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6 V vs 4.8 V on Flight Packs

Old 02-04-2003, 08:33 AM
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bluefronted
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Default 6 V vs 4.8 V on Flight Packs

What are the advantages of using a 6 Volt battery pack as compared to a 4.8 Volt pack on the flight pack.

Are all JR and Futaba RX's , Servos and Gyros compatible to 4.8 and 6 volts.

Thanks again
Old 02-04-2003, 01:02 PM
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talybont
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Default 6 V vs 4.8 V on Flight Packs

Hi,

I prefer the 6V version because if one cell fails you have got still another 4 ones to keep the voltage. And your servos are faster and have more power with 6V.


MfG,
Armin
Old 02-04-2003, 01:29 PM
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krayzc-RCU
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Default 6 V vs 4.8 V on Flight Packs

so that you will have plenty of info to read do a seach as this post is hot a few months ago in the battery section.
Old 02-05-2003, 05:41 AM
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Lynx
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Default 6 V vs 4.8 V on Flight Packs

The extra cell gives you a little bit more voltage so when your packs start running low you can go a little bit longer before the transmitter hit's it's blank out voltage. Electronics will continue to function as long as the voltage is above the lowest point at which the regulator can grantee a steady voltage with enough amperage to drive it but voltage drops out before a current that low can't be drawn. With a receivers BEC circuit I'm not sure exactly what that voltage is but it's like a cliff, it works it works, then it stops cold. No slowing down. That's the way voltage regulators work. Also the servo's are driven a little faster cause they have a higher voltage. This also puts more electrical and mechanical wear on the servo but I've never heard from users the difference between 4.8 and 6.0 as far as servo lifetime. Personally, I'd use 4.8 volt packs simply cause it's one less cell in the pack and will lead to at least marginally lower wear on the servo's. If you want to steal a little extra torque out of the deal go with the 6 volt pack. They don't say so, but you can probably use a 7.2 volt pack. But I don't know what the limits on the BEC in most receivers are. Not to mention you'd seriously overdrive the servo's. Might last half as long. But the higher the voltage the higher the torque and speed.
Old 02-05-2003, 05:54 AM
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rajul
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Default 6 V vs 4.8 V on Flight Packs

Given a 4.8V and a 6.0V battery with exactly the same capacity (mAh), which gives a longer flight time assuming everthing else remain the same ? Does the 6V regulator somewhat "shorten" the flying time ? Thx.........
Old 02-05-2003, 06:06 AM
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Lynx
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Default 6 V vs 4.8 V on Flight Packs

It depends what voltage the hardware was designed to run at. Servo's were designed for both, but I've never seen spec sheets at the given voltages for efficiency. Just on general principals I'd say the higher voltage pack would be mildly more efficient, cause lower voltages require higher currents for the same amount of work, generating more heat, which is always waste. I don't think this would be more than a couple 100mAh's difference though. Where's the 6volt regulator though? The BEC circuit in transmitters is usually 3.3 volts I believe, and servo's use battery voltage. Even low cutoff voltage regulators require voltage to be 1-1.5 volts higher than the supplied voltage or they cut out. Some people do use voltage regulators in their setups, but do remember no regulator is 100% efficient, the less complex the setup the better your battery lifetime.
Old 02-05-2003, 06:12 AM
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rajul
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Default 6 V vs 4.8 V on Flight Packs

Lynx, is the 6V regulator necessary ? What are the advantages and disadvantages if I don't use it ? It will be more convenient to just plug a 6V battery to replace a 4.8V in my avionics setup.
Old 02-05-2003, 06:25 AM
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Lynx
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Default 6 V vs 4.8 V on Flight Packs

No regulator is needed.
Old 02-05-2003, 04:55 PM
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BBriBro
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Default 6 V vs 4.8 V on Flight Packs

Originally posted by Lynx
Just on general principals I'd say the higher voltage pack would be mildly more efficient.
It's actually the opposite, That is one drawback to running a 6 volt pack, You need more capacity. With the higher voltage, you also have more current, which is why you get more torque, and more speed, but the higher current draw drains the battery quicker
Originally posted by Lynx .
The BEC circuit in transmitters is usually 3.3 volts I believe.
Doesn' t "BEC" refer to "battery eliminator circuit?" This applies to electric cars where the main battery pack powers the motor and the receiver, But that is contradictory in this case, we are discussing the very component that the BEC eliminates, ( the receiver battery)

Some servos do not work on 6 volts, (Futaba coreless come to mind) they will jitter constantly and won't stay centered, you must run a regulator for those. Even servos designed for 6 volts, are really getting well over 7 if the pack has just come off charge, so untill the surface charge is gone, even "regular" servos may jitter. The advatages of a regulator is that the voltage stays constant, (somewhere around 5.2-5.4 volts depending on the regulator) this gives you slightly more torque and speed than a 4 cell pack, but prevents the high peak voltages from doing any harm. Also as you fly, and the battery voltage goes down, the voltage at the servos remains constant, therefore the servo speed, torque, and "feel" remain constant, (many pattern fliers charge their batteries before each flight for this same reason) There are no disadvantages to a regulator except you have one more component to buy and install. The advantage of No regulator, is simple installation, and you will probably be ok 99% of the time.
Old 02-05-2003, 04:56 PM
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hilleyja
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Default 6 V vs 4.8 V on Flight Packs

