How to Build a Humanoid Body

• Actuators act as physical muscles for humanoid robots, requiring over 40 individual units per machine and accounting for up to 70 percent of total manufacturing costs.
• Achieving precise human movement relies on specialized hardware like strain wave gearing from Harmonic Drive Systems and Nabtesco alongside miniature ball screws from THK.
• Because the commercial viability of physical AI depends on these hardware suppliers, index strategies like the ROBO Global Robotics and Automation Index offer targeted investment exposure.

From a high level, all robot movement can be broken down into two types: rotational (turning/spinning) and linear (up/down, left/right). Almost all standard electric motors natively produce rotational motion. To get straight directional movement, rotational energy can be converted into linear movement using linear motion mechanisms or actuators.

So, while the software brain determines where and how a humanoid robot should move, executing those orders requires specialized hardware. Like actuators to drive joint movement, torque sensors to enable sensitive grasping, and motor electronics to continuously balance power, speed, and positioning.

So, what to buy and who to buy it from?

To mimic the fluid, complex movements of a human, a robot requires an actuator for every desired degree of freedom. Actuators are units that combine motors, gears, and sensors to act as physical muscles to drive joint movement. So, if you want your robot’s arm to match the natural 7 degrees of freedom of a human arm, you will need 7 individual actuators just for that single limb.

Because of this 1:1 requirement, a modern humanoid robot can have over 40 actuators in its total assembly. When you add them all up, this highly specialized hardware can represent up to 70% of the total manufacturing cost of your humanoid.

At the core of every actuator is a motor that converts electrical energy into physical motion. Because space and weight are at an absolute premium inside a humanoid’s joints, you cannot use standard, bulky industrial motors.

You will want frameless torque motors. By eliminating the outer housing and bearings, these motors integrate directly into the robot’s joint assembly. Working alongside the gears, they deliver massive power density in a tightly packaged ring.

Through its Celera Motion division, Novanta Inc. (NOVT) engineers highly specialized frameless motors and precision encoders that can currently be found not only in humanoids, but in other advanced surgical robots and physical exoskeletons. Together, these core components provide the foundational driving force required for dynamic robotic motion.

While a motor provides the raw rotational power, an actuator relies on internal precision gearing to control the exact output torque and speed sent to the joint. Matching a human arm’s dexterity requires compact rotary transmissions, which must manage heavy loads while maintaining precise control over joint positioning.

For joints like wrists, elbows, and hips, you will need strain wave gearing, more popularly known as harmonic drives. These gears operate through the continuous elastic deformation of a flexible metal cup, delivering high torque density, zero backlash (no mechanical play), and extreme positioning accuracy in an exceptionally lightweight form factor.

Harmonic Drive Systems Inc. (6324), the historical leader in this technology, actively supplies these gear sets for integration into modern humanoid joint modules. Meanwhile, competitors like Nabtesco Corp. (6268) are innovating rapidly, introducing compact “short gears” explicitly engineered to deliver 20% higher torque capacity and longer service life in a reduced footprint.

As humanoid designs mature, this constant push for higher power density ensures that tomorrow’s robotic joints will be stronger, lighter, and more durable than today’s.

Because electric motors natively produce rotational motion, executing straight-line movements, like extending a leg, flexing a knee, or absorbing the impact of a footstep, requires integrating linear actuators.

They translate that rotational spin into linear force, and are often built around precision components like miniature ball screws for motion conversion and cross-roller rings for structural stability. These act as the tendons and push-rod mechanisms within a robotic limb.

Companies like THK Co., Ltd. (6481) have long been established leaders in precision factory automation. Today, their specialized ball screws and linear actuators are actively deployed in the arms and legs of modern human-centric prototypes, converting rotational motor force into fluid, multi-axis linear movement.

If you were to actually order every item on this shopping list, your bill of materials would quickly reveal where the real cost of physical AI lies. High-performance semiconductors and AI software might teach your humanoid how to think, but specialized mechanical hardware dictates whether it can actually move. With integrated actuators generally representing more than half of a humanoid’s total manufacturing cost, the commercial viability of bipedal robotics rests squarely on this mechanical supply chain.

For those who would rather invest in the hardware ecosystem than assemble custom strain wave gears in their garage, you don’t have to bet on a single robot manufacturer. Strategies like the ROBO Global Robotics and Automation Index provide targeted exposure to the precision component leaders supplying the essential hardware that brings these machines to life.

ROBO is the underlying index for the ROBO Global Robotics & Automation ETF (ROBO), the L&G ROBO Global Robotics and Automation UCITS ETF (ROBO.LN), and the Global X ROBO Global Robotics & Automation ETF (ROBO.AU).

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