In the images presented below, you see a flamingo, a zebra, a spider, and a squirrel. These animals are quite different from each other, and their way of staying balanced is no exception to this. All four have a different way of staying balanced: the flamingo can stand on one leg thanks to its large feet; the zebra has four feet to stand on, the spider even has eight legs; and the squirrel utilizes its tail to stay balanced in the trees! Balance is not something that can be achieved in just one way, and nature has therefore evolved to create a wide variety of balancing methods.

 

  

  

Balance is all about preventing something from falling over, independent of whether this is an object, animal, or human. Generally, if your center of mass is outside your area of support, think about your feet, you will generate momentum and fall over. While you will learn more about what this means exactly later this week, we can look at the implications of that statement by looking at the animals. The feet of the flamingo have evolved to be relatively large. If they had the same area as a coin, it would have much more difficulty balancing itself on one foot. For the squirrel, it moves at high speeds which makes balancing difficult. Its tail can help change its center of mass during movement, to keep it above the area of support: its two feet and two arms. The movement of their tails is comparable to humans extending their arms when almost falling over. The zebra’s area of support is large, thanks to its four feet, decreasing the chance that its center of mass falls outside this area. The same is true for the spider, although it has eight legs instead of four. Additionally, the spider’s height is relatively low – which also helps stay balanced.

Humans aren’t that different from animals in this sense. With our two feet, we have a bigger chance of falling over than a zebra and a spider, but the relatively large size of our feet helps us prevent this – like the flamingo. As previously mentioned, we can also extend our arms to change our center of mass, much like the squirrel with its tail can do. Even exoskeletons are comparable to animals and humans: when its center of mass is outside its area of support – it will fall over. Exoskeleton manufacturers, therefore, try to prevent this in many different ways. For example, the relatively large feet that are used in the Wandercraft exoskeleton. At Project MARCH, however, our pilot currently balances using crutches! But, research is being done into methods where these crutches are not necessary anymore. Interesting enough, attaching a robotic tail to the exoskeleton to help with balance was one of the ideas, just like the squirrel! You will learn more about all this later this week. Before that, we have to answer a very important question: “What is the definition of balance?”

 

According to the Merriam-Webster dictionary, the definition is “stability produced by even distribution of weight on each side of the vertical axis”. When placing this in the context of our balancing situation, this makes sense: whenever the weight of something is equal on both sides, like with the flamingo, it won’t fall over. For an exoskeleton, this definition is applicable too. To maintain the balance in an exoskeleton, you can produce stability by making sure that the weight distribution is equal on each side of the vertical axis. This definition is therefore the one we will be using throughout this week of the course.