LargeScale88

Hello. I have a new airplane, its a .90 size Yak 54. For servos I'm running (4) Hitec 645 mg, (1) Hitec 425, and (1) Hitec 985 for the rudder. All these servos are analog. I'm using a DSM2 Spetrum 7 channel radio, with an AR7000 receiver. My question is, with the servos I'm running, would Ibe better off running a 6v receiver battery, or a 4.8v receiver battery? I've read how Hitec servos don't like 6v but I know plenty of people running 6v and they have no problems. I've always used 4.8 soi'm wondering now if I should make the switch over to 6v.

Thanks

Jason

flyinwalenda

My Feedback: (5)

I've never had any Hites servos rated for 6v give fits on a 6volt pack. Sometimes coming off a fresh charge some servos don't like that peak 7 volts and will jitter until the pack discharges a bit. Usually when you fully charge a NiMh the day or night before it has self discharged a bit by the time you go fly with it.   I would rather 6 volts on a larger plane with heavier servos.

jetmech05

I fly HiTech in most of my airplanes even giants...I looked in the spec for the 645 and Tower has it rated for 6V. I have run 6V with no problems... I wouldn't hesitate to run 6V especailly with Speckrum....the only servos that ever twiched on me with a full charge were JR's

maukaonyx

I don't think I have a single plane left on 4.8V. I only use 6V nimh's for higher speed and torque....and I do have Hitec 645's in some of the planes, with no issues about 6V. Jon

Jetdesign

My Feedback: (8)

I personally would not run 4.8v with Spektrum (or anything else for that matter, but especially with Spektrum). Performance wise the best thing would be a 6v battery (or lipo) on a regulator, where you can limit the output voltage to 5.8v and know you will always have the same power and speed to all your servos, regardless of battery charge, and you are keeping the voltage below the max limit of the servos.

JohnBuckner

My Feedback: (1)

As most all have indicated it is unwise to use 4.8 volts with any 2.4 system and not just Spectrum

I use nothing but 6 volt packs on almost all my 53 plug and play aircraft and almost all use Hitec servos as well as systems and have failed to find any Hitec servo that has a problem using 6 volts.

John

macdona

My Feedback: (3)

I must be the only one in the world still using 4.8 volt packs. I use high amp receiver packs and have since the day Spectrum radios came out. Have never had a glitch.

JohnBuckner

My Feedback: (1)

Macdona I would speculate that you have never experianced a brown out simply because you have likely been very carefull about your battery care and charging protocol but that does not deter from the safety advantages of using 6ers over 4.8's for 2.4 systems.

Actually you are not totally alone as I do have two airplanes in my fleet that I now use 2.4 systems for throttle control only and tiny servos. These I do use 4.8 packs and are controlline airplanes, they are never more than sixty feet away.

Oh and 4.8 packs are kinda needed on many (not all) gasser ignition systems.

John

opjose

Make the switch!

Note however that the move up in voltage also requires a higher capacity pack at the same time.

At 6 volts the servos draw SUBSTANTIALLY more power from the battery pack sometimes doubling the load.

In addition, the servos you are using will draw around 700mA in normal use ( control surfaces moving ) EACH and can approach 2000mA as they get to a full stall.

This introduces a momentary "spike" in the power draw that can drop the supply voltage enough to cause the RX to glitch or reboot.

I would size my packs given your described configuration to handle a nominal 8 to 10 AMPS draw. Remember that some regulators rated at 10A can really on sustain 5A, check the specs carefully if you use a regulator.

If you want to save weight consider using LiFe packs. A 3200mAh 20C 6v LiFe pack weights about half of what a similiar NiMH pack does and does not need a regulator.

I've used the Turnigy LiFe packs with great success and they are cheaper than NiMH packs. Their 2200mAh 20C LiFe packs are around $7.00/ea shipped from the states, same chemistry as the A123's.

For larger planes I'll put in two of them in parallel to give me an effective 4400mA and a degree of redundancy. These weigh about the same as one 2200 NiMH pack.

macdona

My Feedback: (3)

Here is Spetrum's say on voltage. This I have done and never had voltage fall below 5 volts. Then again I do not fly huge aircraft but some of my planes are high performance, around 140 mph.






