Tech Torqs #14: What Are the Main Methods for Mounting a Frameless Motor Rotor?

Featuring Angus McWilliam, Senior Commissioning Engineer at Alva Industries.

A frameless motor consists of a rotor and stator without a housing, shaft, or bearings, giving engineers greater flexibility when integrating the motor into their own mechanical assemblies.

In this episode of Tech Torqs, we explore some of the most common methods for mounting a frameless motor rotor.

A press fit is one of the most widely used solutions. The rotor is pressed onto the shaft, while a mechanical shoulder can be used to accurately control its axial position.

Another common approach is a heat shrink fit. However, it's important to avoid heating the rotor itself. Excessive heat can permanently demagnetize the magnets, reducing motor performance. Instead, cooling the shaft before assembly is the preferred solution.

For additional retention, press fits and shrink fits can be combined with adhesive bonding. Adhesives may also be used on their own, provided the joint is designed correctly. As a general guideline, the adhesive bond line should cover approximately 50–75% of the rotor height, while allowing sufficient space for adhesive grooves to achieve the required bond strength.

Selecting the right mounting method is essential for ensuring reliable performance and maintaining the integrity of a frameless motor throughout its lifetime.