When to Use Differences between single, double and telescopic joints？

Single Universal Joints

Single universal joints can compensate an angular offset of up to 45° between the input and output shaft.
They typically operate at larger angles and higher torques than other types of couplings. They are also torsionally rigid and do not flex or wind up.

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Single joints are subject to non-uniform speeds at input and output shafts. This means that when the speed at the input shaft is constant, the speed at the output shaft fluctuates.

Double Universal Joints

Double Universal Joints can be created from two single joints by pinning or butting the hubs together, or specially designing the double joints with a single center section, to eliminate additional machining and assembling.

The advantage over a single joint is either an increased operating angle (W configuration) or the capacity to compensate parallel misalignment
(Z Configuration). They can also compensate the non-constant veloctiy between driving and driven shaft on a Single Universal Joint as long as they are oriented correctly.

Telescopic Joints

Telescopic drive shafts or double cardan joints are essentially a double joint with a section in the center that allows a flexible length of the center piece. The adjustable center element of a double cardan joint allows the shaft's length to be varied for easy installation or to compensate for axial play. This type of shaft can be used wherever a drive and its output shaft have not only parallel and angular misalignment, but axial displacement as well. Anywhere the position of the motor (drive) or the load (output) is frequently changed, an articulated shaft with a telescopic segment allows quicker, simpler repositioning than possible with a rigid two-joint shaft.
 

There are also applications that require a length change of the drive shaft in operation since one or both ends move. Depending on the application and environment, different profiles can be selected to design the center sliding feature. The simplest form is a square or hex shaft on one side with a mating hub on the other side. These connections are robust and cost-efficient.

For more precision and /or torque capacity, parallel-sided splines or shafts with multiple keys are a better option. Angled or involute spline profiles are available for extreme cases, but they come at a significantly higher cost.

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Wear on the shaft can be an issue when the sliding features move under load and during rotation – especially for stainless steels. Heat treatment or special coatings can be used to counter the negative effects.

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In some cases, ball splines may offer a low friction and low wear option for long life.

Single Universal Joints

Single Universal Joints are capable of accommodating an angular offset of up to 45° between the input and output shaft. They are designed to handle larger angles and higher torques compared to other types of couplings. Additionally, they are rigid in torsion and do not exhibit any flexing or winding up.

However, single joints experience non-uniform speeds at the input and output shafts. This means that while the speed at the input shaft remains constant, the speed at the output shaft fluctuates.

Double Universal Joints

On the other hand, Double Universal Joints can be formed by combining two single joints through pinning or butting the hubs together. Alternatively, they can be specially designed with a single center section to eliminate the need for additional machining and assembling. The advantage of using double joints is either an increased operating angle in a W configuration or the ability to compensate for parallel misalignment in a Z configuration. Moreover, when oriented correctly, double joints can also compensate for the non-constant velocity between the driving and driven shafts on a Single Universal Joint.

Telescopic joints

Telescopic joints, also known as telescopic drive shafts or double cardan joints, consist of a double joint with a flexible center section that allows for length adjustment. The adjustable center element of a double cardan joint enables the shaft's length to be changed for easy installation or to compensate for axial play. These joints are suitable for applications where there is parallel and angular misalignment, as well as axial displacement between the drive and output shaft. In situations where the position of the motor or load is frequently altered, an articulated shaft with a telescopic segment allows for quicker and easier repositioning compared to a rigid two-joint shaft.

In certain applications, the drive shaft needs to change length during operation due to movement at one or both ends. Depending on the specific requirements and operating conditions, different profiles can be chosen for the center sliding feature. While a square or hex shaft with a mating hub is a simple and cost-effective option, parallel-sided splines or shafts with multiple keys offer higher precision and torque capacity. For extreme cases, angled or involute spline profiles are available, although they come with a higher cost.

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The wear and tear on the shaft can pose a problem when the sliding components are subjected to load and rotation, particularly for stainless steels. To mitigate the adverse effects, heat treatment or specialized coatings can be employed.

In certain instances, ball splines may present a viable solution with their ability to provide a long-lasting option that boasts low friction and minimal wear.