[slopeflyer]

Does anyone know what the minimum battery level is for correct operation in volts.

For example should a FRsky faast operate at 4.91v? Would a genuine Futaba work at the same level?

What is fully charged value?

At what voltage do you recharge.

What happened on a 'dead' battery? Does it register a voltage at all or is the current supplying value limited. Is this determinable by the voltage?

Thanks.

[Windy]

This is a bit like asking how close you can walk to the edge of Beachy Head. It's easy enough to keep away!

[tomkfly]

Does anyone know what the minimum battery level is for correct operation in volts.

For example should a FRsky faast operate at 4.91v? Would a genuine Futaba work at the same level?

What is fully charged value?

At what voltage do you recharge.

What happened on a 'dead' battery? Does it register a voltage at all or is the current supplying value limited. Is this determinable by the voltage?

Thanks.

Frsky say  3.5v min operating voltage and I believe Futaba failsafe operates at 3.8volts.
A fully charged 4 cell NiMh should come off the charger at about 6 volts and a 5 cell around 7.5 volts
You should recharge just before a flying session no matter what the pack voltage is and never let the pack go below 1 volt checked under load.
There is more than one way a battery can go faulty and checking with a votmeter may not show the problem. If the dead cell has gone high resistance it can show full voltage, but as soon as a load is placed on it the voltage will drop. The best way to check is to cycle the cells and check how much goes in and how much you get back out.


  Tom

[slopeflyer]

The reason i ask is i had a battery yesterday that died on me. I lost complete control. No response from surfaces. Anyway i checked the voltage and it registered 4.91V, which is one above caution on my led checker. Anyway i stuck in on charge and it still registers 4.91V.

[marcellus]

As said above, it needs cycling to determine health! The Rx minht have been happy with the voltage but at some point the servos give up!

[tomkfly]

The reason i ask is i had a battery yesterday that died on me. I lost complete control. No response from surfaces. Anyway i checked the voltage and it registered 4.91V, which is one above caution on my led checker. Anyway i stuck in on charge and it still registers 4.91V.

Sounds like it is kaput. Does your LED checker apply a load whilst it is checking?

  Tom

[FrankS]

It may read 4.91v, but fully charged with no load it should be at least 5.5v. The problem you've got is that one of the cells has probably died and the rest when under load, i.e. servos moving, the volts drop below 3.5v and the Rx shuts down, when the volts recover the Rx reboots but that takes some time.

One of the issues with the high capacity AA cells is that they have a fairly high internal resistance, under a low load this doesn't matter as the voltage drop will be low, but under a high load the voltage drop can be quite significant.

[brand1068]

If it was the low volatage though your throttle would have dropped well before loosing control.

I remember setting up my cap with an old battery - the servos has so little power they were very slow - but the RX was still powered on.

I did a low power test on the TX as the time and it still responded well beyond the recomended distance.

The throttle cutoff was working well still

Chris

[FrankS]

If it was the low volatage though your throttle would have dropped well before loosing control.

I remember setting up my cap with an old battery - the servos has so little power they were very slow - but the RX was still powered on.

I did a low power test on the TX as the time and it still responded well beyond the recomended distance.

The throttle cutoff was working well still

Chris

No, if the Rx losses signal it will go to the failsafe position, low volts is the same as switching it off, I can't think of any 2.4 rx which has a throttle cut off on low volts, a 35 mhz ppm Rx which is analogue will keep working at low volts but digital Rx's (i.e. 2.4 and 35 mhz PCM) will just shutdown if the battery volts get too low.

[tomkfly]

Futaba have  a low battery warning failsafe. The throttle goes to low, you then resett it by closing the throttle on the Tx, you can then reopen it and get another 30sec, before it closes again.

  Tom

[bobt]

Futaba have  a low battery warning failsafe. The throttle goes to low, you then resett it by closing the throttle on the Tx, you can then reopen it and get another 30sec, before it closes again.

  Tom

It is on PCM 35- is it the same with 2.4?

[tomkfly]

It is on PCM 35- is it the same with 2.4?

yes it is on pcm and 2.4g but not on ppm.

  Tom

[slopeflyer]

Thanks guys. I have invested in an accucell 6 with cigarette lighter socket so I can check/charge at the slope.

[Phil_G]

...low volts is the same as switching it off

Sorry, have to disagree there. Digital & microprocessor circuitry doesnt switch off cleanly when the voltage is reduced slowly, as an example, pic chips have a brownout detect option which will reset the chip and a brownout detect flag which you can monitor in software. At the point of brownout, ie the point at which the absolute minimum working voltage is crossed, spurious events can happen such as eeprom corruption, clock cycle skips or bursts, RAM corruption, etc.  Without a complete reset (reboot), voltage recovery from the point of brownout can leave the processor in an unpredictable state.  This situation is typical of many digital systems.  Low volts isn't the same as switching it off 

I can't think of any 2.4 rx which has a throttle cut off on low volts

As others have said, Futabas do, they give low rx volts warning by closing the throttle, but the value at which this happens is so low, you really shouldnt ever experience it 
Cheers
Phil

[FrankS]

As others have said, Futabas do, they give low rx volts warning by closing the throttle, but the value at which this happens is so low, you really shouldnt ever experience it 
Cheers
Phil

Well I've learned something, I didn't realise the Futaba 2.4 sets did that, I've programmed a couple for other fliers and also read the manuals and advertising blurb but not come across this, I thought they would have made more of this safety feature.

