Most snake robots, being biologically inspired, tend to look like real snakes: long, thin, and have a somewhat slithery motion. But a new snake robot design, called the trident snake robot, isn’t biologically inspired. Instead, it has a central “body” with three “branch legs,” each of which has a wheel.
The trident snake robot is an example of a “nonholonomic” mobile robot, designed by Masato Ishikawa, Yuki Minami, and Toshiharu Sugie from Kyoto University. As a nonholonomic system, the trident snake robot has fewer controllable degrees of freedom than total degrees of freedom. In contrast, a holonomic robot has an equal number of controllable and total degrees of freedom. (And a robotic system that has more controllable degrees of freedom than total degrees is called redundant.)
Being nonholonomic, the trident snake robot is difficult to control, since steering it depends on the way it has previously been oriented. A rough analogy is parallel parking a car, which is difficult because when a driver turns the steering wheel, this also affects the car’s orientation (a car is also a nonholonomic system).
In previous studies, the researchers designed the robot, which is about 540 mm (21 inches) in diameter and weights about 1.25 kg (2.75 lbs). In their latest study, which will be published in an upcoming issue of IEEE Transactions on Mechatronics, the researchers have experimented with the robot in an attempt to investigate the best methods for controlling its motion.
“Its control is a challenging problem, not only because it cannot be treated by continuous control law, but because it cannot be converted to any easy class of nonholonomic systems” since it is also a multi-generator system, the researchers wrote in their study. But the group found a method – a periodic control algorithm based on Lie bracket motion – that could be used to control the robot. Part of the solution, they explained, is finding a balance between speed and error.
As a three-legged snake robot, the device represents an entirely new locomotive mechanism, although the researchers note that the invention is motivated purely by mathematical interest in nonholonomic systems with multi-generators.
“Control problem for these systems is relatively a new field and is quite complicated as yet; we believe this robot would cast a fascinating stimulation to this field,” the researchers wrote on their webpage.
In the future, the researchers plan to improve the robot’s dynamic behavior and its ability for intelligent navigation, such as obstacle avoidance.