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Axial flux motors – The new hope

Axial flux motors are considered the ultimate future of electric vehicles and most importantly of electric aviation because they have a high torque-to-weight ratio, which is ideal for aircraft. Companies like Rolls Royce and Magnax have intense research and development in progress on these motors. Interestingly, the first-ever electrical generator, developed by the genius Michael Faraday, was an axial flux type. You can see the axis of rotation is parallel to flux lines. However, it never got its day in the sun back then.

Axial flux motors are considered the ultimate future of electric vehicles and most importantly of electric aviation because they have a high torque to weight ratio which is ideal for aircraft companies like rolls royce and magnex have intense research and development in progress on these motors interestingly the first ever electrical generator developed by the genius

Michael faraday was an axial flux type you can see the axis of rotation is parallel to flux lines however it never got its day in the sun back then based on the orientation of magnetic flux electric machines can be divided into two types first is the radial flux motor which is used in 99 of applications today and second is the axial flux motor in a radial flux motor

The magnetic flux is perpendicular to the axis of rotation in an axial flux motor the magnetic flux lines are parallel to the axis of rotation now let’s see how the axial flux motor actually works the axial motor’s operation is based on the interaction between the permanent magnet and the electromagnets when coils are energized they become electromagnets the most

Common design of axial flux motors have fixed coils and freely rotating permanent magnets here the mortar’s coil arrangement is shown when a direct current supply is given to one of the coils it gets energized and becomes an electromagnet when coil a gets energized in this way the s pole of the rotor is attracted to the stator’s opposite end pole simultaneously

The like poles repel the tangential component of these two forces is shown here the tangential force components make the rotor rotate when the rotor aligns with coil a the net force acting on the permanent magnet becomes zero will the rotor motion stop at this point the rotor’s speed or the inertia effect causes it to travel ahead of the perfect alignment angle

During this time the next coil b gets energized because of the same forces of attraction and repulsion the rotor then reaches near to coil b later coil c gets energized after that in the next half rotation coil a energizes again but this time with the opposite polarity just by changing the supply directions the process constantly repeats and the rotor continues

To rotate however in this operation you can see two coils are always dead these coils drastically reduce the motor’s power output here’s the trick to overcome this problem we simply have to pass the opposite polarity current through the second coil to ease the understanding let’s focus just on the nearest pairs of magnets you can see that at the stator side

Two south poles are together the combined effect of these two poles will be here and based on this we can have an easy force analysis here again a net tangential force is developed the combined effect produces more torque and power output from the rotor interestingly this process also ensures that the motor has a constant torque output the question is how will

You decide which coil to energize to get continuous rotation for this purpose we use a smart electronics controller the sensor determines the rotor’s position and based on this information the controller decides which coil to energize theoretically the rectangular pulses like this produces a constant torque output for the axial motors however in practice when

You suddenly switch on or switch off a phase current ripples will be produced in the other two phases thus the torque quality will be affected the best solution to overcome the issue is to gradually kill or raise the phase current resulting into a pattern like this let’s compare the axial flux motor with the most commonly used motor the radial flux induction

Motor the first differentiating factor is the flux flow path in the machines if you compare the magnetic flux pattern of both the motors you can see that the axial motor’s flux flow path is much more dense and shorter when compared to the induction motor to confirm the flux paths let’s take help from the fea here is an fea result in em works 2d software paired

Alongside solidworks the interaction between rotor and the stator magnetic field generates torque here some field loops rarely interact with the rotor on the other hand in the axial motors the majority of the flux lines lie in the useful work area to generate torque for this reason the axial flux motor gets a higher density of flux thus generating a higher torque

Output from the same size of the motor the second differentiating factor is the larger diameter in axial flux motors the rotor magnets can be located further away from the central rotating axis this larger radius allows the motor to generate more torque made clear by this simple torque equation however if you try to increase the diameter of the induction motors

The rotor’s inertia will increase which can lead to the motor sniffing up huge currents during the start axial flux motors keep this issue under control as the rotors already have less inertia there you have it a 200 year old motor is currently the most powerful and efficient motor of our day these lightweight motors are the best choice for electric airplanes in

Aviation every ounce you save is a boon the ion bird craft developed by rolls-royce uses three such motors by yasa these motors are powered by 6000 lithium ion batteries and a smart electronics controller with an incredible efficiency level promise of more than 96 percent and their compact size axial flux motors can even become a good choice in electric cars we

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Transcribed from video
Axial flux motors – The new hope By Lesics