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  #11  
Old 05-10-2012, 04:41 PM
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mizlplix mizlplix is offline
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Default Re: AC induction motor thoughts

Single speed electric propulsion is A worthy ideal.

Tesla does it by ultra high motor RPMs and appropriate gearing.

The reverse can be done also. Low RPMs with high torque and appropriate gearing.

Anytime you can eliminate a component, it is a good thing.

In this case it is the transmission.

(weight, heat, cost, friction). Gone.....

Miz
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  #12  
Old 05-10-2012, 05:55 PM
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Default Re: AC induction motor thoughts

Curtis or Sevcon. Both have CAN communication so you can use multiple controllers. I know with sevcon it takes an additional potentiometer input from the steering wheel to apply torques independently to both right and left wheel. I have not checked this on curtis yet, I have a sevcon for testing.
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  #13  
Old 05-10-2012, 06:44 PM
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Default Re: AC induction motor thoughts

Quote:
Originally Posted by JimDanielson View Post
Curtis or Sevcon. Both have CAN communication so you can use multiple controllers. I know with sevcon it takes an additional potentiometer input from the steering wheel to apply torques independently to both right and left wheel. I have not checked this on curtis yet, I have a sevcon for testing.
based on my direct drive system, you should design your own Vehicle Control Unit that takes into account each wheel speed, like a anti-skid module. you may be able to pick that off the current Canbus of your vehicle.
you also have to adjust for wheel speed when turning, since you don't have the gear box that takes care of that..
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  #14  
Old 05-10-2012, 09:42 PM
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Default Re: AC induction motor thoughts

I am very interested in the details of this project. My original goal was to make a direct drive induction motor and use the maximum number of poles to get a low speed at 60 Hz, and then overclock by 6x (keeping the same V/F ratio), which I thought would produce 6 times the power for the same weight and size.

But, I found that higher number of poles in the same size motor reduces the horsepower while it increases torque. For instance, I have the following motors:

1.0 HP 8 pole 850 RPM 6.2 lb-ft
1.5 HP 4 pole 1725 RPM 4.56 lb-ft
2.0 HP 2 pole 3450 RPM 3.04 lb-ft

I think this is due to the overlap of the windings for the poles. The motor I rewound had a 36 slot stator, and I wound it for the maximum number of poles (12). This means that each slot has two windings, which include phases which are 120 degrees apart, so the combination is at 60 degrees, but the vector magnitude is 1/2. When there are fewer poles, there is less reduction in amplitude because of variable overlap.

It seems that larger motors have a more linear relationship of HP and torque vs RPM, so a 50 HP motor is the same size for 2, 4, 6, or 8 poles. I think this is because they have many more slots and can have a more efficient winding pattern. So, depending on the number of slots in your 12 and 24 pole motors, this phenomenon may come into play. I may not have a full understanding of this, and I may not be explaining it well, but it seems to account for the figures above.

I was unable to measure the torque of my motor, but it seemed lower than I had expected and hoped. It was originally a 1/2 HP 120V single phase PSC motor, with 36 slots, and I rewound it with much heavier magnet wire for 8 VAC three phase and 12 poles, for sync speed of 600 RPM at 60 Hz. I overclocked it to 4x, I think, and verified that it ran about 2400 RPM (and about 32 VAC). I had intended to make an automotive direct-drive motor for the rear axles of a FWD car as a hybrid, but it was not really practical for even 5 HP per wheel. Using 48 VDC, the motor would need wires for 80 amps. It was even more problematic for overclocking a small 1.5 HP nominal rated motor.

I am now only working on a project for a small utility vehicle or tractor, which has a more limited range of speeds and torque than a road vehicle, but I could use a slow speed motor as you are designing. I think it would be best to design it with multiple windings so that it could be connected for 120/240/480 volts. And thus it should be possible to use the 120V connection on a 480 VAC controller to get 4x RPM and HP. So your 24 pole motor might run at 300 RPM on 60 Hz, but 1200 RPM at 240 Hz. Then it could possibly be overclockd beyond that to as much as 600 Hz and 3000 RPM, but keeping voltage at 480 which reduces torque. But you don't really need as much torque at the high end unless you have very high wind resistance or absolutely need to maintain maximum speed fully loaded on steep inclines.

The usual argument against overclocking is eddy current and magnetization losses due to the material and thickness of standard laminations. But if you are designing from scratch with custom laminations, you may be able to get them of higher grade material and much thinner. I look forward to more details and test data on your prototype.
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  #15  
Old 05-10-2012, 10:02 PM
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Default Re: AC induction motor thoughts

Thing is about rewinding motors, it goes back to what peggus said, you can't just rewind a 2 pole motor into a 8 pole motor and make more torque.(well you can to a certain extent anyway but you lose power) For making more torque you actually need a physically bigger motor since you run out of magnetizeable material with a small one.

