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Old 11-17-2012, 07:55 PM   #1
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Default Servo question

Was just looking at picking up a half dozen servo's and realized they have a power rating as to what they can be fed. The plane I am building is going to have a 14.4 volt battery, this is much greater than the 4-6 volts the servo says it takes. Is this all managed by the ESC??? Do you power your servo's off a separate battery? I thought the ESC with BEC was the way to go. Thanks. Scott
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Old 11-17-2012, 09:27 PM   #2
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Your good to go the power is supplied by the SBEC, or UBEC in the ESC so no worries.
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Old 11-17-2012, 10:09 PM   #3
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Originally Posted by Yakfishingfool View Post
Was just looking at picking up a half dozen servo's and realized they have a power rating as to what they can be fed. The plane I am building is going to have a 14.4 volt battery, this is much greater than the 4-6 volts the servo says it takes. Is this all managed by the ESC??? Do you power your servo's off a separate battery? I thought the ESC with BEC was the way to go. Thanks. Scott
It very much depends on the ESC and the type of BEC it has. But yes the BEC is responsible for dropping the voltage to ~5v for the radio system.

Of note many BEC's max at 3s voltage so watch that. You want to see switch mode BEC for more than three cells.

Above 5s I always use a separate LiFe battery. On 4s and above I generally use a separate battery.

Mike
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Old 11-17-2012, 10:56 PM   #4
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hello scott,you should also note the esc's bec capabilty to power more than 3 or 4 micro servos[not sure what plane your getting].i'v heard hxt900's draw a fair amount of juice and can push the bec on the cheaper escs to much while also powering the rest of the system[rx,motor]causing them to over heat.

on my hog,and extra300s using 4 standard hitec servos ,i use a 6volt auxillary rx battery. on a fun jet using 4cell with 2 micro mg servos i use a 100amp cc ice with the bec since castle builds a great esc and the esc is way over sized as an 80amp would work fine.

but i have to wonder on the stinger edf i just bought using 5 mg micro servos ,factory 30 or 40 amp esc using 3cell 2200mah zippy and flying wot a lot would be pushing it to hard.

what plane are you buying and what is the power train your setting up,maybe you can get help choosing what she needs plus i'd just be curious. buy the way,if i haven't said so already welcome to wattflyer!

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Old 11-18-2012, 12:56 AM   #5
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Thanks guys.

Stuart, I am building the great planes perfect trainer 40. I am going with a larger wheel set to try and get a 12x8 or a 13x8 but that is changeable for a prop. I have gone with a Tacon bigfoot 32: 32/35 770kv motor to a turnigy trust 70 amp SBEC. Batteries are 3000mAh 4S 30C battery and a servo's will be two standard Hi TEc 311's and a pair of micro HS-81's for ailerons. Hopefully that is a fully compatible set up. Still learning all the ins and outs. Thanks for the welcome!!!
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Old 11-18-2012, 02:33 AM   #6
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Scott,i just looked the GP perfect trainer size up and at 60 inch wing span i wouldn't think twice about using a rx auxiliary battery. this allow all your 4cell 4000mah to power only the motor and you'll not worry about the rx and servos getting power. it's a good size plane and you may end up pushing all components up front anyway to gain cg,the location of the rx battery is the perfect weight to move around to get cg without adding dead weight.

this is the size plane the a rx switch gets used to turn on the rx and get the one that doubles with the battery charging port. if you do go this route,all you need to do to the esc is disconnect the [red]center wire that goes to the rx by pulling the pin out of the plug and tape it out of the way. this way you can repair the connection if needed.

now don't quote me as the source,but i also read that the 6v auxiliary rx battery is better to use with 2.4 tx/rx systems...something about brownouts occurring with the smaller 4.8v rx battery that ran 3 or more servos. i guess i'm the kind of builder that thinks better safe than sorry.

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Old 11-18-2012, 02:49 AM   #7
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Great info, thanks. Lipo 6v or nimh? Life???
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Old 11-19-2012, 05:54 AM   #8
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you can run an external battery pack for your receiver, or you could just use an external bec (like the castle creations 10 amp bec). i personally would use an external bec as it would simplify installation and keep you from having to watch another battery in the plane. the external bec's are easy to install, and with the castle link you can program the output voltage to maximize your servos.
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Old 11-19-2012, 06:58 AM   #9
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Originally Posted by hoghead5150 View Post
you can run an external battery pack for your receiver, or you could just use an external bec (like the castle creations 10 amp bec). i personally would use an external bec as it would simplify installation and keep you from having to watch another battery in the plane. the external bec's are easy to install, and with the castle link you can program the output voltage to maximize your servos.
Yeah, agree on the Castle Creations 10 Amp uBEC. I've been using them in my kilowatt and larger models for several years. Even have them in a smaller 350 watt model. They work, and work very well.

They do pull a little bit of power away from the electric motor and its propeller, but percentage wise, its insignificant.

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Old 11-19-2012, 01:40 PM   #10
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Originally Posted by Yakfishingfool View Post
Great info, thanks. Lipo 6v or nimh? Life???
IMHO LiFe are the way to go. No expense and potential issues (albeit small) with a regulator/BEC and voltage is just fine.

I use them with great results on my bigger planes. Make sure your servos are rated for 5 cell NiMh/NiCad use and you are good to go.

Just don't forget to charge that battery too!

