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4.8v or 6.0v receiver pack

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LHR Dave28/08/2014 20:47:30
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Hi

Apologies if this topic has been discussed in the past. I have a general sport model aircraft (mick reeved Gangster 63). It has 5 futaba 30003 standard servos.

The radio is Futaba 2.4ghz, for this set up would it be better to have a 4.8v or a 6.0v receiver pack.

I would be interested in your views.

john melia 128/08/2014 20:51:04
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1770 forum posts
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I run all my 2.4 spektrum rx's on 6v , 2s life packs

john melia 128/08/2014 20:52:08
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Your servos will be fine on 6v as well

LHR Dave28/08/2014 20:56:33
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So your saying its my choice 4.8 or 6.0 v , there equally suitable for my installation.

john melia 128/08/2014 21:01:48
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Apparently its safer to use 6v with spektrum gear

Masher28/08/2014 21:06:10
1080 forum posts
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Coincidently, I have just tonight finished my Gangster Lite!

I am all Spektrum through my fleet and quite happy on 4.8V. I have standardised on eneloop 2000mA and have no issues.

I will be very interested to see how the Gangster flies since it is so light and, as seems popular, I have an Irvine 53 up front. I initially had a smaller engine (instructions say 20-40) but CofG was hopeless so put bigger engine rather than lead in the front

john melia 128/08/2014 21:09:39
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Masher i did the same with my zlin , it now sports a 91 two stroke up front , and it was only meant for a 60/70 , comes in pretty hot now though , I found it balances just right with this engine as it was very tail heavy

Masher28/08/2014 21:21:09
1080 forum posts
160 photos

Yes John, this is not the first time I've put a bigger lump into get the balance. Seems wrong to me - why doesn't the CofG come out closer to design? Worst one I've got is the H9 RV8 - massive engine, batteries on top of engine, still needed lead????

The Gangster Lite is particularly annoying because it is such a light build - there is nothing at the back end but it still doesn't balance!

Jamie sawyer28/08/2014 22:06:36
390 forum posts
99 photos

I fly 4.8 and 6 volts. Most rc gear allows for 6 volts Dave. I think the other plus side is the servos have more torque and speed according to the servo specs when you read them any way. I dont think you would notice though.....

I still fly nicad range but lipos might be on the horizon .lol

john melia 128/08/2014 22:07:34
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1770 forum posts
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I agree , even with the 91 I still had to put a 3000mah life pack underneath the engine mount on a shelf

Denis Watkins24/05/2018 07:03:51
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Bump

Edited By Denis Watkins on 24/05/2018 07:07:05

Allan Bennett24/05/2018 19:56:31
1399 forum posts
37 photos

The choice of 4.8v or 6.0v receiver pack depends mainly on the receiver's minimum operating voltage, the capacity and condition of the battery, and how many and what type of servos you're using.

More, bigger, and digital servos will potentially draw more amps from the battery, which will cause its voltage to temporarily sag. The smaller the battery capacity, the greater the sag will be, and with a 4.8v pack it could temporarily drop below the receiver's operating voltage, causing it to re-boot. Some Spektrum models seem to be more susceptible to this than other makes, hence the advice often given to use a 6.0v receiver pack with Spektrum. Futabas seem to be able to tolerate lower voltage, so 4.8v will be fine for them.

Another factor though may be that you want to get the most torque out of your servos, which are usually rated for at least 4.8v to 6.0v -- and often higher these days -- and will give more torque with higher voltage.

Steve J24/05/2018 20:28:57
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Posted by Allan Bennett on 24/05/2018 19:56:31:

Some Spektrum models seem to be more susceptible to this than other makes

Why do people still post this nonsense.

Steve, thousands of flights on Spektrum and no brownouts.

ChrisB24/05/2018 23:36:40
1226 forum posts
34 photos

I'm flying a Precedent Funfly on a Spekky G1 DX8 and an AR400 with a 4.8v Nimh. Can have 3 or 4, 20 minute flights with no issue.

Larger models I use 6v Sub C Nimhs. All ok!

Cuban825/05/2018 07:25:10
2169 forum posts
5 photos

My thoughts on this from the recent 'Brownouts' thread. Still a lot of confusion and misconceptions surrounding what constitutes an adequate power supply to a model's RX. Think of it this way, the 12V battery in your flight box may well be able to run the ancillaries, lights etc in your car, but would fail miserably if you tried to start the engine. Also, be careful with 2S LiFe packs, not all servos are able to handle the higher voltage, some Hitecs I had didn't seem to centre as well on anything over 6.5V.

