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Old 10-10-2013, 12:42 PM   #1
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Default Super Endurance

I am the first to admit there is absolutely no point in this except for my own personal curiosity. I already have an electric powered plane that can fly longer than I can so why go for longer still?

This plane had 4 LiFe cells built into its wing. They were charged insitu.
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Although a sound technical solution that allowed the plane to carry batteries that weighed 60% of its total the widely spread load did result in some stability issues which were never completely resolved. Its wayward flying characteristics prevented it from getting anywhere near demonstrating its potential 2 hour endurance.
In its final version the LiFe cells were replaced with Li-ion. Of exactly the same dimensions they had 3 times the capacity, delivered 3.7V instead of 3V and were 5% lighter but they have a very limited 1.5C rating. However for endurance flying such a low C is not really a problem as at cruise the current required is very small, 0.5C or less.

My Endurance plane carries a 5000mAh 2s LiPo that weighs 7.2oz and it flies on 1A.
6 Li-ion cells in a 2s3p arrangement would give 9000mAh capacity and weigh just 8oz. If they could be housed in a plane that could also fly on 1A its duration would be.......silly!

Tubular cells can be efficiently arranged in a triangle and if stacked 2 deep it would neatly give a 2s3p arrangement.
A test section of a triangular Depron fuselage to demonstrate the layout.
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As the Li-ion cells have to charged individually they have to be removable. A single cell sized hatch is one possibility.
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Would this even work or ever show the potential endurance?
I have no idea, but there is really only one way to find out!


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Old 10-10-2013, 12:58 PM   #2
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Interesting! I have several of those Li-ion batteries in LED bike lights. I tend to think they dont quite live up to their mAh rating so I'm interested to see what you find.

I successfully charge mine in series with my iCharger. I rigged up a balance connector that allows me to balance charge a 2s 2p pack. No issues other than you need to keep the charge rate low or they warm up. I'm sure you could do the same which would much simplify charging.
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Old 10-10-2013, 06:37 PM   #3
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Originally Posted by quorneng View Post
I am the first to admit there is absolutely no point in this except for my own personal curiosity. I already have an electric powered plane that can fly longer than I can so why go for longer still?


Would this even work or ever show the potential endurance?
I have no idea, but there is really only one way to find out!
For what it's worth, those Alkaline "D" cells have something like 14 Ampere Hours capacity.

Ah, never mind. I just weighed one, they are 4.76 ounce each, and you'd need 5 of them.

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Old 10-10-2013, 06:59 PM   #4
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This video adds more weight to the questionmark about the true mAh of those batteries:
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.

The results I got weren't that bad but still miles short of the claimed capacity.

This web page details tests of a few Ultrafire batteries from different sources and gets wildly different results, varying from poor to truly abysmal. Seems like there may be some fakes going around?

Looks like the Chinese manufacturers of these batteries have found a great way to make more profit. Simply take the same old 1800-2400mAh battery and put a label on it stating 3000mAh. Inflate the price by 50% and job done! Most people probably wont even notice anyway.

Same policy applies to 'c' rating on LiPos
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Old 10-10-2013, 08:17 PM   #5
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JPF
I fear you may be right about the capacity of these cells but as I understand it they have a relatively high (compared to a LiPo) internal resistance. To achieve anything like the rated capacity the current has to be very low.
My guess at this stage is both charge and discharge have to be as low as 0.1C so a single cell in a torch at 1A is way over its optimum discharge rate.
I am aiming for a cruise discharge of just 0.11C.

This project is purely an experiment and in my heart of hearts I will be surprised if a hard cased Li-ion cell really can better a soft case LiPo for power density.
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Old 10-10-2013, 09:18 PM   #6
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Originally Posted by quorneng View Post
JPF
I fear you may be right about the capacity of these cells but as I understand it they have a relatively high (compared to a LiPo) internal resistance. To achieve anything like the rated capacity the current has to be very low.
Yeah, even those lead acid batteries we use to field charge our models have a very low effective "C" rate. If you try to discharge them in less than 10 hours or so, with an effective 1/10C, you really shorten their life. Been there, done that.

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Old 10-11-2013, 11:40 AM   #7
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The triangular arrangement looked reasonable so a complete fuselage in 6mm Depron.
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The space between the formers defines the battery compartment.
After some thought I decided the most practical way to load the batteries was to hinge the complete nose section including the motor and prop in such a way that the very act of closing it made contact with the cells.
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As in a torch this requires an individual spring contact for the negative end of each battery.
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The wire is soldered to the end of the spring so no current passes through the spring steel itself.
The individual contact wires are joined together and the cable run forward to the nose.
The radio will also be placed in this area.
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The 6 cells in place ready to be compressed on their spring contacts by the nose section as it is secured in place.
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The nose will also house the ESC.
The wing and tail surfaces will be mounted on the top of the fuselage.


