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Old 04-30-2011, 01:03 AM   #1
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Hi everyone, I am going to be running a futaba 617fs receiver and four standard size servos, (JR nes 537) on a Kadet senior. Not sure what size battery pack to use? I have a 600mah 4.8v, but wanting to know if I should get a larger capacity pack. Any input would be greatly appreciated!
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Old 04-30-2011, 01:25 AM   #2
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That pack with that plane will likely be all you need for 6+ flights, maybe more.

How many flights do you generally do?

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Old 04-30-2011, 03:17 AM   #3
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I will probably only fly this plane two times. I just finished converting this plane to electric and as of now I only have one lipo for the motor. Not sure what I will get for flight time's yet. I am going to do some testing. When I get some more funds, I will get another battery, then I may fly it three or four times. Sounds like I will be fine with the pack I have! I really appreciate the help!

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Old 04-30-2011, 03:29 AM   #4
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Originally Posted by 2manyhobbies View Post
Hi everyone, I am going to be running a futaba 617fs receiver and four standard size servos, (JR nes 537) on a Kadet senior. Not sure what size battery pack to use? I have a 600mah 4.8v, but wanting to know if I should get a larger capacity pack. Any input would be greatly appreciated!
Hi here is some great info from Dennis, Get a 10 Amp Castle Creation UBEC and 2 Diodes, your Battery pack will now be a back up battery, and you can Fly all day long, Hope that helps, Chellie


http://www.wattflyer.com/forums/showthread.php?t=58310

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Originally Posted by CHELLIE
Thats interesting, I was just wondering, could you put a diode on the pos feed on the battery and one on the UBEC, they would both feed, but there would not be a feed back between them, just a thought, Take care, Chellie
Hi Chellie
Yes you can. I'd recommend a Shottky diode, NOT a silicon diode for this purpose. Shottky diodes have a lower forward voltage drop of about 0.4 volts DC under load, making it better for our purpose. They do cost more however, about $2.00 each, not including shipping. A number of club members have gone to this based on an article I wrote in the club newsletter last year.

You need to adjust the uBEC output voltage high enough so that the backup Nicad battery is not loaded during flight.

Schottky Diode www.digikey.com # 90SQ035-ND (Digikey only has 5000 left, better hurry!)

(http://search.digikey.com/scripts/Dk...5-ND&x=27&y=21).

This is a 9 ampere Shottky diode that will handle any type of receiver load you'd ever require.

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Old 04-30-2011, 03:38 AM   #5
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Originally Posted by 2manyhobbies View Post
I will probably only fly this plane two times. I just finished converting this plane to electric and as of now I only have one lipo for the motor. Not sure what I will get for flight time's yet. I am going to do some testing. When I get some more funds, I will get another battery, then I may fly it three or four times. Sounds like I will be fine with the pack I have! I really appreciate the help!

Tim
Yep it will be fine for that you are all set!
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Old 04-30-2011, 03:40 AM   #6
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Originally Posted by CHELLIE View Post
Hi here is some great info from Dennis, Get a 10 Amp Castle Creation UBEC and 2 Diodes, your Battery pack will now be a back up battery, and you can Fly all day long, Hope that helps, Chellie

.
Thanks Chellie!

Take a look at my latest setup, based on findings on a dozen flights. I'm using a two cell A123 pack, but a Shottky diode, 5 Cell Nih receiver battery and a Castle Creations 10 Amp BEC would work well.

Then adjust the CC BEC's output voltage so the 5 cell Nih battery never carries any current. (You need CC's PC ESC programmer to do this.) About 6.6 Volts DC or so. Just make certain your radio and servos are rated for 5 Nih cells though.

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Old 04-30-2011, 03:56 AM   #7
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Hi Dennis A 4 cell NiCad battery receiver pack is 4.8 volts, each cell is 1.2 volts, so with a 4 cell NiCad receiver pack, I dont think a person would have to set up the UBEC Voltage, because The UBEC output voltage is Higher at 5.1 volts out of the package, please correct me if i am wrong, Take care, Chellie

CC BEC SWITCHING REGULATOR
Current Output: Peak: 10 amps
Continuous:
less than 12 volts input = 7 amps*
less than 24 volts input = 5 amps**Ratings are determined with a 5mph airflow on the BEC. Servo connectors are not rated for current in excess of 5 amps. Users are encouraged to replace the connectors if more than 5 amp currents are anticipated.

