{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T10:26:27Z","timestamp":1775039187953,"version":"3.50.1"},"reference-count":37,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T00:00:00Z","timestamp":1775001600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Robot. AI"],"abstract":"\n Actuated universal joints are used in a wide range of robotic applications, including mobile snake robots, snake-arm robots and robotic tails. They are employed in applications such as search and rescue and confined space inspection. These can use remote cables, fluid driven systems, or inline motors. To realise the benefits of inline actuation while keeping the system compact with a high power to weight ratio, an actuated universal joint (AUJ) was developed using an \u2018\u2018antagonistic triad\u2019\u2019 of three twisted string actuators in our previous work. However, the design had numerous drawbacks in its prototype form, namely, a limited angle range, poor accuracy due to the angular feedback sensors used, and issues with string failure due to mechanical design choices. In this publication, we performed a root-cause analysis of these issues, and partially or fully mitigated some of them by reducing the distance between the twisted string actuator (TSA), removing geometry which caused premature string failure, and exchanging the angular feedback sensors for more accurate ones. As a result, angle range was increased from\n \n \n \n \u00b1<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 14.5\u00b0 to\n \n \n \n \u00b1<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 26\u00b0 for a single axis, and\n \n \n \n \u00b1<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 6\u00b0 to\n \n \n \n \u00b1<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 20\u00b0 for a dual axis movement. Angular feedback sensor accuracy increased from\n \n \n \n \u00b1<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 0.21\u00b0 to\n \n \n \n \u00b1<\/mml:mo>\n <\/mml:mrow>\n <\/mml:math>\n <\/jats:inline-formula>\n 0.11\u00b0, and no string failures occurred within load limits. The performance of the mechanism was further characterised with additional experiments for increased follower load and angular velocity. A novel method to adjust the transmission ratio during operation (active transmission adjustment) was proposed and simulated, and its advantages over existing mechanisms for a snake robot in a multi-segment configuration were theoretically evaluated.\n <\/jats:p>","DOI":"10.3389\/frobt.2026.1761507","type":"journal-article","created":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T08:20:04Z","timestamp":1775031604000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Design and evolution of a triad twisted string actuator for controlling a two degrees of freedom joint: improving performance and simulating active transmission adjustment"],"prefix":"10.3389","volume":"13","author":[{"given":"Damian","family":"Crosby","sequence":"first","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, School of Engineering, Faculty of Science and Engineering, The University of Manchester","place":["Manchester, United Kingdom"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Joaquin","family":"Carrasco","sequence":"additional","affiliation":[{"name":"Department of Electrical and Electronic Engineering, Faculty of Science and Engineering, The University of Manchester","place":["Manchester, United Kingdom"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"William","family":"Heath","sequence":"additional","affiliation":[{"name":"School of Computer Science and Engineering, College of Science and Engineering, Bangor University","place":["Bangor, United Kingdom"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lutong","family":"Li","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, School of Engineering, Faculty of Science and Engineering, The University of Manchester","place":["Manchester, United Kingdom"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Andrew","family":"Weightman","sequence":"additional","affiliation":[{"name":"Department of Mechanical and Aerospace Engineering, School of Engineering, Faculty of Science and Engineering, The University of Manchester","place":["Manchester, United Kingdom"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1965","published-online":{"date-parts":[[2026,4,1]]},"reference":[{"key":"B1","first-page":"2319","article-title":"A snake robot propelling inside of a pipe with helical rolling motion","volume-title":"Proceedings