[Windy]

It saved a clubmate's model. He wondered why his throttle kept cycling up and down before takeoff, and after cussing Futaba for a while he eventually realised his battery was low.

[bobt]

Sorry, have to disagree there. Digital & microprocessor circuitry doesnt switch off cleanly when the voltage is reduced slowly, as an example, pic chips have a brownout detect option which will reset the chip and a brownout detect flag which you can monitor in software. At the point of brownout, ie the point at which the absolute minimum working voltage is crossed, spurious events can happen such as eeprom corruption, clock cycle skips or bursts, RAM corruption, etc.  Without a complete reset (reboot), voltage recovery from the point of brownout can leave the processor in an unpredictable state.  This situation is typical of many digital systems.  Low volts isn't the same as switching it off  ;)As others have said, Futabas do, they give low rx volts warning by closing the throttle, but the value at which this happens is so low, you really shouldnt ever experience it 
Cheers
Phil

Really? I was flying my 1/4 scale pup and the throttle went to idle. Scratching my head, I put the throttle down, and back up. It came back on. did it again. and again. Bit like that Really Useless Machine. I finally landed it, wondering what was up, and found the battery flat. I had been upping and downing that throttle for five minutes! It then dawned on me what had happened....

[Phil_G]

Really?

You sound like you're not convinced Bob, but yes really, the "Futaba battery failsafe" and the brief outline of how brownout affects digital circuitry are both fact.

I was flying my 1/4 scale pup and the throttle went to idle. Scratching my head, I put the throttle down, and back up. It came back on. did it again. and again. Bit like that Really Useless Machine. I finally landed it, wondering what was up, and found the battery flat. I had been upping and downing that throttle for five minutes! It then dawned on me what had happened....

That is exactly how it is supposed to work Bob. Your receiver was warning you that the battery was low enough to engage 'throttle failsafe'. This voltage is a safe margin above the brownout voltage, although in any case with falling voltage a Futaba FASST rx will typically maintain the link long after your servos have stopped. This is easily proven with a variable psu and a scope monitoring the rx outputs     If you do get a battery failsafe you're supposed to get it down ASAP though! 
Cheers
Phil

[bobt]

You sound like you're not convinced Bob, but yes really, the "Futaba battery failsafe" and the brief outline of how brownout affects digital circuitry are both fact.That is exactly how it is supposed to work Bob. Your receiver was warning you that the battery was low enough to engage 'throttle failsafe'. This voltage is a safe margin above the brownout voltage, although in any case with falling voltage a Futaba FASST rx will typically maintain the link long after your servos have stopped. This is easily proven with a variable psu and a scope monitoring the rx outputs     If you do get a battery failsafe you're supposed to get it down ASAP though! 
Cheers
Phil

I was saying 'really' to your comment that you should never experience the throttle cut feature- I was saying that I had, without realising what was wrong I carried on for 5 minutes, finally landing without incident, proving that a) the system works (but it would have been nice for Futaba to tell us about it) and b), you can fly for quite a long while in the 'danger zone'. Although please dont try this at home, kids..

[RFJ]

but it would have been nice for Futaba to tell us about it)

Well they do in the 6EX manual.   Page 30 "Battery Failsafe"   The trip voltage is 3.8v.

[Phil_G]

(but it would have been nice for Futaba to tell us about it)

Ah ok Bob, see what you mean now, it wasnt clear from the combined quote. But battery failsafe is covered in the Futaba manual... 
Cheers
Phil
Edit: Ray got there first!
PS just an additional thought - if you use a 5-cell pack and experience a battery failsafe, then at 3.8v your pack is much, much flatter than a 4-cell at the same voltage. Better get down NOW!!

[bobt]

Well they do in the 6EX manual.   Page 30 "Battery Failsafe"   The trip voltage is 3.8v.

I dont think they did back then (or maybe I didnt bother reading it!) It was a FF8, which had just come out- that dates it!

[tomkfly]

I dont think they did back then (or maybe I didnt bother reading it!) It was a FF8, which had just come out- that dates it!

They did: Page 29 of manual


Tom

[bobt]

They did: Page 29 of manual


Tom

I never got that far!

[grayuk]

I dont think they did back then (or maybe I didnt bother reading it!) It was a FF8, which had just come out- that dates it!

FF7 had the feature as well. 

[bobt]

FF7 had the feature as well. 

Its strange, because there were 5 of us flying the day I found it out, all Futaba users, and not one of us had heard of it!

