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RPM from Hacker 14XL

Old 06-24-2009, 02:41 AM
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twoturnspin
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Default RPM from Hacker 14XL

Gents,

I have found myself a little disappointed with the powered delivered from my setup and am interested in understanding any thoughts on improvement. Let me explain where I am at:
Setup: Integral with Hacker C50 14XL Comp (4 degrees), Spin 99, APC 20x15e, Hyperion 16C 5350mah
Reading on ground (max throttle, fresh charge): 34.7V, 59A, 2050W, 5600RPM
Reading in air (max throttle, average of top 30 amp draw in 3 flights): 34.8V, 57.6A, 2000W, 5683RPM

I tried serveral other packs to check out battery performance as I thought ~3.5 V/cell was low and found that Zippy and Thunder Power gave approximately the same readings, ie. 3.4-3.5 V/cell. I looked back at other packs that I use in a TRex 600, (Flight Power and Hyperion) finding that ~3.4 V/cell was the result achieved here as well. My conclusion from this is that, under load, I can expect to achieve around 34-35 Volts from a 10S pack.

Extrapolating this out from this voltage I concluded that the maximum RPM I would expect would be 34.5 (Volts) x 1100 (KV) / 6.7 (gearing) = 5664 RPM (regardless of the prop used). So that fact that I am getting 5600 RPM means that this is as good as it gets in terms of RPM from the motor (ie. it won't draw more current) and the only way I can draw more amps is to put on a heavier prop.

So, I'm currently using a 20x15, will a 21x14 put more load on the 14XL motor? Are there any other options to deliver more watts overall with these components? Any thoughts? I would like to be able to pull an extra 500watts or so as this would oversome some weakness towards the ends of a couple of a couple of manouvres.

Simon

PS. As a comparison, the other guys with electrics I was with over the weekend had outrunners which were drawing up to 80amps at full noise (at around 34.5V) and a much higher RPM with a similar prop, this makes sense because their KV's were (approx) 230KV and therefore their max theoretical RPM is around 8000 at this voltage, hence their motor will draw more current on the same prop. To be honest, I hadn't thought about this much before and it did surprise me somewhat. I'm thinking that I would be better off with a higher KV motor in the inrunner style which would allow me to draw more power.
Old 06-24-2009, 08:30 AM
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flyboy91
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Default RE: RPM from Hacker 14XL

For some reason your packs seem to be down on Voltage by quite a bit. My Thunder Power 10s 5000 Pro-lites are about 37 volts when I run my plane up and draw around 72 amps all this testing is done on a 21x14 prop. I would say try the bigger prop and see if it will draw more amps in order for you to get your wattage up.


We ran into this problem at a contest locally where the person had Zippy packs which would drop off to 35 volts and hold there which wasnt giving him enough power at 49 amps being drawn. He went back home put a different motor in which drew 70 amps and the packs still stayed at 35 volts.
Old 06-24-2009, 03:27 PM
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twoturnspin
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Default RE: RPM from Hacker 14XL

Thanks for that Andrew, I wasn't sure if a 21x14 would draw more current than a 20x15 so I'll give that a go. The voltage on your TT packs is great are they new? One of our very experienced pilots who's TT pack I borrowed said that they held 37V when new but dropped to a sustained ~35V after the first dozen or so flights and remained at that level.
Old 06-24-2009, 04:41 PM
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Default RE: RPM from Hacker 14XL

The 21*14 gives the same load as the 20*15
On an old FP pack I have about the same rpm readings. With A Kokam 30C pack it reaches 6K
Perhaps you can try the new Hyperion G3 packs, it is said they hold the voltage better.
Set full power setting of the controller to the max puls-width from the receiver to make sure it goes to 100%
Old 06-24-2009, 06:20 PM
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Default RE: RPM from Hacker 14XL

Thanks for that Hans, sounds lke your Kokams are maintaining ~ 3.7 V/cell, excellent performance. The Hyperion G3's look very good but I will wait until I see some hard data before buying any. I found data on there earlier packs to be very accurate (see attached for a couple of sample discharge curves for two of their packs, data is from www.aircraft-world.com) and matches what I see on an E-Meter or Eagletree. I can't find graphs on the G3's or for other manufacturers but would love to do so.

