Notes on three legged robots


Legged robots represent an important aspect in robotics for their adaptability and ability to traverse diverse and complex terrain environments, which can be an alternative for wheeled machines that usually need specific environments to build. Legged robots can share different solutions in spaces with obstacles or uneven terrain. Three-legged robots can introduce unique aspects on stability and mobility:

01. Stability

A tripod configuration naturally provides a stable base, enabling the robot to maintain balance on uneven surfaces or when handling tasks that require precision.

02. Simplicity and efficiency

Three-legged robots can have simpler, lighter mechanisms with fewer legs than quadrupeds or hexapods.

03. Maneuverability

Three-legged designs allow for innovative locomotion strategies, enabling these robots to navigate spaces in every (x,y) direction and adjust their orientation.


STriDER (Self-Excited Tripedal Dynamic Experimental Robot) is a novel three-legged walking machine that exploits the concept of actuated passive dynamic locomotion to dynamically walk with high energy efficiency and minimal control. Unlike other passive dynamic walking machines, this unique tripedal locomotion robot is inherently stable with its tripod stance, can change directions, and is relatively easy to implement, making it practical to use for real-life applications. STriDER begins its step with a stable stance like a camera tripod. As the centre of gravity of the robot shifts forward past the “pivot line” defined by the two feet of the stance legs, the robot begins to fall in the direction perpendicular to the pivot line. The middle leg naturally swings between the two stance legs using the concept of actuated passive dynamic locomotion. The swing leg then catches the fall and the robot resets to its original tripod posture in preparation for its next step. STriDER can easily change its direction of walking, simply by changing the sequence of choice of the swing leg and the stance legs. In this video, we present the concept of this novel walking machine and the mechanical design of the prototype. The results from the dynamic simulation and a simple experiment for a single step are presented for comparison.


Researchers at Istituto Italiano di Tecnologia have recently realized a new prototype robotic platform for space applications. The new robot, called MARM, has three limbs that can be used to walk, move, grasp and transport payload modules while self-relocating itself on the space infrastructure under a microgravity environment. The robot is meant to assist astronauts in assembling and maintaining infrastructures while they are in space or, in the future, on other planets. The MARM prototype will be tested in a physical simulator arrangement before the development of the space-qualified version. The robot was designed and manufactured by IIT’s Human and Humanoid Centered Mechatronics Lab, coordinated by Nikolaos Tsagarakis, in collaboration with Leonardo S.p.A and GMV. It was born in the framework of MIRROR (Multi-arm Installation Robot for Readying ORUs and Reflectors) project, funded by the European Space Agency (ESA).

In this article, the mechanical design and analysis of a novel three-legged, agile robot with passively compliant 4-degrees-of-freedom legs, comprising a hybrid topology of serial, planar and spherical parallel structures, is presented. The design aims to combine the established principle of the Spring Loaded Inverted Pendulum model for energy-efficient locomotion with the accuracy and strength of parallel mechanisms for manipulation tasks. The study involves several kinematics and Jacobian-based analyses that specifically evaluate the application of a non-overconstrained spherical parallel manipulator as a robot hip joint, decoupling impact forces and actuation torques, suitable for the requirements of legged locomotion. The dexterity is investigated concerning joint limits and workspace boundary contours, showing that the mechanism stays well-conditioned and allows for a sufficient range of motion. Based on the functional redundancy of the constrained serial-parallel architecture it is furthermore revealed that the robot allows for the exploitation of optimal leg postures, resulting in the possible optimization of actuator load distribution and accuracy improvements. Consequently, the workspace of the robot torso as an additional end-effector is investigated for the possible application of object manipulation tasks. Results reveal the existence of a sufficient volume applicable for the spatial motion of the torso in the statically stable tripodal posture. In addition, a critical load estimation is derived, which yields a posture-dependent performance index that evaluates the risks of overload situations for the individual actuators.

