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Old Feb 10, 2013, 06:47 PM
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This may take some account of possible restriction of airflow past a cowl/fuselage/plane.. but it is still a static test [with all its perceived or real drawbacks]. And if you want to compare one motor with another you have to fit it into exactly that same airframe.. I can't see this method being a huge improvement over a calibrated thrust stand set-up.... where one can test 100's of different motors under identical conditions.

Hanging a plane from the ceiling on a digital fish scale is essentially the same as your method: http://www.rcgroups.com/forums/showp...0&postcount=19
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Old Feb 11, 2013, 01:17 PM
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Thanks for your help Dr Kiwi, and for the good work you have put into the motor database. I wasn't aware of the fish-scale method, which seems very similar to my one, but I don't have a fish scale, while I do have a kitchen scale (and table). My method seems useful to me in determining which prop gives the best thrust vs W used in a particular plane for the limited number of motors I use. In considering alternate motors in the future, I will refer to the database and to user/vendor tests for that particular motor/prop combination.

Richard
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Old Feb 12, 2013, 02:04 AM
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I have given this approach some thought before, and what I came up with is the idea of hanging the plane from the fish scale and taring the mass of the plane before beginning the thrust test. That way there are no obstructions, no drag nor inertia to overcome with wheels, etc. I haven't tried it yet because the only fish scale I had was one I used to weight bicycles (in the 10-20 kg range) and I gave that one to the bike shop.
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Old Feb 12, 2013, 07:01 AM
Jack
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This scale (or maybe a 20Kg version of it?) has worked well for me in both handing and dragging configuration. Even with the plane laying with the prop in the clear over the end of a bench or table. I put a loop around the hstab and let the plane pull against the tied off scale. it remembers the reading until cleared.

And you can set it up as a hanging scale with a simple 90 degree turning block.

Very simple and practical.

http://www.ebay.com/itm/280947677057

Jack
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Old Feb 12, 2013, 07:14 AM
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While I think my kitchen Scale/Kitchen table method (above) is fine for park flyer size planes, I'm not sure if I would feel that safe measuring different props with 3S vs 4S for my Haikong Spitfire with a Turnigy 3548 900kV motor (max thrust approx 1650gm @ 715W with 5S), or indeed using any sort of test bench for this.

Thanks again for the fish scale tip for this, which I think would be safer, as I could hold the wing as the thrust built up to stop torque roll, or use some aileron trim. I have lashed out and ordered this one http://www.ebay.com.au/itm/160904584...#ht_6155wt_910 for about $7.
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Old Feb 13, 2013, 02:39 AM
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This may be a long shot.... but is there a program that can actually tell you what motors to consider if you provide the parameters? For example, if I say that I want to use a 12x7 prop on a 4S and generate 3000grams of thrust.... is there a program that can tell me which motors to consider?
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Old Feb 13, 2013, 03:40 AM
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Quote:
Originally Posted by THOMASJONES View Post
This may be a long shot.... but is there a program that can actually tell you what motors to consider if you provide the parameters? For example, if I say that I want to use a 12x7 prop on a 4S and generate 3000grams of thrust.... is there a program that can tell me which motors to consider?
Hi
Not immediately but almost
From 12x7 prop and 3000 gf thrust Scorpion Calc (menu "propellers") is indicating the necessary X rpm (easy when using an horizontal scrolling) and also Y watts.
From X rpm and 4S (14.8V) you compute yourself Kv = 1.2 * X / 14.8
From Y you determine the weight of the motor Wg = Y / 3
You have a library to choose the prop or a custom prop to edit
here : http://www.rcgroups.com/forums/showthread.php?t=736782

Motor weight and Kv are the two main parameters for a motor
Louis
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Old Feb 13, 2013, 03:48 AM
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That's exactly what the Motowizard in Motocalc does if I recall.

