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Old Apr 14, 2012, 07:59 AM
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USA, TX, Mansfield
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Quote:
Originally Posted by target View Post
Rick-
I'm going to preface my reply with "In My Opinion"....

The difference between an eneloop cell and the Elite cells is the internal resistance.
Eneloops are made to be used by devices with low amp draws, like your transmitter, camera flashes, etc, especially where their low self-discharge allows the device to be stored before use.

Elites are made for higher amp draws, like something that moves, has a load on it, a motor, etc. Servos have motors in them, very small, but they are motors none the less.

On a high wind, high strain launch (F3B or F3J), the wing surfaces servos will likley see high load. Folks have done tests to record the amp draws. Its substantial, I don't remember the actual numbers, but 4 wing servos loaded is a decent draw.
Also, the same F3B plane or F3J plane speeding into the LZ for a timed precision landing will see a spike in amperage.

The eneloops will reduce their voltage at this time more so than the cells that are constructed to "put out" when needed.

All this being said, I have several friends that still use a AA Eneloop in their planes without problems.
I have several others who, like me, won't use them for an airborne pack.

IMO....

R,
Target
+1

Internal resistance is key in the aircraft. It's too bad the servo mfg haven't seen the handwriting. A lot of the receivers now operate up to 8v. IMO too, 2S LiFe is the way to go these days. Lots of flexibility to charge and in some config more Mah then NiMH.

Rob
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Old Apr 14, 2012, 11:24 AM
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Quote:
Originally Posted by target View Post
Yes, eneloops still are used in planes. Just not mine.
I had to laugh, cause a lot of the slope guys across the pond were sold on them being able "to use them without charging first." Like I would fly a molded plane with a new battery without cycling it first? Pretty funny.


R,
Target
I'm not sure that's entirely fair (speaking as someone on the right side of the pond )

There will be folk everywhere who may have been sold on the 'instant charge' sales talk. For what it's worth I've sold thousands of Vapextech and Eneloop packs from my ebay shop and I ALWAYS advise that even though there is some residual charge in the packs that they should be fully charged (and tested) prior to use.

To the main point though. I know many people who successfully use 4.8v Eneloop and Instant packs in their F3X mouldies with no problems at all. Personally though I prefer the 2/3A Intellect or Vapextech packs as that extra cell chubbyness gives more current when demand from the servos needs it.

Dave E
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Old Apr 14, 2012, 08:51 PM
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Harbor City, CA
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OK, fair enough, Dave.....
But now you're saying im on the "wrong" side of the pond?!!
JUST KIDDING!

Yes, I thought it was really funny that some of the slope guys wanted to buy those because "they come fully charged!" Thats too funny....

I too am fond of the 2/3A packs for NiMH chemistry, but really, I am prefering the LiFe to everything, and think that I will just try to use servos that can run on 6.6v with reliability.

They have the same non-self discharge as the eneloops, and they can be fast charged....
Perfect, so long as your servos are happy.

R,
Target
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Old Apr 19, 2012, 01:08 PM
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Originally Posted by Silent-AV8R View Post
True enough. I've heard that the memory is the first thing to go. I can't recall what the second thing is.....
Ask your wife
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Old Apr 19, 2012, 01:37 PM
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OK so here is a point of view against lifep04 6.6 and higher packs when considering a 6v max servo. They have some benefits - quick charge for sure - low self discharge - yes - steady voltage - yes but there is a downside.

I am not saying that in a perfect scenario your futaba , ATX or JR servos will fail. What I am saying is that we dont live in a perfect world and the one thing that everyone is missing is that that the internal cel resitance and limited amperage output of say an enloope pack for example might be that saving grace when your surface is binding on something...(fill in the blank) If you NEVER bind a servo EVER then stop reading, this post is not intended for you

One undeniable difference between life \ lipos and enloopes are that Life can supply way more draw capacity (peak) than an enloope the lifep04 can supply 10.5 amps while the Sanyo cells produce far less - I think we all agree right?

Its possible right now that the Life crowd is saying "yes and thats why Life batteries are better - more power!" but more is not always better.

Most digital servos were designed in a previous context....a massive draw potential on a direct battery connection was likely not anticipated and the resulting ability for the servo to draw 10 amps is a little like giving a crack adict a hand full of thousand dollar bills...its not going to lead to apositive outcome if the servo encounters something to bind on. In fact I have seen guys kill servos in under 60 seconds with such robust battery sources.

Food for thought. I like my enloopes - 3 years running now and never a failure...when the life04 product was released I watched about 7 pilots in varying clubs fry product designed for 6 v...it was a mystery to them why it was happening.