James Bruton is a prominent figure in the maker and DIY robotics community, widely recognized for his innovative and educational content on engineering, robotics, and technology. He runs a successful YouTube channel where he shares his projects ranging from 3D printed robots to experimental gadgets, engaging a wide audience of enthusiasts, students, and professionals alike. With a background in product design and a passion for sharing knowledge, Bruton’s work spans the development of sophisticated robotic systems to accessible DIY projects, aiming to inspire and empower individuals to explore the fields of robotics and engineering. His projects often feature open-source designs, making cutting-edge technology more accessible and understandable to the public. Bruton’s contribution to STEM education and the maker movement has established him as a key influencer and educator in the tech community.

link – personal site
link – github

Sunbin Kim is an artist, programmer and robotics engineer known for his work on tripedal robot movement. Note that the body of Sunbin Kim’s robot is a platform

link youtubevideo

The control scheme . . . consists of a phase oscillator and sensory feedback of reaction force from the ground, where the control law for each leg is decoupled from the others (i.e., it has no explicit feedback of the other legs’ information). We show that rotary and forwarding locomotion successfully emerge using the control method, depending on the choice of frequency ratio of the oscillators.

When vertebrates run, their legs exhibit minimal contact with the ground. But insects are different. These six-legged creatures run fastest using a three-legged, or “tripod” gait where they have three legs on the ground at all times – two on one side of their body and one on the other. The tripod gait has long inspired engineers who design six-legged robots, but is it necessarily the fastest and most efficient way for bio-inspired robots to move on the ground?

Also interesting: gait of disabled locomotion

Researchers at EPFL and UNIL revealed that there is a faster way for robots to locomote on flat ground, provided they don’t have the adhesive pads used by insects to climb walls and ceilings. This suggests designers of insect-inspired robots should make a break with the tripod-gait paradigm and instead consider other possibilities including a new locomotor strategy denoted as the “bipod” gait. The researchers’ findings are published in Nature Communications.

The scientists carried out a host of computer simulations, tests on robots and experiments on Drosophila melanogaster – the most commonly studied insect in biology. “We wanted to determine why insects use a tripod gait and identify whether it is, indeed, the fastest way for six-legged animals and robots to walk,” said Pavan Ramdya, co-lead and corresponding author of the study. To test the various combinations, the researchers used an evolutionary-like algorithm to optimize the walking speed of a simulated insect model based on Drosophila. Step-by-step, this algorithm sifted through many different possible gaits, eliminating the slowest and shortlisting the fastest.

Common solving of third-leg robot movement

Also an upside-down design with a lowering body help movement

One of the systems for walking three-legged robot – actually it is an arm movement

Also an upside-down design with a lowering body help movement

Short notes on three-legged robotics

If we summarize some thoughts on three-legged robots, we can see that they can be roughly divided into two groups, where the basic premise lies in how they use their body. Three-legged robots could fall into the category of non-mimetic robots that use an odd number of limbs, asymmetrically distributed across the robot’s body. The division into non-mimetic robots and the emphasis on an odd number of limbs highlight key differences in approaches to design and functionality. Especially important is the emphasis on the fact that an odd number of limbs certainly gives rise to reflection on the mode of movement that does not use the pattern or way of walking.

So how should three-legged robots move? Perhaps from a technical point of view, we should first consider three-legged or four-legged chairs, where a good characteristic of three-legged chairs is that they can more easily adapt to uneven surfaces. The adaptability of three-legged robots to uneven surfaces is indeed an important characteristic that can be highlighted as an advantage. Essentially, it could be derived from this premise that the basic characteristic of three-legged robots is precisely adaptability, that they stand on any surface. On the other hand, it could also be said that another characteristic is that they are not necessarily directed and are almost omnidirectional, that is if the torso does not direct the direction of movement.

Omnidirectional mobility, which is enabled by the non-directionality of the torso, also represents a characteristic that can bring advantages in dynamic environments, where quick adjustments in the direction of movement are needed without the need to turn the entire body of the robot. And precisely, the question of the torso is the question of the concept of three-legged robots.


