If a Tyrannosaurus Rex living 66 million years ago featured a similar leg structure as an ostrich running in the savanna today, then we can assume bird legs stood the test of time (Birdbot)– a good example of evolutionary selection.
Points
- A team of scientists has constructed a robot leg that, like its natural model, is very energy efficient. BirdBot benefits from a foot-leg coupling through a network of muscles and tendons that extends across multiple joints. In this way, BirdBot needs fewer motors than previous legged robots and could, theoretically, scale to a large size.
- Physicists have discovered a new way to coat soft robots in materials that allow them to move and function in a more purposeful way. The research, led by the UK’s University of Bath, is described in Science Advances.
- Researchers have developed a mind-reading system for decoding neural signals from the brain during arm movement. The method, described in the journal Applied Soft Computing, can be used by a person to control a robotic arm through a brain-machine interface (BMI).
Reports
Graceful, elegant, powerful — flightless birds like the ostrich are a mechanical wonder. Ostriches, some of which weigh over 100kg, run through the savanna at up to 55km/h. The ostriches’ outstanding locomotor performance is thought to be enabled by the animal’s leg structure. BirdBot Unlike humans, birds fold their feet back when pulling their legs up towards their bodies. Why do the animals do this? Why is this foot movement pattern energy-efficient for walking and running? And can the bird’s leg structure with all its bones, muscles, and tendons be transferred to walking robots?
Exact Facts
“The foot and leg joints don’t need actuation in the stance phase,” says Aghamaleki Sarvestani. “Springs power these joints, and the multi-joint spring-tendon mechanism coordinates joint movements. When the leg is pulled into swing phase, the foot disengages the leg’s spring — or the muscle-tendon spring, as we believe it happens in animals,” Badri-Spröwitz adds.
“Previously, our robots had to work against the spring or with a motor either when standing or when pulling the leg up, to prevent the leg from colliding with the ground during leg swing. This energy input is not necessary in BirdBot’s legs,” says Badri-Spröwitz and Aghamaleki Sarvestani adds: “Overall, the new robot requires a mere quarter of the energy of its predecessor.”
“Previously, motors were switched depending on whether the leg was in the swing or stance phase. Now the foot takes over this function in the walking machine, mechanically switching between stance and swing. We only need one motor at the hip joint and one motor to bend the knee in the swing phase. We leave leg spring engagement and disengagement to the bird-inspired mechanics. This is robust, fast, and energy-efficient,” says Badri-Spröwitz.
A robot walks on a treadmill
To test their hypothesis, the researchers built a robotic leg modelled after the leg of a flightless bird. They constructed their artificial bird leg so that its foot features no motor, but instead a joint equipped with a spring and cable mechanism.BirdBot has each leg containing only two motors — the hip joints motor, which swings the leg back and forth, and a small motor that flexes the knee joint to pull the leg up. After assembly, the researchers walked BirdBot on a treadmill to observe the robot’s foot folding and unfolding. “The foot and leg joints don’t need actuation in the stance phase,” says Aghamaleki Sarvestani. “Springs power these joints, and the multi-joint spring-tendon mechanism coordinates joint movements.
Zero effort when standing, and when flexing the leg and knee
When standing, the leg expends zero energy. “Previously, our robots had to work against the spring or with a motor either when standing or when pulling the leg up, to prevent the leg from colliding with the ground during leg swing. This energy input is not necessary in BirdBot’s legs,” says Badri-Spröwitz and Aghamaleki Sarvestani adds: “Overall, the new robot requires a mere quarter of the energy of its predecessor.”
Conclusion
Using this idea, scientists could design soft machines with arms made of flexible materials powered by robots embedded in their surfaces. They could also tailor the size and shape of drug delivery capsules, by coating the surface of nanoparticles in a responsive, active material. This in turn could have a dramatic effect on how a drug interacts with cells in the body.
Work on active matter challenges the assumption that the energetic cost of the surface of a liquid or soft solid must always be positive because a certain amount of energy is always necessary to create a surface.
In the next phase of this work — which has already begun — the researchers will apply this general principle to design specific robots, such as soft arms or self-swimming materials. They will also look at collective behaviour — for example, what happens when you have many active solids, all packed together.
