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Matt Kirsch
07-22-2005, 01:41 AM
When Hangar 9 announced a .60-size P-40 ARF, I knew I had to have one. Believe it or not, the first model airplane I ever flew successfully was a Cox P-40 Warhawk control line powered by one of those cantankerous Cox .049 reed valve engines.

Most of this project is old hat. I'm using a 6S LiPoly setup powering an AXi 4130/16 motor and 16x10 APC thin electric prop. The modelmotors.cz website claims 878 Watts in, which should give this plane excellent performance. This combo should be more than adequate to power any .60-size sport plane weighing 7-10 pounds.

The motor mounting technique may look familiar to friends and acquaintenances of Greg Covey. It's a simple 1-1/4" PVC coupler, cut to length to provide the correct firewall-to-prop-drive spacing. Long 6-32 screws clamp the spacer between the motor mount and the firewall.

Mike Parsons
07-22-2005, 01:58 AM
Sweet!

Matt Kirsch
07-22-2005, 02:49 AM
Here is the inside of the fuselage, showing the battery tray I installed. The tray extends all the way to the firewall, and is screwed in. Notice the utter and complete lack of servos! The elevator and rudder servos are located in the tail, and there's no need for a throttle servo, so the entire radio compartment is wide open.

You might worry that having the servos in the tail would make the plane too tail heavy. Just balancing the fuselage with the motor installed, it feels like I'll be okay on balance, given that I'm using a 6S1P pack of Kokam 3200mAh LiPoly cells. Yep, 1 single solitary 21oz pack in parallel.

Geoff_Gino
07-22-2005, 03:30 PM
Hi Matt
Read the review and downloaded Greg's video of the Hanger9 F4U that he converted and my Corsair is begging me for an electric. Question. Greg has 3 cell packs in his plane and I see a lot of discussion about Wattage, are the cells all in series (to use a good electrical term) to get the required voltage for the motor and are the motors current or voltage rated. Way I understand it, and may be wrong, is that current is the main source for concern. Having looked at some sites that have motors on offer they all appear to be rated at 35 volts or am I wrong.

Thanks for this great thread
Geoff

Matt Kirsch
07-22-2005, 05:27 PM
I believe the original power setup in Greg's F4U conversion was a combination series/parallel setup made from multiple 3-cell "sub-packs." Two 3-cell packs in series to make a single 6-cell pack for the required voltage, then a few of these 6-cell packs in parallel to get the required current-handling capability.

All motors are rated for a maximum cell count (or voltage) AND a maximum current. This can range from a single LiPoly cell up to a 10-cell (37 Volt) LiPoly for most of what's on the market today. You were probably looking at some pretty large motors if they were rated for 35 Volts, but rest assured, they're not all rated that high. :)

Both voltage and current are sources for concern when working with motors. Voltage determines the RPMs the motor will spin. Too many RPMs, and you start slinging windings or magnets. Current is determined by how much torque is requred to spin that prop. Try to spin too large of a propeller, and you end up drawing too much current. This can overload the battery, or burn out the ESC or motor.

luc
07-23-2005, 03:08 PM
I got one too with the same motor, in 6S, but I use a 15*10E, which gives enough power (I noticed the axi does not like too many amps). Moreover, a bigger prop has more tendency to hit the ground and to be broken in a nose in take off (yes, it happens)

Matt Kirsch
07-23-2005, 11:13 PM
When all ya's got is lemons, ya gotta make lemonade. Prop size is kind of limited until I make a Tower order or go to NEAT. Right now I have a Graupner 15x8 glow prop on the nose. It's the closest to a 15x10 I could find at the local hobby shops. The 16x10 is coming in the mail for another project, so I figured what the hey...

Anyway, to the heart of the system. This isn't just any ordinary 6S Kokam 3200 pack. What I have here is FMA's new SkyVolt system. It's a totally integrated system that's both robust and foolproof.

