Methinks that CC could produce a short paper about motor specs and enlighten the rest of the unwashed masses about what to look for and what the various specs mean.

But then their "competitors" would know what to do... :) Of course knowing what to do and being able to do it are two different things.

It's actually pretty simple:

The no-load current tells you the approximate magnetic efficiency of the motor. Lower is better.

The steel for laminations comes in many varieties. Most of the cheap motors use either .35mm or .5mm laminations. The thinner laminations are more efficient. The cost for the steel goes up significantly with thinner steel (because it needs a LOT more processing to make thinner steels.)

The other variable in steel is the amount of silicon (sand) that they add to the steel. The silicon increases the electrical resistance of the steel, increasing the magnetic efficiency by lowering electrical losses (you want the steel to be good at conducting magnetism, but poor at conducting electricity.) The higher the silicon content, the more brittle the steel and the longer it takes to process (and therefore, the more expensive it is.)

So, the cheap steels are thick with a low silicon content, and the expensive steels are thin with a high silicon content.

We use .2mm thick, high silicon content steel. Most of our competitor use .35mm or .5mm low silicon content steel. The .2mm high silicon steel is about four to five times more expensive than .35mm high silicon steel, and about ten times more expensive than .5mm low silicon steel.

But the difference is large: A 1415-2400Kv motor from Castle has a no-load current of about 2.4A.

To figure the magnetic losses, you multiply the no-load current by the battery voltage.

So, for example:

Hobbyking motor: 5A * 24V = 120 watts of magnetic loss
Castle 1415-2400Kv motor: 2.4A * 24V = 57.6 watts of magnetic loss

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The second type of loss is resistive loss. This is the loss caused by the current flowing through the copper.

The Hobbyking motor lists a 5.8 milliohm resistance. The Castle 1415-2400kV motor has a resistance of 4.2 milliohms.

The formula for resistive losses is (Current in amps) ^2 * resistance (amps squared times resistance)

So, at 125 Amps (the "rating" from the hobbyking motor) the losses would be:

Hobbyking motor: (125)^2 * .0058 (ohms) = ~90 watts
Castle 1415-2400: (125)^2 * .0042 (ohms) = ~65 watts

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These two types of loss (magnetic and resistive) add up in the motor, and get turned into heat.

So to make a good motor, you need both low resistance (for low copper losses) and low no-load current (for low magnetic losses.)

To compare the two motors:

Losses at 24V battery voltage, 120A current:

HobbyKing motor: 90 watts (resistive) + 120 watts (magnetic) = 210 watts of loss
Castle 1415-2400Kv: 65 watts (resistive) + 58 watts (magnetic) = 123 watts of loss

Because the "loss" watts ALL TURN INTO HEAT, the Castle motor will run much cooler in the same setup -- it's efficiency is much higher.

It all comes down to this: It's expensive to make a good quality motor. And, you get what you pay for.

I'm sure they know what to do, but being willing to do it is another story -- like I said, it's expensive to make a good quality motor. And if you are competing for market on price alone, then quality is the easiest thing to sacrifice. :whip:

Yes, thats true too.

Great info Patrick! I added this to the "technical explanations" sticky...

Great information
 

Thanks Patrick that is some great information. That is the first time someone tried to explain efficiancy losses in a way that makes perfect sense to me. It helps a lot knowing this when considering what motor to buy and who to buy them from. Now I understand why certain motors get so hot on a regular basis and are cosidered to be a bad buy. You should share more stuff like this with us, because it equates to better sales as people truly understand what the differences are. I mean its obvious to some of us who have been at this for a while, but for the newbs who have no idea this is an easy way for them to learn. Thank you Sir, and keep up the good work. GO CC.

Thank you Patrick. I've pondered some of these variables, back when I was experimenting with rewinding outrunner motors. John Rob and I were playing around with some ideas at the time.

I wonder why the thinner laminations work so much better at conducting magnetism? I'm sure it has alot to do with, the core of the lamination isn't what does the work since the magnetism follows surface area. The greater number of laminations in the same amount of space equals more surface area, thus conducting more magnetism overall.

I was glad to see that you chose a comparable kv rating for no load current. Kv does directly affect no load current, correct?

Resistive losses change from one motor wind to the next. I'm sure this is why a 1 or 2 turn motor has less overall resistence.

I know this isn't practical, but for the sake of efficiency, wouldn't a motor wound with silver wire work better than copper?

Overall resistence is also based on how good of a conductor, the wind wire is.

Guys, I have a feeling what Patrick posted here is "in a nutshell". I'm sure there's ALOT more to "the big picture".

Yes very understandable.Thanks Pdel.

I believe it has to do with eddy currents. Smaller laminations means smaller eddy currents. Think of them as "magnetic resistance", and like resistors, more flow (magnetic flux in this case) across that "resistance" creates heat (loss).

Yes, very good info!
Thank you CC!

Jesus! 5amp no load current on an inrunner!?:gasp:

I have a big 80-100 outrunner that does 4amps with load :lol:

Patrick, this isn't exactly right, there is a small amount of power which is lost in the bearings and in the air friction no ? :lol:
The motor is not really at "no load" but "air loaded".
Maybe it's only 0,5 or 1% of the no load power... What's your opinion about aerodynamics and bearings losses ?
(I doubt that a lot power is lost in the bearings anyway, other than that they would be quickly ripped apart...)

No load
 

No load just means that there is nothing attached to the rotor creating drag on the rotation of the shaft. The losses at no load are so miniscule that they really do not matter. The losses that really matter are shown in the comparison between the CC motor and the HK motor of the same size and spec. Those huge differences are what create the heat on a cheaper motor, where the CC motor will remain reasonable temp wise.

Yes, and we all know how Brian feels about the use of fans. LOL

All kidding aside, Castle does make a superior product.

Greatness is often imitated but never duplicated. :yes: