# could a wheel motor be made by plugging a ac motor in place of a cv joint



## aeroscott (Jan 5, 2008)

I was thinking of ac motor /diy controller.


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## rankhornjp (Nov 26, 2007)

I dont see why not as long as the output shaft of the motor matched the hub it was going into. The only issue i see is space, as there is not a lot of it in between the a-frame suspension of most cars i've seen.


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## aran8 (Mar 16, 2008)

something to consider when you use wheel hub motors is that when a vehicle turns, each wheel rotates at a different speed. so the motors need to spin at different speeds also.
Another thing to consider with wheel hub motors is whether they are mounted to the suspension or to the body of the car. If they are on the body of the car, they will ride with the suspension--which absorbs the shocks of potholes--which would be less likely to damage the motor.


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## John (Sep 11, 2007)

I think one of the problems you would strike is a lack of torque if you're using a run of the mill motor. The RPM of a hub motor is very low and doesn't have the advantage of any gearing to amplify the torque and allow higher motor RPM relative to the wheel. I think hub motors tend to be quite special for this reason with lots of pole pairs and be of relatively large diameter. Increasing the number of pole pairs will reduce the RPM for a given frequency and the magnetic force will multiply by the number of pole pairs which coupled with the increased radius the force is generated at will greatly improve the torque developed. To develope reasonable power at the very low RPM you need a prodigious amount of torque as power is a product of torque and RPM.


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## aeroscott (Jan 5, 2008)

I agree, saw the Eliica with its small motors and how fast it is. maybe a 3 phase wound rotor six pole with high voltage 600 or higher,oil cooled.I'm working on a diy 3 phase motor controller and checking out junk motors ,what do you think.


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## Dennis (Feb 25, 2008)

I think you meant to say wound stator. Using a wound rotor type 3-phase motor is terrible for a lot of reasons versus using an induction type 3-phase motor that uses iron core rotor with copper or aluminum shorted conductor bars.

Here is what you want to have:











Here is what you do not want to have:










You can always compensate for speed loss of more poles by using a higher frequency. Like for an 8 or 12 pole design 3-phase motor you could run 1 KHz for the 12 pole and 600 Hertz for the 8 pole motor (of course skin effect becomes an issue with higher frequencies). The torque would be absolutely phenomenal. A motor with that many poles would be perfect for drag racing or direct wheel drive.


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## aeroscott (Jan 5, 2008)

Dennis,I was under the impression that wound rotor gave higher start up torque and better efficiency . if we kick up the hz on start up the motor is seeing a lot of slip as the stator field is moving around the stationary armature making large flux in the armature . As armature starts moving the hz( by the motor controller) is reduced in proportion to the increase in rpm (same slip) is this right? how do you count poles on a induction motor?thanks john stubbe


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## Dennis (Feb 25, 2008)

> Dennis,I was under the impression that wound rotor gave higher start up torque and better efficiency . if we kick up the hz on start up the motor is seeing a lot of slip as the stator field is moving around the stationary armature making large flux in the armature . As armature starts moving the hz is reduced in proportion to the increase in rpm (same slip) is this right? how do you count poles on a induction motor?thanks john stubbe



I gave you a reply, but the mods deleted my post.....I will PM you then..


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## aeroscott (Jan 5, 2008)

Dennis, got the pm ,thanks , the moving flux I was referring to is the stator flux movement that we speed up or slow down with the controller .on start up we use a lot of hz. and high volts to build flux in the armature with a loss efficiency (slip) but great torgue.then as things get moving less slip is needed (more efficient but less torque)that about right. john stubbe


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## Dennis (Feb 25, 2008)

> Dennis, got the pm ,thanks , the moving flux I was referring to is the stator flux movement that we speed up or slow down with the controller .on start up we use a lot of hz. and high volts to build flux in the armature with a loss efficiency (slip) but great torgue.then as things get moving less slip is needed (more efficient but less torque)that about right. john stubbe


Running the stator revolving magnetic field at high speed is not necessary when the rotor is initially at standstill. The simple act of the rotor not moving is more than enough to start out with low frequency to produce torque. Besides if you start out with high frequency, but do not increase the voltage to match the frequency then the torque performance will actually suffer much worse than starting with a lower frequency. At start up assuming one is barely pressing the pedal, it would be good to use about 24 AC RMS volts at 1.04 Hertz for starting the motor's rotor to rotate slowly if you plan to use 480 volts and base frequency of 100 Hertz.

Now if someone floors it, then you do not want the controller to throw at the motor top speed frequency of say 400 Hertz as that too would cause torque performance to suffer since the the voltage level will not be adequate enough for current levels needed for the torque value since the inductive reactance will be high. It's best in this case to run the frequency at 100 Hertz at 480 volts which is the max before current starts to fall. Then if the pedal is still held at full position, continue to increase frequency to 400 hertz. The torque will start to fall, but speed will continue to increase.

Here is a picture to help make things clear:


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## aeroscott (Jan 5, 2008)

Dennis this is great, inductive reactance requires higher voltage , say in your example if we went from 100 hertz @480 volts to 200 hertz @960 volts, 300 hertz @1360 volts. heat would build up vary fast in our induction motor melter.great pt. thanks , john stubbe


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## Dennis (Feb 25, 2008)

> heat would build up vary fast in our induction motor melter.great pt. thanks , john stubbe


In the two cases you mentioned heat would be about the same as 480 volt/100 Hertz. Current level did not change as the voltage increase has compensated for inductive reactance increase from the frequency. Now there is one issue that can cause more heat with higher frequencies is the eddy currents flowing through the iron laminations start to become much larger from the the rate of change in the voltage at higher frequencies, induces a higher voltage level in the iron laminations causing more current to flow in the iron laminations resulting in I^2R losses.


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## aeroscott (Jan 5, 2008)

I would have though inductive heating would start to become an issue . So does the presence of the conductors help to reduce inductive heating as well as staying below the frequency where inductive heating becomes a problem. I just saw a picture of Eliica's motor it was hard to see , but looked like 2 motors with a chain between the motors.made me think of a planetary 2 motor cvt. John Stubbe


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## Dennis (Feb 25, 2008)

Inductive reactance power is not real power, but reactive power. The "power" is not loss as heat for capacitors or inductors. Only power is lost as heat if it is electrical resistance.


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