Overview
Acting as the bridge between motors and actuators, reducers play a pivotal role in humanoid robots. By reducing motor speed and amplifying torque, they enable smoother, more precise motion. Without reducers, balancing both speed and power in robotic joints would be nearly impossible.

Three Core Types of Reducers

Precision reducers, with their core function of reducing speed and increasing torque, are indispensable devices in the field of precision transmission. Precision reducers with minimal backlash and high transmission accuracy have high technical barriers and strong market demand. Precision reducers are generally categorized by structure as planetary reducers, harmonic reducers, and RV reducers. They are commonly used in high-end applications such as robotics and CNC machine tools.

1. Harmonic Reducers

Mechanism: Consists of a wave generator, flex spline, and rigid spline, transmitting motion via elastic deformation.

Strengths: Compact, lightweight, high gear ratio, excellent accuracy, and almost zero backlash.

Applications: Ideal for light-load joints such as wrists, fingers, and forearms, enabling dexterous movements.

Limitations: Flex splines are prone to fatigue, and precision may decline over long-term use.

2. Precision Planetary Reducers

Mechanism: Uses a sun gear, multiple planet gears, and a ring gear. Planet gears both spin and orbit, transferring energy efficiently.

Strengths: High efficiency, robust durability, good load-bearing capacity, and stable transmission.

Applications: Commonly used in arms and hip joints, ideal for applications requiring steady and sustained torque.

Limitations: Single-stage ratios are limited; multi-stage setups increase size and mechanical complexity.

3. RV Reducers (Cycloidal/Planetary Hybrid)

Mechanism: Combines a planetary gear stage with a cycloidal drive, taking advantage of both mechanisms.

Strengths: Exceptional precision, rigidity, shock resistance, high load capacity, and long service life.

Applications: Widely used in shoulders, thighs, and torso joints; essential for industrial robots and advanced humanoids.

Limitations: Larger size, more complex structure, and higher production and assembly costs.

Why They Matter
Reducers not only define motion performance but also impact overall energy efficiency, stability, and safety. In a humanoid robot, reducers typically account for a significant portion of total manufacturing costs.
For instance, in Tesla’s Optimus, harmonic reducers alone represent about 13% of the total drive system cost, highlighting their importance in the value chain.

Industry Trends

Foreign leaders: Japanese and German companies dominate in high-precision harmonic and RV reducers.

Rise of domestic players: Chinese manufacturers are improving rapidly in technology and cost, with some products already entering global supply chains.

Growing demand: With humanoid robots moving toward mass production, the market size for precision reducers is expected to expand steadily.

Quick Reference Table

As humanoid robots approach real-world deployment, reducer performance and cost control will directly determine market competitiveness. Selecting the right reducer solution enhances precision, reliability, and cost-effectiveness.

At AIP, we focus on global motor testing,our systems validate reducer-motor compatibility under diverse operating conditions, helping customers identify issues early, improve reliability, and accelerate large-scale adoption of robotics.

Contact us today to explore our motor testing and robot motor test solutions.