Output Voltage: Output 5.1 volts out of the package, user may set output voltage from 4.8 to 9 using the Castle Link (sold separately).

Input Voltage: 5v to 25.2v (2S to 6S LiPo)
Length: 1.2” (30mm)
Width: 0.6” (15mm)
Height: 0.4” (10mm)

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Old 04-30-2011, 05:43 AM   #8
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Originally Posted by CHELLIE View Post
Hi Dennis A 4 cell NiCad battery receiver pack is 4.8 volts, each cell is 1.2 volts, so with a 4 cell NiCad receiver pack, I dont think a person would have to set up the UBEC Voltage, because The UBEC output voltage is Higher at 5.1 volts out of the package, please correct me if i am wrong, Take care, Chellie
Hi Chellie
About 1/2 of our club members are flying giant scale models with 30 cc gassers or larger. And every one of them is using a 5 cell battery pack for the receiver and servos. And on my recommendation, they are using "Sub C" size cells in their receiver batteries.

IMHO, for these expensive, high powered models, a 5 cell battery pack is almost mandatory, and that does NOT allow using those 2700 Mah "AA" receiver packs. I did some checking on this, my Extra 330 with seven Hitec 645MG servos pulls a measured maximum current of 14 Amps when all transmitter sticks are moved violently back and forth. And that will pull down those "AA" receiver batteries to the point where the microcontroller in the receiver is in trouble. That's one big reason the Spektrum 2.4 Ghz radios got a lot of bad publicity a while back.

A lot of people in my club have observed my 2300 Mah A123 cells, and are using either the A123 cells, or the LiFeP04 cells in their receivers.

And, for the 5 cell Nih battery, or the two cell A123 cells, you've got to increase the CC BEC voltage slightly, or the backup battery will be carrying much of the load. The voltage output of the 5 cell Nih battery will vary between about 5.8 to 6.9 Volts DC. Subtract about 0.6 volts for the diode, that's still over 6 volts out of the 5 cell Nih battery and its series diode. Which is why I put two series diodes in my setup with the CC BEC.

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Old 04-30-2011, 05:55 AM   #9
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Hi Dennis Yes I agree with you on the Giant size aircraft that you would need more amp output, because you have giant servos in those aircraft, What I was refering to, is that on a larger RC model, with 4 standard size servos, and a 4 cell 4.8 volt, 600mah NiCad receiver battery, that a CC 10 AMP UBEC would work to power the system and the 4 cell Nicad being a lower voltage would serve to be a back up battery with 2 diodes installed because the UBEC is set at a higher voltage 5.1 volts from the mfg, and that no adjustment of the UBEC voltage would be required in this case, please correct me if i am wrong here take care Chellie

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Old 04-30-2011, 05:59 AM   #10
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Originally Posted by CHELLIE View Post
Hi Dennis Yes I agree with you on the Giant size aircraft that you would need more amp output, because you have giant servos in those aircraft, What I was refering to, is that on a larger RC model, with 4 standard size servos, and a 4 cell 4.8 volt, 600mah NiCad receiver battery, that a CC 10 AMP UBEC would work to power the system and the 4 cell Nicad being a lower voltage would serve to be a back up battery with 2 diodes installed because the UBEC is set at a higher voltage 5.1 volts from the mfg, and that no adjustment of the UBEC voltage would be required in this case, please correct me if i am wrong here take care Chellie
Hi Chellie
Only problem is with a 4 cell Nih battery with two extra diodes added, that's 4.8 volts on the battery, minus about 1.2 volts worst case or 3.6 volts DC. Thats pretty low voltage on the servos, and is getting awfully close to the minimum 3.2 Volts DC on the Spektrum receivers.

Have a good day!

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Old 04-30-2011, 06:10 AM   #11
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Originally Posted by kyleservicetech View Post
Hi Chellie
Only problem is with a 4 cell Nih battery with two extra diodes added, that's 4.8 volts on the battery, minus about 1.2 volts worst case or 3.6 volts DC. Thats pretty low voltage on the servos, and is getting awfully close to the minimum 3.2 Volts DC on the Spektrum receivers.