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Old 10-11-2013, 01:53 PM   #8
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Interesting!

It's never too late to have a happy childhood.
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Old 10-11-2013, 02:34 PM   #9
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Denny, is it possible that these cells need to be "conditioned" like the old type cells?
On those you ran em a couple of cycles to get em built up.

Maybe why folks aren't seeing the rated capacity on new ones.

When I die, I want to go like my Grandfather did, in his sleep...... Not screaming like the passengers in his plane.
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Old 10-11-2013, 03:22 PM   #10
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Originally Posted by Glacier Girl View Post
Denny, is it possible that these cells need to be "conditioned" like the old type cells?
On those you ran em a couple of cycles to get em built up.

Maybe why folks aren't seeing the rated capacity on new ones.

I've got several cycles on mine and they still dont approach their rated capacity, not only on discharge but even when charging you cant put the mAh into them that it says on the label.
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Old 10-11-2013, 10:02 PM   #11
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Completed the nose section today and hinged it onto the rest of the fuselage.
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The Blue Wonder motor is buried under the Depron rings.
The nose raised to show the battery access.
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It is just possible to see the triangular contact plate on the back of the nose that will make contact with positive ends of the batteries
With some Depron cheek pieces added to bring the triangle up to the spinner diameter, a lot of sanding and some lightweight filler.
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I does seem to work ok but whether it will actually drain the 3 parallel paths equally is any bodies guess!


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Old 10-12-2013, 01:28 AM   #12
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Originally Posted by Glacier Girl View Post
Denny, is it possible that these cells need to be "conditioned" like the old type cells?
On those you ran em a couple of cycles to get em built up.

Maybe why folks aren't seeing the rated capacity on new ones.
The problem with those lead acid batteries, is they are rated for a 20 hour discharge rate. So, for those 120 Amp Hour batteries I've been using, that is a maximum discharge of 6 Amps. I've even looked at those $$$$ electric power substation backup batteries. A 130 something Ampere Hour substation battery weighs in at over 150 pounds, and costs some $700. And, even that battery can't handle a continuous 50 Amp discharge cycle.

Problem is, my A123 chargers are pulling 55 Amps out of that poor 120 Amp Hour battery. And, according to Peukerts law, doing 55 Amps on this battery actually reduces it rated ampere hour capacity down to about 25 Amp Hours!!!
Take a look:
http://batteryuniversity.com/learn/a...attery_runtime

That is the big limitation on these giant scale electric models. What to use for field charging. Which is why I've got this setup that will charge at 60 amps as long as the Harbor Freight engine has gasoline.
http://www.wattflyer.com/forums/showthread.php?t=66066

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Old 10-13-2013, 11:57 PM   #13
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Peukerts law? I had to look that up.

Well if you must fly such huge planes......I flew my Fokker V25 for 3 minute test flight today and it took just 71mAh to fully recharge the 800mAh battery!

The existing 15" outer wing panels will be joined to a new 10" inner section.
The new inner wing spar.
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A balsa/Depron/balsa sandwich 3mm thick. The balsa is deeper towards the root.
The top and bottom of the spar is flush with the wing surface to give the maximum possible spar depth.
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The spar and lower skin attached to the tip section.
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With ribs added and the aileron servo wire in place it is ready for the top skin.
The inner panels are symmetrical so two of each component was cut out at the same time. The other wing should build a bit quicker.


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Old 10-14-2013, 02:12 AM   #14
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Originally Posted by quorneng View Post
Peukerts law? I had to look that up.

Well if you must fly such huge planes......I flew my Fokker V25 for 3 minute test flight today and it took just 71mAh to fully recharge the 800mAh battery!
LOL
Yup, I've got a couple of those type model planes. Been saving them for flying when we have snow on the ground.

As for those giant scale models, my Cellpro Powerlab 8 chargers are charging that A123 battery pack at 30 Amps! It's done in 17 minutes.

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Old 10-15-2013, 12:38 AM   #15
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The completed wing sitting on the fuselage to see what it looks like.
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Not very elegant but it is intended to be a low power weight lifter.
It should come out at 15oz all up of which the batteries make up just over half.

It will certainly be interesting to see these cells perform but even it is only 1000mAh each it could still fly for getting on for 3 hours!


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Old 10-18-2013, 12:38 AM   #16
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Completed with th ewing temporarily held in place with rubber bands.
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The Depron pad is to stop the bands damaging the wing , particularly the trailing edge.
It flies!
Quite sedate but after 10 minutes the motor mounting worked loose.
A bit of nose surgery was required to reinforce the motor mount but as the CofG proved satisfactory the wing was glued into position which gives a rather neater installation.
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The 7.5x4 prop has been replaced by a 9x5 which should improve the cruise efficiency.
Next to try to establish just how long it could fly.


