36 replies to this topic

[Mat Wellington]

if i built a carbon frame quad, decent motors (500 gram frame) and ran 4S 12000 mah, thats 1949 grams all up, efficiency around 140 watts per kg, its only 31-32 minuted

so to have a look in, its ultra light frames, and large slow efficient props, and no wind !

[John888]

Like Maineiack said, "our specific OP member endurance" thread is here : http://forums.openpi...__fromsearch__1

What do you think about this Mat?




Already got the motors and props (although stuffing around with them & they might not like the 18A ESC's I have).

My 3000Mah 4s batteries weigh about 310g each (so 2 x 310g = about 50% of total weight).

On a different note, is my guesstimation correct - at about 27" props on the microdrone?
http://microdrones.c...cal_drawing.pdf

And would the microdrone look a bit like the following (assuming custom props and motors)???

Edited by John888, 16 February 2012 - 12:46 AM.

[jbkappirossi]

Mat Wellington, on 15 February 2012 - 10:29 PM, said:

looks like yours takes 110 watts/kg to hover, flying weight of 592 grams

at 3S 8000 mah all up weight will be 1045 grams, best guess watts per kg will increase to 120 , so i reckon all up flight time = 34 minutes, and you dont want to go much heavier (run out of control)

if ya drop your weight to 280 grams, flight time would be closer to 27 minutes

the magic 30 minutes is hard

thanks for the explenation. that makes logics.

So basicly 8a is a littlebit to heavy for my motors? and is it true that my little hackers are probably most efficient at 65/70% throttle?
i wil try again today without the dome (25grams) and see what that wil get me.
Because over a longer period of time every thing wil scale must faster.
What i mean by that is when you got a quad that does, lets say; 10minutes of hovering and you take some weight of and you win 1 minute. but when it can fly for 30minutes with a bigger battery that 1 minute would also multiplie by 3, from that weight you saved.

Also i've re-entered my setup into ecalc and i'm getting 23minutes. wich, in real time was 25minutes + .
When up the battery from 3000mah to 6000mah and leaving the rest unchanged, ecalc gives me 48minutes.

Edited by jbkappirossi, 16 February 2012 - 08:15 AM.

[Mat Wellington]

cant wait to see how it works out at and see if the numbers match real life.
I think the 8000 mah lipo with AUW around 1045 grams is getting up there" for your particular quad and would not  go much heavier

[D-Lite]

John888, on 16 February 2012 - 12:06 AM, said:

On a different note, is my guesstimation correct - at about 27" props on the microdrone?
http://microdrones.c...cal_drawing.pdf

And would the microdrone look a bit like the following (assuming custom props and motors)???

27" looks okay, probably a bit less, 25 or 26. I'm no sure about the weight. They say 2650g depending on configuration so this may be with 6s2p (12Ah) batteries and not with 6s3p (just a guess). In the end, the "secret" to long flight times is always the same: huge props, huge batteries, low weight

[elmuchacho]

D-Lite, on 16 February 2012 - 11:11 AM, said:

In the end, the "secret" to long flight times is always the same: huge props, huge batteries, low weight

I disagree for me it all come down to amount of volt in relation to the KV of a motor this how you get the total rpm and also how you get into the best soft spot of the motor and propeller.

To test that theory
Take any quad that have motor kv below or equal to 750. Run this quad with a 3S and now run exactly the same setting with 4S trying to keep both battery with the same capacity.

The 4S even with the extra weight of 1 more cell will have a longer flight time.

Now from experience the higher the voltage and the lower the kv and the longer flight time has long has the association of volt and kv do give the right rpm for the propeller to be turning at it's best efficiency RPM

[D-Lite]

elmuchacho, on 16 February 2012 - 12:45 PM, said:

I disagree for me it all come down to amount of volt in relation to the KV of a motor this how you get the total rpm and also how you get into the best soft spot of the motor and propeller.

Of course all of this should be optimized to give maximum performance. It doesn't make sense to use a high KV motor and then drive a big prop, this will not be efficient.

elmuchacho, on 16 February 2012 - 12:45 PM, said:

  Run this quad with a 3S and now run exactly the same setting with 4S trying to keep both battery with the same capacity. The 4S even with the extra weight of 1 more cell will have a longer flight time.  

Yes, because it stores more energy. It doesn't make sense to directly compare a 3s and a 4s with the same mAh rating. Instead you should compare Wh (voltage multiplied by Ah). So according to "my" definition, a 4s with 6000mAh would be a "bigger" battery than a 3s with the same capacity,

[elmuchacho]

D-Lite, on 16 February 2012 - 01:55 PM, said:

Yes, because it stores more energy. It doesn't make sense to directly compare a 3s and a 4s with the same mAh rating. Instead you should compare Wh (voltage multiplied by Ah). So according to "my" definition, a 4s with 6000mAh would be a "bigger" battery than a 3s with the same capacity,

Sorry but 6000mah is 6amp hour for a 3S, 4S, 5S, 6S ... this is a constant that allow you to workout how much capacity a battery has.

If you run the proposed test you'll see that with a 4S to get to the same RPM has with a 3S you will use less amp. So this mean that for the same battery capacity you'll fly longer.