Have a good day!
Ok Got you Now the Diodes will lower the voltage a tad, hence the 5 cell NiCad or higher voltage to compensate for DIODE voltage drop, took me a while to figure that one out LOL, you learn something new everyday, Take care, Chellie

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Old 04-30-2011, 12:02 PM   #12
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I find it really interesting how things change ................... in 80's 90's .... most flight systems were powered by standard NiCD 500mAh 4 cell packs. We would be at flight site all day with maybe 3 - 4 flights up to 10min each. ... (IC was usual power in those days not electric).
For longer duration or for a whole weekends competition we would up to a 1200mAh pack using C cells ...
Note in those days - the servos were not the small less power hungry that you have now !

I used to carry a 12v field charger for my flight and Tx packs .... just in case !

Nowadays there's no need to stick with low capacity NiMH's anymore as a standard AA size now can be up to 2500mAh ... an AAA up to 800mAh .... amazing - wish they had those back then !

As to Kyle and Chellie with Diodes .......... be very careful ... standard Diodes can EACH reduce a voltage by up to 0.7V ... even low loss diodes will look at 0.2 - 0.3V reduction ... but Kyle already knows that ... The number of boat installations I see that ignore that simple fact !!

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Old 04-30-2011, 01:32 PM   #13
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Originally Posted by solentlife View Post
Nowadays there's no need to stick with low capacity NiMH's anymore as a standard AA size now can be up to 2500mAh ... an AAA up to 800mAh .... amazing - wish they had those back then !
You hit the nail on the head for low power analog servos the AA cells are OK - maybe even the AAA cells (if they are good ones). But Servos and Receivers now tend to draw a bit more power, or in the case of the power hungry digitals I don't think high capacity AA's are the answer.

I have been using LiFePo4 cells with great results. They are 3.3v Nominal each and provide 6.6v to the RX and servos. They are easily able to handle very high power draws, especially the round cells. Those are the same type of batteries being used in many Hybrid cars.

No BEC's, regulators or such needed just great power. Make sure you servos are rated for 5 cell NiMh or NiCad packs though.

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Old 04-30-2011, 04:47 PM   #14
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I cannot imagine that a Rx and servos nowadays can draw such power frrom a NiMH that it would fail unless it's such small capacity it drains quickly. NiCD, NiMH are quite capable of very high discharge ampages ... such that I have a burn on side of my left leg from one AA cell ! I stupidly forgot I had coins in that pocket .............

I also would question whether todays servos draw as much as my old NES JR servos ... maybe a Digital does but a modern analogue ?

Rx's .... the average mid range size Rx now is less than 1/2 size of the module part of my old JR Propo Rx ... and fraction of the weight. Given the components and boards ... I would bet my JR Propo from 80's draws more mA than todays ...

Anyway - point is original poster can up his capacity in mAh for same size and weight pack .... with same type cells. But if using the one he has - he has enough for a good few flights at a session.

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Old 04-30-2011, 05:17 PM   #15
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I have Hyperion digitals that draw well over 1.5amps EACH! So 4 of those are 6 amps. To be honest that is higher than the capacity of most of our radio connectors. This is why BECs are commonly 5-10 amps and for the large planes are 10+ amps. Yes radio systems and 4-10 power hungry digitals can draw massive power.

There is a reason Futaba, Hitec and Spektrum make supplemental RX inputs for high amp draws in large scale birds. Futaba and Spek even include Dean and EC3 type connectors (respectively) on those receivers!

New 2.4GHz RX's draw 2-3 times the power of your old RX. Generally in the 150-400 mAh range.

Dead shorts of cells isn't a show of power delivery just spectacular instant results as they try to deliver the power you are asking. What happens is those small AAA or AA cells try to deliver, drop voltage, reset your RX cause you to crash and when you walk over everything is working and you are like hey what is the deal?

AA and AAA are NOT capable of delivering high amp draws for digital servos. Some of those very high capacity cells are rated for VERY low current delivery.

You are right though todays analog servos are generally low consumption less than .5 amps each. But 6-8 of those sure add up!



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Old 04-30-2011, 05:19 PM   #16
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Originally Posted by solentlife View Post
I cannot imagine that a Rx and servos nowadays can draw such power frrom a NiMH that it would fail unless it's such small capacity it drains quickly. NiCD, NiMH are quite capable of very high discharge ampages ... such that I have a burn on side of my left leg from one AA cell ! I stupidly forgot I had coins in that pocket .............