of SICE annual conference 2010","author":"Baba","year":"2010"},{"key":"B2","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1109\/ISCON.2009.5156096","article-title":"Angle measurement using a miniature hall effect position sensor","volume-title":"2009 2nd international students conference on electrodynamic and mechatronics","author":"Bienczyk","year":"2009"},{"key":"B3","volume-title":"BNO080 Data Sheet. Hillcrest Laboratories, Inc","year":"2017"},{"key":"B4","doi-asserted-by":"crossref","DOI":"10.1108\/01439911211192448","article-title":"Nuclear snake-arm robots","volume-title":"Ind. Robot","author":"Buckingham","year":"2012"},{"key":"B5","volume-title":"Shigley\u2019s mechanical engineering design","author":"Budynas","year":"2011"},{"key":"B6","doi-asserted-by":"crossref","first-page":"11388","DOI":"10.1109\/ICRA46639.2022.9812124","article-title":"A novel triad twisted string actuator for controlling a two degrees of freedom joint: design and experimental validation","volume-title":"2022 international conference on robotics and automation (ICRA)","author":"Crosby","year":"2022"},{"key":"B7","volume-title":"DC micromotors - precious metal commutation","year":"2020"},{"key":"B8","doi-asserted-by":"publisher","first-page":"817","DOI":"10.1109\/ROBOT.1986.1087559","article-title":"Coordinating control of a two degrees of freedom universal joint structure driven by three servos","volume":"3","author":"Dessen","year":"1986","journal-title":"Proc. 1986 IEEE Int. Conf. Robotics Automation"},{"key":"B9","doi-asserted-by":"publisher","first-page":"55","DOI":"10.1177\/004051757604600109","article-title":"A comparative study of nylon fiber fracture","volume":"46","author":"Goswami","year":"1976","journal-title":"Text. Res. J."},{"key":"B10","volume-title":"JL-12FN20-50-06420","year":"2020"},{"key":"B11","doi-asserted-by":"publisher","first-page":"1","DOI":"10.1115\/1.4062466","article-title":"Kinematic modeling and open-loop control of a twisted string actuator-driven soft robotic manipulator","volume":"16","author":"Konda","year":"2023","journal-title":"J. Mech. Robotics"},{"key":"B12","volume-title":"LCM100 miniature in line load cell","year":"2024"},{"key":"B13","doi-asserted-by":"publisher","first-page":"360","DOI":"10.1109\/tmech.2019.2960825","article-title":"Highly durable bidirectional joint with twisted string actuators and variable radius pulley","volume":"25","author":"Lee","year":"2019","journal-title":"IEEE\/ASME Trans. Mechatronics"},{"key":"B14","doi-asserted-by":"crossref","DOI":"10.1007\/978-1-4471-2996-7","volume-title":"Snake robots: modelling, mechatronics, and control","author":"Liljeb\u00e4ck","year":"2013"},{"key":"B15","first-page":"6","article-title":"Motion controllers - Series MCDC 3002 S. Dr","year":"2018"},{"key":"B16","first-page":"1","article-title":"Twisted string actuation for an active modular hand orthosis","volume-title":"ACTUATOR; international conference and exhibition on new actuator systems and applications 2021","author":"Muehlbauer","year":"2021"},{"key":"B17","doi-asserted-by":"crossref","first-page":"412","DOI":"10.1109\/ICSENS.2014.6985022","article-title":"Magnetostrictive-ring type torque sensor using two hall ICs with differential magnetic field detection","volume-title":"IEEE SENSORS 2014 proceedings","author":"Muro","year":"2014"},{"key":"B18","doi-asserted-by":"publisher","first-page":"3438","DOI":"10.1109\/lra.2020.2970651","article-title":"Accurate dynamic modeling of twisted string actuators accounting for string compliance and friction","volume":"5","author":"Nedelchev","year":"2020","journal-title":"IEEE Robotics Automation Lett."},{"key":"B19","doi-asserted-by":"publisher","first-page":"664","DOI":"10.1109\/tmech.2011.2181855","article-title":"Modeling and control of the twisted string actuation system","volume":"18","author":"Palli","year":"2012","journal-title":"IEEE\/ASME Trans. Mechatronics"},{"key":"B20","doi-asserted-by":"crossref","first-page":"563","DOI":"10.1109\/URAI.2016.7625779","article-title":"Design and control of antagonistic robot joint with twisted string actuators","volume-title":"2016 13th international conference on ubiquitous robots and ambient intelligence (URAI)","author":"Park","year":"2016"},{"key":"B21","doi-asserted-by":"crossref","first-page":"1096","DOI":"10.23919\/ICCAS50221.2020.9268279","article-title":"Control of tendon-driven (twisted-string actuator) robotic joint with adaptive variable-radius pulley","volume-title":"2020 20th international conference on control, automation and