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.
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
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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
An arm 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.