6volts vs 4.8volts:

The basic advantages/dissadvantages are:

1) More torgue with 6 volts => heavier pull capability

e.g., Hitec HS-5625
Stall Torque (4.8V): 109.7 oz/in. (7.9kg.cm)
Stall Torque (6.0V): 130.53 oz/in. (9.4kg.cm)

2) Faster speed with 6 volts => faster response

e.g., Hitec HS-5625
Operating Speed (4.8V): 0.17sec/60 degrees at no load
Operating Speed (6.0V): 0.14sec/60 degrees at no load

3) Higher current drain with 6 volts => less flying time

e.g., Hitec HS-5625
Current Drain (4.8V): 3mA/idle and 400mA no load operating
Current Drain (6.0V): 3mA/idle and 500mA no load operating


If your looking for the advantage that higher speed and heavier torque will give you then go with 6 volts. If you don't need the extra pull and speed stay with the 4.8 volts. Be aware that some components are sensitive to the extra voltage you can get from a 6 volt system and will be erratic. This is usually offset by using a voltage regulator.

Whether a 6volt system provides a safety margin is subjective. How often a single cell in a pack fails is unknown to me. Whether a single cell failure still leaves the rest of the pack capacity available is due to the way the cell fails. One understanding I do have is that a 6volt system does not provide a voltage advantange over the 4.8volt system when it gets down to the level of official discharge. What I'm trying to say is that when you check your voltage to see if you have another flight left in the pack, a 4.8volt system is minimal at around 4.6 volts. If your 6 volt system gets down to that level your dead. Discharge is assume to be when a single cell gets below 1.1volt. That's 4.4volts for a 4.8volt system and 5.5volts for a 6volt system.

I almost made that mistake and found my flight pack to be erratic when my 6volt system got below 6 volts.
Old 02-05-2003, 09:00 PM
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Default 6 V vs 4.8 V on Flight Packs

Hilley hit the nail on the head. More speed and more torque with a higher current draw. I found that you can get more out of cheaper servos!
Old 02-06-2003, 01:04 AM
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Default 6 V vs 4.8 V on Flight Packs

Thanks for the great info guys........
Old 02-06-2003, 02:08 AM
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walton
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Default 6 V vs 4.8 V on Flight Packs

I have a question for you guys. I am thinking about building a plane that is going to take 8 or 9 servos, I will probably use futaba 9405s do I need a 6 volt rx pack to properly supply these servos with enough power. Thanks James
Old 02-06-2003, 02:28 AM
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Lynx
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Default 6 V vs 4.8 V on Flight Packs

You'll probably want to electrically seperate that many servo's cause if you hit them all at the same time you're gonna have a significant voltage drop. Have 4 run off one pack, and 4 run off another pack.
Don't forget to add decreased lifetime. On 6 volt packs, servo's will last roughly speaking half as long as a servo running on 4.8 volts. It's a trade off you make for being able to do more work.
BBriBro was perfectly correct. The better idea might be to run a 6volt pack with regulator. That'll give you better consistancy than either choice. And slightly higher voltage for just a pinch more than 4.8 volt rated torque and turn rates. I don't know the quaility of the regulators that are out there though what current they can source regularly or what not.. Might be better of sticking with 4.8
Old 02-06-2003, 03:50 AM
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Ed
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Default 6 V vs 4.8 V on Flight Packs

Something else to consider: If you are considering a 6 volt pack to provide your Cheap $10 servos with more speed and power, then you are considering a "Band-Aid" fix. The real way to address the problem is with high quality, coreless, ball bearing servos. Don't fool yourself into beleiving that 6 volts is the total answer. 6 volts will result in greater brush arcing and potential receiver interference, shorter brush life, and greater gear wear due to faster reversal times. Shorter servo life regardless of what you are told by others. There ain't no free lunch guys; you gets what you pay for. As far as the receiver continuing to work if a cell fails, that's only in the case if a cell Shorts. Things like open cell tabs, connectors, and switches are not accounted for.
Old 02-06-2003, 12:08 PM
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walton
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Default 6 V vs 4.8 V on Flight Packs

Futaba 9405s are metal geared coreless motored and ball bearing and are way more than ten dollars.
Old 02-06-2003, 12:17 PM
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Default 6 V vs 4.8 V on Flight Packs

I would recommend either multiple packs or a pack with multiple leads to share the load.

Originally posted by walton
I have a question for you guys. I am thinking about building a plane that is going to take 8 or 9 servos, I will probably use futaba 9405s do I need a 6 volt rx pack to properly supply these servos with enough power. Thanks James
Old 02-06-2003, 12:20 PM
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Geistware
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Default 6 V vs 4.8 V on Flight Packs

Jim,
While I never said anything about using $10 servos as a rational to use 6 volts, I do stand behind what I said when you have a good servo and need more torque. An example is if you need 100oz of torque from a Futaba 9202 (rated 98.4oz). You can get a more expensive servo which will get you the torque at 4.8 volts but why do this. Save money and go with a higher voltage.

