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Old Dec 17, 2008, 05:39 PM
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Robert, thanks for starting your website, and for contacting me via PM. I've sent you a reply, and look forward to working out the details with you.

To the question of calculating and displaying efficiency: if you have the three motor constants, you can calculate a very good approximation to the efficiency at any given current and voltage. If you have the fourth motor constant (or, equivalently, the idle current at two different voltages) then you can calculate an even better approximation to the efficiency. If you can estimate the change in Rm with heating (current), you get even a little closer.

Fourdan's Scorpion Calc includes both the change in Io with voltage, and the change in Rm with current.

My Powercalc is still in beta, and the propeller simulation is not very good yet. However the efficiency curves seem to be pretty good, and do include the effect of Io variation with voltage. You can also select an approximate level of motor heating and the software estimates the Rm change due to this.

My point is that a given motor connected to a given ESC and battery has one and only one efficiency curve. It is not necessary to calculate the efficiency separately for every propeller - once you know what current a specific prop draws, all you have to do is look up the motor efficiency at that same current and voltage.

So: I think it would be nice to have an efficiency curve for each motor available along with its other data. But I don't think it's necessary to tabulate the efficiency for every single prop and voltage point. That's a lot more work, and somewhat redundant.

-Flieslikeabeagle
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Old Dec 17, 2008, 05:53 PM
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If it helps, I typically measure no-load Io and rpm at three different voltages (I've only entered those figures for ~10v in Roberts website).
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Old Dec 17, 2008, 06:22 PM
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I apologize, I am aware that my question does not fit this thread very well. I am excited about the information found here. I flew years ago when glow was the way to go. I want to move to electric I have several planes. Does anyone have any suggestions on how I could calculate what i need to do for the planes that I now have. Like an old Butterfly... I've thought about prop size and RPM information to help me make a judgment. I'm just beginning to form this plan so anyone that may have an idea that could speed up the transition would be appreciated...
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Old Dec 17, 2008, 06:48 PM
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Quote:
Originally Posted by flieslikeabeagle
...
Fourdan's Scorpion Calc includes both the change in Io with voltage, and the change in Rm with current.
...
-Flieslikeabeagle
Hi
I try to do my best to take into account
a) Iron losses versus rpm (easy) better than Io versus voltage
b) Rm increase function of temperature (current + running time)
c) ESC losses (difficult)
But all is not perfect
Same politics for Scorpion Calc, Dualsky Calc, MotrolFly Calc ...
I stay open for any Brand Calc
Regards
Louis
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Old Dec 18, 2008, 12:14 AM
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I noticed no NEU specs - is that because the info is "still under construction" or is there another reason ?
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Old Dec 18, 2008, 07:43 AM
homo ludens modellisticus
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Quote:
Originally Posted by oneofsharp
I apologize, I am aware that my question does not fit this thread very well. ...
Welcome. Better start a new thread, e.g. in the Glow to Electric Conversions subforum. This test bench data thread is rather specialized.

Some info for the e-beginner
www.ezonemag.com
-> FAQ

http://www.wattflyer.com/forums/forumdisplay.php?f=3
-> [sticky] Magic numbers for modelers...
and
-> [sticky] Everything You Wanted To Know About Electric Powered Flight

Vriendelijke groeten Ron
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Old Dec 18, 2008, 09:08 AM
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Oneofsharp,

In the future I hope that FlyBrushless.com can help answer your question. However so far the site only has motor data from Dr Kiwi entered and I don't believe any of them are big enough for what you need.
For now Ron is correct and your best chance to get an answer is in the Glow to Electric sub forum.
Quote:
Originally Posted by oneofsharp
I apologize, I am aware that my question does not fit this thread very well. I am excited about the information found here. I flew years ago when glow was the way to go. I want to move to electric I have several planes. Does anyone have any suggestions on how I could calculate what i need to do for the planes that I now have. Like an old Butterfly... I've thought about prop size and RPM information to help me make a judgment. I'm just beginning to form this plan so anyone that may have an idea that could speed up the transition would be appreciated...
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Old Dec 18, 2008, 09:20 AM
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War Machine,

So far Dr Kiwi and MicroDan are the only ones who have added test data to the site. I don't think either of them have tested any NEU motors. Anyone who signs up on the site can submit motors and test data. So as soon as someone comes along and fills in that gap they should show up.

