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Old Jun 20, 2003, 12:49 PM
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Tel-Aviv,Israel
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servos current drain

Hi!
I have a question which is quite relevant to my other current thread (esc's with 4 servos). the question is what is the max current no load published for servos (as shown in this page: http://www.servocity.com/ServoCity/P...sub-micro.html ).

is this the max current they can reach ? what about stalled servos ?

Thanks a lot,
Avi Ernst
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Old Jun 20, 2003, 03:06 PM
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53859 Niederkassel, Germany
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The figures given in ref. link are "no load" running currents. A blocked HS-55 will draw close to 500mA at 5V. Ok, these operating conditions should be avoided, but don't forget the current peaks when servos start moving.

Jürgen
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Old Jun 20, 2003, 03:34 PM
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Tel-Aviv,Israel
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Hi,Jurgen!
thanks for your answer. I take it I have to have 0.5 amp per servo. but one more thing, what is loaded current ? the servo doesn't usually stall during flight, but it is obviously under some strain, isn't it ?

thanks,
Avi
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Old Jun 20, 2003, 04:06 PM
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...which will vary with flight loads
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Old Jun 21, 2003, 04:40 AM
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lymon, thanks for replying, but my question is will it be more then the 170mA 'max no load current' ?

Avi
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Old Jun 21, 2003, 11:03 AM
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Just an example: The max no load curent for the HiTec HS-81 is 220mA at 4.8V. At 5V it is probably around 250mA. That is the current you get when you waggle the stick. If I attach the servo to the aileron of my miniExcel (2m glider) and waggle with the stick, I read up to 500mA (and there isn't much friction there, just some additional mass to be moved). With flight loads, this will be even more!

Jürgen
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Old Jun 21, 2003, 02:10 PM
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Tel-Aviv,Israel
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I was afraid that would be your answer...
so assuming 500mA for each servo, like most of the ESC manufacturers, is the way to. so a SUN 1000 it is !


Thanks a lot !
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Old Jun 21, 2003, 05:25 PM
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Looks like I have got BEC overload on my latest model too. MiniExcel, Magic Control brushless 35A controller, 8 cells, two HiTec HS-81 and two SES-190. "Normal" flying no problem, but aerobatics where all controls are moving, the rx throws in the occasional hold. A small buffer battery should fix this problem.
Jürgen
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Old Jun 22, 2003, 10:25 AM
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Same symptoms even with buffer battery. I'll replace the fancy SCAN 7 with a "conventional" Schulze alpha 835 and see what happens. Jürgen
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Old Jun 22, 2003, 01:06 PM
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wiring. check your servo wiring. too long, too thin, etc, and any buffer won't help as you'll be dropping too much voltage across the wiring. ask me how I know (built a full-house DAW 1-26, painful...)

also, get rid of any servo extensions and solder the wires directly.

I can promise you hs81's use lots more than 250ma for a brief period (couple ms maybe?) anyone have a scope they can check it with as an example? I bet the results would be scary...

jurgen, what's a scan 7 rx? what's so fancy about it?
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Old Jun 22, 2003, 03:32 PM
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Hi Omar,

Everything was the same as in the bigger Excel Competition 2, except the missing buffer battery and the SCAN 7 rx. The SCAN 7 is a synthesizer rx which doesn't need cristals and also checks max/min voltage, tx field strenght etc. All the data can be transferred during flight using a special data terminal (which I haven't got). I really thought the problem was peak currents causing the BEC voltage to drop below the critical limit, but as I still have problems with buffer and BEC, there must be a different reason.

Jürgen
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