Originally posted by GeeBeeJim
Something else to consider: If you are considering a 6 volt pack to provide your Cheap $10 servos with more speed and power, then you are considering a "Band-Aid" fix. The real way to address the problem is with high quality, coreless, ball bearing servos. Don't fool yourself into beleiving that 6 volts is the total answer. 6 volts will result in greater brush arcing and potential receiver interference, shorter brush life, and greater gear wear due to faster reversal times. Shorter servo life regardless of what you are told by others. There ain't no free lunch guys; you gets what you pay for. As far as the receiver continuing to work if a cell fails, that's only in the case if a cell Shorts. Things like open cell tabs, connectors, and switches are not accounted for.
Old 02-06-2003, 01:48 PM
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Default 6 V vs 4.8 V on Flight Packs

Originally posted by walton
do I need a 6 volt rx pack to properly supply these servos with enough power. Thanks James
if you use a 4 cell pack, you have 4.8 volts with one servo, or 9. What you need with that many servos is capacity. The voltage will be the same, (yes like Lynx said, if you operate them simultaneously, there will be a slight voltage drop) But the key to multiple servos is a large capacity battery. Kind of like wiring light bulbs in parallel vs. series. You can add as many as you like in parallel, they will all be the same brightness and have the same voltage provided you have enough current to power them.
Old 02-07-2003, 04:14 PM
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Default Servo power

I don't know how the current draw on these servos is vs a regular electric motor but typically the power is proportional to the voltage times the current, i.e. for a given power a higher supply voltage draws lower current. The servos is only going to product as much torque as the control surface requires of it, independent of what kind of battery is there. So why would a 6v battery have to supply more current?
Old 02-07-2003, 04:48 PM
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Default Re: Servo power

Originally posted by pilot_error
So why would a 6v battery have to supply more current?
I do not know the technical reason, But you do not get something for nothing. the higher voltage gives more speed and torque, at the expense of battery life. A friend of mine has a degree in electronics, I will see if he can explain it.
Old 02-07-2003, 05:45 PM
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Default 6 V vs 4.8 V on Flight Packs

Originally posted by walton
I have a question for you guys. I am thinking about building a plane that is going to take 8 or 9 servos, I will probably use futaba 9405s do I need a 6 volt rx pack to properly supply these servos with enough power. Thanks James
You don't need a 6v pack, but using one gives you some advantages. If you wire the plane poorly, you will need the extra zip of 6v to overcome the voltage losses you added. If you wire it properly, you could get by with 4.8v.

While you may start with 4.8v at the battery, all the wire, connectors (biggest loss of voltage), and long leads will steal some voltage along the way. Buy the time you get out to the servos, you may be operating at a lot less. By starting with 6v from the battery, you are already 1.2v ahead. You will be running more than 4.8v at the servos, but not quite 6v either.

When you hit the system with the full load of all the servos, say in a snap roll, the voltage will drop somewhat. It will all depend on what state the battery is in (i.e., almost empty, or just charged). Again, having the extra margin of 1.2v is nice.

There is a whole bunch on info in this thread I posted a while back for reference.

http://www.rcuniverse.com/showthread...119&forumid=38]
Old 02-07-2003, 09:26 PM
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walton
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Default 6 V vs 4.8 V on Flight Packs

Thanks everyone and Steven for your input.
Old 02-08-2003, 12:12 AM
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Default Re: Servo power

Originally posted by pilot_error
So why would a 6v battery have to supply more current?
Remember ohms law V=IR. For all practical purposes the resistance is not changing, so if the voltage increases the current must also increase.
Old 02-08-2003, 02:35 PM
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Kevin Greene
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Default 6 V vs 4.8 V on Flight Packs

If you go to a six volt pack you MUST increase the capacity of the pack to get the same flight time as a 4.8 volt pack....Period!!!! The reasons for this have been hashed out in previous threads. Also, as some of my fellow jet jockies and I have found, you can get reduced range from your RX running a 6 volt unregulated pack. We checked this with our JR PCM RX's...I do not know if this holds true for Futaba.

I can't understand why modelers insist on running 6 volt packs. If left unregulated a topped of 6 volt pack can measure as high as 7.2 volts!!! This can cause jittery servos, reduced range, and decreased flight times. So, to be safe you must run a voltage regulator. These have been known to fail causing catastrophic (ie mucho $$$$) crashes. So, what is there to gain??? Running 6 volt packs to overcome poor servo wiring is just a bandaid. With the new products out, like the JR matchbox and its' Futaba equivelent, there are no reasons to run 6 volt packs. The matchbox allows you to separate your servos and run a separate battery pack for that group. If you need more power and speed you need to step up and buy better servos. If your voltage losses are too great and caused by multiple servo extensions then fix it with proper servo and battery wiring. I know that some of you will say that "It has always worked for me!" Sooner or later it CAN catch up to you !!!! Why is there never enough time to do it right the first time but plenty of time to do it over???

Kevin

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