


Quote:
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. Robert 




Windsor, Canada, near Detroit
Joined Jul 2007
7,538 Posts

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 Emeter 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. Regards, Phil 



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 



Mark,
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 robert@flybrushless.com Thanks, Robert 



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 
Latest blog entry: XUAV Mini Talon #2





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 http://www.rcgroups.com/forums/showthread.php?t=185271 Robert 


Joined Aug 2009
7 Posts

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Hi, good job! It'll be helpful. 




Quote:
A couple of years ago I worked out the math and wrote a short paper on an improved version of the 3constant motor model. If anyone is interested, you can find it on my RCG website at http://flbeagle.rchomepage.com . 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): http://flbeagle.rchomepage.com/resea...per_ver_02.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 (http://flbeagle.rchomepage.com , 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 todo 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 ( http://www.drivecalc.de/ ) do a better job than PowerCalc does. WebOCalc, on the other hand, appears to be unique, so that's what I keep working on. Flieslikeabeagle 




I was just checking out the specs for an AXI2826/10 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 flyingmodels.org site and thrust for basically the same conditions is over 2000g. Should the 82g be ounces? 



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?




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 2030A, max amps is listed by Axi as 42A/60 seconds.
Motor: Axi 2826/10 Gold; 920rpm/V; 1.7A noload; 0.042 Ohms. Battery: Hyperion HPLVX2500 (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 



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" ) 



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.
Mark 
Latest blog entry: XUAV Mini Talon #2




Australia
Joined Aug 2009
238 Posts

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! 



Mark,
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. Dngo, 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. Robert 
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