This article presents the development and evaluation of Ringbot, a novel leg-wheel transformer robot incorporating a monocycle mechanism with legs. Ringbot aims to provide versatile mobility by replacing the driver and driving components of a conventional monocycle vehicle with legs mounted on compact driving modules inside the wheel. The article covers the hardware and software implementation of a prototype robot. The Ringbot prototype features a wheel and two driving modules located inside, each equipped with a 3-DoF leg for balancing, steering, and legged motions to assist monocycle driving. The driving control is achieved through a decoupled speed controller and steering controller. In addition, active-legged motions are implemented and managed through a finite-state machine. The controllers for wheeled driving and legged motions were tested in a simulation environment, as well as on the hardware prototype, to verify the concept of a monocycle with legs and evaluate the prototype’s capabilities.

In principle, we can talk about the torso when we define, for example, the head and parts of the torso, which can of course be further segmented, where the head always determines the direction of the robot’s movement forward. Alternatively, it could of course move backwards, that is, depending on the position of the head. If we didn’t have a head, we could talk about movement forward in both cases, whether it goes forward or in reverse.

The question of the concept of the torso in three-legged robots opens up reflection on how best to utilize structural and functional capabilities to enable as efficient and adaptable movement as possible. The latter examples are underscored merely in the sense that efficiency and adaptability are related to the fact that we are not only talking about movement but already talking about moving or walking.

Continuing our reflection on three-legged robots, we come to an interesting shift in understanding their movement. Instead of focusing solely on efficiency and the fluid nature of movement, it seems crucial to consider autonomous, individualized movement. Imagine three-legged robots that don’t constantly seek new paths but find a place where they stand and move only when it is necessary for the transition to a new location.

This approach emphasizes the importance of independent thinking and decision-making in three-legged robots. It is no longer important how fast or fluidly a robot moves, but how well it can assess its environment and choose the best place for its placement. Walking becomes a method to achieve a goal, not a constant necessity.

This represents a new way of thinking about robot mobility. Robots would be equipped with the ability to analyze their environment and make decisions based on this, about when and where to move. The movement would thus become a strategic decision that the robot takes when it assesses that this is most sensible for its current task. Essentially, this would best approximate, for example, moving plants.

konSekvence exhibition at the Cukrarna - television RTV Slovenija

Video about konSekvence exhibition

Video made for information program of RTV Slovenija television about konSekvence exhibition at the Cukrarna.


Video is on the link

Presentation of artist

Presentation of the artist by KonS - Platforma za sodobno raziskovalno umetnost // Platform was selected in a call for tender for the selection of operations “Mreža cent.

Post is on the link

Zoran Srdić Janežič is a sculptor, intermedia artist and designer of puppets at the Ljubljana Puppet Theatre. In his art, he works with new materials and technologies: animatronics, a greater connection between the movement mechanisms and the biological material, 3D virtual design, virtual reality installations with AR codes, sculpture, combining different materials and technologies, etc. He develops art projects in collaboration with experts in programming, artificial intelligence, biotechnology, nanotechnology, etc. He held over 20 solo exhibitions and participated in numerous group exhibitions locally and internationally Ars Electronica Festival, Bozar, etc.). His artworks have found their place in the permanent collections of notable galleries. He won the City of Ljubljana tender for a public memorial and was selected for the S+T+ARTS residence in 2019.

Konsekvence: Petnajst del, ki kažejo obrise mogočih ekosistemov

Konsekvence: Petnajst del, ki kažejo obrise mogočih ekosistemov

The announcement of the exhibition Consequences at the Sugar Factory begins by asking How does technology, which has been shaping virtually all aspects of contemporary life at an unstoppable pace for some time now, affect the transformation of traditional values?



Social intervention performance is in Tomaž Brejc's book about Slovene art

Pages from Tomaž Brejc's book: Slovenska umetnost 1880-1918: Čas prebujenja (Slovenian Art 1880-1918: The Era of Awakening.)

Part of the performance that is referencing Berneker’s John Nepomuk’s monument from the book: But Zoran Srdić Janežič utilized the multifaceted substance of this monument and staged a postmodern, associative performance, walking with octopuses from the former, collapsed Berneker’s studio near the Meidling train station to the city center (Ausgestorben – Franc Berneker, Sudbahn-Atelier am Bahnhof Meidling, August 28, 2013, at six o’clock in the afternoon).

an article on the empowerment of scenic elements as equal play vehicles

Technological artifacts as equal game carriers: dynamic management of the gaze

The Contemporary Puppetry website has an article on the empowerment of scenic elements as equal acting for play.

