Repulsion Motor UAER — Drum vs Disc Part I

Introduction

The somewhat cryptic title of this post refers to the "Unenergized Attraction - Energized Repulsion" concept that I've discussed before, as used in both the Kure Tekko motor with its drum-shaped rotor (and its repelling stator magnets), and my version of it with its disc-shaped rotor.

In this and the next post, I'll compare these two versions of the concept, including some magnetostatic modelling of them.


Drum design — good and bad features

A bad feature of the drum design is that a lot of the electromagnet's magnetic flux goes more or less directly between adjacent inner edges of its pole pieces, and so that flux is largely wasted — it has little influence on the rotor magnets. With the disc design's toroidal electromagnet, essentially all of its flux must go across the full airgap between the faces of its pole pieces, and thus it interacts better with the rotor magnet.

A good feature of the drum design is that not only does its electromagnet repel the rotor permanent magnets, but modelling results show that it also attracts a portion of the backing steel in the region immediately behind these magnets. With no backing steel, this feature is not possible in the disc design.

Drum design modelling, without repelling stator magnets

Fig 1a   Drum design model, without stator magnets

Figure 1a is from a model of a drum design, flattened out into a linear configuration. This was done to remove any possible ambiguity in the results, since only forces in the vertical Z-direction are now relevant to the analysis.

In this first model, stator magnets have been omitted.

Data (all dimensions in millimeters):—

Rotor Magnets (blue): Each 96 × 60 × 8, NdFeB35.

Magnet Backing Steel (grey): 130.1 × 25 × 960, M19 steel.
(The backing steel is essentially "infinitely" long in this modelling).

Electromagnet Core (grey): Cross-section 57.15 × 38.1 = 2177.4 mm² 
Core is based on E300 transformer laminations (halved by shearing).
Pole pieces are 96 × 60 × 5, with 0.5 airgaps to magnets.

Electromagnet Coils: Current injection plane area (solid red) = 2 × 19.225 × 105.3 = 4048.8 mm². Total excitation 16400 amp-turns.

The magnet pair is first attracted in to the unenergized core, until there is zero vertical displacement between them, as shown. The electromagnet is then energized as noted above, while the magnet pair is repelled through a vertical distance of 96mm out from the core. The magnet pair then continues to move away from the core until the force between them has diminished to zero.

Fig 1b   Modelling results, drum design without stator magnets

Results

Figure 1b shows graphed results from this modelling.

The dip in the attraction force is probably genuine — I have seen it in several other models. The negative spike in the repulsion force beyond 96mm displacement could of course have been eliminated by continuing the excitation out to say 150mm of magnet displacement.

As modelled above, the total output energy is 46.603 joules.


Drum design modelling, with repelling stator magnets

Fig 2a   Drum design model, with stator magnets

Figure 2a is from a model of the same drum design as before, with a pair of repelling arc-shaped stator magnets and their backing steel added. These magnets are 1500 surface radius × 60 wide × 8 thick, starting tangential to the electromagnet pole pieces, extending 500 in the Z-direction. Their backing steel is also 130.1 × 25 cross-section, M19 steel.

Fig 2b   Modelling results, drum design with stator magnets

Results

Figure 2b shows graphed results from this modelling.

In this case the moving magnets are first attracted-in to the unenergized electromagnet core as before, and are then repelled-out under the stator magnets with the same 16400 amp-turns excitation over the same 96mm magnet displacement as before. They then experience further repulsion from the stator magnets until that repulsion has diminished to zero.

The total energy gained is 47.743 joules. This is only 2.45% higher than when the stator magnets were absent. Note that the increase is all in the attraction-in energy, while the net repulsion-out energy has actually decreased slightly.

Conclusion — stator magnets not worthwhile

The overall conclusion from these results seems clear enough: only a very small increase in total energy is gained at best with the stator magnets added, making the considerable extra cost and complication of adding them not worthwhile.

As is only to be expected, the stator magnets act to "smooth out" the mechanical energy delivered over the repulsion part of an operating cycle, but they do not add any net energy.

Other more cost-effective methods could be used to smooth out the mechanical energy delivered. The simplest method would be just to add a flywheel.

Of course, the more modelling that is done, the more secure will be the conclusion drawn from it. Ideally more modelling should be done for longer excitation durations, and for stator magnets generally closer overall to the moving magnets. However, this modelling would take more time than I can currently spare. (So it becomes one more item for my ever-increasing "to do" list!)

I'll look at the modelling of a comparable disc version of the UAER concept next time.