Matt Kirsch
07-24-2005, 07:15 PM
Well, it looks like I was way off on my CG estimations. Turns out that with the servos in the tail and the battery pack all the way forward, it's way tail heavy... on the order of 12+ ounces. :mad: No maiden today.

I'm going to have to relocate the servos up in the radio compartment near the CG. No biggie, as there is plenty of room up there. For every ounce I take out of the tail, I remove the need for about 4 ounces of lead on the firewall. 1.5 ounces per servo, times two servos, moved up to the CG should do it.

This did give me an opportunity to work out a mounting system for the 6S FMA Skyvolt pack. I'm not just an electric flyer; I make SPADs too, so I have a supply of square vinyl downspout material. Two 1" wide rings of downspout epoxied to the battery tray, and lined with self-stick foam tape makes an awesome battery holder. The battery is cradled, but not smothered so it can get cooling air.

luc
07-24-2005, 07:28 PM
don't forget that CG should be 1/2 farer than design . Mine is 3 1/2 '' behind LE, some even fly @ 3 3/4.
Note than I installed the tail servos inside the fuse (nicer than outside the fuse, and helps on CG too).

Matt Kirsch
07-25-2005, 02:28 AM
I spent the whole day today relocating the servos in the fuselage, and finishing up the battery mount. To make sure I only had to take the plane apart once, I also relocated the receiver pack up on the PVC motor mount.

3-1/2" you say? Drat! Now I have to re-relocate the receiver pack. It balances pretty well at 3" now, so maybe I'll maiden it like this, then move it back.

Unfortunately, both aileron extensions were bad. No roll control means no maiden anyway :( Oh well, at least it looks good.

Geoff_Gino
07-25-2005, 06:56 AM
Hi Matt

Thanks for the info on Greg's setp. I am very interested in the SkyVolt system you have shown here and especially the idea with the downpipe (downspout). That could be used for a lot of other things as well.

Do SkyVolt have a web site or is there a hobby shop that is on line that might have write ups and prices?

Flew my glo-cell this week-end and I am so sick and tired of tweaking, tuning and cleaning that I am ready to thro' in the towel. As soon as budget allows I will be going electric and my Corsair will have to wait for it's electrics. Like Greg said "No glow-cell is going into that baby"

Geoff

modeldesigns
07-25-2005, 12:38 PM
Hi Matt,

I am very pleased with my E converted P40. I am flying with the balance point as per the manual i.e. 3" from the LE with the wheels retracted. I did not have to add nose weight to achieve this, I just arranged the TP 6S3P Pro Lite cells to be posted through a hatch in the top decking and slid into a battery box angled to reach the firewall. All servos are std size and installed as the manual.

Here is the hardware:

65" Hanger 9 P40E Warhawk
8lb-9ozs flying weight
5V UBEC (one for the Rx, one for the retracts)
Axi 4130/16 motor, radial mount
Jeti Advance 45-3P ESC
(Hard timing, no brake)
Thunder Power 6Ah 6s3p LiPo cells
(As two, 6Ah 3s3p in series)
15x10 APC Pattern prop
7200rpm @ 42A
8lb 10ozs static thrust
68mph pitch speed

A 10 minute 'warbird' flight consumes an average of 4.0A with everything landing only warm to touch. Nice model.

The E converted review of the P40 is due to appear in the Traplet QEFI (Quiet and Electric Flight International) magazine.

Cheers,

Pete.

Matt Kirsch
07-25-2005, 08:02 PM
SkyVolt is a new line of totally integrated LiPoly packs, chargers, and protection circuits from FMA Direct. They should be available for general consumption by September:

*The charger will only charge a certain size pack, but it will charge that pack at up to 3C for 80% capacity in 20 minutes! There's no guess work as far as cell count goes, so no chance of choosing the wrong cell count and destroying the pack.

*The on-board protection circuit installs between the ESC and battery, effectively protecting the pack from overdischarge or overcurrent by overriding the throttle like an LVC.