[tomkfly]

FF7 had the feature as well. 

It did, but you had to set the throttle on low on the Tx for it to work.


  Tom

[brand1068]

the first time I heard about the feature was when the 6EX came out we bought 2 to repalce our optic 6 35mhz

Was one of the reasons I went Futaba as oppsed to Spektrum.

Chris

[grayuk]

It did, but you had to set the throttle on low on the Tx for it to work.


  Tom

Tis true, it needs to know which is low throttle.
It is a great feature and i have used it since FF7 days.
It is in all the instructions, just not 'obvious'.
Futaba....great gear, crap instructions 

[Arceenut]

Obviously, not many read all of the instructions

[brand1068]

It may be a generality but you can normally split them into two groups.

Male and Female...

 

[slopeflyer]

Not sure if this question was answered. Let me put it another way. I have a FASST Funabashi and FASST frsky rx. Controlling lets say 4-6 servos on a glider.

Let's say I have 10 mins flights. I start the day with 5.8 v.

I fly, land, check batt.

What is the minimum rx battery that I require before I stop flying.

Presently, I've been stopping at any reading under 5v.

Is this about right or could I go lower?

What's the lowest you would take a 10 min flight at?

[FrankS]

That's a how long is a piece of string question, it would depend on the battery and power demands. What you are trying to avoid is the Rx cutting out due to too low a supply voltage, all batteries sag under load, so it would depend on the battery and load. An Alula would probably be fine for at least another hour, but using 6 digital servos on a fast glider with a small (i.e. AAA or AA ) cells might just cause the battery voltage to drop too low if it's asked to do too much work.

[Phil_G]

Measuring the voltage isnt a good way to determine the state of a nimh or nicd pack Jimbo. Better to time a reasonable period of use then compare the amount of mAh it takes to recharge with the stated cell capacity; then work out from that your maximum theoretical duration and only fly to within say 75% of that time.
This will give you a more reliable indication than any voltage measurement, loaded or not.

The internal resistance of each cell varies greatly with demand and with cell temperature, and the discharge curve is not at all linear, especially during the last 25% or so, which means that a voltage measurement alone is actually a very poor indication of the state of your pack.
It might sound complicated but once it becomes a habit, you just dont worry about battery capacity any more.

Bear in mind that a lot of SLGs (DLGs) and chuckies are flying quite happily on a 1S lipo for the rx & servos, and thats only 4.2v fresh off the charger.

Cheers
Phil

[slopeflyer]

Ok I see what you mean and realise that prolly a better way to measure life one I get my car battery charger working in the house with a suitable supply.
What would be a good point until then? Stick at 5v. I know some are going down to 4.5 with telemetry.

[tomkfly]

Ok I see what you mean and realise that prolly a better way to measure life one I get my car battery charger working in the house with a suitable supply.
What would be a good point until then? Stick at 5v. I know some are going down to 4.5 with telemetry.

As Frank says "That is a how long is a pice of string type question"  Before anyone could attemt to answer they would need to know what the battery type, number of cells, capacity and size of the cells.
Also what are you using to check the voltage with? What current are the servos drawing?

  Tom

[FrankS]

Ok I see what you mean and realise that prolly a better way to measure life one I get my car battery charger working in the house with a suitable supply.
What would be a good point until then? Stick at 5v. I know some are going down to 4.5 with telemetry.

With Telemetry they are measuring the voltage under load and have probably set the alarm at that level, it probably goes off when they have the Rx battery under load. I know a few years back I fitted a battery checker in a plane with a 4 servo wing and on a 2200 mah 4 cell AA Nimh Rx it would drop deep into the red when twiddling the sticks when the battery was fresh off charge, with a 1400 mah 4 cell Sub C cell pack it hardly moved off green.

[Sizzling]

With Telemetry they are measuring the voltage under load and have probably set the alarm at that level, it probably goes off when they have the Rx battery under load. I know a few years back I fitted a battery checker in a plane with a 4 servo wing and on a 2200 mah 4 cell AA Nimh Rx it would drop deep into the red when twiddling the sticks when the battery was fresh off charge, with a 1400 mah 4 cell Sub C cell pack it hardly moved off green.

Had similar. The high capacity AA nihm's I have tried have been awful. Most drop there voltage on just 2-3 standard servos under load. Apart from loosing a model you won't be getting the benefit of higher torque/speed if using higher rated servos and your battery is not up to the job.

[slopeflyer]

I can measure my battery under load on the ground. Stick in the capacity checker and twiddle the sticks.

[tomkfly]

I can measure my battery under load on the ground. Stick in the capacity checker and twiddle the sticks.

What do you mean by " capacity checker"? If it is a Hitec one with the red/amber/green zones, then it has a built in load of about 300ma. The ripmax one has an adjustable load. The cheap led ones probably don't.
Twiddling the sticks on the ground is not a good method of suppling a load.
The Hitec and Ripmax are probably ok to use with a standard club model, with 4/5 servos, but does depend on what cells you are using.

  Tom