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Old Jan 04, 2009, 08:35 AM
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I thought it was clear. In post 74 I am refering to MOTOR INPUT POWER which is the same as BATTERY OUTPUT POWER, and which is casually called WATTS in the flybrushless tables.
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Old Jan 04, 2009, 08:55 AM
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The watts in on FlyBrushless are just Volts*Current
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Old Jan 04, 2009, 01:52 PM
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I can't imagine how a single "average" equation can cope with the variability of motors and props....but...

...if one is trying to determine how much power one needs to put into a system to get a required output (thrust @ a certain pitch speed) I'd rather turn Peter's equation around.

As an example: I want 20oz thrust at 50mph... what do I need to put in?

20 x.14 x 50 = 140W

Not bad: Hacker A20-22L with a 8x6 APC E:

10.9v, 13.55A, 148W, 8670rpm, 49.3mph, 567g, 19.97oz, 3.83g/W
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Old Jan 04, 2009, 02:21 PM
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Just joined this site but am having a problem. The heading comes in on my computer screen loud and clear but the other writing is so tiny I can't read it. I'm no computer whiz, apparently, so can someone help me out here. Tom
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Old Jan 04, 2009, 08:27 PM
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The front size on the site isn't set small, it should be about the same as the font here on RCG. Are you having problems with just my site or other sites as well? Also can you tell me what OS and web browser your using.

If your running windows you can hold down the Ctrl Key and scroll your mouse wheel up to make the font larger. Keep in mind doing this will make the font larger on every site. To undo it use Ctrl and scroll down.

Robert
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Old Jan 04, 2009, 10:56 PM
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There arew a few sites where the printing is so small I can not read it. The main Yahoo site is that way. My computer is running with Windows XP. Tom
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Old Jan 04, 2009, 11:00 PM
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I just tried the control key thingy and it worked. All this time I have been going nuts with these sites and never knew how the heck to fix it. Thanks a million from a computer challenged senior citizen. Tom
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Old Jan 04, 2009, 11:40 PM
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Glad that fixed your problem Tom. That is one of those simple things that can leave you scratching your head for a while if you don't know how to undo it, just like the Alt+Ctrl+Down Key. You probably hit it on accident, I know that's how I found out about it.

Robert
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Old Jan 05, 2009, 12:47 AM
just Some Useless Geek
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Quote:
Originally Posted by rgoble
The watts in on FlyBrushless are just Volts*Current
That's power consumption.

Quote:
Originally Posted by Dr Kiwi
if one is trying to determine how much power one needs to put into a system to get a required output (thrust @ a certain pitch speed) I'd rather turn Peter's equation around.

As an example: I want 20oz thrust at 50mph... what do I need to put in?

20 x.14 x 50 = 140W

Not bad: Hacker A20-22L with a 8x6 APC E:

10.9v, 13.55A, 148W, 8670rpm, 49.3mph, 567g, 19.97oz, 3.83g/W
I question whether these "rule of thumb" calculations do us a lot of good without knowing the exact efficiency curve for a particular motor/prop/RPM combo. My suspicion is that the efficiency effects are far too complex to put into a rule of thumb nutshell; it is far more likely that the efficiency per combo needs to be graphed like any other complex curve.
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Old Jan 05, 2009, 08:19 AM
homo ludens modellisticus
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The Netherlands, GE, Nijmegen
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Quote:
Originally Posted by Tom Smith
I just tried the control key thingy and it worked. All this time I have been going nuts with these sites and never knew how the heck to fix it. Thanks a million from a computer challenged senior citizen. Tom
About every program has an option to change character size under 'view'. <ctrl> + and <ctrl> - usually do the trick.

Vriendelijke groeten Ron
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Old Jan 05, 2009, 12:12 PM
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I added a graph to the motors that have Rm and Io values to show the efficiency curve at 7.2v and 11.1v. I can add the rpm or other plots if it will be useful, but for now I didn't want to clutter the graph up too much.

I am using the formula's found at http://www.rcgroups.com/forums/showthread.php?t=185271 to find Ipmax and I graph out to that current.

Robert
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Old Jan 05, 2009, 12:30 PM
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Quote:
Originally Posted by A Useless Geek

I question whether these "rule of thumb" calculations do us a lot of good without knowing the exact efficiency curve for a particular motor/prop/RPM combo. My suspicion is that the efficiency effects are far too complex to put into a rule of thumb nutshell; it is far more likely that the efficiency per combo needs to be graphed like any other complex curve.
That's why I put in this: I can't imagine how a single "average" equation can cope with the variability of motors and props....but...

But it was interesting to find that the one random sample I selected was in the ballpark!
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Old Jan 06, 2009, 11:54 AM
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Geek and Dr K

In my post #74 I list three constraints.These will filter-out some of the main variabilities. I request that you observe these constraints when you select examples to test the equation.

The third constraint is intended to filter-out examples which are over-propped or under-propped. Such states imply low motor efficiency, and would be of no practical interest.

Two scources of possible large error which cannot be filtered are inaccurate Kvs and inaccurate prop pitches [all too prevalent].

No doubt, there will be room for improvement. But it must not get complicated.

Even if the tolerence on the results is + & - 30%, it may still be worth using. It takes only a few seconds.
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Old Jan 06, 2009, 09:28 PM
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Canton, Michigan USA
Joined Jul 2007
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Quote:
Originally Posted by ..
[COLOR=Indigo
Welcome to FlyBrushless.com

Cheers, Phil

Phil,

I tried registering with FlyBrushless.com but they never sent me a confirmation email. Any email address to them would be good. The "Contact US" doesn't seem to work either.

Bill
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Old Jan 06, 2009, 10:12 PM
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Dayton Montgomery, Ohio, United States
Joined Sep 2004
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Bill,

I activated your account for you so you should be able to login now. I'm not sure what happened but you are the second person that has said they didn't get the email.

Also thanks for pointing out the blank "Contact Us" page, I must of forgotten to go back and fill that one out.

Robert
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