Scientists build an energy-efficient BirdBot – Unite.AI
A team of scientists from the Max Planck Institute for Intelligent Systems (MPI-IS) led by Alexander Badri-Spröwitz have built a robot leg based on the natural model of flightless birds. The new BirdBot was created with fewer motors than other machines, and theoretically it could scale to a large size.
Badri-Spröwitz leads the Dynamic Locomotion Group, which does crossover work in the fields of biology and robotics. The team included Alborz Aghamaleki Sarvestani, PhD student from Badri-Spröwitz; Metin Sitti, roboticist and director at MPI-IS; and Monica A. Daley, professor of biology at the University of California, Irvine.
The research was published in the journal Scientific robotics.
Looking for birds in the wild
The birds rely on a movement of folding their legs backwards when in the swing phase, and the team attributed this movement to mechanical coupling.
“It’s not the nervous system, it’s not electrical impulses, it’s not muscle activity,” says Badri-Spröwitz. “We hypothesized a novel function of the foot-leg coupling through a network of muscles and tendons that spans multiple joints. These multi-joint musculo-tendinous coordinate the bending of the foot in swing phase. In our robot, we have implemented the coupled mechanics in the leg and the foot, which enables energy-saving and robust robot walking. Our results demonstrating this mechanism in a robot lead us to believe that similar efficiency benefits also hold for birds,” he explains.
The team tested their hypothesis by building a robotic leg inspired by the leg of a flightless bird. The artificial bird’s leg was built without a motor. Rather, it relied on a joint equipped with a spring and cable mechanism. The researchers then used cables and pulleys to mechanically couple the foot to the joints of the leg. Each of these legs has a hip joint motor, which is responsible for rocking the leg back and forth, and a small motor which pulls the leg up by bending the knee.
BirdBot was tested on a treadmill while the team observed the folding and unfolding of its food.
“The foot and leg joints do not need actuation in the stance phase,” says Aghamaleki Sarvestani.
“The springs power these joints, and the spring-tendon multi-joint mechanism coordinates the movements of the joints. When the leg is pulled in the swing phase, the foot disengages the leg spring – or the muscle-tendon spring, as we think happens in animals,” Badri-Spröwitz continues.
Zero energy while standing
The robot’s leg uses no energy when standing, which means it only requires a quarter of the energy of its predecessor.
When the robot is running, the foot disengages the leg spring with each leg movement. In order to disengage, the large foot movement releases the cable while the remaining leg joints swing freely. This creates a transition of states between standing and swinging the legs, which is usually provided to robots by a motor at the joint. A sensor also normally sends a signal to a controller that turns the robot’s motors on and off.
“Previously, the motors were switched depending on whether the leg was in swing or stance phase. Now the foot takes over this function in the walking machine, mechanically switching between stance and swing. only need one motor at the hip joint and one motor to bend the knee in the swing phase.We leave the engagement and disengagement of the leg spring to bird-inspired mechanics. is robust, fast and energy efficient,” says Badri-Spröwitz.
BirdBot is a physical model demonstrating many amazing mechanisms of birds in nature, such as those that help them act quickly without having to think. If there is a bump in the ground, BirdBot’s leg swings automatically and without delay. Just like birds in nature, the robot has great locomotion sturdiness.
This new research could lead to legs a meter high that can be implemented to transport robots weighing several tons, all with low power consumption. Building BirdBot could also provide new insights into biology, leading to advances in the field.