Motor Data - test bench data for several hundred brushless motors. - Page 9 - RC Groups
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May 15, 2009, 09:53 PM
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rgoble's Avatar
Originally Posted by A Useless Geek
Just a note: I am working on the XML Schema for the motor database. It appears that we need one for the props, too, since they are a vital part of testing in the Real World. It isn't a bad idea to have a prop database anyway, considering all the grief we have trying to hook small electrics up to the right prop/adapter/prop saver/shaft/yada yada yada.
At one time I was working on a way to pass the motor test data via XML with some other sites, that way we could all share data. I stopped getting message back from the others I was working with so I left it alone. If there is some interest in having me provide a way to download my database as XML I can provide it.

If you guys think it would be useful I don't think it would take me very long to add a Prop database to the site. Keep in mind that I only have a basic understanding of props (bigger diameter more thrust, etc). So I would need an expert or 2 to confer with on how to go about doing it.

If anybody would like to me to add the prop database, or anything else they think would be helpful then let me know.

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May 16, 2009, 02:07 PM
Registered User

prop database

Dear Sir:
I would appreciate whatever info you can provide on props from 6 to 10" diameter, as I use motors from 14 to 28mm (body) dia.
Years ago, the guys that released the E-meter provided some data on props, but have not added any, even if I have tried to contact them about the issue.
Please let me know if you release some data, and if you can do tests on specific props, such as GWS 6/3, 7/3.5, APC 7/4, 7/3.8, 8/3.8, 9/3.8, 10/3.8, to mention a few.
I think that it could be extremely useful to all of us who fly backyard and park size models.
Jul 13, 2009, 11:38 AM
KG7TTQ - Las Vegas
mark_q's Avatar

Wow, Nice thread and discussion!

Just want to say thanks for the great discussions and the good work on Dr. Kiwis data pages. It will help me spend more money more quickly!

I too have been in the data collection business for some time, I just haven't posted any here. Here is a sample chart I did on a Turnigy Motor over the weekend:

Mark Q
Last edited by mark_q; Jul 22, 2009 at 08:24 PM.
Jul 18, 2009, 04:17 PM
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rgoble's Avatar

I'm glad you liked the site and found it helpful. Please feel free to add your data to the site, if you don't mind sharing your hard work with others.

If you have larger chunk of data let me know and I may be able to automate getting your data imported. Feel free to send me a message here or email at

Jul 18, 2009, 05:16 PM
KG7TTQ - Las Vegas
mark_q's Avatar
Thanks Robert,

I will get some data together and send it on in a day or two. I will have to do some scrubing and in many cases I only saved data markers at 0, 25, 50, 75 and 100%. In other cases I saved only the 100% bits.

I am using the Medusa PowerPro system for my data collection so my sample rates and resolution are a little rough, but I think reliable.

I would like to know how to calculate motor and system efficiancies so if you can, point me to the math (I know math), that too would be greatly appreciated.

In any case, thanks again, your site work will help a lot of folks.

Mark Q
Jul 20, 2009, 11:11 PM
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rgoble's Avatar
This is the best source I've found so far that explains all of the motor constants and some of the equations needed to do some calculations. Unfortunately it doesn't cover the math for estimating the current draw, rpm, and thrust for prop x on motor y, but if anybody does know where to find this information I would be interested in reading it.

Here is the link

Aug 16, 2009, 11:46 PM
Registered User
Originally Posted by Dr Kiwi
I'm through all the entered motors.

For some of the motors I tested early on, I did not obtain no-load data... for those I still have, I will, in due time, measure those parameters. For other motors we may have to enter, in the interim, "manufacturer's data" which is a problem since we have no way of knowing how their figures were obtained - hopefully users may be able to contribute measured numbers for some of these. If you don't see a "Dr Kiwi Io data" entry, then you'll know that the Io and Rm are from some other source.

For some motors I did not measure diameter and length [contributions please!] - we could use manufacturers' figures, but these require caution since some include the entire shaft in the "length" measurement (some only give stator length, and some are pure fiction!)... I have consistently used "body" length (end plate to end plate, or front face to rear of bell), since I think that gives the user a better idea of the physical size of the motor.

For shaft size I have simply entered the nominal sizes (2.0mm, 3.0mm, 3.17mm, 4.0mm, 5.0mm) although every shaft is different (usually smaller by a few hundredths of a mm).

Cheers, Phil

Hi, good job!
It'll be helpful.
Sep 02, 2009, 09:40 PM
Got shenpa?
flieslikeabeagle's Avatar
Originally Posted by rgoble
This is the best source I've found so far that explains all of the motor constants and some of the equations needed to do some calculations.

Unfortunately it doesn't cover the math for estimating the current draw, rpm, and thrust for prop x on motor y, but if anybody does know where to find this information I would be interested in reading it.

Here is the link
AstroBob's book and that write-up by Joachim Bergmeyer were my two introductions to the wonderful world of mathematical motor modelling.

A couple of years ago I worked out the math and wrote a short paper on an improved version of the 3-constant motor model. If anyone is interested, you can find it on my RCG website at . Once there, click on "Research", then on the "Modelling motors better" button. Or, if you prefer, here's a direct link to the paper (pdf):

The improved motor model is a step in the right direction, but still does not directly include temperature effects. So there is still more work to be done to create a good analytic motor model.