Now I am not an electrical engineer and I am positive someone reading the thread is..so feel free to speak up.
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Old Apr 19, 2012, 02:17 PM
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An awful lot of the digital servos are designed for high current draw scenarios like helicopter cyclic controls. I would not be concerned about those units.

I will admit, I don't often go flying with a binding surface, that's something to fix in the shop, not at the field. If something starts binding, that's usually a sign to head BACK to the shop for a fix.

I have been using the LiFePo4 2 cell packs for over three years and have had no negative experiences. I run a regulator on a retract servo in one aircraft because that one servo is limited to 5 volts.

YMMV
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Old Apr 19, 2012, 04:47 PM
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Most of the servos we use in our gliders have full stall currents around 2 amps or so. Larger digital like are used in giant scale aerobatic planes will stall at around 4 to 6 amps. If you ever reach full stall during normal use then you have something seriously wrong. Like a flap jammed on landing and then commanded to retract to zero flaps for instance.

Our smaller glider type servos also do not handle heat very well compared to larger servos. A typical helicopter tail rotor servo can be almost too hot to touch and still function fine. A small glider wing servo would likely be toast with that much heat build up (no joke!!).

As we know, being rated for "6v" may or may not mean it is safe at 6.6 volts. Many MKS are not. Others like most Futaba, JR etc. are fine at 6.6 volts. All say rated for 6v.

People should review that facts and then decide for themselves what they want to use. It's a hobby, have fun.
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Old Apr 19, 2012, 04:49 PM
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Quote:
Originally Posted by tkallev View Post
An awful lot of the digital servos are designed for high current draw scenarios like helicopter cyclic controls. I would not be concerned about those units.

I will admit, I don't often go flying with a binding surface, that's something to fix in the shop, not at the field. If something starts binding, that's usually a sign to head BACK to the shop for a fix.

I have been using the LiFePo4 2 cell packs for over three years and have had no negative experiences. I run a regulator on a retract servo in one aircraft because that one servo is limited to 5 volts.

YMMV
You kind of make my argument - agreed if a surface pushrod etc is binding you must fix it before you fly but you can bind a servo on a perfectly well setup model too.

Like a rudder servo with a stalk of hay after landing ...in a hay field...(ask me how I know). Tell me what a high current draw will do to a digi with an off center bind Vs an enloope - I know because I have actually had it happen to both... the lipo powered servo totally melts down in seconds vs an enloope with reduced draw potential... its bad scene either way but sure fire way to destroy the servo with a lipo. Maybe I just had one of those bad days but really the draw potential in the wrong sceenario is a concern.

You can bind a flap servo with a tiny little bump on landing if the skin and wiper are very very close to touching.

Its the stuff outside of the flight envelope that happens quite a lot that concerns me...we dont fly in a perfect world.

Dont get me wrong I like the size capacity and weight of the LifeP04 but I don't want to have to regulate it and add anything further to the model (another point of failure)
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Old Apr 19, 2012, 04:53 PM
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I don't run a regulator except on one 5v retract servo, everything else is unregulated LiFe ... but as it's your investment, test or not, regulate or not, it's up to you to do what you think is best.
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Old Apr 19, 2012, 04:58 PM
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Quote:
Originally Posted by Silent-AV8R View Post
Most of the servos we use in our gliders have full stall currents around 2 amps or so. Larger digital like are used in giant scale aerobatic planes will stall at around 4 to 6 amps. If you ever reach full stall during normal use then you have something seriously wrong. Like a flap jammed on landing and then commanded to retract to zero flaps for instance.

Our smaller glider type servos also do not handle heat very well compared to larger servos. A typical helicopter tail rotor servo can be almost too hot to touch and still function fine. A small glider wing servo would likely be toast with that much heat build up (no joke!!).

As we know, being rated for "6v" may or may not mean it is safe at 6.6 volts. Many MKS are not. Others like most Futaba, JR etc. are fine at 6.6 volts. All say rated for 6v.

People should review that facts and then decide for themselves what they want to use. It's a hobby, have fun.
Exactly - take a 761 that is bonded to a carbon skin and heat it up with an Off center bind (OCB) and it dies quick if you have a good draw source...so did my JR servos and a few Futabas no manufacturer was free from stress that year lol...

If I am flying where I can pick that kind of stuff up in a wiper I just make sure I don't push my luck and land too far away from me...

it would be interesting to do a comparison between an off center bind and a stalled servo to see how long each takes to blow the servo in each battery....
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Old Apr 19, 2012, 06:40 PM
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Your Off Center Bind is the definition of stalled. If the servo is physically stopped from moving to the commanded position that is what is meant by "stalled". It is the maximum amp draw condition for the servo. It is different from the amp draw that results from aerodynamic loads. Those are less than the stalled current.
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