About this Research Topic

Background

Legged robots are mainly designed to traverse unstructured environments where wheeled robots have limited mobility. Their applications range from nuclear decommissioning to mining, search and rescue, inspection and surveillance. In addition, they can be applied to flank human workers in order to reduce labor accidents, as well as in elderly care.

The next generation of legged robots are envisioned to operate either autonomously or semi-autonomously (through tele-operation) over uneven terrains. This requires the rejection and compensation of disturbances, the exploitation of visual feedback, and the ability to manipulate both fragile and heavy objects. The main ingredients for legged locomotion are planning, control, perception and state estimation. Thanks to recent advances, robots can acquire online the 3D map of the terrain (exteroceptive sensing), which can be useful both for inspection and to enhance locomotion (e.g. for foothold selection). At a higher level, navigation algorithms can be developed to avoid (fixed or moving) obstacles, control the locomotion speed and attain a specific position (goal).

The substantial gap between simulation and reality is due to a number of different factors that can make the actual robot state diverge from the original plan. The source of errors can be due to: tracking delays in the controller, sensor calibration errors, filtering delays, inaccuracy in the 3D map, unforeseen events (external pushes, slippages), or dynamically changing and deformable terrains (e.g. rolling stones, mud). Indeed, the stones the robot is stepping onto can collapse, move, roll away, resulting in a (possibly catastrophic) loss of balance. Other sources of error include: structural compliance and modeling errors in general. Re-planning is a crucial feature to intrinsically cope with the problem of error accumulation in real scenarios. It is a mechanism to adapt to the terrain, reject disturbances,
while, at the same time, promptly follow desired user commands.

Heuristic strategies have been proven to be useful for decades in locomotion. However, when the complexity of the terrain to be negotiated increases, or when the execution of the requested task involves highly dynamic motions, optimization-based planning strategies are preferable. Indeed, they enable robots to reach performance limits and achieve agile maneuvers. Being able to merge re-planning and optimization during locomotion (i.e. online) is still an open research problem because of the high computational complexity. Many studies focus on developing simplified models to reduce the complexity of the optimization, trading off accuracy with computational efficiency. Moreover, an effective locomotion framework encompasses different levels of autonomy. At the low level, we have locomotion strategies (e.g. different gaits) that aim to balance the robot while dealing with the terrain, but require high-level commands (e.g. desired velocities). At the high level, the focus is more on improving robot autonomy by orchestrating the locomotion strategies in order to fulfill some user requirements (e.g., reaching a desired location, or opening a door). These algorithms choose the most suitable locomotion strategy and adapt the gait parameters (e.g., according to the terrain difficulty) to accomplish the given task (e.g., reaching a goal, picking up an object). This level takes also care of ensuring smooth transitions between different tasks.

Further scenarios, include robotic systems in cluttered environments. This can require specific strategies that involve whole-body loco-manipulation while exploiting multiple contacts and generate collision-free trajectories. Against this background, this Research Topic solicits research articles on recent results in
legged robotics, including, but not limited to:

• Navigation and obstacle avoidance.
• Online optimization-based re-planning (e.g., to compensate for tracking, modeling, estimation errors).
• Planning of agile non periodic maneuvers (e.g., jumps on high obstacles).
• Reactive strategies (e.g., reflexes).
• Robust planning considering model uncertainties.
• Model-based whole-body control with task priorities.
• Detection, estimation, compensation of external disturbances (e.g., opening a self-closing door with a spring-hinge).
• Loco-manipulation: having a mobile platform (e.g. tracked, legged or wheeled) and a manipulator on top of it (centaur) opens the field to study whole-body reachability exploiting the motion of the mobile platform.
• Locomotion on deformable or dynamically changing terrains. Locomotion strategies that can deal with terrain that can change: moderately (e.g., grass, sand, mud, gravel) or abruptly (e.g., rolling stones).
• Patrolling, surveillance, inspection (e.g., acoustics, gas detection, radiation sensors).
• Walking inside cluttered environments and narrow passages. This involve studies on whole body controller and planners that exploit multiple contacts (e.g. in different points of the body than just hand/feet) and avoid collisions with the environment.
• Datasets and template terrain for benchmarking locomotion algorithms.

Keywords: Legged Robots, Whole-Body Optimization, Perception, Model-Based Control, Dynamic Planning

Important note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.

Frequently asked questions

• What is a Research Topic?

  Frontiers' Research Topics are collaborative hubs built around an emerging theme.Defined, managed, and led by renowned researchers, they bring communities together around a shared area of interest to stimulate collaboration and innovation.

  Unlike section journals, which serve established specialty communities, Research Topics are pioneer hubs, responding to the evolving scientific landscape and catering to new communities.

• Why does Frontiers publish Research Topics? 

  The goal of Frontiers' publishing program is to empower research communities to actively steer the course of scientific publishing. Our program was implemented as a three-part unit with fixed field journals, flexible specialty sections, and dynamically emerging Research Topics, connecting communities of different sizes and maturity.