I also would question whether todays servos draw as much as my old NES JR servos ... maybe a Digital does but a modern analogue ?

Rx's .... the average mid range size Rx now is less than 1/2 size of the module part of my old JR Propo Rx ... and fraction of the weight. Given the components and boards ... I would bet my JR Propo from 80's draws more mA than todays ...

Anyway - point is original poster can up his capacity in mAh for same size and weight pack .... with same type cells. But if using the one he has - he has enough for a good few flights at a session.
I've got a Extra 330 model with seven Hitec 645MG servos in it. By actual test with my Fluke 87V digital multimeter with one millisecond peak recording, one of those servos pulled a maximum of 2.05 Amps, just going back and forth on the transmitter stick.

And checking all 7 servos at once while moving all transmitter sticks back and forth, I measured a peak current of 14 Amps. The power source used was a two cell 2300 Mah A123 battery.

And, out of curiosity, I plugged in a one year old 4 cell "AA" size Nih pack for receiver power that is in good condition, and tried moving the transmitter sticks again. I managed to get the Nih battery to sag down to a measured 3 Volts DC again as measured by the Fluke 87V meter, Minimum/Maximum recording reading. That will reboot the Spektrum AR7000 receiver.

My receiver setup has a Castle Creations 10 Amp BEC plus a two cell 2300 Mah A123 for backup. And, it has my design voltage monitor that checks voltage 4000 times per second. Moving all transmitter sticks resulted in the output voltage of that CC 10 Amp BEC dropping down from a programmed 6.6 volts DC to 5.8 VDC, as measured by my voltage monitor.

IMHO, those "AA" sized batteries should not be used for receiver power in giant scale models. Period. The servos can draw more peak current, and the servos are often operating far larger elevators, rudder or aileron surfaces than models of years ago. Just look at a big "3D" model.

(Last fall, before its maiden flight, I looked inside a club members giant scale model with a 50 cc gas engine and a lot of digital servos. He had selected a 5 cell "AA" receiver battery with a rating of 2800 Mah. I told him DON'T FLY IT! We moved all the transmitter sticks, and got his Spektrum receiver to reboot. He went with a 5 cell receiver pack with sub "C" cells. And has many flights on it now.)

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Old 04-30-2011, 05:28 PM   #17
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Denny - spot on. So many blame their RX for them not providing proper power.

I have in in-flight servo monitor from Dimension Engineering. It is stunning what that can reveal. Imagine in flight loads to your test!

You have shown how even analog servos can suck the juice.
AA = Out.
LiFePo4 = In.

I don't even trust BEC's after I got my CC to croak using 4 power hungry digitals. Hitec has the highest re-boot voltage at around 3.6v. That was a 1k hard knock lesson.

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Old 04-30-2011, 05:30 PM   #18
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Originally Posted by rcers View Post
Denny - spot on. So many blame their RX for them not providing proper power.

I have in in-flight servo monitor from Dimension Engineering. It is stunning what that can reveal. Imagine in flight loads to your test!

You have shown how even analog servos can suck the juice.
AA = Out.
LiFePo4 = In.

I don't even trust BEC's after I got my CC to croak using 4 power hungry digitals. Hitec has the highest re-boot voltage at around 3.6v. That was a 1k hard knock lesson.

Hitec has 3.6 volts for re-boot? Ouch. My pile of Spektrum AR7000's all check out at 3.14 Volts DC plus or minus a few tenths.

Check out page #9 of my thead on backup power for my giant scale model.
http://www.wattflyer.com/forums/showthread.php?t=58310

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Old 04-30-2011, 05:35 PM   #19
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Originally Posted by rcers View Post
I have in in-flight servo monitor from Dimension Engineering. It is stunning what that can reveal. Imagine in flight loads to your test!
Could you provide information on that in-flight servo monitor? Other wattflyer readers might find it interesting.

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Old 04-30-2011, 05:41 PM   #20
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Sadly it is no longer made. It was called the Servo sense from Dimension Engineering. http://www.dimensionengineering.com/ServoSensePlus.htm

Sorry to entice you - he just didn't sell very many.

He still makes great stuff - check it out. His BEC's rock.