Recommended Guidelines




Receiver Power System Requirements

With all radio installations it is vital the onboard power system provides adequate power of 4.5 volts or more without interruption to the receiver even when the system is fully loaded (servos at maximum flight loads). This becomes especially critical with giant scale models that utilize multiple high torque/ high current servos. Inadequate power systems that are unable to provide the necessary minimum voltage to the receiver during flight loads have become the number one cause of in flight failures. Some of the power system components that affect the ability to properly deliver adequate power include: the selected receiver battery pack (number of cells, capacity, cell type, state of charge), switch harness, battery leads, regulator (if used), power bus (if used).

While Spektrum’s receivers’ minimum operational voltage is 3.5 volts, it is highly recommended the system be tested per the guidelines below to a minimum acceptable voltage of 4.8 volts during ground testing. This will provide head room to compensate for battery discharging or if the actual flight loads are greater than the ground test loads.

Recommended power system guidelines:

1. When setting up large or complex aircraft with multiple high torque servos, it’s highly recommend a current and volt meter (Hangar 9 HAN172) be used. Plug the volt meter in an open channel port in the receiver and with the system on, load the control surfaces (apply pressure with your hand) while monitoring the voltage at the receiver. The voltage should remain above 4.5 volts even when all servos are heavily loaded.

2. With the current meter inline with the receiver battery lead, load the control surfaces (apply pressure with your hand) while monitoring the current. The maximum continuous recommended current for a single heavy duty servo/battery lead is three amps while short duration current spikes of up to five amps is acceptable. Consequently if your system draws more than three amps continuous or five amps for short durations, a single battery pack with a single switch harness plugged into the receiver for power will be inadequate. It will be necessary to use multiple packs with multiple switches and multiple leads plugged into the receiver.

3. If using a regulator it’s important the above tests be done for an extended period of 5 minutes. When current passes through a regulator heat is generated and this heat causes the regulator to increase resistance which in turn causes even more heat to build up (thermal runaway). While a regulator may provide adequate power for a short duration it’s important to test its ability over time as the regulator may not be able to maintain voltage at significant power levels.

4. For really large aircraft or complex models (35% and larger or jets) multiple battery packs with multiple switch harnesses are necessary or in many cases one of the commercially available power boxes/ busses is recommended. No matter what power systems you choose always carry out test #1 above making sure that the receiver is constantly provided with 4 volts or more under all conditions.

5. The latest generation of Nickel Metal Hydride batteries incorporate a new chemistry mandated to be more environmentally friendly. These batteries when charged with peak detection fast chargers have tendencies to false peak (not fully charge) repeatedly. These include all brands of NiMh batteries. If using NiMh packs be especially cautious when charging making absolutely sure that the battery is fully charged. It is recommended to use a charger that can display total charge current. Note the number of mAh put into a discharged pack to verify it has been charged to capacity.

Jetdesign

My Feedback: (8)

I'm sure there are a lot of people who have not had problems with 4.8v batteries in Spectrum, or other 2.4g systems. That does not change the fact that 'brown outs' are a wide spread and well-known issue, that can easily be avoided by using 6v battery packs.

It is cheap insurance.

da Rock

I'm not really sure if they are a wide spread problem. I fly OFTEN, and at a number of places and have only seen one ever. It was a perfect example of what used to be "I'M HIT! I'M HIT!" where the pilot lost it and it was the only thing he knew to do.... yell that the plane wasn't doing what he was telling it to, which was full up and full throttle.

Nowadays we have lost our most popular excuse. Brownout is certainly well-known. But I for one haven't seen it to be wide spread.

HOWEVER..........

6Volts is an excellent thing to do just for insurance. And btw, some planes do benefit from having quicker, stronger servo action. Good thing too, is that the 6V replacement packs recently have been higher capacity cells! Might as well add an additional benefit. More insurance never hurts when it isn't significantly more expensive.

Jetdesign

My Feedback: (8)

I just want to share this for people who might still be on the fence about what battery to use. If you do an internet search of receiver brownout, you will see a lot of relevant threads and information. This has been happening to a lot of people, it is not just a few rare instances.

