Chapter 2

Evolution Before ASIMO

“More than a robot, ASIMO became a symbol of human curiosity, engineering excellence, and the courage to imagine the impossible.”

When the world first saw ASIMO gracefully walking, climbing stairs, waving, and interacting with people in the year 2000, many believed it was an overnight technological breakthrough. In reality, ASIMO was the result of nearly 14 years of continuous research and countless experiments. Before ASIMO took its first public steps, Honda engineers had already built numerous prototype robots, each designed to solve a specific engineering problem.

These early machines did not look like friendly humanoids. Some had only legs. Others lacked arms or heads. Several could barely walk a few steps without losing balance. Yet every prototype contributed valuable knowledge that eventually led to one of the most advanced humanoid robots of its time.

This chapter explores the remarkable journey from Honda’s earliest experimental robots to the birth of ASIMO, highlighting the technological breakthroughs that made human-like movement possible.

The Beginning of Honda’s Robotics Program

Honda officially launched its humanoid robotics research program in 1986. At the time, industrial robots had already transformed manufacturing by performing repetitive tasks such as welding, painting, and assembling automobile parts. These machines were powerful and precise, but they were designed to operate inside factories under carefully controlled conditions.

Honda envisioned something completely different.

The company’s engineers wanted to create a robot that could move safely in environments designed for humans. Such a robot would need to navigate hallways, climb stairs, avoid obstacles, and interact naturally with people. Achieving these goals required solving one of robotics’ greatest challenges: bipedal locomotion, or walking on two legs.

Unlike wheeled robots, a two-legged robot is inherently unstable. Every step involves balancing the robot’s weight while moving one foot forward. If the timing or positioning is even slightly incorrect, the robot falls. Honda engineers understood that mastering this challenge would take years of experimentation.

The E-Series: Learning to Walk

The first generation of Honda’s experimental robots became known as the E-Series, with “E” standing for “Experimental.”

These robots focused almost entirely on walking. They had no arms, no expressive heads, and no ability to communicate. Their purpose was simple: to understand how a machine could maintain balance while taking steps.

E0: The First Step

The earliest prototype, E0, was introduced in 1986. It represented Honda’s first attempt to create a robot capable of walking on two legs.

Walking speed was extremely slow—taking several seconds for a single step. Each movement was carefully programmed, and the robot paused before shifting its weight to the next foot. Although its performance appeared primitive, E0 proved that stable bipedal walking was possible.

The engineers learned valuable lessons about:

• Weight distribution
• Foot placement
• Joint coordination
• Motor synchronization
• Stability during movement

These lessons became the foundation for future improvements.

Improving with E1, E2, and E3

After the success of E0, Honda developed E1, E2, and E3.

Each new robot introduced refinements in mechanical design and control software.

The improvements included:

• Faster walking speeds
• Better balance control
• Smoother leg movements
• More efficient electric motors
• Improved joint flexibility

Despite these advances, the robots still moved cautiously. Their walking resembled a slow-motion sequence rather than natural human movement.

Nevertheless, each prototype brought Honda closer to its ultimate goal.

The Challenge of Dynamic Walking

One of the biggest breakthroughs came when Honda engineers shifted their focus from static walking to dynamic walking.

Static Walking

In static walking, the robot keeps its center of gravity directly above the supporting foot before moving the other leg. This method is very stable but extremely slow.

Imagine carefully transferring your entire weight onto one leg, pausing, and then slowly moving the other leg. That is essentially how early robots walked.

Dynamic Walking

Humans walk differently.

We lean forward continuously, allowing momentum to carry us from one step to the next. Our brains constantly adjust balance without conscious effort. Honda engineers wanted their robot to imitate this natural movement.

Dynamic walking required:

• Predicting body motion
• Continuous balance correction
• Real-time sensor feedback
• Fast computer calculations

Mastering dynamic walking became one of Honda’s greatest achievements.

E4, E5, and E6: Faster and Smarter

The later E-Series robots introduced significant improvements.

The robots could:

• Walk faster
• Turn while walking
• Recover from small disturbances
• Maintain smoother balance
• Move with greater confidence

These prototypes demonstrated that robots no longer needed to stop after every step.

Instead, they could walk continuously, making movement appear much more natural.

Engineers also began improving the robot’s mechanical joints, allowing greater flexibility and smoother transitions between steps.

The P-Series: Building a Complete Humanoid

After successfully developing reliable walking technology, Honda began designing robots with complete bodies.

This marked the beginning of the P-Series, where “P” stood for “Prototype.”

Unlike the E-Series, these robots had:

• Arms
• Upper body
• Head
• Torso
• Larger computing systems

The challenge had expanded from walking to full-body coordination.

P1: The First Full-Scale Humanoid

Introduced in 1993, P1 became Honda’s first full-size humanoid robot.

