Toothless gearbox: Revolutionary development by New York University

Less Wear US Researchers Develop Toothless Gearbox

2026-01-16 Source: Press release | Translated by AI 1 min Reading Time

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Researchers at New York University have developed a toothless gearbox. In this design, the driving forces rotate a roller, which sets a viscous fluid in motion.

Air bubbles make the flows in the gearbox visible: The left roller is actively driven by a motor (not shown), while the right roller passively rotates due to the flows.(Image: NYU (Applied Mathematics Laboratory)) — Air bubbles make the flows in the gearbox visible: The left roller is actively driven by a motor (not shown), while the right roller passively rotates due to the flows.
(Image: NYU (Applied Mathematics Laboratory))

In general, gear teeth mesh with each other in transmissions to change rotational speeds or move heavy loads with minimal force. However, these teeth wear out over time or break, which limits the lifespan of the transmission. In Jun Zhang's version from New York University, forces are transferred from one rotating mass to another through a fluid. This reduces wear.

Previous toothless (hydrostatic) transmissions are based on a two-stage process: the driving force is stored in a hydraulic fluid in the form of pressure. This fluid drives a turbine wheel, which is, for example, coupled to the wheels of a locomotive. Its rotational speed is controlled via a valve that directs more or less fluid onto the turbine wheel.

Using Fluid Flows to Rotate Rollers

Zhang's solution is simpler. The driving force causes a roller to rotate. This, in turn, sets a viscous fluid in motion, which transfers through flow onto a second roller. The transmission effect is achieved by controlling the flow generated by the driving roller. Zhang and his colleagues, Leif Ristroph and Jesse Etan Smith, experimented with a water-glycerin mixture, adjusting its viscosity.

The experts' hypothesis: The driven roller generates fluid flows that also cause the passive roller to rotate. To observe the effect, the specialists added tiny bubbles to the mixture, making the flows and their impact on the second roller visible. Depending on the distance, the passive roller rotated faster or slower, and it was even possible to reverse the direction of rotation. This, they concluded, covers all the functions of a mechanical transmission.

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Date: 08.12.2025

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