on the Robot’s tail module. The batteries placed beside the head ensure that the Robot’s centerline stays aligned with its center of mass. The single battery on the tail is used for powering the Robot’s motors.

Here are a few detailed insights on AgnathaX’s batteries:

  • A battery of 7.4 V along with 800 mAh powers the sensor array.
  • Another battery of 11.1 V, placed on the head, powers the computer with 1500 mAh.
  • The third battery is placed on the tail to power the motors.

Regardless of their position, each battery possesses a 25°C nominal discharge rate.

AgnathaX weighs around 4.2 kgs and has a length of about 1250 mm. The Robot is regulated without wires and can locomote on the water’s surface with torque and position commands.

To avoid any self-collisions, the developers programmed a limit of ±60° for every servo motor to be safe. What’s more? AgnathaX is only able to operate for around 30 minutes after every recharge.

An Odroid XU4 computer that is running on Linux is placed inside AgnathaX’s head. The computer is utilized for getting signals from the external sensor from everybody module of the Robot. This includes the motors as well alongside speed, current, position, and voltage.

Once these signals are received in a control loop of 100 Hertz, the corresponding commands are conveyed to the Robot’s motors, commanding it to move.

AgnathaX is unique compared to real animals

AgnathaX isn’t at all a replica of a living animal but an approximation of one. The researchers were able to replicate the neuromechanical control that can be seen in animals in a mathematical representation of the same. This was achieved by observing animals closely and studying them simultaneously. The mathematical representation was utilized to represent locomotion further, therefore, portraying locomotion control on AgnathaX.

Researchers further directed their efforts towards equipping AgnathaX’s design with a real lamprey’s physiological and morphological features.

This can be seen while scaling the swimming Robot, where the morphology feature is utilized in undulatory animals. Furthermore, the inspiration for the muscle model used is taken from viscoelastic characteristics. These characteristics imply actual muscles along with a joint that is rotational.

The essence of undulatory swimming for modular Robots

It is entirely possible for undulatory swimming without CPGs by simply including local force feedback with the help of sensors. This approach can emerge without the need for communication between the Robot’s modules. This is done by attaching individual modules in a sequence manner, for example, modules without any communication bus in between.

To put it in simple terms, the discovery enables researchers and expert developers to curate swimming Robots in many sizes.

This is quite beneficial for modular swimming units, especially their design. These units generally possess an enormous degree of robustness. For example, environmental monitoring or missions that involve search and rescue. Moreover, the modules incorporate sensing units that open gates to a new approach for accurate force sensing while swimming in water. With the introduction of these units, aqua Robots will navigate their way with ease while allowing advanced maneuvers in an unsteady flow.

AgnathaX limitations and applications

A primary limitation of the above approach is that researchers can only study and discover exteroceptive sensory inputs. Regardless, they felt that proprioceptive inputs consist of some other redundant feedback source rather than CPG.

AgnathaX is quite applicable in today’s world since it assists us with its problem-solving approach regarding engineering issues entirely related to how stable underwater automobiles are during unsteady flows. Did you know that Robots developed that can sense specific types of flow accelerations in the water? Similar to this, AgnathaX possesses a segmented build and distributed sensors, which assist the undulatory swimming Robot in responding to any flow perturbations.

EPFL’s BioRobotics Laboratory researchers ultimate purpose – More resilient Robots

Researchers at the EPFL’s BioRobotics Laboratory have a greater purpose of building pretty resilient Robots. To have Robots that possess and follow our entire control architecture are less likely to be faulty.

AgnathaX Swimming Robot

This, along with central and peripheral components, enables the Robots to be robust – the ultimate purpose. Such Robots can withstand several types of environments, have fewer sensor damages and faulty control circuits. AgnathaX is an example of creativity and can swim even if a few sensors are missing or the communication bus is broken.

In an attempt to make AgnathaX more ‘biological,’ researchers have realized that further upgrades won’t be sufficient, and they have accepted the same.

They state that even by introducing new high-tech sensors to the same Robot base, they can upgrade the Robot drastically. However, for doing so, further fluid data will be required.

This includes fluid speed, measuring hydrodynamic pressure, and force sensing. Experts are looking to test the undulatory swimming conception with the help of a three-dimensional Robot; they are currently working on the same.

We are looking forward to similar discoveries and developments by expert Roboticists shortly.