*Each cell is tapped and monitored individually by the charger or protection circuit.

Cool stuff. I can't wait to fly this P-40.

Matt Kirsch
08-07-2005, 04:10 AM
Well, the waiting is over!

The P-40 made its first flight today. It was limited to a few laps around the field, but enough to get a good feel for how it flies. These ARFs these days just keep getting better and better... I can only describe it as absolutely rock solid. Not even a hint of a bad habit.

Like you guys said, it was a little nose heavy, so I moved the battery back to its original location back in the radio bay. Had a couple of nose-overs on the ground, and it sunk a little too quickly when I pulled back the power.

I still don't know how much it weighs, but it certainly flew "light," trucking along at what I'd consider a nice scale speed with the throttle at just below mid-stick.

As for the SkyVolt pack... I didn't even begin to tap its potential. The pack was barely more than ambient temperature, not even warm enough to light up the first square on the temperature indicator. It got warmer sitting in the sun for 2-3 minutes while I loaded the plane back in the van.

Matt Kirsch
08-08-2005, 04:20 PM
Flight #2 is under its belt now. I pushed the envelope a little further and tried a few maneuvers out. It definitely has plenty of power to do nice large loops and sweet slow victory rolls. The plane is absolutely majestic cruising along at half throttle, and it really gets up and goes when I put the spurs to it.

Even with the receiver battery in its original location on the underside of the cockpit floor, she's still a little nose heavy for my tastes. She wants to nose over on the ground, and doesn't want to slow down with power off in the air. I might resort to a 1/4 ounce of lead in a strategic location on the tail just to tweak it a bit. I'd rather not mess with relocating the components at this point. They just work too well where they are.

With this 5 minute flight, I got the first bar on the SkyVolt temperature sensor to light up green, indicating 95 degrees.

luc
08-08-2005, 06:54 PM
CG is ok within 3 1/2 to 3 3/4 in from LE.
A lot of battery packs are ok... I fly with
6S2P Irate 2200 or 2600
6S2P TP 1320
6S2P Tronic 1250 (15C cells)
6S1P Tronic 2100 (15 C cells).
The 2 sets I prefer are the TP 1250 (prolite) and the 2100 tronic which are very light (360 to 380g) and allow 5 minutes flights.
The 6S1P 2100 tronic give me 48A static and 30A in flight (motor time). these cells are also very cheap and a low heat.

Mike Parsons
08-08-2005, 07:17 PM
Congratulations Matt! Now we need Video!!! :). I am very interested in the Skyvolt packs for my next conversion. I need to research them more.

-Mike

feathermerchant
08-14-2005, 04:36 AM
I saw all 3 H9 warbirds - Miss America, P-40 and Corsair fly in the Seff demos this year. They are all great flyers. I have the Miss America on 6S 5,000 Tanic LiPo
The thing is Brian at Tanic will make packs about any shape you want. I find the TP's too long and skinny to get CG forward enough. They have started making shorter packs recently though.

Mike Parsons
08-14-2005, 04:56 AM
Welcome to Wattflyer Feather! It is nice that Brian will custom the packs for a buyer as I agree that sometimes it is very difficult to get the CG up there. TP did a smart thing by offering Vpacks, but even those are ackward if the battery area isnt large enough. Not that I am complaining with as far as we have come with electrics! :)

luc
08-14-2005, 10:38 AM
Feathe
I really don't see the problem of CG on the miss A. On mine, packs are exactly on CG place. I use a variety of packs, from 380 g (TP prolite 1320 6S2P) to 620g (Irate 6S2P 2200), and tronic 6S1P 2100 . All these packs are dead on CG, ez to swap.

