looks like you've been in this hobby 25 years but if you read the post located here it probably explains things better than I can.looks like some rx can operate at alot lower voltage than the servos.anyway I was going from memmory when kraft made the announcement that their seies 72 system would operate even with a bad cell in the flite pack where as my series 70 would not.I did have a cell go bad in it and the result was that while the servos would move they would not return to neautral on their own.returned to kraft and a bad rx pack was replaced end of problem.so I would have to say that rx was still working on 3 cells and unless technology has gone backward since 1972 I would think rx made today should still work on 3 cells.again servos require more than the rx so even if the rx works on 3 cells servos could or could not .I would wonder if the digital servos are capable of reduced voltage as they seem to require more mah capacity rx packs.
http://www.flyinggiants.com/forums/f...r-voltage.html
http://www.flyinggiants.com/forums/f...r-voltage.html
replace the **** with flying giants no space

Aerowoof:

I wasn't trying to set you up, I thought you might have had new information! Here's some receiver information directly from Futaba:

Voltage out is based on Voltage in. Receivers typically operate on a
4.8V DC input voltage. This can be increased to 6.0V, where more
power and speed can be derived from attached servos, but a decrease
in lifespan for said items might result as well due to increased stress.
An ABSOLUTE minimum operating voltage is very near 4.0V. Rx's typically
use a 3.3V regulator which requires an additional 0.7V to power itself,
resulting in the 4.0V minimum. In application, however, it is typical for
performance to become severely degraded as power falls under 4.3V DC.
Ref: http://www.futaba-rc.com/faq/faq-receivers.html

Based on this I would suggest that 4.4v DC (under load) is the lowest voltage for a receiver to work, period.
I would also suggest to you that since today's packs are wired in series (4 times 1.2 equals 4.8) that if a cell
dies, the whole pack is shot.

Again, thanks for your response.

Can anyone recommend a good RX battery tester that tests underload for the field?

Thanx,

Del

Here's a link to Tower's list of tester.

http://www2.towerhobbies.com/cgi-bin...er&FVPROFIL=++

Buy the digital if you can, but the analogs will work.

here are some rx specs showing voltage as low as 3.6 volts this is one of those thing that can be argued back and forth but for some reason i keep posting that link to flying giants which is talking spectrum rx at 3.6 volts.but here is a futaba spec and a gws spec of rx voltage
Futaba Lo and Hi Band 8 Channel PCM Receiver




All Mid Size / Full Size Helis



The Futaba R138DP is a 8 channel PCM receiver. Narrow-band spacing and dual conversion signal filtering combined to provide exceptionally clear, interference-free reception and amazingly smooth, accurate control. Designed for modelers who want to





use a single radio transmitter to fly several different model aircraft, especially pilots who are utilizing computerized radios with multi-model memory.


Channels: 8
Band: 72MHz
Conversion: PCM
Operating Voltage: 3.5-6.0 Volts
Range: 6,000+ Feet
Antenna Length: 39�
Spacing: 20KHz
Case Size: 2.5� x 1.38 x 0.88� (63.5x35x22mm)
Weight: 1.75 oz. (50g)

Go back to: Products > Receivers
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GWS R-4PII/T Pico Receiver for Airtronics/JR Radios $19.20

GWS R-4PII/T Pico Receiver with Micro JST Connector for Airtronics/JR Radios
Quantity:


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GWS R-4PII/T Pico Receiver for Airtronics/JR Radios

This receiver comes with Micro JST connector and is designed for slow/park/indoor flyers. Servos and ESC must have Micro JST Connector to work with this receiver.

Specifications:

Number of Channel: 4
Modulation: FM (PPM) Single Conversion
Signaling: Positive Shift
Operating Voltage: 3.6 to 7.2 V
Current Drain: 5 mA
Weight: 3.6 g (0.13 oz)
Dimensions: 15.0 x.25.0 x 9.5 mm (0.59 x 1.00 x 0.37 in)
Range: 150 m (500 ft)

So if you have a typical 4.8 volt pack and one cell goes bad the pack is down instantly to 3.6 volts and THAT is the cutoff voltage of your examples. Result: CRASH, it won't work.

true voltage of nicad cells is 1.25 volts which gives 3.75 volts,these days everyone is calling nicads nominal voltage of 1.2 volts.that is why on a fully charged pack you see voltages over 5 volts.

So you're saying it's OK to fly with only 0.15 volts above cutoff? Think about the possible meter errors before answering that one.

no I am not saying that all I said was that starting in 1972 flight packs were designed to continue to operate while you were still in the air if one cell went bad,back in those days it was not an uncommon problem.it gave you a chance to land and hopefully you would catch the reduced voltage in the pack before the next flight.no where did I say it was ok to go and fly with a 3 cell pack.someone asked if rx would work on 3.6 volts.I supplied a link to where they were discussing rx operating voltages and the specs of two rx showing what the lowest operating voltage is.for the longest time I used to use an old kraft kps-12 4 wire servo on the throttle.when a cel did go bad the other servos woild still operate but the throtle would not.batteries now are made better than they were 30+ years ago and you may never have a cell go bad but there are alot of old timers that it has happened to.now don't you think if they designed that feature into servo's and rx back then that it would be a standard that should have continued?I will post the old kraft and e-k ads from that time period if I can find them.E-K logictrol was the first to have the 3 wire technology,all other manufactures followed suit.1972 was the first year kraft had 3 wire servos avaiable.that was one reason for buying a 6 channel series 72 for a vk cherokee.

and my point is that unless you get VERY lucky the cells will be low enough from flying that when you lose one cell you will have insufficient voltage left.

