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Old Mar 06, 2002, 08:54 PM
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Doc Watson's Avatar
UK
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EDF thrust calculator

Anybody interested in me 'knocking up' a program which will calculate the thrust for some Wemotec fans given the cells and amp draw???

Im gunna include 2400, 1700, 1300 any others?

I'm also going to assume 1v per cell and use the equations on my site.


Any other 'bells and whistles' you guys might want??? other fans??? etc.

Doc
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Old Mar 06, 2002, 08:59 PM
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Trabuco Canyon, CA
Joined Nov 2000
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Re: EDF thrust calculator

Quote:
Originally posted by Doc Watson
Anybody interested in me 'knocking up' a program which will calculate the thrust for some Wemotec fans given the cells and amp draw???

Im gunna include 2400, 1700, 1300 any others?

I'm also going to assume 1v per cell and use the equations on my site.

Any other 'bells and whistles' you guys might want??? other fans??? etc.
Sure! On one condition. That it doesn't take you away from your X-35 for too long. I want to see that fly much more than I want a thrust calculator.

Dan
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Old Mar 06, 2002, 09:08 PM
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I would love to see The Jepe and Shuebler fans included. Then we'd have a good all around tool to use for most any application. I also second the motion that it shouldn't take too much time away from your big project. I can hardly wait to see it hover, then transition and climb away!

Tim H.
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Old Mar 06, 2002, 09:14 PM
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How do you correlate the number of cells, RPM, and current draw?

Cells and current isn't enough information, I think. Watts would work.

Greg
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Old Mar 06, 2002, 09:47 PM
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If watts would work, why then wouldn't cells and current as watts = volts * amps and he has said he is going with 1 volt per cell as a simplification?
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Old Mar 06, 2002, 10:08 PM
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Well to some extent that works. thatinformation is already on his site.

The problem is that you need to have the motor and battery to run your test to see what kind of current draw you will have. Then you can calculate thrust.

I have made a spreadsheet that will calculate current draw based on motor constants and cells used much like the calc programs. It also outputs thrust and velocity. It works OK but Excel has fits with certain combinations of motors and will not give results.

Greg
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Old Mar 06, 2002, 10:12 PM
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Irvine, Calif USA
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I am not sure I understand what you mean by "calculate". The data has already been measured and is available here for a variety of motors:

www.wemotec.com

Watts (or Volts and Amps) in will give you inaccurate figures for the thrust and efflux velocity, unless you specify the motor and in particular its efficiency (as I think I already mentioned in a previous post on the same subject ).

For ducted fans the results are further affected for ex. by the use of an exit cone:

http://members.chello.at/andreas.markovic/EDFcalc.xls
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Last edited by Herb; Mar 06, 2002 at 10:16 PM.
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Old Mar 06, 2002, 10:29 PM
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Herb, I agree. The data is already there.

Of course watts input is a problem. That is why I made my spreadsheet several years ago. It needs to be updated a bit with things that I've learned about motors and fans since I put it together. The biggest problem is adding effects from ducting. Ducting will drastically effect resulting current draws and thrust figures.

Greg
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Old Mar 07, 2002, 09:43 AM
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I am all for it Doc, that would be great, forget all the graphs! .
I suppose watts in and then a field to plug the motor efficency in and then calculate the watts to the rotor, static thrust out with no duct or cone is just fine, we all know that ducting and exit cone affects thrust.
While your at it you could have a FSA and optimum cone diameter for efflux speed calc that spits out Area for 80 to 90 % FSA, figuring that out is a pain!

I should have never said "Ill never use this stuff man!!! " to my poor math teachers . If she whould have only said " you need this to build RC jets " I would have hit the books!
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