For example, a factory rated 1 HP 8 pole motor is larger than a factory rated 1 HP 2 pole motor. Simply because to make more torque you do need more iron. Trying to get the same magnetic flux density out of a given size motor as a larger one will only cause it to saturate. (the magnetic fields inside a given piece of iron can only be so strong before the iron won't be magnetic anymore)

That doesn't mean I think that OP's idea won't work though, since he's making custom motors, he can design them with enough magnetizeable material for whatever specifications he wishes.
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  #16  
Old 05-10-2012, 10:16 PM
JimDanielson JimDanielson is offline
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Default Re: AC induction motor thoughts

Hi Paul, it sounds interesting what you are doing. My project is a bit different. I have custom designed the laminations for this motor. The 12 pole machine has 72 slots and the 24 pole machine will have 144 slots. Both machines will have an equal flux density on the slots, and therefore, the diameter of the 24 pole motor is nearly double.

The prototype laminations are laser cut. But I will be blanking the final product on a die.

I will not be running this motor over 300 hz as that is the max on the Curtis/Sevcon. And running it higher would start to significantly increase the loses.

For voltage, this will only have one set off windings. I want to achieve maximum slot fill and it will have a very specific application, so there is no need for each motor to fit to multiple voltages. The exact voltage I am planning to use has not been completely decided, but it will most likely be near 100volts.
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  #17  
Old 05-10-2012, 10:54 PM
somanywelps somanywelps is offline
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Default Re: AC induction motor thoughts

If you're making your own motors, make some beefy ones and take on Remy and co. :P

I see where you're going with this, but it's going to have to compete with AC-50's with a transmission.
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  #18  
Old 05-10-2012, 11:28 PM
Ryan800 Ryan800 is offline
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Default Re: AC induction motor thoughts

200ft-lb isn't enough for 2wd - 400ft-lb total to the wheels will just barely pull a geo metro up a slight hill. 800 is much better but still on the low end. For reference, most compact cars, such as a Honda Civic make about 1500ft-lb peak in first gear.

I don't think anyone with an AC-50 starts out in 4th gear, which would be about 400ft-lb to the wheels. From what I've read even starting in 3rd is fairly slow.

On the other hand, I spent some time looking for a reduction gear sets appropriate for EVs and they're very hard to find. Diffs just don't have a high enough ratio unless you go with a really big motor. So eliminating it would be great, just make sure you can get a practical amount of torque otherwise there won't be a market. Speaking of which, the market might not be very big even if the motor does work unless you can convince OEMs to buy.
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  #19  
Old 05-11-2012, 12:20 AM
JimDanielson JimDanielson is offline
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Default Re: AC induction motor thoughts

Thanks for the feedback. I guess I had misread the civic gear ratio chart. I will definitely look into increasing the torque for the 24 pole motor (too late to modify anything on the 12 pole, the stator gets in tomorrow). I am now thinking more like 6 or 7 hundred ftlbs per motor.

As for intended market, DIY is really just a short term plan while I work on finishing my other motor and talking to OEMs. I know that DIY will probably not offer a big enough market to survive.

The other motor is an inductively powered synchronous machine. So, it should have advantages of efficiency similar to PM BLDC machines. But a much lower cost because permanent magnets end up being about half the cost in high power bldc motors. Proof of concept prototypes work, but I am far away from being able to manufacture it.
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  #20  
Old 05-11-2012, 01:24 AM
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Default Re: AC induction motor thoughts

What may be needed is a two-speed planetary drive, which can switch from a reduction drive to a straight-through 1:1 drive by means of electrical actuators. It should be possible to get all the torque needed in the reduction mode, and then all the speed needed in the direct mode, with very little mechanical losses. I had thought about using a system like the old Sturmey-Archer 3 speed bicycle hub, which has reduction, direct drive, and overdrive modes. Here are details of the 2-speed drive: http://www.freshpatents.com/-dt20091...0090247346.php

Maybe something like these:
http://www.axiom.org.za/Torque-Hub-P...tion-Guide.pdf

They're probably expensive.

I wonder if a six-phase motor might be the way to go for a high torque application? It was just a thought, but it seems that someone has done research on this and it greatly improves torque density, among other benefits. I just found it and have not read much of it, but if you have not wound the stator yet, this might be something to try:
http://lipo.ece.wisc.edu/2002pubs/2002_12.pdf

Last edited by PStechPaul; 05-11-2012 at 03:17 AM. Reason: Added Six Phase Motor
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