Some Advice About Battery Life Please...

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Some Advice About Battery Life Please...

Postby Hallmark » Fri Feb 17, 2012 7:06 am

I have just bought, maidened, crashed and repaired my first AXN. Now I feel like I truly belong to the AXN owners club lol

This happened because I assumed the motor would stop and the battery would have enough power left to land the damned thing. We all know what assume means and I shall not make that mistake again.

So I got to thinking... Can I somehow supply power to the servos and receiver separately from the motor? Forgive me if this is a classic 'stupid question', but in my experience the only really stupid Q's are the ones that never get asked.

I'd like to avoid a stack again if I can and transfer this to my future aircraft too.

Thanks in advance,

Hallmark
Last edited by Hallmark on Tue Apr 10, 2012 12:39 pm, edited 1 time in total.
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Re: Some Advice About Battery Life Please...

Postby cynr100 » Fri Feb 17, 2012 7:57 am

Am waiting delivery of my AXN and have heard this issue several times, being a novice this concerns me and have thought about jamming a separate battery into the mix somehow.

Hopefully Bruce is there to enlighten us.........................please..............Bruce!!!!! (help out the lazy ones).
Not enough time in the day for all my crazy ideas, I'm not slow, I'm just pacing myself
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Re: Some Advice About Battery Life Please...

Postby RCModelReviews » Fri Feb 17, 2012 8:28 am

The ESC should turn off the motor before the voltage drops so low that the receiver also stops.

This is programmable so you need to make sure it is set correctly.

I will do a video showing how to set the HK ESCs to the correct settings.

Otherwise, you can set the timer on your transmitter to remind you when you've had a reasonable flight -- before the battery gets that flat.
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Re: Some Advice About Battery Life Please...

Postby Shotglass » Fri Feb 17, 2012 9:39 am

course you can
all you need to do is cut the red wire on the escs servo cable and plug a 5v battery into any free port of the receiver

but as bruce said normally there either should be a noticeably drop in power when the battery goes out or the esc should cut power for you well before you run any risk of being without servo control
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Re: Some Advice About Battery Life Please...

Postby Hallmark » Sat Feb 18, 2012 12:47 am

I found the user manual for the ESC I bought (a cheapie from China) and I will adjust the settings today. I think I might still get the additional battery though because safer is better in my book and I am about to build a twin 70mm EDF F-22 from Sydney RC Jets so I could potentially do the same with that for when I am skilled enough to fly it (some time in the very distant future no doubt!)...

Any suggestions on the best battery or any links you might suggest for a specific brand etc I should look at?
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Re: Some Advice About Battery Life Please...

Postby pldb64 » Sat Feb 18, 2012 1:50 am

Hi All,

As already noted, it is always possible to run a separate battery pack to power your rx, however i would have thought it was appropriate to mention the "good"/"recommended" approach to dealing with LIPOs and the importance of not running them down that far.

The general rule of thumb i've heard repeated in numerous forums is not to run your battery below 80% of rated capacity. (ie for a 2200mah battery, don't go below 1760mah). If you do go below this level, then you run the risk of ending the battery life prematurely.

So how does that impact your flying regime?
Well, you really need to know how many amps your pulling from your battery at WOT. From this you can work out how long your battery should last at WOT and this should give you some guidance as to what your minimum flight time can be without exceeding the 80% rule. If you then also work out how many amps you're pulling at 50% throttle, then you'll have a much better guide as to how long you can fly without overdoing it. Then set your timer to that duration and don't exceed it.

Then when you recharge your batteries, you can actually see how much you put back into the battery. That will allow you to fine tune what your maximum flight time will be. Golden rule - don't exceed 80% battery capacity.

For my AXN, i'm running a 2200mah battery and i'm pulling 16 amps at WOT. That means i've got a minimum flight time of 6:45. I'm using the ER9X software in my 9X so it allow me to set the timer based on % of throttle - so in reality i can fly for approximately 15mins without going over the 80% rule.

Anyone care to offer an refinements to the above?

Peter
Turnigy 9x, FrSky 2-Way/Telemetry DHT DIY, Smartieparts BRD, ER9x FW
AXN-Floater (stock esc, motor & prop, HK orange 9g servos)
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Re: Some Advice About Battery Life Please...

Postby Hallmark » Sat Feb 18, 2012 2:36 am

Thanks Peter that is a great post and much appreciated. I use a 2200mAh battery too and I have no idea what Amps I am pulling (which means you need a follow up post with what I have to buy (don't tell the wife) and how to extrapolate this information please...

As I am a beginner who has crashed his AXN already I guess my choice of 15 minutes on my timer and that I fly at 50% throttle or less is my gift of beginners luck on this occasion... :lol:

So if you have the time and inclination I am to be considered tabula-rasa and I await an injection of your wisdom...
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Re: Some Advice About Battery Life Please...

Postby pldb64 » Sat Feb 18, 2012 6:00 am

Hi HM,

Here is the watt meter i purchased from HK:

http://www.hobbyking.com/hobbyking/stor ... duct=10786

Bruce has previously posted about this watt meter:

http://www.rctimer.com/index.php?gOo=go ... oductname=

But they appeared to never be in stock so i gave up waiting for that to become available.

You can look through the video's on Bruce's RCModelReviews you tube channel for a demo on how to use the watt meter.

Again, as a fellow newbie, i got a watt meter pretty early on in the piece based on others advice. You can't really know what you're model is doing electronically without one.

Enjoy!
Peter
Turnigy 9x, FrSky 2-Way/Telemetry DHT DIY, Smartieparts BRD, ER9x FW
AXN-Floater (stock esc, motor & prop, HK orange 9g servos)
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Re: Some Advice About Battery Life Please...

Postby RCModelReviews » Sat Feb 18, 2012 7:58 pm

Yes, that wattmeter is great because it also measures the remaining capacity in your battery after you land.

After a while you get pretty good at estimating how much you've used when flying and I can judge (within a few percent) how long to fly on the last-flight of the day so as to leave my batteries at a "storage charge" level (3.8V per cell).

Most of the time I fly my batteries down to about 35% capacity and seldom below 20%. This has resulted in all my batteries lasting over two years and hundreds of charge-cycles. I see others who regularly "run them flat" and their packs are usually puffing and sagging after just a few months.
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Re: Some Advice About Battery Life Please...

Postby GRM » Sun Feb 19, 2012 8:01 am

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