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Scorpion Power Scorpion Power
HelicopterMain Discussion › Effect of Cell Count
01-23-2013 06:02 AM  4 years agoPost 141
Ravenhyper50

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Canada's Capital

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24S 4P Video from last page...

Watch at YouTube

Running gear is:

- Futaba BLS253 on cyclic
- Futaba BLS251 on tail
- Scorpion 4530-300kv
- TOM24 Prototype ESC
- Blueline V-bar (fullsize)
- Edge 693mm Mains
- KBDD 105mm Tails
- Gryphon Quasar HV BEC
- 4x cheap and nasty 2450mAh 6s Turnigy packs (proof of concept pack)

Headspeed in ST1 is 2020. ST2 is 2250.

HV or LV that is the question?

Raven
Nitro could have done that for a lot more than 3.5 min.
LOL

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01-23-2013 10:12 AM  4 years agoPost 142
Richardmid1

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Leeds, England

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Ok, 2 reasons Rogman saw what he saw on his 450 going from 3s to 6s.

1. He said he used Volts 6s packs so im guessing they were 1300mah packs as opposed to the standard 2200mah 3s packs. (6s should be 1100mah for fair comparison)

2. If he went (again im guessing) from a 12T pinion on the 4400kv 3s setup to a 13T on the 2010kv 6s setup, his 6s setup is still slightly lower geared than the 3s setup.

60% of the time, it works every time!

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01-23-2013 10:22 AM  4 years agoPost 143
Richardmid1

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Leeds, England

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Again the 24s X7 video proves higher voltage beyond a certain point is not more efficient, it still only got 3.5 mins, just the same as a 12s 700 flown like that at 2250 RPM.

60% of the time, it works every time!

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01-23-2013 10:29 AM  4 years agoPost 144
ChristianM

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Oslo, Norway

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All good points. But they don't change what I've concluded so far.
Battery - doesn't care
Wire loss - pretty insignificant
Wire weight - some impact but may be offset by eliminating other weight (like using a bec instead of a separate pack) Jury still out but just in princepal, I have always thought it is moronic to run the control system of an electric heli off an RX pack.
ESC - HV less efficient
ESC Weight - if efficient enough it may not need a heat sink. Jury still out.
I agree with you on the battery and the wire loss but not necessarily on the efficiency of the ESC. You may have a point regarding resistance due to the switching frequency and that higher voltages can have higher resistance in this regard, I do not know if this is the case or how significant it is.

However there is still the internal resistance in the FETs and the rest of the circuitry in the ESC that also factors in. As others have mentioned and also in my own experience, if you use a bigger ESC then they come down cooler since the larger FETs have less resistance. The resistance due to the switching would be the same for the same brand ESC so that has not changed but the internal resistance has so this leads me to think that the internal resistance is a significant portion of the overall resistance in the ESC. As previously discussed higher voltages result in lower power losses for a given power level.

On the weight side then there is a significant weight difference. If we compare the Kontronic JIVE 150 for 6S at 140 gram vs the JIVE 80 at 12S at 84 grams then that is 54 grams lower for the HV setup which is significant weight saving and both have an internal BEC. Then there is the difference in price between the two but that is another story.

I think this is a great discussion so keep it coming.

Christian

Burn fuel, be happy

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01-23-2013 06:12 PM  4 years agoPost 145
KC

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WA

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That 24s is AWESOME

four 6s 2450mah 30C turnigy packs

each 420g $35.00 USD

1680g and $140

VS.

two 6s 5000ma 65C g6 thunderpower packs

each 805g $250 USD

1610g $500

A battery is about 1/4 the weight of a 700 so if the turnigy is 1680/1610 = 1.043 more the weight, then there is only a 1% weight penalty for using it and a 1.01^2 power penalty (2%...big deal)

Only 3.5 minutes? your flight time in an electric depends on how much headspeed you got to waste and that flight could be done with 85-90% as much rpm if geared down, so:

1+[(1.1 + 1.15)/2)^2 = 1.265

multiplied by 3.5 minutes translates to a comfortable 4.5 minutes of absolutely wild performance with a $140 battery.

gear it down some more and it will fly long enough to melt your brain trying to still keep up with what's there.

imho most of you are missing the elephant in the room: everyone crashes some day.

Even if you got only 140/500 as many flights from the turnigies as the brand name batteries, implying that you got the same $/charge from the two batteries, you've increased your stick time 500/140 times without spending any more $$$ since you can buy that many turnigies for each TP you would have bought when you were a battery snob

There isn't a better way to learn how to tune electric helis than using these cheap packs to work out the details for 140/500 the price and getting 500/140 times more experience.

"or just get a nitro"

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01-23-2013 06:59 PM  4 years agoPost 146
Richardmid1

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Leeds, England

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My 6s 5000 20-30c turnigy's are $44 each!

Kc, I mentioned the 3.5 min flight time but I also acknowledged the flying style and the 2250 rpm head speed, same as a 12s 5000 700 flown the same at that head speed. Gearing it down would still give the same flight times as a geared down 12s 5000 700.

The 24s x7 could have been 12s and you wouldn't have noticed the difference, power is down to the monster scorpion 4530 motor.

60% of the time, it works every time!

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01-23-2013 07:46 PM  4 years agoPost 147
KC

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WA

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Here's what I see in his flying style (24s vid)...he's "off" of it most of the time. He's being easy to it.

if he did a couple of 3 minutes flights both "on it" vs off it, he'll notice the average current is almost the same for that thing whether in 3d or swan lake.

listen to the rpm on it, so consistent it would be a real surprise if a hovering flight and a 3d flight were off by much more than 10% average to average.

doesn't matter the voltage, thats a set up that needs NO improvement: leave it like it is to get crazy, detune it a little to get flight time...DONE.

