Brown out refers to flight power voltage drop. There can be several causes with the most often cause to be too great of load.

Edit: my answer was likely incomplete.. as it colloquially means that the reception ability of the receiver is degraded due to the lower power of the flight system due to higher energy demands.

In what circumstance would a novice like me worry about that? Much bigger and sophisticated aircraft? I'm not clear on your reply. THX

Digital servos require greater energy than standards for example so any system with a full house (four or more) digital servos should be a 6v system rather than 4.8 so as to avoid brown out. To make this easy... any plane larger or more complicated than a sport .60 size should probably use a 6v system.

I just started flying recently, so IDK what any of that means. LOL

Like a house, understanding is built one board or brick at a time. Enjoy the journey.

A brown out is defined as the loss of signal caused by to low a voltage on the receiver buss. This varies depending on the receiver design but is usually about 3 volts. This can be cause by several factors some of which are 1; to small a battery in so far as mah's go, to high an internal resistance of the battery, 2: high impedance between the battery terminals and the receiver buss (such as to small a gage wire or bad switch) 3: insufficient capacity from an ESC's BEC, 4: stalled servo or to much current demand from any device getting commands from the receiver, 5; many other possible causes. In most cases this can be prevented by just having an adequate power source for the receiver with good connections.

I like this, someone not afraid to say they don't know something. Okay, lets see if I can put everything into "layman's terms":
1) Brown out-pretty much covered but it's not enough battery for the load placed on it causing the servos to react slowly to not at all
2) Full house aircraft-one that has servos operating all the basic functions; ailerons, rudder, elevator and throttle.
3) Servo types-Servos have changed a lot over the years:

• A basic servo like a Futaba S148 is perfectly happy with a 4.8 volt battery pack. This is plenty for a trainer
• A digital servo like a Futaba S3152 will work on 4.8 volts but will work better on a 6.0 volt pack. This is good for larger sport planes
• A specialty or high torque servo like a BLS171 programmable requires between 6.0 and 7.2 volts. These are very expensive and would be used on high end planes

4) Battery types-These are plentiful and each has it's pros and cons. Many require a charger that is compatible with their chemistry
5) Transmitter Functions-These need to be gone over with an instructor since not everything your transmitter can do is needed by a trainer

Always use 6v or better packs in the plane. If going higher than 6v make sure the rx and servos are rated for the higher voltage.

I strongly recommend you use professionally built packs with soldered or welded connections. Loose cells in holders have caused many a crash.

Why? I run digital servos in my 1/8 scale hydroplane that are rated at 4.8 volts for the throttle while the rudder servo is dual rated at 4.8 and 6 volts. The load on the rudder servo is several times higher than anything you will ever see on airplanes and it works fine at racing speeds on 4.8 volts. I've run a full weekend, totaling eight five to six minute heats on one NR4J 600mah 4.8 volt pack without recharging the pack. Come to think about it, I charged that pack with a "wall wart" charger a few days prior to that weekend, put it in the boat and never pulled the radio box tape off until I'd been home for three days

If a servo makes enough torque at 4.8v to operate the control surface it is attached to, then there isn't a problem using 4.8v. But it has become standard practice with RC planes to use 6v for two reasons. First, it lets us use a little bit lower end servo and still get the torque we need. Second, it prevents the aforementioned brownouts.

Okay, I get it that 6 volts is "standard practice". I just can't agree with J.Dunker's statement about always using 6+ volt packs. IF the only servos that will work for a given application are rated at 4.8 volts, to use 6 volts will burn them out in a very short amount of time. The way I see it, there is a big difference between having a bit of power in reserve and just carrying extra power just to have it. Does a Kadet really need 6 or 7.2 volts to fly well? In a word, NO. They were designed back in the day of 4.8 volts and S-48 servos. HELL, my first plane, a Kadet Jr, was built using 4.8 volts powering three S-19 servos and even that was considered overkill for a 48" trainer. The Kadets haven't changed, only the radio gear and batteries used to control them. Even in the Kadet Sr kit assembly instructions, it lists this Airtronics servo:
94102 Precision Heavy Duty Bushed Standard 50oz-in at 4.8 volts, .22 second transit time for 60 degrees
If that's what was listed when the kit was first kitted, why do I need to use a 6 volt pack now? It wasn't needed back then so why the change? Is it because it's needed or just because it's there to satisfy those that think they need, to quote Tim Allen, "MORE POWER"?

You don't need to use 6v but it may be convenient to do so. I've fifteen plus planes in the hanger, all of them use LiFe battery technology because doing so simplifies things.

That said, I do have one old Cub flight system and a couple of ignitions with 4.8v restrictions. I've chosen to voltage drop for those requirements with diodes.

Each RC pilot has choices of what works best for them. There are no requirements that one must do things like others. If a method works for you... your good.

