How a Single Differential Drives Dual-Wheel Capstan With Constant Linear SpeedJanuary 5, 2024


In wire and cable manufacturing, dual-wheel capstans are used to pull crush-sensitive materials through a processing line at a constant linear speed. If the diameters of the two capstan wheels are slightly different and driven directly by standard speed reducers, the linear speed of the product will be different on each capstan. This can cause slipping, which can lead to wear to the capstan or the product. Installing a differential between the two reducers ensures that the wheels run at the required rotational speed to provide a constant linear speed while avoiding slipping issues.

In our previous blog post, we described how a differential can be used to drive two belts in a linear capstan. This ensures a constant linear speed of both belts without the variability that often occurs when using two gearboxes. The single differential approach prevents wear to the cable being pulled and also avoids expensive damage to the linear capstan belt.

For a dual-wheel capstan, the wheels pulling the cable also must have identical torque, but the rotational speed can vary to accommodate diameter differences and maintain a constant linear speed between the wheels. Like a linear capstan, it also requires an effective driving method to maintain the necessary balance of torque and speed to avoid slipping between the belts and the cable. The right differential can prevent product wear and damage to the capstan’s wheels or product being processed that typically occurs due to slipping.

The SR differential from Redex USA is well-suited for this type of application, thanks to a compound epicyclic gearing design that incorporates two sun gears within the casing along with two gears for each planet axis. Redex’s patented assembly process ensures equal load sharing between the sun gears. It can be installed between the wheels using one input and two outputs. The output speeds can vary slightly to accommodate diameter differences on the capstan wheels.

This differential corrects any variations in wheel diameters, eliminates transmission errors and drives the capstan wheels in the same rotational direction. This allows effective linear speed control and ensures precise pulling forces between the capstan wheels.

Ensure Product Quality and Machine Reliability
When designing a dual-wheel capstan for wire and cable production, the quality of the finished products and equipment reliability depend on your driving method’s ability to ensure precise tension control between the wheels. Redex USA’s SR Series differentials feature a unique compound epicyclic design and special assembly process to share the load equally between planet gears to deliver precise speed and tension control. Our sales engineers are available to help you specify an ideal differential gearbox for your single- or dual-wheel capstan design.

For more information about Redex differential gearboxes for wire and cable manufacturing, visit our product page.

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