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Power loss


TonyS
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Hi everyone,

probably been covered before somewhere but....

I took my old Vampire foamy out today to give it an airing but only remembered why it’s been sitting unused for years...

it has retracts and therefore takes off from the ground rather than being hand launched. Several times I put it down powered up then increased to full throttle only for the motor to ‘die’ as the throttle lever hit the max.

Needless to say it never got off the ground.

i have flown this before so not sure what’s going on. I tried a second battery but had exactly the same result so I doubt it’s the batteries (unless they;re both knackered in the same way).

basically the power curve seems to increase until the throttle hits c 75-80% of travel after which it starts to drop off.

could I have inadvertently messed up the settings on my DX7 TX?

could it be an issue with the ESC?

anything else?

Answers on a postcard (or in this thread) please.......

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Highly unlikely to be the TX, ESC or motor if nothing was changed since the last time it flew, even if that was a long time ago. Check the batteries on a wattmeter and the cell IR on your charger - my guess would be they are end of life. How were they stored, at full charge or storage voltage (3.7-3.8V/cell)? If it’s the former and they were unused for a lengthy period then they will almost certainly be knackered.

Ps - The Durafly Vampire is a great model, but the gear is a weak point and adds weight - they are easier to operate from a hand launch, and fly better too.

Edited By MattyB on 06/09/2020 20:33:32

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Posted by TonyS on 06/09/2020 20:36:17:

Thanks Mike,

I’m using the highest rated batteries I can find - Turnigy Nano Tec 2200 4s 90c. If that isn’t enough I’m lost....!

Case closed - Nano-tecs are notoriously inconsistent, especially the highest C-rated ones. I’ll bet you a knackered 4S 2200 that when you put them on the wattmeter you’ll find the voltage is collapsing under load.

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Voltage on the batteries falling until the ESC hits low voltage cut out which may be a slow down setting rather than a complete cur off, so as you push the throttle up, the ESC ignores the increasing throttle and actually trims the power back to keep the voltage above the low voltage setting.

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Turnigy Graphenes are the ones I have found to be most consistent in high drain applications like EDF - I’ve not used the new Panther variant yet, but have two packs on order for my 3.6m esoarer which will pull very hard in short bursts. Remember whatever the C-rating on the sticker you won’t get anything like that in real life (if you do pull that hard cycle life will be significantly reduced).

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I also found the Turnigy heavy duty 2200s worked well in my Vampire. RapidRC have them in stock:

https://www.rapidrcmodels.com/turnigy-heavy-duty-2200mah-4s-60c-lipo-pack-4248-p.asp

Matty's advice on the u/c is sound, but I kept mine on as I enjoy the take-off and landing parts of a flight, although fairly smooth grass is important for this model. I only ever had problems with the nose gear, had to beef up the mount area with some timber!

Re your original problem, I'd agree that the batteries are almost certainly the culprit. This could be confirmed with a cell checker plugged onto the balance connector when the motor is spooled up.

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Awesome. Great advice as always so thanks all.

I do find that the nose leg on this collapses easily - the slightest knock and so I tend to take off on my driveway which is tarmac but very narrow so little room for rudder error. The lawn is like a bowling green so I might try hitting that and see what happens.
(I live on a farm in case any of you are wondering if I’ve lost my marbles).
Will report back when I’ve got hold of a new battery!

Thanks again.

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Posted by Martin Harris on 07/09/2020 00:35:49:

I don't have one but most people at the club run these on 3200 - 3800 mAh 4S packs. These will naturally supply higher currents for any given (true) C rating than 2200s. There seems little penalty for the additional weight.

Completely agree with this. The Vampire has a very large battery bay and carries that extra weight well, so going to a larger pack is a good idea. PS - Many people on RCGroups have gone to 5 or even 6S on this model (with uprated powertrains of course); they fly really well and sound great too...

Edited By MattyB on 07/09/2020 12:09:18

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That 6s version can really shift!

placed an order for the Turnigy Heavy Duty 4s 2200 today but have just been refunded as they’d made a mistake with stock levels and are out of stock. Oh well, I guess it’ll be parked gathering dust a while longer.....

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A friend and I compared some Turnigy Graphine against normal Turnigy hi C rated packs in an edf last year. The Graphine were new and the other batteries were well used . The Graphine were to say the least , disappointing. The standard blue Turnigy batteries out performed them easily . Our opinion / experience is that the Graphine batteries are an overpriced gimmick . Ordinary lipo batteries with adequate C rating is the way to go.

When batteries no longer power EDF models I've found them fine for lower power hungry models . My FMS zero fly's for long flights on batteries that are no longer fit for high power applications.

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Posted by Engine Doctor on 08/09/2020 10:06:31:

A friend and I compared some Turnigy Graphine against normal Turnigy hi C rated packs in an edf last year. The Graphine were new and the other batteries were well used . The Graphine were to say the least , disappointing. The standard blue Turnigy batteries out performed them easily . Our opinion / experience is that the Graphine batteries are an overpriced gimmick . Ordinary lipo batteries with adequate C rating is the way to go.

Interesting - most of my Graphenes were from very early batches that were very well reviewed, and they have performed superbly for me, but I have heard that later batches have not been so good. Did you test IR and calculate the real world C-ratings on one of the online Lipo performance calculators?

Edited By MattyB on 08/09/2020 11:26:34

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