# Translation or rotation with sliding surface

## Introduction

This paragraph deals with rotation or translation motion with sliding motion of the moving part with respect to the fixed part.

## Example: presentation

The example presented in this paragraph is drawn from the Technical Paper “ Rear-view mirror motor analysis with Flux 3D ”. It deals with a small permanent magnet motor used to position an automobile rear-view mirror.

## Assignment of regions

The assignment of regions is done in the following way:

• moving part: the rotor, the rotor coils (not represented in the figure) and an inner area of air
• fixed part: the stator, composed of two permanent magnets, the metallic frame and an outer area of air

## Mechanical sets

The regions in this example can be assigned to two mechanical sets : a fixed mechanical set and a mobile mechanical set.

There is no compressible area of air. The displacement area, that is the air gap region, is subdivided into two zones:

• half of the air gap area, in contact with the rotor, belongs to the inner air regions (moving part)
• half of the air gap area, in contact with the permanent magnet, belongs to the outer air regions (fixed part)

## Important note

To obtain good results, it is preferable if possible to place the surface that divides the fixed and moving mechanical sets between two regions with the same physical properties. That is why in the previous example this surface is placed in the middle of the motor's air gap.

## Rules to be respected (in 3D only)

In the “automatic formulations” mode, the formulations for different regions are automatically chosen by Flux 3D. However, some rules must be respected.

The rules to be respected are the followings:

• Connectivity problem:

With coils, one must pay attention to the connectivity problem. To avoid this problem, at the level of the sliding surface, it is preferable to place an air gap region in contact with the sliding surface.

• Restrictions on materials:

Permanent magnets, conducting or non-conducting magnetic materials and conducting non-magnetic materials are not authorized to be in contact with the sliding surface.