Motor Basics

Quality Components: The importance of using quality components in any motor design is of a crucial importance. As was the case with audible noise, the use of cheap, poorly constructed motors adds to the electrical noise problem. "Open case" motors do not effectively block EMI radiated from the coil windings. Poorly fitted brush holders and inadequate brush tension contribute to radiated EMI as well.

Coreless motors: Coreless DC motors have much lower armature inductance than iron-core motors of comparable size. Since armature inductance is the primary cause of EMI problems, minimizing it through selection of coreless motors is recommended where EMI is a critical factor.

Lead Wires and Shielding: Motor lead wires should be placed as close together as possible so that EMI radiated from the two leads can cancel each other. This canceling effect can be improved by using so-called "twisted pairs" where the positive and negative lead wires are twisted together. Motor leads should be physically separated from data lines or encoder outputs to reduce the possibility of coupling motor noise onto them. This means that when using shielded pigtails, the feedback lines should be shielded separately from the motor leads. If noise is still causing problems with the encoder signals than it may be time to consider using a differential encoder to eliminate the effect of interference on the encoder. PWM switching noise is another source of EMI problems. Most commonly, PWM switching results in radiated noise from motor lead wires. Shielding and lead wire placement can also help mitigate the effect of PWM generated EMI.