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Old Jun 27, 2010, 11:28 AM
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Question
use of a ubec

How many standard servos would an ESC (Plush 80 amp) support, before I would have to use a separate UBEC (hextronic ubec)?
I am changing a scratch built "Seadancer" floatplane from a 91 4 stroke to electric.
It will have only 3 standard servos. (I removed the throttle servo). I already have 4 or 5 ESC's that handle many small HS-55 style servos but this plane has all standard servos.
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Old Jun 27, 2010, 11:33 AM
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I wouldn't trust it with powering a micro servo. Use a UBEC.
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Old Jun 27, 2010, 12:59 PM
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Tucson
Joined Nov 2009
912 Posts
Snow Bird Flier,
I have tried to find the threshold of danger (where I should start to use a
separate UBEC), and have lost a few planes. I fly in a very hot place, which
does not like electronics. And I have come to the conclusion that any plane
size 40 and bigger, that uses strong servo action, should have a separate
UBEC.
It’s not just the servos that cause problems. Using a motor that puts out
high wattage can overheat the motor, and the SC will shut down the motor.
The SC can overheat, and completely shut itself down. The servos can
draw enough current to brown out the receiver, causing it to reboot. The best
scenario here is that you lose electric motor power, and have to glide home.
The other options may involve watching your plane plant itself.

I know some seasoned fliers who really like the Turniy 80A with BEC, but
these only have a 3A safety net. I believe that 4 regular servos can easily
overdraw 3A.

I have tried to add an external UBEC with these plush 80A Turnigys (with
internal BEC), but I can’t get them to work with the + wire to the receiver
disabled (to avoid shorting out the system when a separate UBEC power
line is added).

Try buying a SC that is listed with the “OPTO” option – that is, no internal
BEC. And try plugging in a separate Turnigy UBEC (5-7A version). This should
not require disabling any + wire to the receiver. Stress test the system on your
plane.
The other question is how big a battery you should connect to the UBEC. You
may need 1800-2200 mAh size. See how long the battery will run your servos,
and choose a big enough UBEC battery.

Stephen from Tucson
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Old Jun 27, 2010, 10:19 PM
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If you use a 3S (3-cell) lipo and 4 or more standard servos, you should use an add-on switching type BEC. If you use a Dimension Engineering brand BEC, you don't normally need to disconnect the red wire from ESC to receiver. You can get good info from the DE website
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Old Jun 28, 2010, 09:01 AM
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But having said all that, the Plush 80A is listed as having a 3A UBEC, which ought in normal circumstances to be adequate.
I would suggest that, given that equipment, I would only go for an add-on uBEC if I was planning to use it with more that a 3s battery pack. This because of the heat caused in dropping to 5V from the supply voltage (greatly reduced in a switching uBEC
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Old Jun 28, 2010, 09:57 AM
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I received a call from a RC friend of mine who happens to be an electrical engineer. He said that if I am using 3 standard servos, and all three were stalled, it would not use up 3 amps!
He did however say to check the specs of the servos, hook it all up, and use my watt meter to check amp peaks of the whole system.
Since the brushless motor I am using for the float plane is designed for a 3 cell pack, and I live in the great white north (LOL), heat should not be a factor.
When I finish this electric float plane conversion, I hope to post results and pictures.
Many thanks to all of you for your most helpful and excellent imput.
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Old Jun 28, 2010, 01:09 PM
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Not advocating anyone else try it, but I regularly fly my Pulse XT40 with a Plush 60A with its 3A switching BEC with 4 Hitec HS 25HB standard size servos on 5S.

Using a separate Rx pack through my EagleTree logger the highest Amp draw I could see was spike of 2.2A during a violent flick roll the rest of the time was a fairly constant 1.7A.

The motor pulls up to 50A so I am working everthing pretty hard but neither side of the ESC, FETs or BEC come down more than barely warm.

Again just my 0.02c, don't try this at home folks.
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Old Jun 28, 2010, 04:06 PM
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I just realized that I have jinxed myself and I cannot fly the Pulse again until I have fitted a UBEC!

Come to think of it, if they are no better than linear, why waste money on a Plush with a switching BEC, why not buy a cheap no-name ESC at twice the rated power and add a UBEC?
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Old Jun 28, 2010, 06:02 PM
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I'm sorry for assuming that the poster's ESC had a linear BEC, not a switching type BEC. If the Plush's built-in switching type BEC is rated for four full size servos, you should not need an add-on switching type BEC device. BTW the acronym "UBEC" is not correct term for a generic switching type BEC device. UBEC originally meant "Ultimate BEC", a high capacity specific device sold by Kool Flight Systems. There are other add-on switching type BEC's sold by Dimension Engineering and others.

Just read that the Hobby King Plush 80-amp esc ad, there is no mention of number of standard or micro servos that the BEC circuit will safely support other than the mention of "3 amps" which should be ample for four servos under normal non-stalled operating conditions.
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Old Jun 29, 2010, 01:24 AM
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Quote:
Originally Posted by E-Challenged View Post
BTW the acronym "UBEC" is not correct term for a generic switching type BEC device. UBEC originally meant "Ultimate BEC", a high capacity specific device sold by Kool Flight Systems.
Maybe we should use EBEC for External BEC?
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Old Jun 29, 2010, 04:18 AM
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Oh dear.... Geek alert!...

