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ROBOTS ALIVE!: Toddler's First Steps

Walking is hard to learn to do, especially when you're a robot. Robotics engineers have been trying to teach robots to walk for several decades. Some of the earliest robots took steps, but every move they made was programmed. And they were likely to fall over. Enter the University of New Hampshire's biped walking robot, "Toddler," which is programmed to learn from its experiences. Before it starts to walk, it will learn how to stay in balance.

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Related Activities
Activity: A Balancing Act






science fiction

biomechanics, center of mass,
dynamic balance

inventions, robotics

flying machines, robotics


21st Century Medicine (Show 605): "Virtual Fear" -- Center of Gravity activity


Engineers who design machines like the biped robot seen on FRONTIERS must address a variety of physical considerations in their design, including moment of force and center of mass. But the key consideration is balance. The robot (with its computer-based "brain") has the difficult task of perceiving itself in space and balancing in Earth's gravitational field.

Earlier walking robots like the six-legged walker seen on FRONTIERS employed static balance; if one of these robots stopped walking and went out of balance, it would fall over. By contrast, the strategy used with the current generation of walking robots, like "Toddler," is that of dynamic balance. Modeled on the human body, Toddler takes advantage of momentum to move forward.


Study the physics involved in balancing.


The center of mass (center of gravity) is the point at which the whole weight of an object balances. The center of mass might be considered the "average" point of all the matter in the object. You're probably not aware of it, but adjustments when you move affect your center of gravity and help you stay in balance. Tightrope walkers, for example, adjust their arms, hips and other body parts in order to move their center of gravity and stay atop the rope.

You can use cardboard cutouts to explore the effects of center of mass, as follows:

  1. Pierce each shape with a hole punch.

  2. Allow the cutout to hang freely on a nail that is mounted on a ring stand.

  3. Hang a plumb line and trace the line along the cutout.

  4. Repeat the procedure with a hole somewhere else on the cutout.
  5. The point where the lines intersect is the center of mass! You can test by piercing at this intersection. The object will spin freely about that point, remaining in balance.

  6. Repeat with other shapes.


  • The center of mass in people varies, depending on height and weight. Because the biped robot has a lot of weight in its legs, its center of mass is lower than it is on a person. Where is your center of mass? How does your center of mass help you stay balanced and not fall over?

  • Explore more about dynamic balance and how we use it when we walk. For example, when you walk and lift one leg off the floor, your body is making adjustments so that you don't fall over. The next time you are walking, think about the work your body must do to stay balanced.

  • How do other animals stay in balance? Cats, for example, can flip themselves over during a fall and land on all four feet -- a neat balancing act.

  • What biological systems help vertebrates stay in equilibrium? Consider the vision system, vestibular system (inner ear) and the brain and muscles (proprioception).


Hold a contest to test your designs. Which designs produce the highest- and longest-flying craft? Draw "blueprints" of the winning aircraft and use these illustrations to discuss effective aviation design.

CREDIT: Science writer and educator Marc Rosner contributed to this activity.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.