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Old Oct 11, 2014, 09:14 AM
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Weight to Thrust on Motor Failure

So I know you need 1:2 Weight to Thrust to have a nice flying Multi, so on a custom Hex I should expect the AUW to be the Max Thrust of 3 motors. Now I know several FC's have some basic motor on motor failure handling for a HEX, but I also understand that no matter how good or bad that failure algorithm is if your over weight you drop.

So the question I have is 1:2 still the same number to shoot for in Motor failure? so I would say the AUW would be the MAX thrust of 2.5 Motors? or do you need even higher ratio?

I am not expecting a graceful oh my motor went out? lets bring her down landing like I would get from an Octo, I just don't want a There goes my nikkor lens landing.

Thank you for your input and patients.
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Old Oct 11, 2014, 11:45 AM
Team WarpSquad
United States, PA, Doylestown
Joined Jan 2014
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The 1:2 weight/thrust ratio is a minimum. I like 1:3 and even up to 1:5.
If you are designing with the possibility of a motor out then design for a larger weight/thrust ratio.
This also depends on what you plan the copter to be able to do with one motor out.
1- just get it down under control to land
2- still have good maneuverability and lift
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Old Oct 11, 2014, 12:13 PM
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Originally Posted by waltr View Post
The 1:2 weight/thrust ratio is a minimum. I like 1:3 and even up to 1:5.
If you are designing with the possibility of a motor out then design for a larger weight/thrust ratio.
This also depends on what you plan the copter to be able to do with one motor out.
1- just get it down under control to land
2- still have good maneuverability and lift
I would like to be able to move it enough to get out of tree lines if I am above the trees or water. I dont have the need to keep flying or to have precise control. My only desire is to move the craft out of an unlandable area to one where I can land, and bring it down in a manor more gental than slamming into the ground.
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Old Oct 11, 2014, 12:19 PM
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With 1:5 wouldn't the power be so great that the difference between power to climb and the power to hoover be nonexistent. Where you couldnt hover.
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Old Oct 11, 2014, 12:35 PM
Team WarpSquad
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Quote:
Originally Posted by nfored View Post
With 1:5 wouldn't the power be so great that the difference between power to climb and the power to hoover be nonexistent. Where you couldnt hover.
That is false. I fly quads with 1:5 and greater thrust. They hover just fine.
Go look up any of the videos from Warthox, quadmovr or Soma. These quads have very high thrust to weight ratios and hover very well to the point he does a hover then reaches up to grab the quad.
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Old Oct 11, 2014, 07:16 PM
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So if I shoot for 1:3 with one motor out does that sound realistic ratio for one motor failure and navigating away from trees and then landing?
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Old Oct 12, 2014, 09:29 AM
Team WarpSquad
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Originally Posted by nfored View Post
So if I shoot for 1:3 with one motor out does that sound realistic ratio for one motor failure and navigating away from trees and then landing?
I would say yes, that should be reasonable and easily achievable.
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Old Oct 12, 2014, 10:07 AM
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Thank your for your help. I reall appreciate it
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Old Oct 17, 2014, 02:26 AM
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Yes, 1:3 is right for other reasons too... check this diagram, it is typical for any BL.
The green plot is the efficiency, as you can see it tops at 13Amps, about 1/3 of the red point value 40Amps, which is motor current limit.
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Old Oct 17, 2014, 10:52 AM
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Hum that seems like an awesome program is it expensive? So if I shoot for 1:3 at motor failure, then I will be at greater ratio with all motors running. Looking at that graph running at either side of that magic 1/3 the loss is about the same. So hoping 99% of the time I will have 6 motors running should I shoot for 1:3 with all motors running to get max efficiency? Which would put my failure ratio at 1:2.5

This has made me see I have only scratched the surface of understanding here.
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Old Oct 17, 2014, 12:07 PM
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DC is free, but you can donate
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