HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Dec 10, 2012, 12:29 PM
Jack
USA, ME, Ellsworth
Joined May 2008
17,111 Posts
Quote:
Originally Posted by catspaw View Post
Well now, thinking about it, why would there be a 8K rpm limit if it's rated for 6S? Doesn't make sense.
I assumed that was a limit for the propellor, not the motor. The normal estimate of the motor's no load RPM would be the Kv x battery voltage. So with a charged and rested 5S at 21V the no load RPM would be about 21 x 580 or 12,180 RPM.

And it is typical for motor that are running at their maximum continuous power (the current draw where the temperature is stable and they do not overheat) to be at about 75% of their no load RPM. So that would be 12,180 x .75 or 9,135 RPM.

And it is up to the user to not choose a prop that cannot handle the 9,135 RPM. As the battery is used up and the voltage falls, the RPM will wane a little so starting with a motor that can attain a little more than the 12,180 RPM no load RPM is OK as long as you keep an eye on the details.

Here is a summary of published or learned in use RPM limits that are considered sensible by most. I or no one else guarantees any of props to the following limits but is it reasonable to be able to expect them not to fail at these limits:

Prop RPM Limits Summary:

Aero-Naut - See Propeller info page for links to each type and more detailed info) - http://www.aero-naut.de/en/products/...es/propellers/

CAMcarbon folding props - 6,000 to 16,000 depending on size
classicPROP folding props - 8,500 to 16,000 depending on size
CAMcarbon Power-Prop (fixed) - no published limit
CAMcarbon Light-Prop (fixed) - no published limit
Reverse Rotation Blades (fixed) - 16,000
Mini-Prop series (folding prop series w/ integrated mounting) - no published limit
Slow-Flyer props (fixed, plastic) - no published limit

APC Glow/Speed 400 Electric = 190,000 RPM / Diameter (inches)
APC Thin/Folding Electric = 145,000 RPM / Diameter (inches)
APC Slow Fly = 65,000 RPM / Diameter (inches)
APC Racing (8.75 N,W,8.8,Series 40 Pylon) = 225,000 RPM / Diameter (inches)

Great Planes Slow Fly = 65,000 RPM / Diameter (inches)

Graupner Slow Fly = About 88,000 RPM / Diameter (inches) (actual limits vary with size)

GWS Reduction Series = 45,000 RPM / Diameter (inches)
GWS 6" to 10" Direct Drive (HD or DD) Series = 80,000-100,000 RPM / Diameter (inches)
GWS 5" or smaller Direct Drive Series = much tested/used at 15,000-20,000, max safe RPM 80,000 RPM / Diameter (inches) or more

Master Airscrew (Windsor) = 165,000 RPM / Diameter (inches) (some consider this to be a little too high, but that is what the maker says is OK)

XYH (EMP-Neodym) Electric Scimitar (ES) = 205,000 RPM / Diameter (inches)

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Sign up now
to remove ads between posts
Old Dec 10, 2012, 08:04 PM
Registered User
manuel v's Avatar
Mexico, BC, Mexicali
Joined Aug 2004
5,324 Posts
I assumed that was a limit for the propellor, not the motor. The normal estimate of the motor's no load RPM would be the Kv x battery voltage. So with a charged and rested 5S at 21V the no load RPM would be about 21 x 580 or 12,180 RPM.

And it is typical for motor that are running at their maximum continuous power (the current draw where the temperature is stable and they do not overheat) to be at about 75% of their no load RPM. So that would be 12,180 x .75 or 9,135 RPM.

Jack.
I wrote this once, to clarify the rpm of a motor, can be equal to one propeller, but the percentages will be different to the EDF.)

72-76% NLS
70-73% efficiency.


To calculate your fan rpm’s:

Take the voltaje of the battery and multiply the Kv of the motor = fan RPM.
11.1V x 3600= 39,960.

A reality more about:

3 cell lipo, have a voltage of approximately 12.6Volts.
The new batteries 30 and 20 C 40C sustain discharge voltage 11V average. (Use the voltage rating is very rough and correct)

A very important factor that is missing from this equation is the NLS% (percentage of No Load Speed.)
In EDF is very important that the engine is not charged too much for this factor does not drop below 80%. Possibly in some applications where the motor is much torture can be used up to 75%. But it is highly not recommended.

Also consider the actual motor Kv can vary the die post for the manufacturer.


Take the voltaje of the battery and multiply the Kv of the motor and multiply for %NLS factor = fan RPM.
11.1V x 3600 x 80%= 31,968 RPM.


To Calculate what Kv motor you need:
Take the desired fan RPM, divide it by the battery voltaje = Need ed motor Kv.

45,000 / 14.8 = 3,040 kv.

As in the example above to factor% NLS,

45,000/14.8=3040*100/80= 3800 Kv.

