The Choke Point in Every Robot

Every viral clip of a Chinese humanoid doing backflips obscures a quieter dependency. Inside each robot sit twenty to thirty precision reducers, the harmonic and RV gearboxes that act as its joints, and for decades those were made almost entirely in Japan.^[1]

The concentration is extreme. Japan’s Harmonic Drive Systems held roughly 85% of the global harmonic-reducer market in 2023; Nabtesco supplies around 60% of the larger RV reducers used in heavier robots.^[1] A single humanoid can require on the order of thirty actuators, and the reducer is the costly, hard-to-make heart of each one.^[2]

China can build a $16,000 robot. It still can’t easily build the gearboxes in its joints, or the machine tools that cut them.

The challenger, and the layer beneath

China is closing the gap. Leaderdrive took an estimated 15% of the global harmonic-reducer market and 26% of China’s by 2023; on humanoid demand its 2025 revenue rose 47% to 570.7 million yuan and net profit more than doubled, with AgiBot and UBTech among its clients.^[1][3] Zhejiang Shuanghuan now supplies reducers to Tesla’s Optimus and Unitree’s G1.^[1] But the dependency has merely moved down a layer: even where China makes most of its own reducers, it still imports roughly 90% of the precision machine tools needed to produce them, mostly, again, from Japan.^[1]

The reason the reducer is such a durable chokepoint is metallurgical, not merely industrial. A harmonic gearbox demands sub-micron machining tolerances, specialty alloys and decades of accumulated process know-how, which is why two Japanese firms held the category for a generation. China closing the gap at the component level while remaining dependent on imported machine tools is therefore the whole story in miniature: localisation at one layer routinely exposes a deeper dependency at the layer below. It is a caution against reading any single “we now make our own X” headline as evidence that the chain beneath X is domestic too.

What to watch from here

Supply chains reveal where the durable value and the real risk sit. In the humanoid build-out, the reducer and actuator are both the largest cost line and the tightest bottleneck, which makes the component makers, not the robot brands, some of the highest-quality exposure and the most defensible margins. It also flags a second-order dependency, machine tools, that a headline “localisation” number can hide. We map the whole stack, from joint to gearbox to the tools that cut the gears.