# induction rotor shape, size in relation to efficiency and output



## NintendoKD (Apr 29, 2012)

how about this, no matter the three pole orientation, there is an inherent imbalance, between poles, lets say, like a clock, a pole+ @12, another [email protected], another pole- @4, another pole- @ 6, another pole - @8, another pole+ @10. That accounts for all 3 poles, both magnetic polarizations, and no matter what, one will have a weaker effect on the section of rotor, than the other, leading to an imbalance of pull push, however, for each pole this is reversed, where one half cycle, will have a stronger pos orientation, and the other half will have a more neg orientation, and this is repeated. It allows for easier starting, and smoother rotation. add a slight twist to this design, along the length of the rotor and now it moves air very effectively, as well as cools the coils and rotor. Or..... maybe I don't know what I'm talking about here. Anyways, just spitballin here.


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## NintendoKD (Apr 29, 2012)

I believe that this will also assist in reducing magnetic polarization at high speed, where the rotor retains a charge. The off balancing effect means that the poles are spaced between hills and valleys, so that at the center a magnetic flux turns with the rotor assisting the spinning action. so as the rotor turns, so does the induced magnetic field, from peak to valley. I may be wrong here, but I think that the magnetic field frequency is directly related to the flux density. For a visual demonstration, use a weak neo magnet, n30 or so, glue it to a penny, and stick it to the electrode of a sparkplug. now use a flyback of other high voltage producing device, and watch as the sparks create a rotating electromagnetic field from the tip to the ground "threads" use a stronger magnet to get a faster rotation. What does it mean? I think that when flux density changes, and fluctuates, depending on half cycle of the rotor, as peak flux density is reached, regardless of frequency the rotor will spin in relation to flux density "to a point", similar to a fluid filled clutch fan. or maybe that is difficult to understand. sometimes I have extreme difficulty in putting the images in my mind into words.


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## mizlplix (May 1, 2011)

*Rotor design thoughts*

With rotors (as in other things), Size is foremost in attributes........

A large diameter AC motor is more efficient, current wise, than a smaller motor.

The magnetic force in the stator is relatively the same in both sizes, it is just applied with more leverage in the larger diameter motor (more torque per the same current draw).

This torque increase is somewhat diminished by an attendant motor weight increase. 

There is a lot of experimentation going on presently in the world EV community with making custom AC motors. It is an effort to fill in the apparent gap in factory-supplied motors.

This development is somewhat hampered by the lack of a good high current/voltage controller-inverter unit.

There are some European built AC controllers that trump the Curtis 1238R but are way more expensive. 

The apparent non-success of a home built controller is discouraging also.

MY THEORY: The 1238R controller is capable of running a larger AC motor with good results because of the above mentioned larger rotor efficiency over a smaller motor.

Several of these combos are currently running around to make this seem plausible, of coarse it too has it's limits. (I am talking a motor 10%-20%
larger than the AC50).

The RMS voltage of the AC50 is in the 76 volt range (with a 96 volt pack).

Most 3 phase AC motors here in the USA are built for 240-480 volts. If you want to use one of these as-wound, you connect it 240VAC and series up your cells to match this in an RMS rating.(about 75 cells) Which is way over the 1238R's capability.

You need to bring the motor requirement down to the Curtis controller's range. About 76 volts RMS, which means rewinding the motor.

So, a rough rule of thumb is to half the stator winding count and double the size of the wire gauge to cut required motor voltage by half. (240 down to 120 volts) and get it into the 1238R's range.

At the same time, you can up the motor's insulation class, cheaply.

The one caveat is that not every AC induction motor will support this rewinding due to the lack of sufficient "Back Iron" in the stator.

I did some quick and dirty cost estimates and a custom motor of this type can be made for $1,000 or so. *motor cost-salvage $200 and rewinding $400 and some custom machining)

You can even convert your motor to a "C" face, turn the shaft down to a common 1-1/8" O.D.(so all current adapters/couplers will still fit), install a thermister and add an encoder- so it will communicate with your controller.

I am watching/reading and planning a "next generation" motor for my car already>

Miz


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## aeroscott (Jan 5, 2008)

switched or variable reluctance motors use a rotor that is smiler to what you are saying .very good low end torque ,less heating (inductive) of the rotor . LTI uses these to power there high powered wheel drive earth moving machines .very hard to figure out control , as they do not fit motor theory . LTI said they could tell me but would have to kill me. LOL


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## Zak650 (Sep 20, 2008)

aeroscott said:


> switched or variable reluctance motors use a rotor that is smiler to what you are saying .very good low end torque ,less heating (inductive) of the rotor . LTI uses these to power there high powered wheel drive earth moving machines .very hard to figure out control , as they do not fit motor theory . LTI said they could tell me but would have to kill me. LOL


Hi,
I have ServoII drive system on my retrofit Bridgeport mill that uses variable reluctance servo motors. I have found these motors to be amazing, great low speed torque and control, never get hot. I don't know exactly how they work but I am totally impressed


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## NintendoKD (Apr 29, 2012)

I had no idea that this design was already in use, they do not get hot, because less back emf is generated. all useable current is used in every half phase, and less is wasted in heat, because of current "bouncing back" into the coils, this translates in to more electromotive force. Control should be simple, same as before, just match the poles with the amount of input necessary, one half will require less per coil that the other half phase. ex. 0-480 would require more input "depending on if a valley or hill is lined up to the pole" than during the 0to -480v curve. the rotor also doubles as a fan, the air is drawn inward because of the rotating screw shape, and despite the effect of centrifugal force, air draws inward to the aerodynamic planes of the screw, also polarizing the air, to add passive movement due to induced electromagnetic currents. air turns the rotor, instead of working as a load, and in reverse of what you would think works for the rotor and assists in efficiency. It also has the added effect of cooling, and drawing away any waste heat that is produced, removing drag from a conventional fan.


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## NintendoKD (Apr 29, 2012)

This type of design would benefit greatly from enhanced voltage controllers. I surmise, that controllers capable of much higher voltages would see significant gains in power and efficiency from a higher voltage controller.


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## NintendoKD (Apr 29, 2012)

Something else interesting about this design, running the motor, without magnets, will induce a static charge in the rotor, therefore producing a weak magnetic field as it rotates, thereby putting electromagnetic energy into the coils in the stator, so it can, in fact, work as a generator by itself, no magnets necessary.


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## mizlplix (May 1, 2011)

My first impression of a "twisted" rotor design was that it might reduce cogging some, but who really knows.

The idea of pumping air through the core of the motor is interesting, but the space is small.

The increase in air gap will affect the torque output. Not for the good I think.

Miz


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## NintendoKD (Apr 29, 2012)

I think, that as voltage rises, that distance will matter much less for torque, than you might think. This is of course if you are using high voltage to drive the poles, as opposed to high current. The difference will be like using a bucket of water to turn a wheel "high current" or like putting your thumb over the hose "high voltage" with higher voltage relative distance to the stream will not effect the performance "to a point" I think


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