Custom motor designs cover a broad range of modifications from simple mechanical changes to ground up development projects. Customizations allow the designer to optimize servo motor performance to improve machine productivity and value. When and how to customize a standard servo motor depends on the predicted benefits derived from the customization that should include a solution tied to form, fit, and function. Knowledge of which design elements can be modified and which are fixed, as well as the associated cost drivers, should be determined before any changes are made.
The major components of motor electromechanical design are, unsurprisingly, mechanical and electrical (or a combination of both). The complexity of customization will depend on the extent of change to the original design. A mechanical change, like an output shaft diameter reduction, may be an easy modification, while an increase in shaft diameter may necessitate changes to other aspects of the design. Adjusting the electrical characteristics of the motor winding may be as simple as changing the number of turns in the stator coil, while increasing the design voltage may require changing insulation materials and even slot design.
Mechanical changes are usually compelled by the machine mechanism’s shaft and mounting requirements. Common mounting modifications include the pilot diameter and depth, shaft diameter and length, mount type (face or flange), and location and orientation of the power/feedback connections. Standard NEMA mounting specifications identify the arrangement of bolt circle, pilot, and shaft diameter. While a mounting arrangement based on NEMA standards minimizes the need for customization, there may be space considerations that require shaft or mounting changes to optimize space utilization.
The motor application environment may also require simple mechanical changes, such as improved sealing to accommodate a wet environment, or more complex changes that require alternate materials to accommodate chemical or radiation environments. In addition, material adjustments for hazardous environments can drive design element changes that can increase costs considerably.
Most cost drivers for mechanical changes are determined by the initial standard design specifications. Reducing the shaft diameter is typically a lower cost modification than increasing the shaft diameter, potentially causing additional changes in the bearing design and endbell machining. Changes to the mounting arrangement (pilot, bolt circle) may also require modifications to the end bell casting that force additional tooling charges.
Electrical modifications typically involve an adjustment in the number of turns in the motor coil windings to accommodate the available voltage and current. Other electrical considerations include improved EMI shielding, alternate feedback devices, or adjustments in connectorization.
The cost drivers of electrical modifications vary depending on how extensive the changes are to the electrical winding or feedback elements. The number of wire turns in a coil is directly related to the rated speed/torque points based on a specific voltage/current. Winding changes that optimize speed and torque based on the available voltage and current are relatively easy to accomplish. When changes are made to accommodate significantly lower or higher voltages, however, other resulting design modifications (such as insulation adjustments or slot design changes) will cause the customization costs to increase.
Customizing a standard motor is best accomplished working with a motor manufacturer who can identify the advantages specific modifications add to the overall value of the machine. Review associated cost-benefits of each electrical or mechanical modification to ensure that any customization adds value to improve machine operation efficiency.