John
Quote:
Originally Posted by THOMASJONES View Post
This may be a long shot.... but is there a program that can actually tell you what motors to consider if you provide the parameters? For example, if I say that I want to use a 12x7 prop on a 4S and generate 3000grams of thrust.... is there a program that can tell me which motors to consider?
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Old Feb 13, 2013, 05:48 AM
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Ken Myers's Avatar
Commerce Township, MI
Joined Aug 2001
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Quote:
Originally Posted by THOMASJONES View Post
This may be a long shot.... but is there a program that can actually tell you what motors to consider if you provide the parameters? For example, if I say that I want to use a 12x7 prop on a 4S and generate 3000grams of thrust.... is there a program that can tell me which motors to consider?
The FREE Drive Calculator program
http://www.drivecalc.de
will do this when the Match Prop function is used with the number of cells.
I chose to use a constant voltage of 14.8 to represent a 4S pack, but different packs and configurations may also be selected in the program.
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Old Feb 13, 2013, 11:42 AM
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Quote:
Originally Posted by Fourdan View Post
Hi
Not immediately but almost
From 12x7 prop and 3000 gf thrust Scorpion Calc (menu "propellers") is indicating the necessary X rpm (easy when using an horizontal scrolling) and also Y watts.
From X rpm and 4S (14.8V) you compute yourself Kv = 1.2 * X / 14.8
From Y you determine the weight of the motor Wg = Y / 3
You have a library to choose the prop or a custom prop to edit
here : http://www.rcgroups.com/forums/showthread.php?t=736782

Motor weight and Kv are the two main parameters for a motor
Louis
Super helpful. Much thanks fellas
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Originally Posted by jj604 View Post
That's exactly what the Motowizard in Motocalc does if I recall.

John
Quote:
Originally Posted by Ken Myers View Post
The FREE Drive Calculator program
http://www.drivecalc.de
will do this when the Match Prop function is used with the number of cells.
I chose to use a constant voltage of 14.8 to represent a 4S pack, but different packs and configurations may also be selected in the program.
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Old Feb 13, 2013, 01:05 PM
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DriveCalc

I too would recommend using DriveCalc. Read the instructions. It will take a bit of time to get used to the many features, but I find it very useful. Plus, it's free. Mine just updated a few days ago when I used it. Nice touch as well.
Unlike Motocalc, as far as I can tell, it is more squarely aimed at folding props and for the electric sailplane emthusiast. I've been able to calculate a number of configurations based on the required prop size, some which were quite surprising. I've double checked these results using other programs and they were quite close.
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Old Feb 13, 2013, 08:15 PM
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Those of us who contribute a LOT of data to DriveCalc (in my case motors and props) do try to deliver REALISTIC/ACCURATE data, so that DriveCalc computations are as good as you are going to get. I must say though, that even in DriveCalc there are still some motors for which, as yet, only one Io data point has been entered (no prop data), so for those we cannot expect the computations to yield accurate results. I fear that some other motor calculators have the same failing... garbage in-garbage out.
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Old Feb 14, 2013, 01:54 AM
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Quote:
Originally Posted by Dr Kiwi View Post
Those of us who contribute a LOT of data to DriveCalc (in my case motors and props) do try to deliver REALISTIC/ACCURATE data, so that DriveCalc computations are as good as you are going to get. I must say though, that even in DriveCalc there are still some motors for which, as yet, only one Io data point has been entered (no prop data), so for those we cannot expect the computations to yield accurate results. I fear that some other motor calculators have the same failing... garbage in-garbage out.
You're absolutely right Dr.Kiwi. I can see that a lot of time and effort has gone into this program. Thank you, and all others who have made this possible, a whole bunch. We all appreciate you guy's efforts
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Old Feb 14, 2013, 08:55 AM
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near Nijmegen, Netherlands
Joined Feb 2001
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Quote:
Originally Posted by THOMASJONES View Post
... but is there a program that can actually tell you what motors to consider if you provide the parameters?
e-flight calculators (compilation) (sticky in Power Systems subforum)

Vriendelijke groeten Ron
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Old Feb 19, 2013, 07:10 PM
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1236 Fremont St. Lancaster, PA 17603-6812
Joined Mar 2005
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To one and all

My question seems so basic, I hate to ask it, but can't find the answer anywhere. I have several electric planes, and use the esc, motor and prop recommended. I would like to know more.

I have a plane with a motor which runs and flies just fine. However, I am ignorant of some facts like KV. My motor is rated at 2200 KV. I read that KV is rpm/volt. Dividing my 11.1 voltage into 2200 give me the number 198.19. However, I know the rpm is higher than that.
Also, I bought a watt meter but don't know whether I should use it to get the max out of the motor or the minimum. So far, I have used it to make sure the esc can handle the current.
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