To translate into the Math of things
Take a quad that pull around 10amps
To estimate the time you do the following
lipo capacity in amp hour * amount of min in 1 hours / amp

6 * 60 / 10 = 36min

Has you can see that formula do not involve the voltage of the battery

If you where to calculate the amount of watt produce then it will be different
Volts * amps = watt


then with a 3S of 11.7V nominal voltage 11.7*10=117watt
with a 4S 14.8V nominal voltage 14.8*10 = 148watt

Then accordingly to your logic yes a 4S will have generated more energy/power but it's capacity only define for how long you can use it in relation to the amount of amp you need.

[D-Lite]

elmuchacho, on 16 February 2012 - 02:17 PM, said:

Sorry but 6000mah is 6amp hour for a 3S, 4S, 5S, 6S ... this is a constant that allow you to workout how much capacity a battery has.

It does allow you to calculate how much amps it can deliver for how long - not more and not less. But all the amps alone say nothing about power without looking at the voltage. To lift off and hover you need a certain amount of power. It doesn't matter so much (in a simplified view) if you have 50 volts and 1 amp or 5 volt and 10 amps - it's always 50 watt. If that's the power you need to hover, you'll be fine. If you now want to know how long you can hover, you have to know how long the battery can deliver 50 watts, that's all.

elmuchacho, on 16 February 2012 - 02:17 PM, said:

  Take a quad that pull around 10amps To estimate the time you do the following lipo capacity in amp hour * amount of min in 1 hours / amp 6 * 60 / 10 = 36min Has you can see that formula do not involve the voltage of the battery

No, because you take "10 amps" as a fixed value. But with a higher voltage (e.g. 4s instead of 3s), you would need less amps to get the same performance.

[z-axis]

Hmm...well,

elmuchacho, on 16 February 2012 - 02:17 PM, said:

Sorry but 6000mah is 6amp hour for a 3S, 4S, 5S, 6S ... this is a constant that allow you to workout how much capacity a battery has.

This is true, within a very small range of error attributable to several power system design variables.

D-Lite, on 16 February 2012 - 02:39 PM, said:

It doesn't matter so much (in a simplified view) if you have 50 volts and 1 amp or 5 volt and 10 amps - it's always 50 watt.

This is not totally true, as it does not take efficiency into consideration. As an example, running a server+ps at 110V might draw 8A, but running the same server+ps at 220V draws 3A. If this were not the case, there would be no reason to run motors at different voltages. 4S tends to be more efficient at using the available mAh energy store.

[D-Lite]

z-axis, on 16 February 2012 - 03:01 PM, said:

This is not totally true, as it does not take efficiency into consideration.

That's one of the reasons why I wrote "in a simplified view" :-)

[elmuchacho]

Guy we can argue as much as we want on interpretation, at the end of the day this are Math formula how we understand them is our point of view but if you whishes to disagree you'll have to come up with a formula that allow calculating the estimate According to your definition.

Let's remember that most of us are from different country that speak different language!

Edited by elmuchacho, 16 February 2012 - 03:28 PM.

[John888]

Being new to the hobby, seeing how custom, super high-end units work is a great way to learn.

Technology often starts at a really expensive level, then filters down within reach of the general public.

Watching this video, it says the motors are 250W. Is a guess of  around 150 KV custom motors reasonably correct?



Hypothetically, if they were using our GCS, wonder what their Kp & Ki settings would be to accommodate extra large, slow flying props and low KV motors (although on 6s)?

Or wouldn't there be a difference?

Edited by John888, 16 February 2012 - 03:30 PM.

[D-Lite]

elmuchacho, on 16 February 2012 - 03:28 PM, said:

Let's remember that most of us are from different country that speak different language!

Yes, I think in the end we don't disagree that much:

elmuchacho, on 16 February 2012 - 12:45 PM, said:

Run this quad with a 3S and now run exactly the same setting with 4S trying to keep both battery with the same capacity.
The 4S even with the extra weight of 1 more cell will have a longer flight time.

Agreed

elmuchacho, on 16 February 2012 - 02:17 PM, said:

If you run the proposed test you'll see that with a 4S to get to the same RPM has with a 3S you will use less amp. So this mean that for the same battery capacity you'll fly longer.

Also agreed.
The only thing that I wanted to point out is that a 4s stores more enery than a 3s with the same capacity and that this is the reason why it flies longer.

[D-Lite]

John888, on 16 February 2012 - 03:29 PM, said:

Watching this video, it says the motors are 250W. Is a guess of  around 150 KV custom motors reasonably correct?

I think so, between 120-180 would be my guess.

John888, on 16 February 2012 - 03:29 PM, said:

Hypothetically, if they were using our GCS, wonder what their Kp & Ki settings would be to accommodate extra large, slow flying props and low KV motors (although on 6s)? Or wouldn't there be a difference?

Hard to tell because it depends on so many factors like inertia of the frame, motor response etc...

[jbkappirossi]

Mat Wellington, on 16 February 2012 - 09:27 AM, said:

cant wait to see how it works out at and see if the numbers match real life.
I think the 8000 mah lipo with AUW around 1045 grams is getting up there" for your particular quad and would not  go much heavier

well, i've just finnished my second flight without the dome and saving 25gram.
Rest is the same. Now i got a run of 26.4minutes.
So with my setup you could say; that 25gram costs or wins 1minute of flighttime.

[Terrier]

Drawing on an idea I read somewhere on here or the RCG, if someone would just invent a wedge-shaped, X configuration mylar balloon to attach under the frame, you could get your AUW way down...  Fill that sucker with helium, and fly it alllllll day.  

Fill it with hydrogen, and you could have your very own fireworks display

Edited by Terrier, 22 February 2012 - 07:38 AM.