As for estimating the current draw, rpm, and thrust for prop x on motor y, that is another and more complex story.

Firstly, there are equations that tell you how much power a given propeller absorbs, and how much thrust it makes, at any given rpm.

We also have equations that tell you how much power a motor puts out at any given rpm (voltage being fixed).

So, to find out what a given prop will do on a given motor, all we have to do is find the rpm at which the power the motor puts out equals the power that particular propeller absorbs. If there is a gearbox involved, then we adjust the two rpms accordingly...i.e., if there is a 3:1 gearbox, we find the motor rpm at which the prop, spinning at 1/3 of that rpm, absorbs the entire power output of the motor.

Simple enough in principle, but when you look at the actual equations, an exact analytical solution is very difficult to find, or even impossible to find depending on what propeller equations you use.

Fortunately, it is very easy to use a computer to find an approximate numerical solution. The general idea is to guess at the current, work out the motor power out and prop power absorbed, and based on the results, adjust the current and try again. If the motor's making too little power, we increase the current; if the motor's making too much power, we decrease it. Sooner or later we'll find a current that makes the two powers essentially equal, and at that point we're done.

This is the approach I took when I wrote PowerCalc ( , Software, PowerCalc ). PowerCalc is Open Source, and anyone who's curious can read through the (Javascript) source code to see what I did. I won't even pretend that it is an exemplary example of how to write code, but it does get the job done.

PowerCalc, by the way, does a reasonably good job of simulating a motor, but at the moment the propeller simulation is still rather rudimentary. That means you can expect better accuracy in the plotted curves than in the actual predicted motor current draw with a specific prop.

It's been on my to-do list for a long time to swap in a better prop model, but my programming time has been spent on WebOCalc instead. PowerCalc is a fairly generic motor sim program, and other programs like Drive Calc ( ) do a better job than PowerCalc does. WebOCalc, on the other hand, appears to be unique, so that's what I keep working on.

Sep 03, 2009, 12:56 PM
She blinded me with science!
FourPlay's Avatar
I was just checking out the specs for an AXI-2826/10 on the Flybrushless web site and noticed that the thrust rating for an APC E 11x7 prop (14.79v, 49.68A) was 82g.
Checked out the same motor on the site and thrust for basically the same conditions is over 2000g. Should the 82g be ounces?
Sep 03, 2009, 01:59 PM
Registered User

Axi 2826 ??

Just looked up AXI 2826 on the site and figures don't make any sense?? 11 x 7 prop on nearly 15 Volts drawing 49 amps and producing about 80 grams of thrust??!! also motor spec is put down as 30 amps max?
Sep 03, 2009, 03:31 PM
Registered User
Dr Kiwi's Avatar
Thankfully that Axi entry was not one of mine! Here is what Motocalc has to say... so, yes, 82oz seems about right. Max. efficiency current is said to be 20-30A, max amps is listed by Axi as 42A/60 seconds.

Motor: Axi 2826/10 Gold; 920rpm/V; 1.7A no-load; 0.042 Ohms.
Battery: Hyperion HP-LVX2500 (20C); 4 cells; 2500mAh @ 3.7V; 0.0067 Ohms/cell.
Speed Control: Castle Creations Phoenix 60; 0.0012 Ohms; High rate.
Drive System: Direct; 11x7 (Pconst=1.17; Tconst=1) direct drive.
Airframe: Anything you want.
Motor Amps = 47.5
Motor Volts = 13.5
Input (W) = 639.8
Loss (W) = 114.3
MGbOut (W) = 525.5
MotGb Ef(%) = 82.1
Shaft Ef(%) = 74.8
Prop RPM = 10557
Thrust (oz) = 81.1
PSpd (mph) = 70.0
Sep 03, 2009, 04:52 PM
KG7TTQ - Las Vegas
mark_q's Avatar

Sorry for the confusion

The AXI 2826/10 was my post and some how the values for thrust dropped into the wrong column. The values in the grams column should be in the ounces column. I'll see if I can get it fixed. Here is a picture of my test data on this unit:

(Also, when I test, I overprop well past "recomended" )
Last edited by mark_q; Sep 03, 2009 at 04:58 PM. Reason: Add-on
Sep 03, 2009, 06:11 PM
KG7TTQ - Las Vegas
mark_q's Avatar

Sorry for the confusion 2

I was not able to fix the charts so I added comments to the bottom of the page. Hopefully this will be corrected soon.

Sep 09, 2009, 07:41 PM
Registered User
Hi all, great chart, for a newbie it proved my little profile edge is way over propped for my set up.
I have a brushless outrunner that came in a thing called a hydrofoam a couple of years ago. Does anyone know what it might be so I can get specs on it? It had a 3s 1200ma battery and an unknown esc. I currently have it in a fun foamie turning a 8 x 6 and it is amazing. (prop that came with it was a little 6" job.)
Thanks for the site and any help!
Sep 09, 2009, 09:16 PM
Registered User
rgoble's Avatar

Sorry for the confusion I messed up when I input your motors and left it as grams instead of ounces. I went back and fixed the numbers so it should be correct now.


You can try posting a picture of the motor in the Power systems forum and I'm sure somebody can help you identify it. I never had a hydrofoam so I'm not familiar with it. Sorry I couldn't be of more help on it.


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