What is a RADAX motor?

What is a RADAX motor?

The RADAX motor is a hybrid radial-axial (RADAX) flux motor. It combines a radial flux motor with one or more axial flux motors within the same motor housing. It reportedly offers several advantages, including higher torque, higher back EMF, compact size, and suitability for direct drive systems. RADAX technology is recommended for applications requiring high volumetric density and for vehicles that spend a significant amount of time idling or in other low-speed maneuvers. However, there is no "free lunch" in nature. That is, the RADAX motor is subject to high axial forces acting on the axial rotor as well as high initial cogging torque.

    Figure 1. Exploded view of the SolidWorks model of the RADAX motor

    Figure 2. 3D view of the SolidWorks model of the RADAX motor

    EMS Simulation of RADAX Motor

To help understand this new and promising technology, we used our virtual prototyping motor software, EMS, to study and simulate the RADAX Flux motor as shown above. A no-load analysis was performed to calculate the back EMF and cogging torque. Here are some EMS no-load results:

    Figure 3 Magnetic flux density fringe diagram in the entire model

    Figure 4. Magnetic field fringes in the stator and surrounding permanent magnets

    Figure 5. Temperature distribution of the stator core

    Figure 6. Comparison of back EMF of radial, axial, and RADAX motors

    Figure 7. Load torque for three configurations

Clearly, the RADAX motor generates a much higher back EMF compared to the radial and axial configurations. In fact, the RADAX back EMF is nearly the sum of the radial and axial combined. Likewise, the load torque of the RADAX configuration is much higher. Nonetheless, the impressive back EMF and load torque come with a price tag as shown in the figure below.

    Figure 8 Comparison of axial forces acting on the axially external rotor

    Figure 9. Comparison of maximum cogging torque

Obviously, with the new RADAX design, the axial forces and cogging torque are much higher, which is problematic; high axial forces can cause the rotor to deform or even brake completely; and high cogging torque is notorious for causing ripples and vibrations.