Strain-wave gearing

Many of today’s precision applications necessitate gears capable of dramatic speed reductions, power densities, and transmission accuracies. Leading choices in these designs include trochoidal and cycloidal gearing as well as gearsets relying on wave-inducing subcomponents having an elliptical or Reuleaux or other polygonal shape.


Recall from geometry that trochoidal and cycloidal gearing includes elements that rotate and trace curves around some other element. More specifically, cycloids traced by a point on a rolling element’s circumference include epicycloids (for which the element rolls along the outside of a sun gear or other reference component) and hypocycloids for which the element rolls within a ring or other reference component. In contrast, trochoids (and their subtypes) are traced not by a point on the rolling element’s circumference but rather some point within or without. One particularly common subtype of epicyclic gearing is planetary gearing.


In the following articles, the editors of Design World explain the variations of (and applications for) these strain-wave and cycloidal gear offerings in high-end machine tool, aerospace, material handling, and robotic applications.

Lisa Eitel

Executive editor, Design World

Strain-wave Gearing Classroom sponsored by:

Basics of waveand cycloidal gearing for robotics and servo designs

Many of today’s precision applications necessitate gears capable of dramatic speed reductions, power densities, and transmission accuracies. Leading choices in these designs include trochoidal and cycloidal gearing as well as gearsets relying on wave-inducing subcomponents having an elliptical or Reuleaux or other polygonal shape. Trochoidal and cycloidal gearing includes elements that rotate and trace curves around some other element. 

Back to Servogear Basics

How do cycloidal gears work and where are they used?

What’s the best type of gearbox for servo applications?

What are gears for power transmission? Technical summary for design engineers

How to get zero backlash out of gearing?

One way to classify gears is by the profile of the gear teeth: involute, cycloidal, or trochoidal. (Note that trochoidal gears are used primarily in pumps.) The majority of gears used in motion control applications — including spur, helical, and bevel designs — are involute gears.

Gearboxes provide torque multiplication, speed reduction, and inertia matching for motor-driven systems. Servo systems, specifically, require gearboxes that can supply not only high torque with low added inertia, but also high precision and stiffness. 

Gearmotors use gears to reduce speed, which makes more torque available. The kind of gears used in gearmotors have an impact on the available torque, but also on things like noise levels and accuracy.

The function of a gear is to mesh with other gears to transmit altered torque and rotation. In fact, gearing can change the speed, torque and direction of motion from a drive source.

What are the key parameters to consider when sizing and selecting a rotary actuator?

Servogear application examples

Strain-wave, planocentric, cycloidal, planetary, and thrusted-tooth gearing

What are the drawbacks to using a planetary gearbox?

Motion applications for gearing are as varied as the motors with which these power-transmission devices pair. Just consider how designs ranging from amusement rides to consumer-grade beard trimmers make use of spur gears. 

Rotary actuators — and their counterparts, rotary stages and rotary indexing tables — are designed to move loads radially with high positioning accuracy. Similar to linear actuators, sizing a rotary actuator requires evaluating parameters such as torque, speed, and inertia, etc.

Trochoidal and cycloidal gearing includes elements that rotate and trace curves around some other element. More specifically, cycloids traced by a point on a rolling element’s circumference include epicycloids.

One type of gearbox meets all the design criteria of servo applications while providing relatively long operating life with low maintenance requirements — the planetary gearbox. 

Strain-wave and other robotic-grade gearing applications

Mobile robotics present new ethics questions

ROS must account for robots’ mechanical design

Strain-wave gears and other components in off-highway + mobile robotics

Leading motion-control and actuation options for robotics

In 2016, bomb-disposal robot became the delivery system for 1-lb C4 explosive — essentially becoming an improvised explosive device (IED) to kill a Dallas sniper — in turn responsible for shooting and killing five police officers. Strange as it seems, the bomb robot became a bomb delivery system.

Software development for a robot is not trivial. However, the Robot Operating System or ROS (like Linux) is an open platform on which teams all over the world have worked in parallel for close to two decades now.

Advanced robotics for industrial and consumer applications demand sophisticated power-dense motion components for joints and linkages that must run smoothly, often at high torque and relatively low speed. 

Automated mobile equipment, which transports items in warehouses and freight centers as well as assembly operations, continues to boost demand for power-transmission and motion control systems. 

Trends in gears and gearmotors for eMobility • washdown • customization

More on the mechatronics of robotics

Solar tracking: More complicated than it seems

New ways of controlling indexing tables for precision motion

The fundamental mode of operation for gearing and its transmission of mechanical power remains unchanged — as has that for the electric motors with which they pair. But innovative variations have become increasingly common and include more custom gearing, compact designs, etc.


The mechatronics challenge of robotics is multifaceted. In an earlier post we touched on some of these design facets; now let’s consider a few more.

Solar tracking is an interesting mechatronics challenge. That’s because it seems a simple design objective: Keep the solar panel oriented perpendicular to the sun in the sky — no big deal.

There are key differences between fixed-position indexing tables and closed-loop position indexing tables. Here we review them and how to control for maximum accuracy.

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Servo-gear performance considerations

How custom BLDC motors boost performance and lower costs

Lost motion in precision gear systems

Environmental effects on motion components in robots

Sizing and selecting servos: The need for a system approach

Mechanical “lost motion” in the form of play, backlash, and friction complicate motion design. Mechanical systems have very defined properties which are easy to characterize. For example, the performance of a gearbox is well understood and usually very consistent over time. 

From packaging to communications, BLDC servomotors are gaining market share in a variety of industries — and for good reason. They deliver high torque and smooth rotation (with minimal torque ripple) and lend themselves well to cost-saving customization.

Recent years have seen continuous demand in numerous industries — automotive manufacturing to computer, communication, and consumer electronics (3C) product fabrication — for industrial robots. 

Never sized and selected a servo? Here we outline the basics of how interrelated parameters need a system approach.

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Datorker® Strain Wave Gearing System

Datorker® Robot Reducer

HIWIN is the world leader in motion control and system technology, providing high quality and reliable standard and custom components and complete motion control solutions with precision quality, at competitive prices. With an extensive inventory in Chicago, our products are widely used in industrial equipment, lab equipment, semi-conductor and more.