Here are notes from a Spektrum receiver manual. Brownouts are enough of a problem that they have been added into the Spektrum owners manual (I do not see any notes about seconds long reboots in Futaba manual, for the record). Clearly, a system setup properly should not have any issue. However I believe that most people don't really know the condition of their Rx batteries; I didn't until I finally started load testing batteries, and was surprised to see how low the voltage can drop under load of a battery that seemed to work/charge quite well. So a 4.8V battery is technically enough to work with a 2.4g Spektrum system, but using a 6.0v battery moves you well away from that critical point. With the number of cheap, low quality batteries on the market along with neglect of properly checking and maintaining batteries, a 6.0v battery is really a smart choice.

DadsToysBG

My Feedback: (35)

I made the move to 6v packs before 2.4 came out. It was a cheap way to increase servo performance. now I only use A-123's. Dennis

tazzzz

Ive heard of this battery before what is an A123? TAZZZZ

Jetdesign

My Feedback: (8)

LiFe - Lithium Iron Phosphate battery. It is another lithium based battery. It has a slightly lower potential (voltage) than a lithium ion or lithium polymer battery, so it can be used w/o a regulator in *most setups.

It is a 'safer' battery chemistry. The only down-side I know of really is only for power packs, because the energy:weight of the packs is reduced from the LiPo's we're used to. A 10C LiFe flight pack is something like a 9C LiPo.

Also if you are using a mixed bag of battery technologies, you have to remember to change the settings in your charger (like for me, most of my batteries are LiPo, I have one LiFe for an Rx battery, need to change the charger setting when I charge that battery).

YAT-28E

Wow am I out of it!! I have and still use NiMH 4.8 packs....Then again I am still on 72 mhz....that's like saying " Hey, what is that thing attached to the phone?" Oh that, it is a rotary dial we used to use to dial a number to make a call......What's that thin thing over there?...Oh that's what we used to use to listen to music..it is a vinyl record....and on and on and on....

Moving to 2.4 soon and LiFe with a regulator....and some day I will stop wiping my planes clean of oil and go to gas or electric.....

Not in a hurry as no need to yet!!

BarracudaHockey

My Feedback: (11)

Two things.

OpJose, this statement really isn't true. Increased consumption (proven through testing) is on the order of 5 to 7 percent.


A123's dont need a regulator unless you're running old servos or the few sold today for special applications that can't take 6v.

raptureboy

I would suggest you check out this site for all the information you will ever need regarding all the battery types. I have switched over to LiFe batteries and they are superior to all other types in my opinion. Steve at NoBS is an expert in the industry, there is a difference between A123's and LiFe type batteries. Here is the question to ask; is my plane worth the extra cost of good batteries? http://hangtimes.com/

opjose

Typical test....

@ 4.8v a digital servo at end of throw with little binding. 300mA draw, idle current draw 80mA
@ 6.0v the same servo on the same plane with no other adjustment 535mA draw, idle current draw 100mA.

That is far more than 5-7 percent.

opjose

They need not cost more too.

I've been putting in 6.6v 2100mAh 20-40c LiFe Packs that cost a whopping $13.00/ea

( Note that they are mislabeled "transmitter packs" in the link... these have standard RX leads on them.)

[link=http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=28650]$13.00 RX LiFe Packs[/link]

They weight so little that two of them together are still lighter than a NiMH pack with the capacity of one of these packs.

They also hold up to the high draw demands of digital servos.

Great packs IMHO...

BarracudaHockey

My Feedback: (11)

I find that atypical. We did a lot of testing a while back when this first came up and found consistently less increased consumption increase than you're seeing.

opjose

I've tested quite a number of different servos under load of various brands.

When you consider mA x voltage, even under best conditions the difference is FAR more than 5-7 percent.

We had a club member demonstrate the same thing to everyone at a recent meeting.

Jetdesign

My Feedback: (8)

Just a refresher: LiFE batteries do not have as much energy density as Lithium Polymer. If you are talking about batteries to power your motor, you need more cells/weight with LiFe to achieve the same power output. For those of us that fly 'large' electrics, LiFe batteries do not make sense to use for power other than Rx power.

opjose

Right, not as "flight packs"... powering an ESC.

But to power the electronics and servos they are fantastic.

I've switched most of my planes to them, and they are particularly good on my gassers that have a lot of servos...