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Bearing Design | 26 Aug 2014 | |

Bearing Design

Valid for Cartridge DDR


A Cartridge DDR Motor does not have bearings. It attaches directly to the driven machine and relies on the machine’s bearings to support the rotor inside the stator. This document provides the machine designer with some basic information about the requirements of the bearing system that supports the Cartridge DDR Motor in a successful application. Two sample bearing configurations are presented that, when properly implemented, meet the requirements of the Cartridge DDR motor.

The requirement of the bearing system is to maintain the radial and axial orientation of the shaft in consideration of machine process force, magnetic forces applied by the Cartridge DDR Motor, thermal expansion, and machine manufacturing tolerance. Maintaining radial alignment with these considerations is the primary concern. Under the worst-case combination of these variables, the radial displacement of the end of the shaft that engages the Cartridge DDR Motor must not move more than 0.13 mm (0.005 inch) from center!

An additional consideration is the axial alignment. Thermal expansion of the machine should be directed away from the Cartridge DDR Motor to minimize the axial movement of the motor’s stator and rotor during thermal growth. Therefore, the bearing located closest to the motor must be axially fixed.

Forbidden Designs

Do not insert a coupling or extend the shaft with using a third bearing for example. The coupling or long shaft does not provide sufficient stiffness and the poling force inside the Cartridge DDR Motor deflects the shaft and the motor poles and does not run.

Polling Force

The permanent magnets inside the Cartridge DDR Motor assert a force that pulls the shaft away from the center. This force is called a poling force. A grossly insufficient bearing structure allows the shaft to deflect until the rotor comes in contact with the stator. If this happens, the motor is said to be “poled” and must be returned to the factory for a non-warranty repair or alignment. The poling force of each standard Cartridge DDR Motor is listed in the table below. This is the largest poling force that the motor applies to the end of the shaft (includes the weight of the rotor).

Model Poling Force {N} Model Poling Force {N}
C(H)041   C(H)061  
C(H)042   C(H)062  
C(H)043   C(H)063  
C(H)044   C(H)091 574
C(H)051   C(H)092 1130
C(H)052   C(H)093 1681
C(H)053   C(H)131 712
C(H)054   C(H)132 1388
    C(H)133 2068


Converting machine

The figure below is an example of a roller in a typical converting machine.


The roll and machine processes are inside a frame with a bearing at either end of the roll. The shaft extends beyond the machine frame on one side where the Cartridge DDR Motor is mounted. The fixed bearing is located near the motor and the bearing mounting at the other end of the roll accommodates thermal growth of the roll.

Overhung load

This example is a configuration where the Cartridge DDR Motor is mounted on one side of a machine frame member and the load is on the other side.


For this example, preloaded, tapered roller bearings are applied (other angular contact type bearings may be used). The preload of the bearing is critical to resist the overturning moment applied to the shaft from the load and from the poling force of the Cartridge DDR Motor, which can act in tandem.

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