Robert
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I noticed no NEU specs - is that because the info is "still under construction" or is there another reason ?
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Old Dec 18, 2008, 09:40 AM
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1. The site is currently down, hopefully it will be back up and running this evening. I suppose this is the price you pay for free web hosting. I will start looking for a new host today.

2. I found the formulas for calculating efficiency (Pout/PIN), but I wasn't sure if this was something worth display for each prop/voltage combo or not. I could work on generating a graph to show the curve based on the available test data. If nothing else I could find the peak efficiency from the test data and display that at the top of the page.

Thanks for the ideas guys,
Robert
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Old Dec 18, 2008, 09:52 AM
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Yes, I suppose one could have another column with Pout/Pin for every motor/prop/voltage, but anyone who really wants to see this Pout/Pin efficiency for a specific combo can always plug the numbers into www.badcock.net or Drive Calc...

I think this would be "gilding the lily".
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Old Dec 18, 2008, 01:57 PM
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FWIW, my suggestion is to design the new site to do only one task, but to do that one task very well. When one tries to do a dozen things at once, what usually happens is the quality of each one drops.

Perhaps the thing to do is to spell out exactly what the goal of the new site (flybrushless.com) is. So far, the site is a database of motor measurements, so presumably the purpose is to make all this data available to any interested party from one single location.

Are there other goals for the website other than being a database of measured values? As Robert has suggested, adding some sort of search capability is one way to make any database more valuable. I'd suggest having the ability to search for motors within a certain Kv range and within a certain range of motor currents. So for example, it would be nice to be able to search for all motors with Kv between 700 and 800 rpm/V and able to handle 35 amps burst current draw. (Yes, burst current is not very well specified, but it's all we've got!)

Once the search returned (hopefully) several motors, it would be nice to have ways to narrow the pack. Weight is an obvious one (and automatically takes care of efficiency - a lightweight motor that can handle lots of power HAS to be efficient, otherwise it would overheat and be damaged). Price is another obvious one, but since that is a moving target, it would be an onerous task to keep the database up to date.

Finally, it's nice to know about other websites that have attempted to do similar things in the past. I know of at least two: First, "the great motor test" is a database of motor measurements, now many years old and gradually becoming obsolete. Here's a link to this database at flyingmodels.org: http://www.flyingmodels.org/motortest/index_e.htm

Second, Peak Eff: http://www.peakeff.com/ (The creator of this site is an RCG member, username "mattay" if I remember right. Edit: sorry, it's actually "matttay" with three t's.)

PeakEff also includes several tools for searching and visualizing database content. One thing to investigate might be whether Robert and Matttay might perhaps join forces and both jointly improve one website, rather than having twin sites that both attempt to do somewhat the same thing?

-Flieslikeabeagle
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Last edited by flieslikeabeagle; Dec 18, 2008 at 02:24 PM. Reason: correct "mattay" to "matttay".
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Old Dec 18, 2008, 02:11 PM
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You have some good points about the site trying to do too much. There are quite a few items I want to get done left on my list. Improving the search is one of them.

As for the other sites thanks for pointing them out to me. I knew about "the great motor test" and tried emailing the guy who runs the site about including those motors in my site. I still have not heard back from him yet.

I didn't know about Peak Eff, I will take a look at it and try and talk to mattay about it.

Robert
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Old Dec 18, 2008, 02:18 PM
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Robert, I misremembered the username "mattay". Turns out it has one more "t", it's actually "matttay". And here's a post in which he (afaik) first introduced Peak Eff:
http://www.rcgroups.com/forums/showthread.php?t=572159

-Flieslikeabeagle
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Old Dec 18, 2008, 02:22 PM
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Quote:
Originally Posted by oneofsharp
I want to move to electric I have several planes. Does anyone have any suggestions on how I could calculate what i need to do for the planes that I now have.
Firstly, welcome to the world of quiet and clean power. Second, I do have suggestions - I wrote a software tool (WebOCalc) to help with exactly the task you've undertaken. Please post to the current WebOCalc thread (and shoot me a PM if I don't show up to help you right away!) and I'll do my best to help you pick power systems for your models. You might also find the answers you want simply by reading through the thread and then heading over to my site to use WebOCalc.

Link to the current WebOCalc thread: http://www.rcgroups.com/forums/showthread.php?t=930018

-Flieslikeabeagle
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Old Dec 18, 2008, 09:43 PM
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The website is back up and running. For now its will only work if you include the www.
So http://www.flybrushless.com
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