Wheels and legs - why and how

How come you never saw a cheetah speeding through the savanna on wheels?

Why have only recently legged robots started to walk in a way which is not so pathetic?

And how is all this connected to a ball robot concept developed by NASA?

There are some seriously fast animals out there. Swimmers, runners, and flyers. But none utilize propellers or wheels. All animals use fins, legs, and wings.

Animals use reciprocating motion and not circular for a very good reason. Unlike machines, animal bodies are relatively sealed objects. They interact with the environment through designated organs and are generally covered in a flexible or hard shell, protecting it from the environment.

Eyeballs are unique in that sense. They can move in two directions simultaneously while keeping a relatively good level of impenetrability to foreign objects. Yet, eyeballs are relatively small organs, making it relatively easy to keep them sealed.

With wide angle movement, most body organs can move in only one direction. This allows a continuous protective layer like the skin to cover the entire organ through the whole range of motion.

Protection is important. But there is another significant advantage of legs over wheels. Just try claiming a steep surface, an uneven one, or a slippery one. It could be challenging, but not impossible. Think of a climbing wall. While your legs push you, your hands grab the surface and pull you. This is a level of traction unachievable by wheels. Even tracked vehicles cannot do that.

A goat can climb almost vertical cliffs, while an off-roAD or tracked vehicle can hardly climb 45 degrees elevation. Using legs requires intelligence while spinning a wheel does not. Even small animals with tiny brains can do things with their legs, fins, and wings that the most advanced computer can't. This is because they have dedicated brains that have evolved to perform those tasks perfectly.

Another aspect is the skeleton itself. In the case of mammals, reptiles, fish, and birds, its construction and behavior are entirely different from how mechanical robots are. The term that defines animal skeletons is Tensegrity - meaning that bones relate to each other by tension rather than by pressure. Muscles and tendons connect the bones, so the resulted stiffness of the bones combined with the tension between them, allow skeletons to behave the way they are

Based on this concept, At NASA's Innovative Advanced Concepts Program, they developed the Super Ball Bot. This experimental robot can move similarly to the way animals use their skeletons. It requires no wheels to move and can be wrapped in a flexible material - making it 100% sealed to the environment.

image by nasa

Only in recent years can we see robots that can walk, swim and fly in a way that reminds us of biological creatures' natural movements. This is only because of advancements in artificial intelligence.

This robot by Hyundai combines wheels, legs, and AI. im many ways, it shows the potential for creating a robot that will have the advantages of the speed of wheels and the multi capabilities of legs.