To Calculate what battery you need: Take desired fan RPM , divide by the motor Kv, = Battery size.
45,000 / 3600=12.5Volts (3cell)


Once you factor% but the NLS was ignored the formula would be:
45,000 / (3600 * 80%) = 15.62V (can not say they are 4 cell)
It is impossible to change the voltages of the Lipo. Will always be multiples of 3.7.
So we have to recalculate to 4 or 5 cells. To calculate the Kv busy, since it is the only viable option we have, change the engine to the appropriate one.

45000/14.8 = 3040 * 100/80 = 3800Kv.
Using 4 cells occupy a Kv of 3800.

45000/18.5 = 2432 * / 80 = 3040Kv.

Using 5 cells occupy a Kv of 3040.
After all this formula is the same as the previous one and is virtually unnecessary.


For convenience we use an Excel for these calculations.

your example.

18.3V*580=10614
10614*75%= 7960 rpm.
manuel v is offline Find More Posts by manuel v
Reply With Quote
Old Dec 10, 2012, 08:52 PM
Shut up and fly
papabatman's Avatar
United States, CO, Firestone
Joined Jun 2008
10,739 Posts
wow my head hurts now
papabatman is offline Find More Posts by papabatman
RCG Plus Member
Latest blog entry: fun with a parkzone
Reply With Quote
Old Dec 10, 2012, 08:54 PM
Shut up and fly
papabatman's Avatar
United States, CO, Firestone
Joined Jun 2008
10,739 Posts
so if it has 14 magnics how many poles is that?
papabatman is offline Find More Posts by papabatman
RCG Plus Member
Latest blog entry: fun with a parkzone
Reply With Quote
Old Dec 10, 2012, 10:58 PM
Jack
USA, ME, Ellsworth
Joined May 2008
17,111 Posts
Quote:
Originally Posted by papabatman View Post
so if it has 14 magnics how many poles is that?
14 magnets = 14 poles

A commonly used designator like 12N14P means 12 arms (N = Nuten = groove in German) and 14 poles (P = poles or magnets or magnetpoles).

I'm going to say this just because it can be a point of confusion to some. Even though a magnet has a North pole and a South pole, a one piece magnet with those two poles on it is considered to be one pole on a motor.

Jack
jackerbes is offline Find More Posts by jackerbes
Reply With Quote
Old Dec 10, 2012, 11:17 PM
Shut up and fly
papabatman's Avatar
United States, CO, Firestone
Joined Jun 2008
10,739 Posts
thank you. that is what i thought, keep forgetting
papabatman is offline Find More Posts by papabatman
RCG Plus Member
Latest blog entry: fun with a parkzone
Reply With Quote
Old Dec 11, 2012, 01:25 AM
Certifiable
Dacono Air's Avatar
USA, CO, Dacono
Joined Aug 2009
1,868 Posts
Notam

2 steps back!...so i cracked open the 5050 this evening to give those glued magnets a good look, HK did a good job on this one there was a liberal amount of epoxy all around the magnets with good pooling in the valleys between.
Needless to say I found a couple of lightly glued spots so i thought I'd fill them in with Some JB Weld...well I knew i was in trouble after mixing the weld as the glue literaly jumped from the end of the toothpick to a magnet!.
I knew JB Weld had steel in the mix but i didn't expect it had that much, long story short - after fighting the glue for over an hour to stay in place without creeping up the sides and all over the magnets I gave up and wiped it all back out...what a mess.
2nd step back was that I may have trashed the nose end bearing in the process of pressing out the shaft, it was a very tight press so I most likely put to much force on it and it feels like it spinning with gravel for bearings...Boca's got more money headed there way
I don't know if steel laden epoxy would dissrupted the magnetic feild between the magnets so I'm gonna give JB Weld the Boot on this type of application.
Dacono Air is offline Find More Posts by Dacono Air
Reply With Quote
Old Dec 11, 2012, 11:03 PM
Shut up and fly
papabatman's Avatar
United States, CO, Firestone
Joined Jun 2008
10,739 Posts
i found this confessed on the pole thing

This motor is listed as an SK5055-580 in Leader Hobby's catalog, but is physically labeled N5055 580. There is also a "red" version of this EMP motor listed in the catalog a N5055 580.

This particular motor was listed at $41.71, and normally discounted to about $34, but was purchased in a sale for $17.

Catalog Data:
kV............. 580
Power...... 1580
Wire winds... 5
Resistance.. 16 mohm
Idle Current 1.5 amps

Shaft Diameter.. 8mm
Weight................332 gm

My motor :

12 poles and 14 magnetsStator size: 40mm dia. x 25 mm length
Bearings 17 mm OD, 8mm ID

Measured DC resistance .014 ohm

(I'll add more as I find it out)
papabatman is offline Find More Posts by papabatman
RCG Plus Member
Latest blog entry: fun with a parkzone
Reply With Quote
Old Dec 12, 2012, 09:03 AM
Registered User
Joined Nov 2012
33 Posts
Although all the tech talk is useful, sometimes you just have fly it to see if it performs how you like to fly. Otherwise you just bogged down with numbers and text!