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Old 10-18-2013, 12:55 PM   #17
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Originally Posted by quorneng View Post
It flies!
Congrats!

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Old 10-18-2013, 04:40 PM   #18
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A rather boring video of its second flight but the first with the wing glued on.
Nothing very exciting but I just had to make use of the dull but calm weather.
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.

The plan is to find out how much current it takes at minimum cruise speed.
I will build a ballast battery the same weight as the six LI-ion cells but with a small 1000mAh LiPo instead.
Once I have achieved the best duration with that battery the average current can be calculated. The Li-ion cells can then be bench tested at that load to see how long they last. Easier than actually flying for hours and hours!
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Old 10-23-2013, 05:54 PM   #19
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The next step (once I get some decent weather) is to establish how much current it take at minimum cruise power.

I will use a 1000mAh 2S LiPo but ballasted up to the same weight (7.4oz) and size as the six Li-ion cells. It will need over 6oz of lead!
The beginnings of the 'ballast' battery with the six cells for comparison.
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The LiPo will be inside it and wired up to use the same contacts as the Li-ion cells.
A 1000mAh is chosen simply for convenience and cost as running it down to LVC on each duration test flight will not do it any good.
If I can get a 1 hour flight, like I did with the Endurance, I know it will be flying on 1A average.


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Old 11-02-2013, 11:32 PM   #20
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In a lull between seeming endless Atlantic depressions I managed a long (1hr 7 minute) test flight with the Super Endurance.
The flight was terminated because it was getting dark and the ESC cut out and reset itself. Fortunately it does pretty quickly (<2s) but I could clearly hear the arming beeps so I cut the power and glided in.
I am not quite sure why the ESC did this. On the LiPo powered Endurance it just went into a normal 'low power' LVC mode. Perhaps the voltage had dropped so low that the ESC treated it as a complete cut in power.

I am concerned that a 9x5 is not the ideal prop and the efficiency of folders in low power installations is questionable so the next flight (weather permitting) will use a fixed 8x4.3 which is the same as the LiPo Endurance uses. It already uses the same type of motor.
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The 'spinner behind' layout makes best use of the very small diameter hub on the slow fly prop.

So not 9 hours (I doubt it will ever achieve it) but just over 1 hour is a start.


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Old 11-02-2013, 11:51 PM   #21
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WoWser! super job, I'm inspired to try one as well, I have a plane thats been in hanger for a few years,, I'll put a 250 outie and a 10ESc , bubsteve


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Old 11-03-2013, 09:07 AM   #22
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Originally Posted by quorneng View Post
I am not quite sure why the ESC did this. On the LiPo powered Endurance it just went into a normal 'low power' LVC mode. Perhaps the voltage had dropped so low that the ESC treated it as a complete cut in power.
Those cells have a built in low voltage protection circuit, if their voltage drops below a certain value they shut themselves down. Possibly explains what you observed?

I'm with you on the endless Atlantic depressions. I managed to fly twice last week, three quick flights in my lunch break in 20mph wind, and one maiden flight of my new heli Saturday morning in a brief lull in the wind before the rain and wind kicked in yet again. That time of year I guess
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Old 11-03-2013, 12:34 PM   #23
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JPF
If the low voltage protection actually works then it would certainly have such an effect.

However with 3 sets in parallel there is the possibility that individual cells may cut out several times before all three paths do it simultaneously so discharging the batteries that bit further which may not do them any good.

I have been doing some discharge tests and it does appear that their capacity rating is hopelessly optimistic, just 650MAh on two cells I have tested so far and that is at a low 0.3A (0.1c) rate.

9 hours it ain't ever going to do!
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Old 11-08-2013, 08:14 PM   #24
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Having established that the Li-ion cells I am using are never going to give the duration I intended (top quality ones may be better but are actually more expensive than a LiPo) I will move the objective a bit to investigate the comparison between tractor and pusher configurations.
So we have two planes with the same span, same weight, same battery, same motor, same prop.
I have flown for 61 minutes with the pusher using 1000mAh 2s. The task is to see if I achieve the same (or better) with the tractor layout.
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Old 11-11-2013, 09:00 PM   #25
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Just a quick up date
Last Saturday I flew both the Endurances.
43 minutes with the tractor Super Endurance taking its Li-ion cells to LVC which needed 1600mAh to recharge the 2s3p set.
47 minutes with the pusher Endurance needing just 600mAh to recharge its 1000mAh 2s LiPo.

The object of these flights was more to compare their flight characteristics (the pusher is nicer to fly) in ideal blue sky little wind conditions rather than test their endurance although the difference in power consumption is remarkable given both planes have similar aerodynamics and total weight along with the same motors and props.

So did I by chance build the pusher version exactly on the 'sweet spot' or is the pod and boom pusher layout actually more efficient for ultra low power flying?

I might have to build a specific test plane to prove this one way or the other.
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