Hi Boner 321, I got back into rc after a 10 plus year lapse and went with 4.8 volt nicads for my recievers(it is what I know). The plus to this is that the charger that comes with your radio will charge them(400 to 700 MAH range). the disadvantage is first, nicads will form a memory and need to be run down(not too much though) to around 1.1 volt per cell before charging. Another disadvantage is at 400 to 700 MAH I am limited to around 3 flights. I will switch all my stuff over to LIFE once it is time to change them out(five years?) I am not sure even if life is the same voltage per cell as nicad, but for me 4.8 volts is all I need as I fly 40 size birds. I have built battery cyclers for all my aircraft so I can simply plug each of my 5 aircraft into a cycler and it will automatically discharge and recharge by receiver battery whith the battery still in the aircraft.

For anyone worried about ' burning out a servo ' on 6v instead of 4.8 v I have run a large variety of servos on 6v without any issues at all. Everything from sub miniature 2.4g indoor stuff to the brick size stuff in 150 cc 3 D monsters. You get a little more torque and a little more speed both of which are good. No body in the clubs I flew with ever reported a burnt out servo.

My main concern with advising beginners to avoid running on 4.8v is that some 2.4 gh receivers can temporarily fail and lock up when the voltage drops below a critical threshold even momentarily. This is called a brown out.

Lots more here on this topic http://www.rcuniverse.com/forum/begi...-brownout.html

Running 6 v is a low cost insurance policy.

You are running two servos that are not constantly in motion....instead of 4 or more that are constantly in motion...

Not true. I'm constantly having to work the throttle and make course corrections to avoid other boats as well as navigate the course. Our race course measurements are given below:
The standard race course shall:
be oval in shape
have two parallel straightaways
be a minimum of 60 feet from the closest shore
have dimensions that must be: turns 60’ to 120’ in diameter and straightaways 275’ to 400’ in length
Taking all of that into consideration, a boat doing 50 MPH will go the length of the straight in less than 3.5 seconds and complete the turn at one end in around 1 second if the boat is running right on the buoy line.. Unlike an airplane, my boat's rudder is constantly having to hold pressure on its left side as the prop is trying to push the boat's transom to the left. Also, the rudder, prop, and turn fin are going through a substance that 784 times more dense than the air meaning that the servo has to deal with 784 times the pressure on every square inch of the rudder that is in the water as compared to a control surfaces on an aircraft This means that a boat rudder servo alone will used much more power than the combined total used by the servos of an airplane. By the way, my boat weighs in at 14lbs and runs a .67 that can turn up to 28,000 RPM, more than twice the speed of a similar sized aircraft engine
https://static.wixstatic.com/media/1...d0a973d93.webp

True, the torque requirements for servo speed haven't changed. For trainers and basic sport planes, no one "needs" 6v servo performance.

However...

In the days when 4 cell NiCd packs became standard, we had analog servos and 72mhz radios. Analog servos weren't power hungry, and 72mhz radios were very tolerant of low voltage situations. Today, nearly everyone flies 2.4ghz, quite a few the Spektrum brand. Spektrum equipped planes will often crash just from a split second drop below 3.5v. Analog servos probably won't cause that with a good 4.8v pack, but if the pack is marginal and the pilot is really working the sticks, it can definitely happen. Digital servos will routinely cause a 1v and more voltage drop when they start demanding power, so it becomes good practice to use 6v batteries and be done with it. Very few currently manufactured servos are 4.8v only, so there isn't much reason not to go ahead and use 6v.

For someone starting out, like myself, sounds like 6 vt is the way to go regardless of what I fly, just to avoid the possible brown out.

;) Excellent Matt and you are indeed correct. Facts as I well remember when most of us where changing over from 72 to 2.4 is simply that the 2.4 systems were/are a little less tolerant of low voltage spikes and using a five cell Nimh or Nicd (6 volt) as opposed to the old four cell (4.8 volt) Nimh/Nicd is indeed a very effective defense aginst the feared brown out.

For many years now I advise all my students or any who would listen To Never use a 4.8 volt Nimh/Nicd with any brand 2.4 system. In those early years Spectrum took the biggest hit with these brown outs happening almost everywhere. Problem was the manufacturers reluctance to tell folks that their old 4.8's was just not suited to this new technology.

I first started using 2.4 with XPS which beat Spectrum with full range 2.4 by just a few weeks then later three generations of Hitec 2.4 and currently for my most expensive stuff Futaba (FASST) But guess what I have never experienced a brownout with any of it.

John:cool:

To be fair, Spektrum really is the only manufacturer that has an issue with radio voltage, at least as far as I know. 3.5v is the cutoff for them. At that point, the receiver shuts off and will reboot itself when the voltage rises above 3.5v. It takes about a second for that to happen, so it may cause a crash, or you may not even know it has happened at all. Other manufacturers saw the early problems Spektrum had back when the reset time was 3 seconds and designed receivers that can work with lower voltage. Realistically, Futaba, Hitec, and JR receivers shouldn't experience brownouts with any 4.8v pack that is appropriately sized for the plane it is in. That said, you pay a 1/2 ounce weight penalty for that extra cell and maybe $5, so there isn't much reason not to have it.