  Research Topics originate from the scientific community. Many of our Research Topics are suggested by existing editorial board members who have identified critical challenges or areas of interest in their field.

• Why are Research Topics important for journals?

  As an editor, Research Topics will help you build your journal, as well as your community, around emerging, cutting-edge research. As research trailblazers, Research Topics attract high-quality submissions from leading experts all over the world.

  A thriving Research Topic can potentially evolve into a new specialty section if there is sustained interest and a growing community around it.

• How do we ensure the quality of articles within Research Topics?

  Each Research Topic must be approved by the specialty chief editor, and it falls under the editorial oversight of our editorial boards, supported by our in-house research integrity team. The same standards and rigorous peer review processes apply to articles published as part of a Research Topic as for any other article we publish.

  In 2023, 80% of the Research Topics we published were edited or co-edited by our editorial board members, who are already familiar with their journal's scope, ethos, and publishing model. All other topics are guest edited by leaders in their field, each vetted and formally approved by the specialty chief editor.

• What are the benefits of publishing my article in a Research Topic?

  Publishing your article within a Research Topic with other related articles increases its discoverability and visibility, which can lead to more views, downloads, and citations. Research Topics grow dynamically as more published articles are added, causing frequent revisiting, and further visibility.

  As Research Topics are multidisciplinary, they are cross-listed in several fields and section journals – increasing your reach even more and giving you the chance to expand your network and collaborate with researchers in different fields, all focusing on expanding knowledge around the same important topic.

  Our larger Research Topics are also converted into ebooks and receive social media promotion from our digital marketing team.

   
• What types of articles can be published in a Research Topic?

  Frontiers offers multiple article types, but it will depend on the field and section journals in which the Research Topic will be featured. The available article types for a Research Topic will appear in the drop-down menu during the submission process.

  Check available article types here 

• Can I suggest a new Research Topic? 

  Yes, we would love to hear your ideas for a topic. Most of our Research Topics are community-led and suggested by researchers in the field. Our in-house editorial team will contact you to talk about your idea and whether you’d like to edit the topic. If you’re an early-stage researcher, we will offer you the opportunity to coordinate your topic, with the support of a senior researcher as the topic editor. 

  Suggest your topic here 

• Who leads a Research Topic? 

  A team of guest editors (called topic editors) lead their Research Topic. This editorial team oversees the entire process, from the initial topic proposal to calls for participation, the peer review, and final publications.

  The team may also include topic coordinators, who help the topic editors send calls for participation, liaise with topic editors on abstracts, and support contributing authors. In some cases, they can also be assigned as reviewers.

• What is the role of a topic editor?

  As a topic editor (TE), you will take the lead on all editorial decisions for the Research Topic, starting with defining its scope. This allows you to curate research around a topic that interests you, bring together different perspectives from leading researchers across different fields and shape the future of your field. 

   

  You will choose your team of co-editors, curate a list of potential authors, send calls for participation and oversee the peer review process, accepting or recommending rejection for each manuscript submitted.

• What support will I receive when editing a new Research Topic? 

  As a topic editor, you're supported at every stage by our in-house team. You will be assigned a single point of contact to help you on both editorial and technical matters. Your topic is managed through our user-friendly online platform, and the peer review process is supported by our industry-first AI review assistant (AIRA).

• As a junior researcher, can I be involved in editing a Research Topic? 

  If you’re an early-stage researcher, we will offer you the opportunity to coordinate your topic, with the support of a senior researcher as the topic editor. This provides you with valuable editorial experience, improving your ability to critically evaluate research articles and enhancing your understanding of the quality standards and requirements for scientific publishing, as well as the opportunity to discover new research in your field, and expand your professional network.

• Can I get a certificate for editing a Research Topic?

  Yes, certificates can be issued on request. We are happy to provide a certificate for your contribution to editing a successful Research Topic.

• Who will I collaborate with?

  Research Topics thrive on collaboration and their multi-disciplinary approach around emerging, cutting-edge themes, attract leading researchers from all over the world.

• How long does it take to publish a Research Topic?

  As a topic editor, you can set the timeline for your Research Topic, and we will work with you at your pace. Typically, Research Topics are online and open for submissions within a few weeks and remain open for participation for 6 – 12 months. Individual articles within a Research Topic are published as soon as they are ready.

  Find out more about our Research Topics

• What fee support is available to authors publishing in a Research Topic?

  Our fee support program ensures that all articles that pass peer review, including those published in Research Topics, can benefit from open access – regardless of the author's field or funding situation.

  Authors and institutions with insufficient funding can apply for a discount on their publishing fees. A fee support application form is available on our website.

• Will there be a printed version of my Research Topic?

  In line with our mission to promote healthy lives on a healthy planet, we do not provide printed materials. All our articles and ebooks are available under a CC-BY license, so you can share and print copies.