Perfecting Humanoids is an Endurance Challenge, Not a Test of Speed

The world’s first humanoid half-marathon in Beijing this past April was decidedly a test of Murphy’s Law: a spectacle riddled with countless ways that hardware can break down.

To participate in the showdown, humanoids had to run on two legs and participating companies and universities were permitted to pull their robots in for battery swaps at pitstops, reported Smithsonian magazine. Additionally, a dedicated 13.1-mile racetrack was allotted to 21 humanoid runners that were pitted against thousands of humans.

In the end, the terrain proved to be too much. Gauging by media footage, there just wasn’t enough latitude to withstand multi-factorial issues such as mechanical tolerance, fatigue or other unexpected effects.

Braun vs. Brain, Form vs. Function

Humanoids are advancing steadily with great potential. The field of humanoid robotics is interdisciplinary, straddling mechanics, electronics, computer science, artificial intelligence, sensing and actuation. Specifications such as degrees of freedom, overall weight, physical size, type of power supply and sensor configuration provide insights into the capabilities and constraints.

Still, there are an infinite number of ways in which hardware can break down. The mechanical design of humanoid robots—typically modeled after the complex human anatomy—is especially fundamental to the overall functionality. But as the Beijing race demonstrated, emulating the human’s detailed, graceful mobility is no easy feat.

To understand how humanoids emulate human muscles and joints, for example, look to the actuators. By replicating their mechanical functions, control dynamics and emulating patterns of movement, actuators can mimic control dynamics ranging from walking and grasping to fine motor skills. Various categories of actuators (including electric, pneumatic, hydraulic, cable-driven or compliant) are designed with distinct properties, each with its pros and cons that influence the performance, efficiency and design intricacies.

Electric actuators, for example, can be comprised of both brushed and brushless DC motors. A reasonably compact form factor can offer precise control, strong torque output and efficient energy utilization. The tradeoff between compact dimensions and weight is the ability to recapture energy, which in turn means engineers need to specify and refine control strategies to ensure smooth and adaptable movement.

For their effort, the humanoids in the experimental Beijing race were awarded prizes for endurance, best gait design and the most innovative form. And the half-marathon relayed a message that rings loud and clear: While humanoids are nowhere close to perfection, their makers are going head-to-head to surpass the competition.

It Works, but is it Good Enough? Optimal Choices in High-Precision Components

By supporting efficient, accurate and compact design, mechanical components contribute significantly to making humanoids more agile in complex environments. To really understand what drives performance characteristics in robotics design, consider the two examples below. Each offers distinct advantages, depending on the application. Analyzing their performance will help determine the optimal choice.

1. A Reliable Robotic Actuator System

For show-and-tell, maxon has been showcasing its high efficiency joint (HEJ) at trade fairs this year. Designed to speed up the development of various robotics applications, including AGVs, AMRs, quadrupeds and bipedals, this modular system integrates the motor, transmission, electronics and sensors.

The company has brought out two variants—the HEJ 70 and HEJ 90—both of which are compact and characterized by high dynamics and modern impedance control with integrated torque measurement. “The HEJ 90 is a highly efficient actuator based around planetary gearboxes,” explained Biren Patel, business development manager for Mobility Solutions and Electronic Systems at Maxon.

Patel said that the solution stands out for its peak torque of 50 Nm and reaches speeds up to 28 rad/sec—all while maintaining a mass just above 1 kg. Another characteristic is its high torque density, which supports mobile manipulation tasks.

The HEJ 90 is equipped with necessary subsystems, including electronics, motor, gearbox and sensors. The system is lightweight (the HEJ 90 weighs just over 4 lb) and is fully encapsulated, making it robust and ready for continuous operation. “It features integrated EtherCAT controllers, impedance control and precise torque measurement without a separate sensor, reducing costs and failure points,” said Patel.

2. Compact Actuators with Integrated Servo Drives

Harmonic drives, also known as strain wave gears, are unique mechanical gearing systems that allow high reduction ratios in a lightweight, compact form factor.

They are designed around three components—the wave generator, circular spline and flex spline—and are characterized by highly accurate and repeatable motion, making them essential in applications such as robot joints that require precision.

Strain wave gears have been around for decades (they were invented by C. Walton Musser in 1955). They are engineered with high reduction ratios in a single stage, offer zero backlash and a measure of high precision that’s matched by conventional gear trains, according to Eugene Niselson, director of sales, U.S. Eastern Region, Harmonic Drive, in this QuickChat with Machine Design.

The high gear reduction ratio is critical for greater control and stability, particularly in tasks that require fine motors skills and load-bearing capabilities. Aside from humanoids, common applications are cobots, medical equipment, aerospace, milling machines and manufacturing equipment.

Today, a shift toward integrated solutions in motion control is driven by a preference for simpler designs that eliminate the work of matching and connecting separate components. To boot, this approach reduces costs and improves performance, explained Harmonic Drive’s regional sales engineer, Henry Kim. That includes the development of actuator designs with integrated servo drives, motors and controllers that help streamline design and assembly processes while enhancing efficiency and reliability, he said.