systems (ICCAS)","author":"Park","year":"2020"},{"key":"B22","year":"2021","journal-title":"BournsPDB08 - 8 mm micro rotary potentiometer"},{"key":"B23","doi-asserted-by":"crossref","first-page":"5853","DOI":"10.1109\/IROS.2013.6697204","article-title":"Bidirectional elbow exoskeleton based on twisted-string actuators","volume-title":"2013 IEEE\/RSJ international conference on intelligent robots and systems","author":"Popov","year":"2013"},{"key":"B24","doi-asserted-by":"publisher","DOI":"10.1016\/j.net.2023.10.026","article-title":"Research on the cable-driven endoscopic manipulator for fusion reactors","author":"Qin","year":"2023","journal-title":"Nucl. Eng. Technol"},{"key":"B25","doi-asserted-by":"crossref","first-page":"191","DOI":"10.1109\/ICCCE.2008.4580594","article-title":"Design and control of a snake robot according to snake anatomy","volume-title":"2008 international conference on computer and communication engineering","author":"Rezaei","year":"2008"},{"key":"B26","first-page":"4630","volume-title":"Design and architecture of a series elastic snake robot","author":"Rollinson","year":"2014"},{"key":"B27","doi-asserted-by":"publisher","first-page":"041001","DOI":"10.1115\/1.4039500","article-title":"Design, modeling, and integration of a flexible universal spatial robotic tail","volume":"10","author":"Rone","year":"2018","journal-title":"J. Mech. Robotics"},{"key":"B28","doi-asserted-by":"publisher","first-page":"1036","DOI":"10.1109\/tnano.2018.2856265","article-title":"Graphene-based composite protective coating for twisted strings and its experimental evaluation","volume":"17","author":"Sarkar","year":"2018","journal-title":"IEEE Trans. Nanotechnol."},{"key":"B29","volume-title":"Robot modeling and control","author":"Spong","year":"2020"},{"key":"B30","doi-asserted-by":"publisher","first-page":"5769","DOI":"10.1109\/lra.2021.3084890","article-title":"Design and feasibility analysis of a foldable robot arm for drones using a twisted string actuator: frad-Tsa","volume":"6","author":"Suthar","year":"2021","journal-title":"IEEE Robotics Automation Lett."},{"key":"B31","doi-asserted-by":"publisher","first-page":"2023","DOI":"10.1002\/app.1992.070461114","article-title":"Bending and torsional fatigue of nylon 66 monofilaments","volume":"46","author":"Toney","year":"1992","journal-title":"J. Applied Polymer Science"},{"key":"B32","first-page":"4680","volume-title":"A study on life cycle of twisted string actuators: preliminary results","author":"Usman","year":""},{"key":"B33","first-page":"3714","article-title":"Passive returning mechanism for twisted string actuators","volume-title":"2017 IEEE international conference on robotics and automation (ICRA)","author":"Usman","year":""},{"key":"B34","doi-asserted-by":"publisher","first-page":"012037","DOI":"10.1088\/1742-6596\/1326\/1\/012037","article-title":"Comparative analysis of the virtual and physical experiments with a snake robot\u2019s rectilinear movement","volume":"1326","author":"Varlashin","year":"2019","journal-title":"J. Phys, Conf. Ser"},{"key":"B35","doi-asserted-by":"crossref","first-page":"4347","DOI":"10.1109\/ICRA.2012.6225255","article-title":"Design and architecture of the unified modular snake robot","volume-title":"2012 IEEE international conference on robotics and automation","author":"Wright","year":"2012"},{"key":"B36","doi-asserted-by":"crossref","first-page":"1215","DOI":"10.1109\/AIM.2010.5695720","article-title":"The twisted string actuation system: modeling and control","volume-title":"2010 IEEE\/ASME international conference on advanced intelligent mechatronics","author":"W\u00fcrtz","year":"2010"},{"key":"B37","article-title":"S. Development of amphibious snake-like robot acm-r5","volume-title":"The 36th international symposium on robotics (ISR 2005), Tokyo","author":"Yamada","year":"2005"}],"container-title":["Frontiers in Robotics and AI"],"original-title":[],"link":[{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/frobt.2026.1761507\/full","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T08:20:16Z","timestamp":1775031616000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.frontiersin.org\/articles\/10.3389\/frobt.2026.1761507\/full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,1]]},"references-count":37,"alternative-id":["10.3389\/frobt.2026.1761507"],"URL":"https:\/\/doi.org\/10.3389\/frobt.2026.1761507","relation":{},"ISSN":["2296-9144"],"issn-type":[{"value":"2296-9144","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,1]]},"article-number":"1761507"}}