Mike
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Old 11-19-2012, 06:17 PM   #11
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Originally Posted by rcers View Post
IMHO LiFe are the way to go. No expense and potential issues (albeit small) with a regulator/BEC and voltage is just fine.

I use them with great results on my bigger planes. Make sure your servos are rated for 5 cell NiMh/NiCad use and you are good to go.

Just don't forget to charge that battery too!

Mike
Agreed:
Many if not most of the guys in my club that fly models from 60 sized glow engines to twin cylinder gassers have gone to those LiFe batteries. The giant twin cylinder models have primary and backup LiFe battery packs.

One member that flys wet turbine models has gone to those A123 batteries. Everyone of them is quite satisfied with these batteries. In fact, one club member had a structure failure on his model and it went straight in at full power. Bent the LiFe battery at 30 degrees. No fire, no nothing, and that battery still worked!!!

As for me with my giant scale models, I've gone to the CC 10 Amp uBEC with a two cell A123 battery as a backup. This has worked out very well for 200+ flights. The A123 battery only needs to be topped of for a few dozen milliampere hours every dozen flights or so.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=63794

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Old 11-19-2012, 09:08 PM   #12
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Hijack question: What is the difference between a BEC (Battery Eliminator Circuit - I know that much), a UBEC and an SBEC?

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Old 11-20-2012, 12:16 AM   #13
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Originally Posted by FlyWheel View Post
Hijack question: What is the difference between a BEC (Battery Eliminator Circuit - I know that much), a UBEC and an SBEC?

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The sBEC is typically a switching power supply type of a BEC circuit, usually able to handle far more current on a continuous rate than a linear type BEC.

So, if your model has a pile of servos, the peak currents that can be pulled by those servos can get pretty high. I've got two models with seven Hitec 645MG servos in each of them. The peak current pulled by those 645MG servos has been measured with my Fluke 87V digital multimeter on its one millisecond peak recording feature. EACH servo can pull two amperes!. I've measured a peak current of 14 Amps on all 7 servos just moving the transmitter sticks round and round.

As for those linear voltage regulators in your ESC's BEC, IMHO, I'd never use one of them on any model with more than two Series LiPo cells in the battery pack. It's just to much of a risk.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=63779

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Old 11-20-2012, 12:25 AM   #14
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UBEC is a brand name BEC, if I recall correctly.
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Old 11-20-2012, 12:33 AM   #15
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Originally Posted by rcers View Post
UBEC is a brand name BEC, if I recall correctly.
That's interesting. I googled UBEC and found Universal Battery Elimination Circuit. Several different Mfgs showed up. Also found some were switching type BEC's, and some were apparently linear type BEC's.
http://www.trendtimes.com/integy-c23...FYVFMgodYyAAmg#

So, just how do you know if it's switching or linear?? Danged if I know, but if the advertisement states "Switching BEC", that ID's it pretty well. The Trendtimes uBEC is only rated for 6 to 9 Volts DC input. Methinks that makes it a linear type BEC. That 3 Amp rating would then be very intermittent duty with a linear type regulator.

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Old 11-20-2012, 01:38 AM   #16
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I believe the term UBEC started with the Ultimate BEC made by Kool Flight. See link.

http://www.aeromicro.com/Catalog/koo...5v_3982367.htm

The term UBEC has since ben hijacked by others and I don't think it has any reliable significance. SBEC generally stands for switching or switch mode BEC but the truth is in the specs. If they don't specifically say switching or switch mode look elsewhere.
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Old 12-11-2012, 06:28 PM   #17
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Go to Dimension Engineering's website and read the FAQ's about when you need to use "switch-mode" BEC's either built into the speed control or add-on units such as the Park and Sport BEC's sold by DM and others. You need to read the specifications of speed controls to verify whether it has a linear-type or switch-mode BEC and how many and of what type servos that the BEC can power when using 2,3 or more cell lipos. Example: I have an E-Flite 30-amp rated speed control that has only a 700ma (0.7 amp)switch mode BEC. It is fine when used with a 3S lipo and four mini-servos. I crashed due to receiver brown-out after adding a fifth servo for flaps.

Many add-on BEC's switch mode BEC's are limited to 3S lipos and won't work with 4S. "High-voltage" switch mode BEC's can work with higher cell-count Lipos with a specified number of certain sized servos.
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Old 12-12-2012, 05:19 AM   #18
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Originally Posted by E-Challenged View Post
Go to Dimension Engineering's website and read the FAQ's about when you need to use "switch-mode" BEC's either built into the speed control or add-on units such as the Park and Sport BEC's sold by DM and others. You need to read the specifications of speed controls to verify whether it has a linear-type or switch-mode BEC and how many and of what type servos that the BEC can power when using 2,3 or more cell lipos. Example: I have an E-Flite 30-amp rated speed control that has only a 700ma (0.7 amp)switch mode BEC. It is fine when used with a 3S lipo and four mini-servos. I crashed due to receiver brown-out after adding a fifth servo for flaps.

Many add-on BEC's switch mode BEC's are limited to 3S lipos and won't work with 4S. "High-voltage" switch mode BEC's can work with higher cell-count Lipos with a specified number of certain sized servos.

For the larger models, I've been using the Castle Creations 10 Amp uBEC sucessfully in a half dozen models. They range from about 400 watts to 3000.

FYI, I've measured the maximum current pulled by ONE Hitec 645MG servo at two amperes, that with a $$$$ Fluke 87v digital multimeter, and its 1 millisecond response time peak reading feature.

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