"A five cell RX pack will do you no good if it's constructed from batteries with a poor C rating i.e so called 'high capacity' AAs (sometimes as bad as 1C for a certain 2200mA size that I've tested) . If the pack can only deliver 2A, before collapsing, whether 4 or 5 cells, then that's all you're going to get and if your servos at any time need 3A, then you'll be in bother - no matter what brand of radio you use.

Nimh RX packs never seem to come marked with their C rating, so the user is guessing as to whether the battery is going to be sufficient, you wouldn't normally guess about the performance of your Lipos/motor/engine/strength of airframe etc, so why take a chance with the performance of certain receiver batteries?

Be honest, do you know how much current the RX batteries in your models can safely supply and what the worst case scenario for current drain from your models is? Would you know how to check?"

Edited By Cuban8 on 25/05/2018 07:39:59

Andy Blackburn25/05/2018 09:01:58
448 forum posts
483 photos
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I hesitate to add more fuel to the fire than is strictly necessary, but here's my experience;

  • I usually use 4 cell 2000+ mAH Eneloops sourced from somewhere reputable (like Overlander) and the biggest, simplest switch I can find with 4-8 standard size digital servos and have never (yet!) had a problem.
  • I've used 5 cell Eneloops on a couple of occasions and whilst there might be a small difference in servo performance (difficult to tell without a back-to-back comparison), there wasn't much difference between that and a 4-cell pack. But some servos don't like 5 cells, particularly on a full charge.
  • I've been using Spektrum receivers for years and have never had any sort of receiver failure or brownout when using a receiver battery, but
  • I've had a failure that appeared to be due to a failed BEC in a speed controller.

I think you'll be absolutely fine with a large (or very large, if you need the nose weight) 4 cell Eneloop as long as it's a quality one because if it fails it'll take the model with it. Same applies to the switch harness.

A.

MattyB25/05/2018 11:02:14
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1843 forum posts
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Posted by Steve J on 24/05/2018 20:28:57:
Posted by Allan Bennett on 24/05/2018 19:56:31:

Some Spektrum models seem to be more susceptible to this than other makes

Why do people still post this nonsense.

Steve, thousands of flights on Spektrum and no brownouts.

There were definitely some early DSM2 RXs that did suffer from high brownout voltages and slow reboot times a long time ago (a friend of mine had some issue with Spek many moons ago we did comparative with a variable voltage supply against FrSky and the difference was significant). However you are right that this was addressed a long time ago and no currently sold RXs seem to suffer from the same issue. Unfortunately though on the internet echoes do tend to reverberate for a long time...!

Edited By MattyB on 25/05/2018 11:04:07

Steve J25/05/2018 12:13:25
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763 forum posts
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Posted by MattyB on 25/05/2018 11:02:14:

However you are right that this was addressed a long time ago and no currently sold RXs seem to suffer from the same issue. Unfortunately though on the internet echoes do tend to reverberate for a long time...!

The QuickConnect firmware to get the signal reacquisition time following a reboot down to 100's of milliseconds was released in January 2008.

I recently tested an AR7000 that I bought ten years ago, it works fine down to (and a little bit below) it's specified voltage of 3.5V.

Steve

Cuban825/05/2018 13:37:41
2169 forum posts
5 photos
I think the early Spektrum receivers would fail at something like 4V, ie the voltage of a flat four cell nimh battery or a really dead 6V. I believe it's something like 3.3V now but the issue is how well any battery can quickly source and maintain a much higher than normal current. Loading servos with transient high control surface loads caused by excessive airspeed or violent aerobatics may just push a battery beyond what it can supply. Some of the small 9g cheap servos are very current hungry when stalled and I believe that a lot of models have been lost because of them where they've been run from inadequate batteries.
Steve J25/05/2018 14:23:15
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763 forum posts
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Posted by Cuban8 on 25/05/2018 13:37:41:

I think the early Spektrum receivers would fail at something like 4V

Model number? The AR7000 is an early DSM2 receiver and it's fine down to 3.5V.

Most 2.4GHz manufacturers seem to specify their receivers down to 3.5V, an exception being Jeti who go down to 3.2V. Futaba just say 4.8V which is as much use as a not very useful thing.

Steve

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