100 KV U10 Motors on 12S and 28X9.2" props ... not efficient !!!??

[khaled_abobakr]

Hi

I was under the impression that the U10 100 KV T-motors on 12S and 28X9.2" props .. are the way to go for maximum efficiency .. but I've just maidened my X8 Gryphon Dynamics 1400mm frame using only 12S 10,000 mah for testing and I flew for about 5- 10 mins and the batteries were 3.85 when I landed ....


Any help is greatly appreciated ... I'm after the longest flight possible with this frame ...

Thanks a lot

Khaled

 

[FerdinandK]

This is very few data you share, what AUW ...

3,85 is not even close to empty ...

With new low C-rate battery you can fly until 3,3-3,4V under load.



best regards
Ferdinand

 

[jdennings]

What's your AUW and amp draw?
Depending on your answer, 10AH may be too little, and/or 12S may be too much efficiency wise, 8S could be better.
You are also a little vague (5-10 minutes to 3.85), if it ends up being 12-15 minutes say down to 3.6V it's not that bad ...
And 20-30 AH+ at 8S could start you seeing much better results ...

 

[khaled_abobakr]

Hi FerdinandK,

Your videos were my inspiration for this build ... but for sure I don't have your knowledge ... AUW is about 10.7 Kg including 2 X 12S old Gens ace lipo batteries that are 3.2 Kg for both of them

Empty frame is 7.5 Kg
Batteries is 3.2 Kg

What low c batteries do you recommend ... HK .. or are there better brands ??

Thanks a lot

Khaled

 

[khaled_abobakr]

What's your AUW and amp draw?
Depending on your answer, 10AH may be too little, and/or 12S may be too much efficiency wise, 8S could be better.
You are also a little vague (5-10 minutes to 3.85), if it ends up being 12-15 minutes say down to 3.6V it's not that bad ...
And 20-30 AH+ at 8S could start you seeing much better results ...

I'll measure the flight time and amp draw tomorrow and report back ... to be more precise ..

Please elaborate more about 8s being more efficient than 12S ... I've seen several efficient 8S setups .. and I thought if I go higher to 12S then I will be more efficient ..

Please enlighten me

Thanks

Khaled

 

[R_Lefebvre]

The idea that high voltage is just magically more efficient is a myth. It's not. There are many other things you need to get right that are more important than voltage.

 

[R_Lefebvre]

This is very few data you share, what AUW ...

3,85 is not even close to empty ...

With new low C-rate battery you can fly until 3,3-3,4V under load.

Ferdinand, which ones are you using? I'm using the new HK Multistar batteries, and like them so far. With 20C batteries, I used to land at 3.5 v/cell, 3.3v absolute minimum. You think the 10C batteries can go even lower, probably due to the voltage sag?

 

[jdennings]

> Please elaborate more about 8s being more efficient than 12S ... I've seen several efficient 8S setups .. and I thought if I go higher to 12S then I will be more efficient ..

It all depends on where you actually end up on that amp/thrust curve for the motor/propeller combination and AUW. And these curves are also (obviously) different at different voltages.
12S vs 8S leads to less amp draw and better efficiency only by itself, going to 12S from 8S also results in an increase in battery weight for the same battery mAH capacity, so with 8S you can increase battery capacity for the same AUW Once you take that into consideration there are set-ups where increasing voltage does not necessarily lead to overall higher efficiency and longer flight times. Also depends on batteries ...

Sometimes it's just easier to just try and fly different combinations, 8S vs 10S vs 12S, say, although it is a time consuming process ..

 

[jdennings]

Double post

 

[FerdinandK]

@Khaled
The first thing is to measure more exact data, how long do you fly, and how much do you recharge, based on that information you can continue.

With my X8 with u8100KV I fly up to 10kg with 6S, and up to 15kg with 8S. Since your motors have more power, 8S or 10S should be enough, but still 12S seems to be possible if you want to go for high loads.
You always fly most efficient with the lowest voltage possible (since the ESC do pulse full throttle bursts at motors, so the higher the voltage the higher the amps running through your motor but for less time). Of course when comparing different voltage setups, the battery mass (energy) stays constant.
[MENTION=3314]R_Lefebvre[/MENTION]
I am using GensAce (Tattu) Batteries, (which are rated 5C). I am flying them down to 3,3 3,4V a cell, which is where the discharge curve is getting (again) steeper (since it was flat in the middle). This low C batteries have a lower "discharge end" voltage in common. If you do not know where to (immediately) stop flying, it is the point where you can watch the voltage dropping in telemetry.

best regards
Ferdinand

 

[R_Lefebvre]

Quick eCalc shows that it will fly 50% longer on 8S 15,000 than 12S 10,000.

 

[Quinton]

I am using GensAce (Tattu) Batteries, (which are rated 5C).

best regards
Ferdinand

Just wondering where you get them from?
The lowest C rating I can see in Tattu range is is 15C?
http://www.gensace.de/tattu/tattu-10000mah-22-2v-15c-6s1p-lipo-battery-pack.html

 

[FerdinandK]

Possibly what was 5 on mine (ordered before tattu was existing) is now 15 on the sticker on the packs, possibly some guy from sales and marketing thought, that no one would buy a 5C pack, since they are all used to the 30/60 and 60/90 numbers on the stickers so far. I am not sure if it would be a good idea to discharge such a pack within 4min (neither I think it would be a good idea to discharge a 60/90 rated pack in one minute, or do 900A bursts).