I have checked the pulse width on my Rx using the Spin Box (it's a very cool function to use). I found the same results whether I fixed the end points or used the automatic settings.

One other thing I intend to try is pre-heating the packs. At our comp last weekend I found that early in the morning (ambient temperature ~5degC/41degF) the packs were sluggish. I'm going to try pre-heating to 30degC/85degF and see if that makes a difference to performance. Have you any thoughts about this?
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Old 06-24-2009, 07:15 PM
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Default RE: RPM from Hacker 14XL

Do you warm up your packs prior to use?

If your ambient temperature is too low the batteries will not supply their full potential (no pun intended). In winter I use a hot water bottle in an eski to warm up my packs. It doesn't take long and makes a real difference to the packs ability to supply big amps. I assume that warmth lowers the packs internal resistance. I've also been told by the supplier of my TP packs that warming them prior to use will also prolong their life... I'm shortly going to build an electric warmer that works off a car battery or generator.

Cheers
Jason.
Old 06-24-2009, 07:41 PM
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Default RE: RPM from Hacker 14XL

FWIW, when wanting to get maximum performance right off the bat out of lipos the fast electric boats guy typically heat their packs to 110 deg F (43 deg C). I will see a 5 MPH (HUGE) difference in speed between packs at 80 deg F and 110 deg F.

I put my airplane packs on my dashboard and let the solar oven do the work. Even on cool days it is amazing how warm they will get. And being around 100 degrees F will make a huge difference in performance.
Old 06-24-2009, 09:28 PM
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Default RE: RPM from Hacker 14XL

Thanks Jason & Silent, I'll try that and measure the results.
Old 06-24-2009, 10:04 PM
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Default RE: RPM from Hacker 14XL

Hi Guys,

I have been warming my batteries for a few weeks now, it's made a huge difference.

I have modified a Waeco car heater/cooler. Currently i have been setting the box to 40 degrees Celsius

It's made a huge difference, with cold batteries i can barely go vertical. I now have consistency from the start to the finish

Cheers

Chris
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Old 06-24-2009, 10:12 PM
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Jason Arnold
 
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Default RE: RPM from Hacker 14XL

Hi Chris,

Was going to mention your name about the warmer thingy but thought you may not want your name up in lights!

I got my box the other day.. It's a nice neat little unit.

Cheers
Jason.
Old 06-25-2009, 12:01 AM
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Default RE: RPM from Hacker 14XL

In fact, using cold lipos, less than about 75 deg F (24 C) will shorten the cell life as well as reduce performance. You are not going to hurt cells warming them up, but you can hurt them bu not doing so. I have even stuck them on the floor of my truck and run the heater on them if there is not enough sun to warm them.
Old 06-25-2009, 12:09 AM
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Default RE: RPM from Hacker 14XL


ORIGINAL: Silent-AV8R

In fact, using cold lipos, less than about 75 deg F (24 C) will shorten the cell life as well as reduce performance. You are not going to hurt cells warming them up, but you can hurt them bu not doing so. I have even stuck them on the floor of my truck and run the heater on them if there is not enough sun to warm them.

I used to put them on my V8 engine after arriving at the field, even that was too inconsistent, having a box helps heaps.

With older style Lipo's with lower C ratings it is not as big an issue i don't think. With the newer generation cells i think it is going to be more of a problem.

I could be wrong but as the C rating goes up the internal resistance is dropping making it harder for the cells to develop any heat. I have a Funjet with Flightmax 30c 2650 cells drawing nearly 90 amps peak.

and the battery comes out barely warm, throttle usage helps too.

Chris

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