The reflection is based on the link between technology and the performing arts. The use of technology is also based on the empowerment of artifacts as role-players.

In the Slovene language

More at the link.

Ars Electronica Filckr post

Ars Electronica Filckr post

From the link:

The project is focused on tissue engineering and the harvesting of an electric signal from neurons which influences the movement and shape of a biobot. The artistic and expert team grows neurons on an array with electrodes that conduct the electric signal. Through a complex sensing and programming system, the signal is converted from analogue to digital, amplified and used to move the biobot. Artificial intelligence compares the input from neurons with the movements of different arthropods and selects the appropriate number of legs and joints. The result is an unpredictable zoomorphic form. Biobot brings new biotechnological and algorithmic processes to artistic practices. It uses biotech and software developments to create an artistic narrative about the bio-technological body and its representation. The algorithmic search for the shape in relation to biological data becomes an evolutionary process. The biobot aspires to be a living entity with its own intelligence and movement.

Draft as a work of art

Draft as a work of art

From the link:

The exhibition entitled Raz-glednice is on display in the Small Gallery of the Kranj Art Society. In the exhibition, academic sculptor and intermedia artist Zoran Srdić Janežič turns our thoughts to the theme of placing artworks in public spaces.

Kranj – The Society’s gallery is this time presenting a member of the Kranj Fine Arts Society, a native of Kranj, academic sculptor Zoran Srdić Janežič, who, after graduating from the Academy of Fine Arts and Design in Ljubljana, took up a job in the workshop of the Puppet Theatre as a puppet designer – sculptor. In addition to sculpture, he also works in drawing and computer graphics, and in the past, he has also presented several high-profile performances.

The starting point of his current exhibition Raz-glednice is the placement of artworks in public space, which has been one of the central themes of his interest over the last two decades. As Martina Marenčič, the curator of the exhibition, notes, among the sculptor’s developed oeuvres, urban interventions, or – as he calls them – sculptural walks, actual proposals for the erection of monuments, as well as the monitoring of works of art in public space, reflection (essayistic writings) and engagement with public installations, are among the themes he has developed …

Conversation with different participants of a project Biobot

Conversation with different participants of a project Biobot

Zoran Srdić Janežič’s project “Biobot: Laboratory Situation” focuses on tissue engineering and the development of a robot with a working biological muscle that moves the body. At the edges of art, which creates new forms with living materials, new creatures raise ontological and ethical questions about their status and the protocols for dealing with them.
In his previous projects “Biobot 1.1 and 1.2”, the artist designed the mechanical shell of a biobot in different forms and created an information loop from the movement of the bot’s body that can serve as input for neurons to modify and send back to the technological body. The next stage combines the technological and the biological: the ‘artificial’ moving mechanism will no longer be separate from the ‘natural’ tissue.
Biobot brings not only new materials but also new processes into artistic practices and creates a new artistic language. It uses scientific and technological developments in an unscientific way to artistically construct the biological and technological body. A biobot is a living entity with its own intelligence and right to exist as a living being. After the video presentation of the project, Zoran Srdić Janežič with TJasha Lepko and colleagues Erik Krkač, Kristijan Tkalec, Matic Potočnik and moderator Jurij Krpan will talk about the process and answer our questions.

Programming: Matic Potočnik | Biosensor electronics: Erik Krkač | Electronics, PCB: Gregor Krpič | 3D design: Cveto Kuneševič | Neural engineering: BioTehna Lab / Kristijan Tkalec, Tjaša Lepko | Partner: Kambič laboratorijska oprema, d.o.o.

Public monument erected

Public monument erected

At the end of this week, a public monument Ob 100. obletnici priključitve Prekmurja in prekmurskih Slovencev z matičnim narodom was erected on Prekmurski trg in Ljubljana. ZSJ worked on a proposal for this monument with Cveto Kunešević (3DIMENSION) and Tomato Košir. The handling of a stone was by Kamnoseštvo Jerič.

The opening might be in August – planning during corona quarantine at a moment is unpredictable.

Privacy Preference Center