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When a receiver battery goes low...

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Old 09-13-2012, 09:59 PM
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Flight Risk
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Default When a receiver battery goes low...

....what is affected first, the signal or the servos?[X(]
I know I should have a larger battery than the 600mah nicad I was using. I estimate about an hour total time. I was landing and swinging out wide a couple hundred yards away, and I was getting what seemed like an intermittent signal. The throttle was already down which was good. Luckily or not, it was a Kadet Sr. which was slowly flopping around, it would occassionaly respond then flip the other way. Somehow i got it to pancake in and just put a simple crack in the wing and some split monocoat several places.
Is it my understanding that with 2.4 radios, the Rx needs to talk to the Tx. So if the RX battery is low could it have a problem at a distance? Searching here on RCU they seem to claim the servos get sluggish first, but those were very old posts, from FM days.

Thx

RS
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Old 09-14-2012, 02:33 AM
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Default RE: When a receiver battery goes low...

You get RX "browout" where the RX goes off and reboots so you get control on and off. What difference does it make if the servos run slow etc.? When your battery goes low or is too small to handle the servo loads you rish loosing control.

A 600ma battery is way to small for a 40-60 size plane especially running for an hour. Do you check your battery voltage between each flight?

Best to use a 6volt, 5 cell battery at 1200ma or more with 2.4 to play it safe.

Batteries are cheaper than planes...

Have fun!
Jim D
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Old 09-14-2012, 04:46 AM
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Default RE: When a receiver battery goes low...

It will also depend on what system you are using. For example, if you use Spektrum with that battery pack, you will get locked-out (Brownout) at 3.8 volts. With Futaba, at 3.7 volts the throttle channel ONLY will go to fail safe, an indication that something is wrong so land your plane, you can reset that by pulling the throttle stick back, and it will completely locked-out at 2.7volts.

Best thing is not to use that type of battery pack with a 2.4 system.

Doug.
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Old 09-14-2012, 05:30 AM
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Default RE: When a receiver battery goes low...


ORIGINAL: Flight Risk

....what is affected first, the signal or the servos?[X(]
I know I should have a larger battery than the 600mah nicad I was using. I estimate about an hour total time. I was landing and swinging out wide a couple hundred yards away, and I was getting what seemed like an intermittent signal. The throttle was already down which was good. Luckily or not, it was a Kadet Sr. which was slowly flopping around, it would occassionaly respond then flip the other way. Somehow i got it to pancake in and just put a simple crack in the wing and some split monocoat several places.
Is it my understanding that with 2.4 radios, the Rx needs to talk to the Tx. So if the RX battery is low could it have a problem at a distance? Searching here on RCU they seem to claim the servos get sluggish first, but those were very old posts, from FM days.

Thx

RS
I have flown 72Mhz for years and 2.4 since that was first introduced. AM, FM/PPM, and PCM would get very slow and erratic when the voltage went low. Older systems came with 600mah-700mah Tx and Rx batteries. Modern servos, especially Digitals, put much more Current load on the Rx battery. With 2.4 Rx's, this can cause a voltage spike that can Reboot the Rx for a second. If you have to use a 4.8v Rx pack, use at least 2500mah, but 6v is a better choice if the servos can handle it. With this setup, there is less chance of a Brownout and Rx ReBoot.

Check the Rx battery voltage before each flight and use an Expanded Scale Voltmeter (ESV) that puts at least a .5a load on the Rx battery. These devices are cheap at your LHS.

Some 2.4 Rx's have a blinking light that will warn you, after you land, that the Rx had a Brownout. All manufacturer's Rx's can have Brownouts if the Rx battery voltage drops below Critical.

Losing the signal from the Tx, due to Interference or Low Tx battery voltage, will result in a Hold (Failsafe event).
















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Old 09-14-2012, 07:48 AM
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Default RE: When a receiver battery goes low...

Thanks for the answers. I'm using an Airtronix RDS8000 on 2.4, and no one at our field has a clue about them. I bet it was rebooting, cuz I did seem to blip on and off. After the flight someone tested the battery and it was at 4.9 or so, but was probably less under load.

RS
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Old 09-15-2012, 06:06 AM
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Default RE: When a receiver battery goes low...

RS,
I have a lot of servos that limit my voltage to 5.3 volts so on my 2.4GIG radios I run the receiver on a separate battery pack. This way the servos do not pull the receiver voltage below the reboot voltage.
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Old 09-15-2012, 07:07 AM
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Default RE: When a receiver battery goes low...

Looks like some serious study of batteries is inorder
The basic problem -apparantly is that the selection of rx battery is simply incorrect . Additional batteries /seperate for servos is fine IF you understand incompatibility issues ( different voltages .)
So
bite the bullet
get new high capacity, high current type batteries - in NIMH if that is all the charger capability you have
just jumping to higher voltage is not a good plan.

Search internet for RCbatterysuppliers - read up on modern NiMh cells and then get cells which supply power under higher loads and enough capacity for the flying you do.
4 cell packs WILL work with any 2.4 system, provided the cells have adequate C rating (the ability to provide power under loads)
The comments about one brand being able to work under lower power simply is wistful thinking.
2.4 radios are small computers
FORGET all you knew using the 72.xx systems. Those rx would work-tho poorly down to a couple of volts.
The old load tests?
forget those too.
you need cells which WILL NOT loose over one volt-at max load- - when measured with in line volt meter. BTW-I have A Senior a Seniorita and a electric Kadet Seniorita- all on 2.4 all electric power now
great models- I would hate to loose any of em due to as simple a thing as bad batteries.

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