Mike Parsons
08-14-2005, 02:02 PM
Luc,
Nice photos! If I recall, you use seperate 3S packs and harness them together..correct? I think you would have much more flexability where you put the packs and how you stack them to obtain CG. The prebuilt 3S3P and 3S3S2P make it a challenge at times.

luc
08-14-2005, 02:25 PM
You're right on most planes as I use 3S (or 3S2P for smaller cells) packs with a multiplug.
But for the P-51 MA, CG is exactly at the center of the batteries (for me, at least), so that is not really an issue on this plane (only).

feathermerchant
08-14-2005, 05:25 PM
Mine is pretty close but forward of the CG I think. I have the rudder servo in the fuse and a retractable and steerable tailwheel. Flexibility is the key. I had Brian make me 2 matched 3S 5,000 packs for my GP DR1. They are just behind the firewall for CG and in series so they need to be matched because I cannot remove them easily in the field for charging. I can charge them in series. I also use them in the twin CAP (Siamese CAP). One pack goes in each fuselage and they are not interconnected. About to have another 6S pack made for my GeeBee. The space is very limited to get the CG where it needs to be.

luc
08-15-2005, 08:41 AM
GP DR1...:)

Mines are inside the recess around the motor

really a nice plane...

rcers
08-15-2005, 02:39 PM
Matt - fantastic conversion.

I love the setup and the p40 is in my top two warbirds......Love it!

Mike

Greg Covey
08-26-2005, 12:45 AM
I saw Matt's P-40 fly several times at last weekend's local electric show. Even though it was quite windy, the P-40 flew great!

Hopefully, Matt or Ed got some photos.

dirtypool
08-26-2005, 03:13 AM
Hi. I have the H9 T-6 and am interested in going electric.

I noticed that AXI (and all others) have different "turns" selection on the motors. i.e. 16 turn, 18 turn... How do I know which is better for my application? What benefit does one have over the other.

Also, I was looking at the AXI and I noticed that they recommend the Jeti 77. I was thinking of the CC80 until I saw that some of you use 45 amp esc's. How do I know how much current my setup will draw without buying an esc and metering it? Seems like a chicken and egg thing. Cant measure it til I hook it up, cant hook it up til I know how much current....

Suggestions????

The number of turns and its effect on the power system has always eluded me.

Thanks.
Rob

feathermerchant
08-26-2005, 04:12 AM
For the T-6 I think Luc uses a 6S pack and AXI 4130/16 with APCE 15X10.
My Miss America has a 6S 5,000 An AXI 4130/16 APCE 16X10 or 16X12 and Phoenix 80. I prefer the programability and upgradability of the Castle controllers and they're made in the US. A 6S 5,000 Tanic battery will give you 10min flying time with reserves for going around. On the T6 with a 15X10 maybe 12-15min total. We usually land before we drain the batteries completely on these larger planes.

dirtypool
08-26-2005, 04:29 AM
Thanks.

So that would be 2 3s packs in series? To get 5000 mah then also run another set in parallel? Thats like $400 if my logic is correct.

luc
08-26-2005, 08:07 AM
yup, all my H9 planes have the axi 4130/16 in 6S and a 15*10E apc
I use light setups such as 6S1P tronic 2100 15C 380g
or 6S2P TP 1320 360g
The lightest is the one I just got from Charlie Wang I saw last week here en route to the world championships: new TP2100 15C pro lites.
6S1P will only weigh 290g !!!
I like these light setups because these planes have a weak point: the retractable LG and the lighter the better. Note, however I got FTE mech retracts on the MA, which are perfect!
here are pics of the new TP 2100 15C: 44.5g. These cells are not yet on the market.
as far as price, Tronic cells are really cheap, you can get them straight from the factory, ordering directly in China (takes some time, though....).

dirtypool
08-26-2005, 05:22 PM
So, would this be a good battery selection? 2 3s2p 3000 mah packs run in series?

Or, would a 6s1p pack be enough?

I will be using an axi 4130/16

Thanks.