Not saying don't get the basics in place so you know it will have enough power etc but get it up there and then take a view!

I'm very pleased with mine so far, and on inspection after flight it's all rock solid.
theheed is offline Find More Posts by theheed
Reply With Quote
Old Dec 12, 2012, 07:42 PM
Rangers Lead the Way
Joined Mar 2010
2,162 Posts
Quote:
Originally Posted by Dacono Air View Post
2 steps back!...so i cracked open the 5050 this evening to give those glued magnets a good look, HK did a good job on this one there was a liberal amount of epoxy all around the magnets with good pooling in the valleys between.
Needless to say I found a couple of lightly glued spots so i thought I'd fill them in with Some JB Weld...well I knew i was in trouble after mixing the weld as the glue literaly jumped from the end of the toothpick to a magnet!.
I knew JB Weld had steel in the mix but i didn't expect it had that much, long story short - after fighting the glue for over an hour to stay in place without creeping up the sides and all over the magnets I gave up and wiped it all back out...what a mess.
2nd step back was that I may have trashed the nose end bearing in the process of pressing out the shaft, it was a very tight press so I most likely put to much force on it and it feels like it spinning with gravel for bearings...Boca's got more money headed there way
I don't know if steel laden epoxy would dissrupted the magnetic feild between the magnets so I'm gonna give JB Weld the Boot on this type of application.
Ah jeez I'm sorry about the mess. I personally use CA but mentioned JB as others have used it or claim to have used it. Of course it would go towards the magnets! Duh.

Regarding the grainy feel, are you sure that this is not because the bell is too close to the stator frame, or you have a glue blob interfering with the rotation? The tolerances are much closer on these motors than others I have seen. I find it hard to believe bearings would be damaged. I have a plane that crashed straight in from 300' up and impacted on the spinner. The alu spinner was shattered, so was the prop, and so was the rest of the plane. The Power 60 motor runs as if nothing ever happened. Maybe a bit mor bearing noise, but that's it.
TTRotary is offline Find More Posts by TTRotary
Reply With Quote
Old Dec 12, 2012, 08:18 PM
Certifiable
Dacono Air's Avatar
USA, CO, Dacono
Joined Aug 2009
1,868 Posts
Na...the bearings shot..I have it out and it has "Catchy" places in it's rotation, the rear bearing is smooth as glass.
Don't blame yourself for the JB mess...I have also seen it mentioned numerous places as well but hey i'll try anything once!
Time for me to mix up some "special" epoxy for the job
Dacono Air is offline Find More Posts by Dacono Air
Reply With Quote
Old Dec 12, 2012, 08:27 PM
Certifiable
Dacono Air's Avatar
USA, CO, Dacono
Joined Aug 2009
1,868 Posts
PS: As far as JB weld goes...Its still great stuff and from this last little snafu I have also learned a new neat trick to keep under my cap.
That neat trick is: now I know how i could possibly Draw JB Weld into places using a magnet!
Dacono Air is offline Find More Posts by Dacono Air
Reply With Quote
Old Dec 13, 2012, 02:22 PM
Registered User
Doug Bartley's Avatar
Canada, ON, Owen Sound
Joined Oct 2008
2,838 Posts
Use the JB weld specifically designed for ALUMINUM. Rather than steel or iron particles, it will have aluminum powder in the mix, hence no magnetism. Doug B
Doug Bartley is offline Find More Posts by Doug Bartley
Reply With Quote
Old Dec 13, 2012, 09:23 PM
Certifiable
Dacono Air's Avatar
USA, CO, Dacono
Joined Aug 2009
1,868 Posts
You Know I thought they had some Aluminum JB weld, But I'd be darned if I can find it!
Dacono Air is offline Find More Posts by Dacono Air
Reply With Quote
Old Dec 15, 2012, 12:23 AM
Registered User
United States, FL, Melbourne
Joined Apr 2009
431 Posts
i just got this one in the mail today along with a watt meter. was hoping to use my 5 cells with a 16x10 prop. maybe ill have to use 4 cell instead. im going to see how a bench test works.
paulatgis is offline Find More Posts by paulatgis
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion 4258 turnigy ntm motor on sebart angel 50 theheed Power Systems 0 Nov 06, 2012 09:54 AM
Discussion Turnigy Park480 vs NTM Prop Drive Series 35-30 NetCode Power Systems 10 May 17, 2012 06:40 PM
For Sale Turnigy NTM 42-58 500kv LICobra Aircraft - Electric - Power Systems (FS/W) 1 Feb 10, 2012 04:55 PM
Sold Turnigy NTM Prop Drive Series 35-30A 1400kv scottc39 Aircraft - Electric - Power Systems (FS/W) 6 Jan 02, 2012 08:12 AM
Question How similar are Turnigy, SK3, and NTM motors? wopachop Power Systems 5 Nov 28, 2011 01:33 PM