Standing nearly 1.9 meters (6 feet 2 inches) tall and weighing approximately 175 kilograms, P1 was much larger than an average person.

Although impressive, the robot had several limitations:

• Very heavy
• Slow movement
• High energy consumption
• Limited agility

However, P1 demonstrated that a full humanoid robot could maintain balance while walking.

This achievement encouraged Honda engineers to continue refining the design. P2: Greater Independence

By 1996, Honda introduced P2, a significant improvement over P1. The robot was:

• Smaller
• Lighter
• More autonomous

Unlike previous prototypes, P2 carried its own batteries and onboard computers. This meant it no longer needed to remain connected to external power supplies during demonstrations. P2 could:

• Walk independently
• Turn corners
• Climb gentle slopes
• Maintain balance more effectively

For the first time, the public saw a humanoid robot capable of moving freely without external support.

P3: Preparing for ASIMO

Honda’s next prototype, P3, represented the final major step before ASIMO. Compared with P2, P3 featured:

• Reduced height
• Lower weight
• Better battery technology
• More powerful computers
• Improved walking algorithms
• Enhanced stability

P3 stood approximately 160 centimeters tall, making it much closer to average human height. Its smaller size made it safer and more practical for indoor environments. Engineers also redesigned many mechanical components to improve reliability while reducing overall weight.

Advances in Actuators

One of the most important technologies developed during the E-Series and P-Series was the actuator system. An actuator functions like a muscle in a human body. Each joint required carefully designed electric motors capable of:

• Precise positioning
• Smooth acceleration
• Rapid response
• Controlled force generation

Honda engineers developed lightweight, high-performance servo motors that allowed the robot to move naturally without jerky motions. The combination of advanced actuators and sophisticated software became a hallmark of ASIMO’s movement.

The Importance of Sensors

Walking safely requires continuous awareness of the environment.

Throughout the E-Series and P-Series development, Honda gradually introduced numerous sensors.

These included:

• Gyroscopes for balance
• Accelerometers for motion detection
• Foot pressure sensors
• Joint angle sensors
• Vision systems
• Force sensors

The robot constantly analyzed information from these sensors, allowing it to adjust posture hundreds of times each second.

This real-time feedback dramatically improved walking stability.

Computer Control Systems

The complexity of bipedal walking required increasingly powerful onboard computers.

Early prototypes relied on relatively simple control programs.

Later robots used sophisticated algorithms capable of:

• Predicting movement
• Calculating joint trajectories
• Monitoring balance
• Coordinating multiple motors simultaneously
• Responding instantly to unexpected disturbances

These control systems eventually evolved into one of ASIMO’s greatest strengths.

Learning Through Failure

Every successful engineering project involves failure.

Honda’s robotics program was no exception.

During testing, robots frequently:

• Lost balance
• Fell forward
• Fell backward
• Missed steps
• Overheated motors
• Experienced software errors

Rather than discouraging the engineers, these failures provided essential information.

Each fall revealed weaknesses in mechanical design or control algorithms.

By studying these problems carefully, engineers continuously improved the robots.

This philosophy of learning through experimentation became central to Honda’s robotics success.

Reducing Size and Weight

As the prototypes evolved, Honda realized that a practical household robot needed to be compact and lightweight. A smaller robot offered several advantages:

• Greater safety around people
• Lower energy consumption
• Easier movement indoors
• Faster reactions
• Improved stability

These considerations heavily influenced ASIMO’s final design.

The robot eventually stood approximately 130 centimeters (4 feet 3 inches) tall and weighed about 54 kilograms, making it well suited for human environments.

Preparing for the Next Generation

By the late 1990s, Honda had solved many of the most difficult problems in humanoid locomotion.

The company had developed:

• Reliable bipedal walking
• Dynamic balance control
• Lightweight actuators
• Advanced sensors
• Compact onboard computers
• Improved battery systems
• Safe mechanical structures

The foundation was complete. What remained was to combine all these technologies into a single robot capable not only of walking but also of interacting naturally with people. That robot would become ASIMO.

Chapter Summary

The journey from the first E-Series robots to the sophisticated P-Series prototypes demonstrates that revolutionary innovations rarely happen overnight. Honda engineers spent years refining every aspect of humanoid robotics, from walking algorithms and mechanical joints to sensors and computer control systems. Each prototype represented another step toward creating a robot capable of sharing the human world. Without the lessons learned from the E-Series and P-Series, ASIMO would never have achieved its extraordinary abilities. These early machines laid the scientific and engineering foundation for one of the most celebrated humanoid robots in history. In the next chapter, we will examine ASIMO itself in detail, exploring its anatomy, body structure, joints, sensors, batteries, and the remarkable engineering that enabled it to move with such agility and precision.