Rob

luc
08-26-2005, 05:27 PM
You need to be able to draw 26 to 30A from your pack. If your 3000mA pack is a true 10C, pack, 1P is enough (2 packs 3S). Also don't use a prop too big (more draw). 15*10e apc is ok.
I prefer this setup rather than the 2P (lighter plane), although flights are shorter...

dirtypool
08-27-2005, 02:43 AM
Thanks.
Ok, well I dont know what the rating is on these:
LIPOLY Kokam HD 3000 mAh Pack 11.1 V 3 S 2 P 210 g 75 x 38 x 36 mm pre wired.

I thought 2 of them in series would give me all the room I need.

Or 2 of these in series since they are 12C:

DYMOND Lipoly hd 3000 12C 11.1 V 260 g 140x43x18 mm PC board for easy soldering and parallel packing

These are from the dymond website in case you havent noticed.

I just dont want to get the wrong batteries nor do I want to push them to their limits.

A CC 45 should be plenty?

luc
08-27-2005, 06:46 AM
ok for the kokam 3000 with 2 packs 3S in serie.
For the esc, you need the CC 45 HV as the std one will not accept the 20 cell equivalent voltage.
Best for Rx is to use a ubec, as the controller is opto.

dirtypool
08-27-2005, 06:56 AM
Ok, so the CC 60 says it will take 20 cells if you dont use the built in BEC. The HV does not have a BEC? So I would get an external one anyway, so would the CC 60 be ok? The HV is backordered.

byoung
08-29-2005, 06:24 PM
Luc,
Did you have to modify your retract pushrods or servo horn at all to install the FTE retracts in your Miss Am?

Thanks,
Brad

luc
08-29-2005, 06:46 PM
nope, that's a direct drop in

Matt Kirsch
08-30-2005, 01:48 AM
The Castle Phoenix 60 is exactly what I'm using in my P-40. A 6S LiPoly is a near-perfect equivalent for 20 NiCd cells, so you're not going to hurt it.

I disabled the BEC, and used a separate receiver pack in mine. Much cheaper than a UBEC or any other alternative.

As far as the whole "chicken and egg" thing... Check out www.modelmotors.cz. AXi publishes extensive application tables for each of their motors, so all you really need to know is how many Watts you need, and how much prop clearance you have. Just pick the lightest motor that will spin the biggest prop and consume the Watts necessary to fly the plane.

luc
08-30-2005, 06:45 AM
interesting....
for another application with 6S too, I am hesitating between the CC60 and the CC45HV.
same weight, slightly cheaper on the 60, but this one is on the limit on 6S and the CC45 might be also close to the limit for the amps....which one to choose?

feathermerchant
08-30-2005, 01:50 PM
Which has the lowest resistance? That one will have less heating. The HV is capable of 50A on 10S with good cooling. That's a lot of watts. Not many motors are rated for 12S.

Mustang11
09-08-2005, 02:28 PM
Luc,
you mentioned Tronic cells in post #30, I'm not familiar with those..................... might they have a web site? Thanks, LRV.

luc
09-08-2005, 03:54 PM
yup...
http://www.tronicshz.com

you can order straight from them (but it takes time and DHL costs a lot, so better order a bunch of cells).

Mustang11
09-08-2005, 06:32 PM
Luc, thanks I'll check it out. LRV

Tweet
10-12-2005, 03:50 AM
Luc,

Where did you put the servos in your P-40? Also, is everyone using standard size servos in this airplane? Anyone using one of the minis such as a Hitec HS85MG? I saw one of these in my local hobby shop and would really like to have one.

luc
10-12-2005, 07:00 AM
I use HS85MG inside the fuse, HS 81-MG in the wing (and HS 75BB for retract).
servos are inside he fuse on the back part, similar to what I did on the P-51 MA (see pic). It has several advantages:
- nicer
- helps on CG
- original place is rather flimsy for servo support and some have got problems there.

Tweet
10-12-2005, 10:55 AM
Luc,

Thanks for the response. I have four HS85-MGs, a 4130-16, PCM receiver, and a Phoenix 60 laying around so might as well go out and get the P-40 later today.