But hey, what do I know. I only service Ni-Cad batteries for full scale jets, you know DC-10 and Airbus's and the like. $100 or more per cell and 21-22 cells per assembly. Ands we scrap cells on a regular basis.

so by your logic we should go back to using 4 wire servos because we will crash anyway when a cell in a pack goes bad?

This has nothing to do with 4-wire servos and don't put words in my mouth please. I am merely saying that the chances of getting a plane down safely with a dead cell is unlikely.

why do you think 3 wire servos replaced 4 wire servos back in 1972?it was to allow you to land if a cell went bad prior to that with the 4 wire servo you had no chance at all.that bit of history is what I was refering to when I made my statement.so unless radio design went backward at some point with out informing the public that breakthrough should have been maintained.

For all the beginners reading this thread....the absolute minimum battery voltage, using a "loaded" meter, should be not less than 4.8v before takeoff and the flight should be not more than 10 - 11 minutes. At this point please recharge or quit for the day.
If you want to safely fly more than 4 flights when you go to the field, either buy a 1500 - 1800 mah 4.8v battery or get a field charger.
I'm sure that there are other opinions, but remember it's your plane up in the air, not theirs.

Hey Delbert Pierce,

Sry to hear abot your loss we all crash, its on of the annoying parts of the hobby. [:'(]

As for your reciever pack, im surprised it was starting out at 5.2volts and dropped to 4.6volts. I thought i heard somewhere that most reciever packs, the standard ones that is usually shouldnt be flown below 4.8volts or so. Not sure if the reciever pack dropping below this "safe zone" might of caused a problem or not, but its definetley possible.

I know the receiver packs i run are just the standard ones that come with the transmitter when you buy that, i think its a 4 cell 4.8volt 650mah or something like that, a nicad pack. Mine when fully charged on the wall charger after 12-15hrs of charging are usually up to 5.85volts. After 4-6 flights at the field without any extra charging, ill return from the day of flying and check and they usually dont drop below 5.24-5.40 So im wondering if maybe the reciever pack might of played a part in the problem and the crash? Just my guesstimation as to what might of happened, id definetley get a new receiver pack tho sorry again to hear about the crash man.

-David

OK. As totall newbie, I charge everything for 24 hours, sometimes longer if I forget to disconnect it, regardless of what's already good in the batteries. Am I damaging anything by overcharging? I don't have any voltage measuring equipment. My transmitter has a basic meter which shows a good charge or not. Futaba F4V I think. Can you overcharge batteries?

mbilar1,

I think on your transmitter/receiver wall charger it says how many hours you should be charging them for. If its not there i know the receiver battery pack should say on it how many hours it should charge for. Funny to say actually..... but i discharge my reciever pack with a christmas tree light bulb (the small ones) till the bulb goes out/burns out. usually goes for a few hours. i do this after a day at the field. Then i recharge the pack the full charge time of 12-15 hours.

I think the only thing the extra charging might do is affect the memory of the nicad cells overtime. overcharging gradually overtime could possibly reduce the life of the battery and affect the voltage it can take, ability to hold charge, effectiveness, etc... Others will have to add to that question, im not 100% positive.

As for a thing to measure voltage, i just use one from the hardware store to check when i start charging, when its done charging, and when im done flying for the day. Just a standard digital voltage reader would work great for what you want.

-David

here is the kraft ad from 1972 read it carefully about one cell shorted or dead.

OK folks, from practical experience and testing most receivers will lock out at 4.6volts. It's that simple. He was at 4.62volts at rest, no load. Now start moving servos and guess what happens next. The pack drops below 4.6volts and at that low voltage probably below 4 volts altogether guss what's gonna happen, you'll get intermittent lockout with the receiver eventually locking out altogether.

Doing a flight with 5.2 and then 4.62 after just one flight also indicates a bad cell in the pack. I will not even fly with a pack at 5 volts because of servo load. Remember, quick servo movements put more load on the battery than nice smooth ones.

So taking all that into account and the pilots inexperience you have someone who is probably not very smooth as yet, probably is a bit jerky and now toss in a possible bad battery without any load checking and guess what is gonna happen

Moral: never fly without checking LOADED voltage and leave that load on for a minute or two, not just a few seconds. Battery was this cause nothing else.

I do not hang out in this forum much anymore but even doing the 33% - 40% birds I can ell you that I still load check every other flight and I am running Li-IONs regulated down to 6volts and those at full charge are 8.4volts so depending on the plane I can usually get 15 - 20 flights between charges but I load test because a battery can go bad

I think the secondary problem is the instructor not properly showing how to check a plane properly for flight and if he did then shame on the pilot for not listening.

In any case I am sorry for being so direct and I hope you get your solo soon

I read it carefully as you requested. It's also good to know that they have "eliminated" battery problems. Something that hasn't actually happened to date.

I have a bridge I'd be willing to sell if you want it. It'll NEVER rust.