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Old Aug 26, 2012, 05:37 AM
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Dornbirn / Austria
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How to optimize for duration?

Hi there,

I'm very impressed by the 'long duration' quad threads and videos. For a photo/video project, I want a quad with an optimized flight time (no acrobatics or any kind of excessive reserves).

I wondered how, in general, the experts here start with the target platform and this goal in mind and keep adding components? I had a look at the multicopter calculator and am curious about how you teak it

I would guess:

1. Build the frame + components as light as possible (base)
2. Find low KV motors
3. Fill up the remaining payload with lipos until hover efficiency is near to optimum efficiency?

I'm curious how you would do this..
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Old Aug 26, 2012, 06:23 AM
Hamburger
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Selec motors with only minimal excessive power beyond copter weoght. Aim for 2 to 1 ratio or even 1.5 to 1.
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Old Aug 26, 2012, 06:24 AM
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Use large diameter blades woth low pitch
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Old Aug 26, 2012, 11:05 AM
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Quote:
Originally Posted by hamburger View Post
Selec motors with only minimal excessive power beyond copter weoght. Aim for 2 to 1 ratio or even 1.5 to 1.
how would you calculate this? based on what?
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Old Aug 26, 2012, 11:22 AM
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Once you go below 2:1 the coptor becomes difficult to control but the lower the ratio the longer the flight time. If you are going to actually fly it rather than hover stay with no lower than 2:1. Experience and testing has shown the above to be true and ecalc seems to back it up.
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Old Aug 26, 2012, 11:41 AM
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+1 for the thrust/weight ratio. This is because these motors have peak efficiency at ~85% of their max power output. So you need to be running close to that most of the flight to get long durations.
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Old Aug 26, 2012, 11:45 AM
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Romania, Dolj, Craiova
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Quote:
Originally Posted by solars View Post
how would you calculate this? based on what?
No calculate, estimate.
Every motor page has somewhere a manufacturer notes, like: prop 11x5, 1000 grams thrust, this is supposed at full throttle

Assuming you can trust this... because usually the prop type is not specified, assume APC, then you do some math... if one motor thrust is 1000 grams, then 2 motors will hover 2000 grams, at full throttle, so 4 motors will hover 2000 grams at half throttle. This is 2:1 rule.

However, for high efficiency, the 50% area in a typical motor diagram is not the best where to hover, the 25-40% area is where a BL motor tops its efficiency. See graph bellow for better understanding, the red plot.



The graph above is valid for ANY brushless motor, any brand, power, and kv.
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Old Aug 26, 2012, 11:46 AM
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Originally Posted by TS00 View Post
+1 for the thrust/weight ratio. This is because these motors have peak efficiency at ~85% of their max power output. So you need to be running close to that most of the flight to get long durations.
85% ?!!! lol
Based on what ?
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Old Aug 26, 2012, 11:48 AM
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Originally Posted by RENATOA View Post
85% ?!!! lol
Based on what ?
On about a zillion graphs that people pointed me at when I asked a similar question on the motors subforum.

I don't claim divine knowledge here, so please feel free to correct me.
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Old Aug 26, 2012, 11:51 AM
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Originally Posted by RENATOA View Post
However, for high efficiency, the 50% area in a typical motor diagram is not the best where to hover, the 25-40% area is where a BL motor tops its efficiency. See graph bellow for better understanding, the red plot.
You're suggesting peak efficiency is at 25% - 40% what - power or rpm? It doesn't match up with other graphs I've seen, and it doesn't match my experience of using different power motors on the same frame.
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Old Aug 26, 2012, 11:55 AM
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Please, post link to such graph.
The above can be seen in any manufacturer page who post this diagram, and also any propulsion calculator (ecalc) draws something similar.

You have on that graph power, rpm, and Amp. The last is the X axis, and this graphs are drawn usually versus Amp.

Other interesting article on this subject, based on similar shaped graphs:
http://diydrones.com/profiles/blogs/motor-efficiency
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Old Aug 26, 2012, 12:02 PM
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TS00 is it possible that you are confusing the values? usually ~85% is the actual efficiency given by the calculators, e.g. if you use: http://www.ecalc.ch/xcoptercalc_e.htm

I think renatoa is referring to _where_ this peak is, e.g. at 25% of power if I understand right

if I think right, the goal is, to get the efficiency in motor @ hover as close to the optimum efficiency in this calculator, by doing what renatoa suggests. then you are hovering as efficient as possible.

@Renatoa, thanks for the explanation - you are right, either the motor is in the database, or it is missing and the description does not list all the necessary values this is a bit of a pain
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Old Aug 26, 2012, 12:06 PM
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Quote:
Originally Posted by RENATOA View Post
Please, post link to such graph.
The above can be seen in any manufacturer page who post this diagram, and also any propulsion calculator (ecalc) draws something similar.

You have on that graph power, rpm, and Amp. The last is the X axis, and this graphs are drawn usually versus Amp.

Other interesting article on this subject, based on similar shaped graphs:
http://diydrones.com/profiles/blogs/motor-efficiency
I think the confusion stems from the fact that you can plot efficiency against any one of a number of variables. The graph you posted shows efficiency v. current, with a peak between 30-50%.

This graph shows efficiency v. rmp:



The peak is much later.

Same here:

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Old Aug 26, 2012, 12:10 PM
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don't worry about it guys. With his first post sounds like he is on the right track and he will see for himself what the efficiency range is for different motors as it is usually listed. ecalc will also simulate all of that for him. First thing is to guesstimate coptor weight and then juggle motors, props and battery from there while at the same time recalculating weight based on new config. 30 minutes should be a good target.
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Old Aug 26, 2012, 12:19 PM
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don't stop them from contributing!
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