Cycloidal gears or strain wave gears: When is which the better choice?

Both technologies meet the highest standards for precision, torque capacity, and torque density, making them particularly suitable for applications where maximum accuracy is essential. While cycloidal gearboxes are specialists for higher torques due to their outstanding rigidity, the backlash-free strain wave gears are primarily at home in the lower torque range and are used wherever high performance is required but only limited installation space is available.

Size isn’t always the deciding factor

In most cases, geometric size is the decisive criterion for or against one of the two technologies. However, there is also an overlap where both gear types are viable—namely for outer diameters between 100 and 150 mm and/or torques between 250 and 450 Nm. Which technology is the better choice depends largely on the requirements of the specific application. When high torques are the focus, cycloidal precision gears demonstrate their strengths. If zero backlash is the primary concern, strain wave gears have the advantage (developed and manufactured at the Ovalo GmbH facility in Limburg/Lahn).
 

The most important features in detail:

Design Principle

In cycloidal gearboxes, power is transmitted via cam discs and rollers. In strain wave gears, this function is performed by a cylindrical, elastically deformable steel component with external teeth, known as a flexspline. The respective design principle forms the basis for the characteristic properties of both technologies.

Torque

Our strain wave gears deliver torques ranging from 4.5 to 382 Nm. This torque range is largely attributable to the Flexspline as an elastic transmission element and the elliptical deformation of the shaft generator’s bearing, as both would lead to significantly higher mechanical stress and thus a shorter service life at very high torques. Our cycloidal gearboxes cover a torque range up to 70,000 Nm. The nearly complete contact and the uniform force distribution within the gearbox ensure high rigidity, thereby enabling the transmission of very high torques.

Precision / Backlash

The accuracy of a gearbox is largely characterized by backlash and hysteresis loss. The lower the value, the more precisely the gearbox operates. Strain wave gears are absolutely backlash-free, meaning the backlash is zero. Our cycloidal gearboxes are backlash-reduced or virtually backlash-free, with a pure backlash of only 0.1–0.2 arcmin. The hysteresis loss for both technologies is a maximum of 1 arcmin. By comparison: Conventional backlash-reduced planetary gearboxes typically have a backlash of approx. 3 arcmin, while standard planetary gearboxes can have as much as 7 arcmin.

Moment rigidity

Due to their design, cycloidal gearboxes are significantly more tilt-resistant than strain wave gears gears. This is particularly advantageous with long lever arms, where high moment rigidity act on the gearbox. High moment rigidity helps minimize elastic deformation and maintain accuracy even under load.

Torsional rigidity

Cycloidal gears exhibit higher torsional rigidity. They are thus more resistant to twisting about the longitudinal axis, resulting in lower elastic deformations under torsional stress. This has a positive effect on precision. Strain wave gears also achieve high values but are designed more for absolute backlash-free operation and compact sizes.

Load Capacity

For very high loads, cycloidal gearboxes are the first choice. With a rated torque of 28,000 Nm and a maximum dynamic torque of 70,000 Nm, our RV-2800N is the world’s largest precision gearbox and can move entire vehicles effortlessly. Our rotary tables are also designed for high loads: for example, the RS-900A positions axial loads of up to 9 t with high precision.

Overload Capacity

Both technologies offer substantial safety margins. The emergency stop torque is up to 500% of the rated torque, and for cycloidal gearheads, optionally up to 800%. This ensures high overload protection and increases reliability even under demanding conditions.

Installation space and weight

When it comes to installation space and weight, strain wave gears have the edge. They are more compact and lighter than precision gears in cycloidal design, making them particularly suitable for applications where installation space is limited. This makes them especially attractive for small axes that require high precision and dynamics despite their compact dimensions.
 

Direct Comparison of Properties

Typical applications

The Dream Team of Automation

In virtually every application, machine, or system, there are larger and smaller axes. If the larger axes are equipped with cycloidal gears and the smaller ones in the end-effector area with strain wave gears, the best possible precision can be achieved through the overall coordination of all axes. A true dream team of automation.

Would you like to learn more about the advantages of our precision gears and their applications? Our experts are here to support you with your project. Contact us now!