You can reverse engineer and find such packs when looking at the energy density. Mine 4S12500 have 1000gr, which means 14,8*12,5=185Wh/kg so if the energy-density is similar or higher, it is very unlikely, that you hold a "high-discharge" pack in hands. (I just want to add, that if I fly 30min, I can use 12500mAh so 100% of the pack, at 3,3-3,4V discharge end under load).

best regards
Ferdinand

 

[Quinton]

(I just want to add, that if I fly 30min, I can use 12500mAh so 100% of the pack, at 3,3-3,4V discharge end under load).

best regards
Ferdinand

You do realise that you have just opened yourself up to lots of questions from confused users reading this
Please explain further how you are able to use 100% of pack without causing damage.

 

[FerdinandK]

Discharge end of the pack is not when 80% are reached (this is/was a rule of thumb), it is when the discharge curve is getting steep again. So the less (current) you draw, the more (capacity) you can take out. The manufacturers of the cells (not the hobby-shops) do even publish these discharge-curves at different load-levels. So possibly if you fly 10min, you only can use 80% (before the curve is getting steep). Also it makes no sense to discharge to a lower voltage of the pack, as (because the discharge curve is getting steeper and steeper) you possibly gain only 30 more seconds if you fly until 2,5V-3,0V under load (instead of 3,3V) even if you flew 30min before.

A pack is empty when it is empty, not when a rule of thumb is telling you that it should be empty, when flying with telemetry, I only rely on telemetry-data, not on the rule of thumb.

Of course it is mandatory, that the correct capacity number is written on the pack, shops tend to exaggerate and manufacturers write the numbers on the pack you want to have written there.

best regards
Ferdinand

 

[Quinton]

You can reverse engineer and find such packs when looking at the energy density. Mine 4S12500 have 1000gr, which means 14,8*12,5=185Wh/kg so if the energy-density is similar or higher, it is very unlikely, that you hold a "high-discharge" pack in hands.

best regards
Ferdinand

Surely you can not really use this also, it would depend on what sort of Lipo you have.
Example I have a Desire 6200 mAh 35C which is 889g
using your formula .. 22.2*6.2= 137.6/889=0.154*1000=154.82Wh/kg

A 10400 Desire 35C = 1464g
22.2*10.2=226.44/1464= 0.154*1000 = 154.67Wh/kg (Now that is interesting almost identical)

 

[FerdinandK]

Why not, these are "standard"/"high discharge rate" packs the energy density is what is should be for these (150-160Wh/kg). The "high-capa"/"low discharge rate" have up to 180-200wh/kg, LiIon (1C application) up to 260wh/kg. There is no magic behind.

If you compare to this pack:
http://www.gensace.de/tattu/lipo-4s/tattu-16000mah-14-8v-15-30c-4s1p-lipo-battery-pack.html
14.8*16000/1241 = 190Wh/kg -> high density / low discharge rate pack
You will notice the difference in energy density in your average flighttime with your copter (if you fly > 12min-15min with your standard packs)

Also this is not my formula, it is the way you calculate the energy density of a pack, (nominal voltage* nominal capacity)/weight= energy density

best regards
Ferdinand

 

[Quinton]

Why not, these are "standard"/"high discharge rate" packs the energy density is what is should be for these (150-160Wh/kg). The "high-capa"/"low discharge rate" have up to 180-200wh/kg, LiIon (1C application) up to 260wh/kg. There is no magic behind.

best regards
Ferdinand

Thanks for sharing, it is certainly interesting.
There was a spreadsheet @R_Lefebvre posted in another thread I am not sure if you seen it, regarding making a list for different batteries.

https://docs.google.com/spreadsheets/d/1w9q_FbrBPAP8LMWmLNRe3lyF9J1yJXdhu3pNmemVJtg/edit#gid=0

 

[artecton]

Hi, i make a calculation of using one and 2 lipos in paralel ,example 14.8x5500/560gr=145.35
and 14.8x11000/1120gr=145.35 now what....?

Thanks for any explanation to understand it.

 

[FerdinandK]

This tells you that they have the same energy density (since they are the same batteries this is no surprise). The engergy density is an attribute of the cell, it is regardless how many of them you switch parallel or serial.
[MENTION=9737]Quinton[/MENTION],

The spreadsheet just shows you the same (the energy density is just written as the inverse value, from my point of view ENERGYdensity should be ENERGY/ ... and not the other way round, but that is a detail).
Low discharge have different energy density that high discharge (that has to be because of the cell chemistry as long as no other technologie is available) more "storage" vs. more "transport"

Just curious about the maxamps C-rating. The maxamps-"Dual core" with 8000mAh and 150(!) C you can completely discharge with 1200(!) A within 24(!)s. This battery gives you 26,64 kW for 24s which everyone who buys such a battery should try out, and if the battery explodes, or burns under that load, (or the wires desintegrate) should send the pack back with ".... does not meet the advertised specs" .

best regards
Ferdinand