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Jun 20, 2003, 12:49 PM
Registered User

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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Jun 20, 2003, 03:06 PM
Registered User
Jurgen Heilig's Avatar
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
Jun 20, 2003, 03:34 PM
Registered User
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
Jun 20, 2003, 04:06 PM
Senior Member
...which will vary with flight loads
Jun 21, 2003, 04:40 AM
Registered User
lymon, thanks for replying, but my question is will it be more then the 170mA 'max no load current' ?

Avi
Jun 21, 2003, 11:03 AM
Registered User
Jurgen Heilig's Avatar
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
Jun 21, 2003, 02:10 PM
Registered User
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 !
Jun 21, 2003, 05:25 PM
Registered User
Jurgen Heilig's Avatar
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
Jun 22, 2003, 10:25 AM
Registered User
Jurgen Heilig's Avatar
Same symptoms even with buffer battery. I'll replace the fancy SCAN 7 with a "conventional" Schulze alpha 835 and see what happens. Jürgen
Jun 22, 2003, 01:06 PM
high-speed freak
opualuan's Avatar
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?
Jun 22, 2003, 03:32 PM
Registered User
Jurgen Heilig's Avatar
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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