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Old 04-30-2011, 06:08 PM   #21
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Originally Posted by rcers View Post
Sadly it is no longer made. It was called the Servo sense from Dimension Engineering. http://www.dimensionengineering.com/ServoSensePlus.htm

Sorry to entice you - he just didn't sell very many.

He still makes great stuff - check it out. His BEC's rock.

Mike
To bad
I made my own, but it's not really practical to provide drawings and stuff for it. Pretty complex.

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Old 04-30-2011, 07:49 PM   #22
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The units have a limit of 5 amps - so that was a bottleneck as well. Due to the connector and the amp limit I never tested them with digital servos where I felt that would be an issue.
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Old 04-30-2011, 10:15 PM   #23
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Note that it takes some pretty good instrumentation to accurately measure the dynamic currents drawn during servo operation. You need a fast response like an oscilloscope will give or some very high priced peak reading ammeters. You cannot get an accurate reading just putting any old ammeter into the circuit. Since a momentary drop in bus voltage of only a microsecond or so duration can reboot many of the 2.4GHz systems, this fast response is mandatory if you want usable information. Very often, just the impedance of the switch wiring and contacts can cause this momentary drop in the receiver bus voltage and you will never see it with a common VOM meter. For ultimate reliability, you want the receiver bus powered by a different bus and supply than what powers the servo so that no servo load will pull down the receiver bus.
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Old 04-30-2011, 10:42 PM   #24
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Originally Posted by Rodneh View Post
Note that it takes some pretty good instrumentation to accurately measure the dynamic currents drawn during servo operation. You need a fast response like an oscilloscope will give or some very high priced peak reading ammeters. You cannot get an accurate reading just putting any old ammeter into the circuit. Since a momentary drop in bus voltage of only a microsecond or so duration can reboot many of the 2.4GHz systems, this fast response is mandatory if you want usable information. Very often, just the impedance of the switch wiring and contacts can cause this momentary drop in the receiver bus voltage and you will never see it with a common VOM meter. For ultimate reliability, you want the receiver bus powered by a different bus and supply than what powers the servo so that no servo load will pull down the receiver bus.
Agreed:

I've got two Fluke 87V meters, worth about $350 each. This is what it takes to measure this stuff. Also have a Tektronix 2236 oscilloscope to backup what the Flukes were reading.

A project I had over the winter is a microcontroller operated voltage monitor for the receiver batteries, or CC 10 Amp BEC, (Or both if dual supplies)

This little microcontroller is measuring the receiver voltage 4000 times per second, and if it ever drops below the programmed 6.0 Volts DC, it flashes the actual voltage through a very bright LED, placed in the side of the fuse. (The brown and yellow wires connect to that LED, poked through the fuselage side) If all is well, the LED stays on. If the voltage drops to say 5.7 VDC, the device flashes that LED first five times, pauses, then seven times, pauses, pauses, and repeats endlessly until powered down.

It continuously monitors the voltage, showing the lowest reading ever reached. I sold 16 of them to club members, probably made about 50 cents per hour doing it.

So far, the CC 10 Amp BEC has never dropped below that 6.0 volts during 15 flights so far on the model. The BEC is programmed for 6.6 VDC.

This AR7000 Receiver has the CC 10 Amp BEC connected to the standard battery input, and the two cell A123 backup battery system plugged into the receiver gear connections. (The A123 cells have a pair of series diodes in the red wire to prevent interactions between the A123 batteries and the CC ESC.)


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Old 05-01-2011, 06:04 PM   #25
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I was wondering if I could get some guidance on how to choose the best Rx pack for some of my planes.
I have some basic electronics knowledge but not yet clear on what the best procedure would be to choose a Rx battery.

For example, I'd like to intall a Rx bat for a 6lb e-Flite P-51B nearing completion. Current servos include six (6) control surface HS-81 servos and a set of eFlite EFLG310 e-tracts.

I don't see any amp draw for the HS-81's but voltage will either be 4.8 or 6v]

EFLG310 e-tract specs:
Idle - 5mA
Operating - 900mA (max)
Volt Range -4.8-7.4V

I have some other larger warbirds awaiting maiden as well pending choice of the receiver battery but I've procrastinated picking the Rx bat.

I know if I use a Lipo I'll need a UBEC to reduce voltage but won't with Nicad or NmH or A123....so what's the best choice and how do you determine the size required...?

Thanks very much....

Dick

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