Looks like the HS85s actually meet the torque specification of the standard servo recommended by Hangar 9 for this airplane.

viflyer
10-12-2005, 12:57 PM
What about geared setups ( Hacker , Cyclon ) running 5S packs?

Matt Kirsch
10-12-2005, 01:28 PM
viflyer,

Are you looking for a specific geared setup, or just asking in general? Do you have something in mind?

If the setup spins a 15"-16" prop and can draw about 800 Watts, it'll work fine on this plane. Truthfully, I haven't done a Wattmeter pull on mine yet, but judging by the total lack of heat buildup in the battery pack, I am not drawing anywhere near 40 Amps with my 6S setup.

Tweet
10-12-2005, 04:41 PM
Matt, how is yours flying? How did the CG issue work out?

I am planning to use the HS85MGs I have which are lighter than a standard servo. I am also planning to use a separate receiver battery. Wondering if I should go ahead and put the HS85s in the tail.

Planning to go with a TP 6S2P 4000mah.

luc
10-12-2005, 05:59 PM
tweet, no problem for the HS-85MG...
I uyse a ubec to save added weight, w/o any problem (all of my 3 H9 warbirds).
TP 6S2P is perfect.
CG: go 1/2 in behind what is mentioned (31/2 to 33/4 is perfect), that will avoid nose ins.

Tweet
10-12-2005, 06:21 PM
Luc,

Do you recommend still placing the lighter HS-85MGs in the fuselage as you did or will they work in the tail to get the best CG with the TP6S2P?

Just trying to save some of the trouble that Matt went through.

luc
10-12-2005, 06:49 PM
I definitely prefer them in the fuse: the difference in CG is not that big (pushrods are longer) but the plane looks nicer and the support on the fuse below the tail is not that sturdy, according to some flyers.

dirtypool
10-17-2005, 03:33 AM
another question. Went out to fly today. I did not check it with the whatt meter first. took off and motor cut out (low voltage) so I landed and took it home. The meter says I am pulling 38amps with the 15x10e. My packs are 3000 mah 12C which should give me 36 amps available right?
So, what prop should I go to to get me under the 36 amps? How far under should I be?
I would rather not get new packs at the moment....

dirtypool
10-17-2005, 04:20 AM
You need to be able to draw 26 to 30A from your pack. If your 3000mA pack is a true 10C, pack, 1P is enough (2 packs 3S). Also don't use a prop too big (more draw). 15*10e apc is ok.
I prefer this setup rather than the 2P (lighter plane), although flights are shorter...

I went back and re-read this thread....
Why is my plane drawing 38 amps on a 15x10e? What could cause this? (AXI 4130/16 + 6S 3000mah 12C LiPo + Phoenix 60 ESC)
My voltage cutoff is at Auto, not using a BEC. Any speed controller settings that could be the culprit? Timing? etc?

Thanks

Rob

luc
10-17-2005, 06:20 AM
38A static is ok. In flight, you will be around 30A, which is ok for your cells. I got the same data on my plane (same motor and prop).
As far as lvc, personally I set it very low (equivalent to disable it) @ 5V, as your plane will be down before you are under low voltage for the cells.
If you set it too high, you run the risk of a shut in, in flight, sometimes even in the first seconds, as batteries show always a dip at the start in voltage before recovering.

dirtypool
10-17-2005, 06:03 PM
Thanks Luc.

I'll try that. So, you will notice the power decrease before the cells reach 3v per cell?

luc
10-17-2005, 07:41 PM
sure you will...you just can't fly @ 3V per cell....impossible (it can only be done on low consuming parkflyers, not that kinda plane).
Fot this one, with 6S 3000mA, you can count (with a safety margin of 20% unused amps) on 5'30" motor time, equivalent (depending on your dead stick time in flight) to a total flight time above 6 minutes.

dirtypool
10-17-2005, 07:49 PM
Thanks for all of your help Luc.

I'll give that a shot.

I never would have tried this without the help from you and all on this forum.

