Wheeled robots are typically quite energy efficient and simple to control. However, other forms of locomotion may be more appropriate for a number of reasons, for example traversing rough terrain, as well as moving and interacting in human environments. Furthermore, studying bipedal and insect-like robots may beneficially impact on biomechanics.
A major goal in this field is in developing capabilities for robots to autonomously decide how, when, and where to move. However, coordinating a large number of robot joints for even simple matters, like negotiating stairs, is difficult. Autonomous robot locomotion is a major technological obstacle for many areas of robotics, such as humanoids (like Honda's Asimo).
Types of locomotion
Walking robots simulate human or animal motion, as a replacement for wheeled motion. Legged motion makes it possible to negotiate uneven surfaces, steps, and other areas that would be difficult for a wheeled robot to reach, as well as causes less damage to environmental terrain as wheeled robots, which would erode it.
Hexapod robots are based on insect locomotion, most popularly the cockroach and stick insect, whose neurological and sensory output is less complex than other animals. Multiple legs allow several different gaits, even if a leg is damaged, making their movements more useful in robots transporting objects.
In terms of energy efficiency on flat surfaces, wheeled robots are the most efficient. This is because an ideal rolling (but not slipping) wheel loses no energy. A wheel rolling at a given velocity needs no input to maintain its motion. This is in contrast to legged robots which suffer an impact with the ground at heelstrike and lose energy as a result.
For simplicity most mobile robots have four wheels or a number of continuous tracks. Some researchers have tried to create more complex wheeled robots with only one or two wheels. These can have certain advantages such as greater efficiency and reduced parts, as well as allowing a robot to navigate in confined places that a four-wheeled robot would not be able to.
Examples: Boe-Bot, Cosmobot, Elmer, Elsie, Enon, HERO, IRobot Create, iRobot's Roomba, Johns Hopkins Beast, Land Walker, Modulus robot, Musa, Omnibot, PaPeRo, Phobot, Pocketdelta robot, Push the Talking Trash Can, RB5X, Rovio, Seropi, Shakey the robot, Sony Rolly, Spykee, TiLR, Topo, TR Araña, and Wakamaru.
Several robots, built in the 1980s by Marc Raibert at the MIT Leg Laboratory, successfully demonstrated very dynamic walking. Initially, a robot with only one leg, and a very small foot, could stay upright simply by hopping. The movement is the same as that of a person on a pogo stick. As the robot falls to one side, it would jump slightly in that direction, in order to catch itself. Soon, the algorithm was generalised to two and four legs. A bipedal robot was demonstrated running and even performing somersaults. A quadruped was also demonstrated which could trot, run, pace, and bound.
- The MIT cheetah cub is an electrically powered quadruped robot with passive compliant legs capable of self-stabilizing in large range of speeds.
- The Tekken II is a small quadruped designed to walk on irregular terrains adaptively.
Coordinated, sequential mechanical action having the appearance of a traveling wave is called a metachronal rhythm or wave, and is employed in nature by ciliates for transport, and by worms and arthropods for locomotion.
Several snake robots have been successfully developed. Mimicking the way real snakes move, these robots can navigate very confined spaces, meaning they may one day be used to search for people trapped in collapsed buildings. The Japanese ACM-R5 snake robot can even navigate both on land and in water.
Brachiation allows robots to travel by swinging, using energy only to grab and release surfaces. This motion is similar to an ape swinging from tree to tree. The two types of brachiation can be compared to bipedal walking motions (continuous contact) or running (richochetal). Continuous contact is when a hand/grasping mechanism is always attached to the surface being crossed; richochetal employs a phase of aerial "flight" from one surface/limb to the next.
Robots can also be designed to perform locomotion in multiple modes. For example, the Bipedal Snake Robo  can both slither like a snake and walk like a biped robot.
- Gait engineering
- Product optimization
- Motion planning
- Motion capture may be performed on humans, insects and other organisms.
- Machine learning, typically with reinforcement learning.
Notable researchers in the field
- Ghassaei, Amanda (20 April 2011). The Design and Optimization of a Crank-Based Leg Mechanism (PDF) (Thesis). Pomona College. Archived (PDF) from the original on 29 October 2013. Retrieved 18 October 2018.
- Sneiderman, Phil (13 February 2018). "By studying cockroach locomotion, scientists learn how to build better, more mobile robots". Hub. Johns Hopkins University. Retrieved 18 October 2018.
- "3D One-Leg Hopper (1983–1984)". MIT Leg Laboratory. Retrieved 2007-10-22.
- "3D Biped (1989–1995)". MIT Leg Laboratory.
- "Quadruped (1984–1987)". MIT Leg Laboratory.
- A. Spröwitz, A. Tuleu, M. Vespignani, M. Ajallooeian, E. Badri, A. J. Ijspeert (2013). "Towards dynamic trot gait locomotion: Design control and experiments with cheetah-cub a compliant quadruped robot". The International Journal of Robotics Research. 32: 932–950.CS1 maint: Multiple names: authors list (link)
- H. Kimura, Y. Fukuoka, A. H. Cohen (2004). "Biologically inspired adaptive dynamic walking of a quadruped robot". Proceedings of the International Conference on the Simulation of Adaptive Behavior: 201–210.CS1 maint: Multiple names: authors list (link)
- Miller, Gavin. "Introduction". snakerobots.com. Retrieved 2007-10-22.
- ACM-R5 Archived 2011-10-11 at the Wayback Machine
- Swimming snake robot (commentary in Japanese)
- "Video: Brachiating 'Bot Swings Its Arm Like An Ape"
- Rohan Thakker, Ajinkya Kamat, Sachin Bharambe, Shital Chiddarwar and K. M. Bhurchandi. “ReBiS- Reconfigurable Bipedal Snake Robot.” In Proceedings of the 2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2014.
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