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Old Mar 22, 2004, 06:34 AM
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Joined Mar 2001
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One hour CD ROM motor construction PART 4!!

I thought I'd take the liberty before the mods step in.

Tony Turley

EDIT ooooops! Links to the first three parts follow:

Part 1
Part 2
Part 3
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Last edited by t-turley; Mar 22, 2004 at 01:02 PM.
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Old Mar 22, 2004, 06:55 AM
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Old Mar 22, 2004, 07:05 AM
Impossible? Hah!
KreAture's Avatar
Oslo Fornebu, Norway
Joined Jun 2003
3,074 Posts
Well, glad you all are awake again. Now fix my problem with the loss of synch!
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Old Mar 22, 2004, 11:21 AM
Semper Fi, Do or Die
kscbob1's Avatar
Titusville, Fla
Joined Jan 2003
1,069 Posts
KreAture

Stop using delta!
For our use, the Wye-wind is more effichient. Aveox has prooven this in actual tests and have even stopped manufacturing the delta-winds. Just read their site.[B]

Curious as to why you said stop using delta? Do you have a URL to the Aveox writeup? When I first approached this thread I asked what would be the best configuration to run a 20mm stator CD-Rom motor in a GWS EDF-50 and was told to use a delta wind with a 12 magnet NN SS NN SS ... configuration. This suggestion was echoed by several thread contributers. My total configuration for my GWS A-10 is:

2 CC Pheonix-10 speed controllers
2 2S1P Kokam 1500 MAH LiPos
1 6 channel GWS receiver.
2 EDF-50 with five blade 2030

A 14T 26 gauge configuration in a delta wind yields me a 6.7 Amp draw.

A 14T 26 gauge configuration in a wye wind yields a 2.6 Amp draw with a lot lower rpm. thrust feels less than the stock brushed motor configuration. I need to set up something th measure actual thrust.

A 10T 26 gauge configuration in a wye wind yields about 3.7 Amps but still a lot less thrust than the delta wind.

I'm trying to get the A-10 to fly with more power giving it the ability to get out of trouble and not have to fly it "on the wing".


Bob
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Old Mar 22, 2004, 11:35 AM
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Chandler, AZ
Joined Mar 2002
1,859 Posts
The only reason I can think of is that their are possibly more efficient ways to accomplish the same thing. Since delta eats more current (about 1.7x as much I think) Why not just decrease the air gap, or increase magnet strength or use more or less winds. Not to mention propping differently, different input voltage, etc.

-Josh
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Old Mar 22, 2004, 12:56 PM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
1,714 Posts
Quote:
Originally posted by kscbob1
Stop using delta!
Stop saying that
I did a lot of thinking after your first post about that and in the following posts I will present the results. Thanks for the Aveox site - from there I got all the information about ESC I was always not sure about.

Are you ready? Here it goes, but SORRY, it will be very long post

RysiuM
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Last edited by rysium; Mar 22, 2004 at 01:02 PM.
Old Mar 22, 2004, 12:57 PM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
1,714 Posts
Star or Delta - that is the question

Hi guys,

I sorry for a long posts, but I want to give you my conclusions I got from the calculations I did. If you don't want to go through all the details, please jump to the conclusion post. But please, read at least the assumptions I made, so we can discuss on the same level.

I did some thinking about star (wye) and delta connection - which one is better, or maybe another way: what the difference in performance is.. It's common opinion, that Star is for torque, Delta is for speed.
Before I present my calculations and conclusions, I want say it at loud: "I'm not and Alpha and Omega". I might be wrong. If so please correct me as soon as possible. But please don't just say: "You are wrong" - show me "where I'm wrong".

Let's start with assumptions.
1. We used optimum wire diameter and number of turns. Optimum, that means we will be running the current through the coil that will go up to the core saturation level. That means the more power we want from the motor, the more current we need to run, that the less number of turns we have to use. That goes up to the limit, where ESC will loose a sync. So let's assume we used number of turns = n for optimum current = Imax.
2. We run the motor under the optimum load, that means no pole is saturated (the current in the single coil in no grater than Imax)
3. ESC is running square wave (not a sin wave) so the motor behaves a little different than industrial alternating current synchronous motor. ESC is switching power between A-B-C in the way that one wire has plus, other has minus and the last one is open (not connected). So at any moment only two wires carry the current and one is neutral. For static calculation (like a snapshot) let's assume the A is plus, B is minus, C is open.

See the picture below for reference.

Continued on the next post....
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Old Mar 22, 2004, 12:58 PM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
1,714 Posts
Star or Delta - that is the question

So let's analyze Star connection:

The total current going through the motor is Imax (green line) going from A to O (center) and then to B.
The power of the motor = U * Imax
The torque from a single pole = I * n (n = some constant factor from number of turns)
The motor's torque is sum of torque from two poles = Imax * n + Imax * n = 2 * Imax * n
Because power = Torque times rpm then:
RPM = (U * Imax ) / (2 * Imax * n) = U / (2 * n)

About the efficiency:
for a single pole copper loss = R * I^2 So for Star configuration:
Copper loss = 2 * R * Imax ^2
Efficiency = 1 - (loss / power), so for Star configuration:
Copper efficiency = 1 - ( 2 * R * Imax^2) / (U * Imax) = 1 - (2 * R * Imax / U)

Now it's time for Delta:

The total current going through the motor is sum of Imax (green line) going from A to B and 1/2 Imax (red line) going from A to C and then to B.
The power of the motor = 1.5 * U * Imax
The motor's torque is sum of torque from all three poles = Imax * n + 1/2* Imax * n + 1/2* Imax * n = 2 * Imax * n
Because power = Torque times rpm then:
RPM = (U * 1.5* Imax ) / (2 * Imax * n) = 1.5*U / (2 * n)

About the efficiency:
Copper loss = R * Imax ^2 + 2 * R * (1/2 * Imax)^2 = 1.5 * R * Imax ^2
Efficiency = 1 - (loss / power), so for Star configuration:
Copper efficiency = 1 - ( 1.5 * R * Imax^2) / (1.5 *U * Imax) = 1 - ( R * Imax / U)

Continued on the next post....
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Old Mar 22, 2004, 01:00 PM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
1,714 Posts
Star or Delta - that is the question

Conclusions.

It is what I expected, and all my experiments confirmed that. Remember that we are trying to get the most of the power from the least of weight and size or torque with the minimum current.

Maximum power:
Delta connection can deliver 50% more power than Star before the stator is saturated.

Maximum torque:
Maximum torque of Star and Delta is the same, but will take 50% more current to run (giving 50% more rpm than Star).


Torque from current:
If you run both motors on the same current (For the same power) Delta will have 50% more rpm than Star, but Star will deliver 50% more torque than Delta.

Loss:
Copper loss is 1.5 times higher in Star than Delta, so the copper efficiency of Delta is much better.

How does it translate for the speed and static thrust? Here it is:

For maximum power from the weight and size use Delta. It can deliver 50% more power than Star, and at maximum power it will deliver the same torque at 50% higher rpm. But it doesn't mean you can use the same prop size. Because the prop will be running higher rpm, you have to use smaller prop, so the thrust will be the same.
For the best torque to power ratio use Star. In example 10 x 4.7 in star will give the same static thrust as 8 x 4.7 in Delta, but Delta will take 1.5 more amps from the battery.

Continued on the next post....
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Old Mar 22, 2004, 01:01 PM
Why not Delta?
rysium's Avatar
Sacramento, CA
Joined Jun 2003
1,714 Posts
Star or Delta - that is the question (The last one)

Going beyond the power limits.

What If we want beyond the efficiency level and oversaturate the stator a little. Let's say in that condition Stator will deliver 50% more magnetic field strength from 2 times more current.
In Star configuration if we run 2 * Imax we will oversaturate both poles so the torque would be 50% more. In Delta connection we will oversaturate one pole only, and other two will go to the saturation limit so the torque would be 75% more.

I still don't know what is the saturation level in our small motors and how we are doing running 5A through 24 turns where the single pole has 1.6mm x 5mm iron core area. But for sure with Delta configuration we are on the safer side than with Star.

RysiuM
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Old Mar 22, 2004, 01:03 PM
Semper Fi, Do or Die
kscbob1's Avatar
Titusville, Fla
Joined Jan 2003
1,069 Posts
I'm already using 5x5x1 N45 magnets with less than a .5mm gap and as far as decreasing or increasing windings there are limits. With these 20mm stators I can get 16 to 18 windings max. After that I get the bell rubbing on exposed windings. On the minimum side. I've gone down to 8T windings in a wye configuration and the relative thrust is still less than the 14T winding delta. This whole experiment is to get a cheap upgrade to the stock EDF-50s with the hopes of the A-10 flying faster and better. All CD-Rom tests have been using the 7.4v 2S1P Kokam 1500s.

I have a stock EDF-50 hooked up to a 9.6v 8 cell NiMH and I compare the output of that ducted fan to that of the CD-Rom modified ducted fan. It's a relative compare by placing my hand behind the unit as I have no measuring device constructed yet.

Bob
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Old Mar 22, 2004, 01:16 PM
Semper Fi, Do or Die
kscbob1's Avatar
Titusville, Fla
Joined Jan 2003
1,069 Posts
Thanks rysium that helps some. I was composing my last post while you were posting. For some reason when I tried to highlight the [B]"Stop using delta"[B] quote from KreAture it didn't work and it looked like I was making that statement. I think I have to manually input the bold commands, we'll see with this post.

Bob
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Old Mar 22, 2004, 01:18 PM
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Put a forward slash in front of the second "B", like this: [/B]

Tony Turley
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Old Mar 22, 2004, 01:25 PM
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USA, NY, Jamestown
Joined Jun 2000
2,908 Posts
removing the magnet ring

rysium- gotta thank you for the advice to use acetone to soften the adhesive for the magnet ring. Worked like a charm. I tried heating the bell with a paint stripping gun but it did not work and was hard to handle when hot. Soaked the bell overnight in acetone and magnet ring came out (in pieces) very easily.
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Old Mar 22, 2004, 01:26 PM
Watts Rule, Glows Drool
dogon1013's Avatar
orlando, FL
Joined Mar 2003
3,197 Posts
Rysium,

I think you are compareing apples with oranges (sorta).

You are compareing a Y wind pulling a total of I-max current to a Delta wind pulling a total of 1.5*I-max current (I-max + 1/2 I-max)
To be totally fair you would have to compare the same winds pulling the same TOTAL CURRENT. anyone can get more torque with more current.

Toby
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