30 Years Ago, Robots Learned to Walk Without Falling

When you hear the term humanoid robot, you may think of C-3PO, the human-cyborg-relations android from Star Wars. C-3PO was designed to assist humans in communicating with robots and alien species. The droid, which first appeared on screen in 1977, joined the characters on their adventures, walking, talking, and interacting with the environment like a human. It was ahead of its time.

Before the release of Star Wars, a few androids did exist and could move and interact with their environment, but none could do so without losing its balance. It wasn’t until 1996 that the first autonomous robot capable of walking without falling was developed in Japan. Honda’s Prototype 2 (P2) was nearly 183 centimeters tall and weighed 210 kilograms. It could control its posture to maintain balance, and it could move multiple joints simultaneously.

In recognition of that decades-old feat, P2 has been honored as an IEEE Milestone. The dedication ceremony is scheduled for 28 April at the Honda Collection Hall, located on the grounds of the Mobility Resort Motegi, in Japan. The machine is on display in the hall’s robotics exhibit, which showcases the evolution of Honda’s humanoid technology.

In support of the Milestone nomination, members of the IEEE Nagoya (Japan) Section wrote: “This milestone demonstrated the feasibility of humanlike locomotion in machines, setting a new standard in robotics.”

Developing a domestic android

In 1986 Honda researchers Kazuo Hirai, Masato Hirose, Yuji Haikawa, and Toru Takenaka set out to develop what they called a “domestic robot” to collaborate with humans. It would be able to climb stairs, remove impediments in its path, and tighten a nut with a wrench, according to their research paper on the project.

But to create a machine that would do household chores, it had to be able to move around obstacles such as furniture, stairs, and doorways. It needed to autonomously walk and read its environment like a human. But no robot could do that at the time. The closest technologists got was the WABOT-1. Built in 1973 at Waseda University, in Tokyo, the WABOT had eyes and ears, could speak Japanese, and used tactile sensors embedded on its hands. Although the WABOT could walk, albeit unsteadily, it couldn’t maneuver around obstacles or maintain its balance. It was powered by an external battery and computer.

To build an android, the Honda team began by analyzing how people move, using themselves as models. Once they began building the machine, the engineers found it difficult to satisfy every specification. Adjustments were made to the number of joints. The researchers installed existing Honda motors and hydraulics in the hips, knees, and ankles to enable the robot to walk. Each joint was operated by a DC motor with a harmonic-drive reduction gear system.

To test their ideas, the engineers built E0. The robot, which was just a pair of connected legs, successfully walked. It took about 15 seconds to take each step, however, and it moved using static walking in a straight line. The researchers then created several algorithms to enable the robot to use dynamic walking, whereby the robot stays upright by constantly moving and adjusting its balance, rather than keeping its center of mass over its feet.

The Honda team installed rubber brushes on the bottom of the machine’s feet to reduce vibrations from landing impacts. Between 1987 and 1991, three more prototypes (E1, E2, and E3) were built. With the dynamic walking mechanism complete, the team added 6-axis sensors to detect the force at which the ground pushed back against the robot’s feet, allowing the robot to adjust its gait in real time. They also developed a posture-stabilizing control system.

In 1993 the team was finally ready to build an android with arms and a head, dubbed Prototype 1 (P1). When they finished building P1, it was 191.5 cm tall, weighed 175 kg, and used an external power source. It could turn a switch on and off, grab a doorknob, and carry a 70 kg object.

For P2, four video cameras were installed in its head. A computer with four microSparc II processors running a real-time operating system was added into the robot’s torso. Also within the body were DC servo amplifiers, a 20-kg nickel-zinc battery, and a wireless Ethernet modem. P2, which was launched publicly in 1996, could walk freely, climb up and down stairs, push carts, and perform some actions wirelessly.

The following year, Honda’s engineers released the smaller and lighter P3. In 2000 the popular ASIMO robot was introduced. Although shorter than its predecessors at 130 cm, it could walk, run, climb stairs, and recognize voices and faces. Thanks to P2, today’s androids are not just ideas in a laboratory.