If I remember right, that 24S esc is over 600 grams. That helicopter has a considerable weight penalty against a typical 12s jive AND its doing just as good

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01-24-2013 07:48 PM  4 years agoPost 148
Rogman88

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West Monroe, LA

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This is one of what must be calculated before comparing HV to LV!
2200mah X 3 is 6600 mah
1300mah X 6 is 7800 mah

I'n not shoehorning a 2600 mah 3S pack in the front of my 450 as the dimensions are longer than necessary. Weight will be shifted forward more than needed and the canopy holes would need to be altered. The 6S voltz pack fits just fine and the weight is closer to the shaft for better CoG. I'll keep my 6S setup as it's much better than the 3S that I had....

High Voltage just works better

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01-24-2013 08:44 PM  4 years agoPost 149
BobOD

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New York- USA

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At least you understand the difference and state a correct reason one worked better. Cool.

Team POP Secret

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01-24-2013 09:16 PM  4 years agoPost 150
Ravenhyper50

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Canada's Capital

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Nice

Raven

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01-24-2013 09:43 PM  4 years agoPost 151
BobOD

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New York- USA

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And BTW Rog, one might figure from your earlier post that you thought the increased performance was mainly from going 3s to 6s. And now you realize that you simply put in a battery with higher capacity.

You're welcome.

Don't feel bad, some STILL haven't figured it out.

Team POP Secret

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01-25-2013 02:40 AM  4 years agoPost 152
Rogman88

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West Monroe, LA

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Yep, shorter and fatter works best for me....

You can only get so many of those plates lined up in a cell.

High Voltage just works better

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01-25-2013 07:44 AM  4 years agoPost 153
Richardmid1

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Leeds, England

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If I remember rightly tp's older 3s2600 packs were the same as the 2200 just thicker but your right most 3s 2600 packs are larger and flatter. You could use 2 3s 1350 packs from the blade 300x in parallel to get 3s2p 2700!

60% of the time, it works every time!

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01-26-2013 01:05 AM  4 years agoPost 154
BobOD

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New York- USA

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OK...I'm still pondering this motor thing. Not too much...it's been a busy week.

Let's see, so far for a LV setup we have;
Thicker, shorter wire in the winding.
Higher amp draw.
Almost seems it could be a wash.
Hey, wait a minute, we've already shown that wire losses aren't quite as high as we expected for the rest of the system. How significant are they for a couple inches of wire in the motor? Oh yeah, we have other mechanisms of loss don't we? This in interesting, I'll get back to the pure resistive losses. That's kind of the easy stuff anyhow.

Let's take a quick look at eddie currents. Eddie currents are generated due to changing magnetic field. These currents flow in the stator core and generate that stuff we really hate...heat. Notice that's "changing" fields. Kinda sounds like time enters the picture huh? Yeah, this could get confusing indeed. Boiling it down to something simple is the goal. We'll see.

Enough for now.

Team POP Secret

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01-26-2013 06:39 PM  4 years agoPost 155
BobOD

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New York- USA

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Getting back to the ESC for a moment, I did a little experiment to demonstrate a point I made earlier. The point being made is that just because something is hot, this does not necessarily mean it is a significant source of loss.

In this picture, I have a heat sink roughly the size of a typical ESC. There is a load attached to the heat sink and this has 30 volts applied and 0.57 amps. P = V x I = 30 x 0.57 = 17 Watts
After 4 minutes, the temperature of the heat sink was 206 F.
Yeah, I stuck my big thumb on it and..."OUCH".

A lot of people will feel a hot ESC and then conclude that it is very inefficient and will reduce the power and duration. Thus the myth. It's correct, just insignificant. It takes some experience and analytical skills to realize the true impact. You can't just compare such a thing to an arc welding operation and say that means it is significant. That is unethical misleading.

I didn't really do this for me, the result can be calculated and experience shows the same thing. But, a picture is worth a thousand words I guess.

And BTW, this means that the HV esc being less efficient (as it likely is for reasons given) is no real argument for a LV one, at least not as far as how much power it's losing. And for sure, it isn't the other way around.
Myth BUSTED.

Team POP Secret

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01-31-2013 12:21 AM  4 years agoPost 156
BobOD

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New York- USA

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Based on the little experiment above, I think it is reasonable to put a controller in the picture so I've added it. And we can still say the following.
1. There is no difference for the battery. Each cell is loaded exactly the same (it is not harder on the battery).
2. The wire loss does not contribute much to efficiency.
3. The controller loss does not contribute much to efficiency.
4. A load can be configured to produce the same power and operate at the same efficiency.
5. The main reason this differs from many other applications where it is known that HV produces higher efficiencies is due to the short circuit paths.

Keep in mind the 4th doesn't say what "a load" is. If it is a resistive load like a light bulb, then efficiencies would be the same. That is, both would produce the same amount of light. So, the question now becomes, why can light be produced with equal efficiency regardless of voltage but shaft power can't? I think there are reasons for this and the main point here was, whatever difference there is, it is almost entirely due to the motor.

Team POP Secret

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01-31-2013 01:57 AM  4 years agoPost 157
dkshema

rrMaster

Cedar Rapids, IA

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Bob -- minor correction.

Eddy Currents, not Eddie Currents. I've never met Eddie.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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01-31-2013 01:59 AM  4 years agoPost 158
BobOD

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New York- USA

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LOL
Thanks.

Team POP Secret

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Scorpion Power Scorpion Power
HelicopterMain Discussion › Effect of Cell Count
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