Nice to see a bloke who knows his history though!
Never gave it that much thought. I first came across the U rendered as the greek 'mu' which, since it does not appear on my keyboard, I replace with a small 'u' as the nearest character. What it stands for I'm not greatly fussed over so long as we all understand that it refers to a stand alone BEC NOT included within an ESC. Except of course that the Plush ESC in question runs in the face of that by declaring itself to have a built in UBEC! Why it could not be called a 'SBEC' for Switching BEC I don't know.
I suppose we all have our 'little ways'. In ourselves these are seen as 'good sense' whilst in others they are 'stupidity' or even 'sheer bloody-mindedness'!

'EBEC' would work for me, but then we would have to differentiate between the 2 types - perhaps by adding an 'S' for the switching type only - making it 'SEBEC'... but do you think we are going to see the entire industry coming together in conformity?... NAH! Forget it!

I happen to be against the use of kV (whether rended by capitals or lower case) as being non-intuitive since in my education it always stood for multiples of 1,000V - which I do not intend to apply to my motors thank you! Why not 'rpv' 'r/v' or even just 'rv' ? But I'm not going to affect the 'sb-m' of the industry!
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Old Jun 29, 2010, 10:09 AM
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Tucson
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Snow Bird,

Thanks for this thread. This is a topic (UBECs) on which it is very hard to get
enough information to put all the terminology and problems in focus.

Just as I do not buy brushless motors without a watt and kv rating, I wish that
servo manufacturers would all provide power draw for their servo.

The other question that is pertinent to me is -- Does it do any harm to install a
speed controller that can handle many more amps than I ever plan to use? Is
there any harm in installing a 90A HobbyKing ($30.00) and a Turnigy UBEC (5-7A)
and a UBEC battery (2S 1800mAh) for a motor that regularly pulls less than 40A
with a 3S or 6S motor pack, and maybe 4 regular servos? This would cover all
of the 40 to 60 size planes that I plan to fly.

If there's no harm in over-gearing, then I would rather do this and eliminate
the risk of planting a plane.

Stephen
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Old Jun 29, 2010, 02:33 PM
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Ware, herts. U.K.
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I'm using an 8A uBEC for 4 standard servos and a retract servo on my biggest plane (144" span). I doubt if I use half the capacity.
No problem so long as the uBEC is capable of equal to or more than your needs. Get it less than you need and you have a problem. Probably at a very embarrassing moment.
Same goes for ESCs. Bigger is good, less lets the smoke out.

The numbers of the setup you mention above sound well in the safe zone, just the name HobbyKing makes me a little nervous. (probably shouldn't say this too loud on this site!) It's a bit of a lottery - I've just slung a couple of their cheapest 50A jobs because they were playing up. Just refused to run properly despite all their programming items - not worth the risk in the air. Replaced them with ESCs that were twice the price and auto sensing everything but simply work.
Good luck!
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Old Jun 30, 2010, 03:26 AM
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USA, GA, Marietta
Joined Aug 2005
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Quote:
Originally Posted by wuest3141 View Post
Snow Bird,

Thanks for this thread. This is a topic (UBECs) on which it is very hard to get
enough information to put all the terminology and problems in focus.

Just as I do not buy brushless motors without a watt and kv rating, I wish that
servo manufacturers would all provide power draw for their servo.

The other question that is pertinent to me is -- Does it do any harm to install a
speed controller that can handle many more amps than I ever plan to use? Is
there any harm in installing a 90A HobbyKing ($30.00) and a Turnigy UBEC (5-7A)
and a UBEC battery (2S 1800mAh) for a motor that regularly pulls less than 40A
with a 3S or 6S motor pack, and maybe 4 regular servos? This would cover all
of the 40 to 60 size planes that I plan to fly.

If there's no harm in over-gearing, then I would rather do this and eliminate
the risk of planting a plane.

Stephen
The only disadvantage to installing an overrated (not over geared) ESC is weight and cost. If you can stand the extra cost and the plane can carry the extra weight then go with the bigger ESC. BTW the current rating of an ESC is just that. The maximum amount of current it can handle with out smoking. It has nothing to do with speed. If your system requires 40 amps and you put in an 80 amp ESC that just means that the ESC will only have to operate at half capacity and will probably run a bit cooler.

Glen
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Old Jun 30, 2010, 07:15 AM
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Joined Feb 2010
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I have 5 HK Plush ESC's, non of which have given me any trouble,( 30's, 40's, and an 80).
My philosophy has been to have a larger ESC than needed in each case. The planes I fly are from 3D woodies to twin EDF's.
The HK brushless motors, Turnigy batteries I use have never failed me yet.
The failures that I have read about on the forums are mostly due to going over suggested parameters (props,cells,too small an ESC etc).
HK is the reason I have got rid of all my fuelies, (mostly scratch built,1/5,1/4 scale).
It was now affordable to convert without breaking the bank.
PS......... I plan to wave at you Glen in GA as I pass on my way to PCB beach in December....LOL

Larry
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