Rob

Matt Kirsch
10-17-2005, 08:49 PM
dirtypool,

AXi posts real-world data for most of their motors, including the 4130/16, on their website: www.modelmotors.cz (http://www.modelmotors.cz). You're right in the ballpark if you're drawing 38A on 6S with a 15x10 prop. It's probably a little much for 12C cells if you like running the horses, but okay if you cruise and fly the P-40 in a scale manner.

feathermerchant
10-20-2005, 11:01 PM
Considering the expense of batteries, I'd never set the ESC cutoff below what is recommended. If you fly using relatively high power it will cut off with plenty of extra capacity to get to the runway. Now if it quits just as you add power to go around, you're in deep doodoo either way. I was flying my H9 P-51 Miss America around and forgot I didn't takeoff with a full battery. When it cutoff, it really got my attention but I cycled the throttle, and flew the pattern just remembering that I had to make one good approach. Landed fine with enough power to taxi in.
To avoid shutdown altogether, make your maiden short. Say shoot for 3min and time it. I use my Tx timer. Then recherge and if you found you used 33% of your battery capacity, you can expect 9 min or so. The next flight can be 5min and again time it and recharge and see how you are doing. After a few filghts like this you'll have a good idea how long you can safely fly. Remember that as you get more familiar with the plane you'll fly more agressively and thus shorten your flight time somewhat.

dirtypool
10-20-2005, 11:11 PM
Well, it actually cut out after about 30 seconds. I am exceeding the pack's amperage draw rating by 2 amps when static. Even at partial throttle, it cuts out at 30-45 seconds when set to 3v per cell (18v). I am going to prop it down a size and see where it comes in, but the batteries do not even get warm as it is cutting out so soon.
My foamie lvc works great, but this larger setup seems to have an issue.
My concern is only that I keep the batteries safe. I am using a separate rx pack. I will try a "full run" with the lvc disabled and see how my temps are, etc. Whatt meter will tell.
Using a Phoenix 60 if that matters.
Thanks!

feathermerchant
10-21-2005, 05:01 AM
I would not run it long on the ground. That's a recipe for destruction. At least remove the cowl and don't run it long. Propping down is a good idea.

luc
10-21-2005, 07:56 AM
15*10E prop is ok...the problem comes from the dip at the initial discharge. YTHis dip is very pronounced on kokam cells, not as much on other brands 'TP, tronic,...) Setting lvc very low will not damage anything and avoid the cutoff. Of course, you have to monitor (with timer) your flight duration.

Matt Kirsch
10-21-2005, 01:19 PM
dirtypool's using 12C cells, so they're definitely not Kokams. I didn't go that far back in the thread to see exactly what he's using. Anyway, if the LVC is kicking in after only 30 seconds, that's no "dip." He's definitely overdrawing on the batteries. Not a good idea to fly it like that...

I'm not sure about this whole "dip" idea... Dip implies that the voltage drops then comes back up. None of the discharge graphs I've ever seen show such a dip, and I know I've never seen it personally. Doesn't mean it doesn't happen, but I know enough about physics and chemistry, and with the evidence I've seen to this point, I just don't buy the "dip" theory. Under a constant load, once the voltage starts dropping, it keeps dropping. How quickly it drops depends on the design of the cells in the pack. Higher C-rated packs should drop more slowly.

Regardless, if the dip is enough to kick in the LVC within 30 seconds on the ground, you're pushing the batteries too hard, period... Lowering the LVC is not the solution. The real solution is to reduce the load on the packs, add parallel packs to better handle the load, or use a pack with a higher C rating.

luc
10-21-2005, 01:33 PM
None of the discharge graphs I've ever seen show such a dip
just ask...:) and this battery was only @7C....
http://www.rcgroups.com/forums/attachment.php?attachmentid=455981
I still agree with you on the conclusions, except if the draw is really close to the limit. The initial draw is important during take off and getting the altitude, then you should be able to cruise with a lower draw on batteries.