Servo Amp Draws?

[Seared Ice]

Does anyone have any info on the operating current draw of common servos such as GWS Pico/Naro and other brands' pico and naro servos? What about standard-sized ones?

I will be putting this info towards a BEC design.
~John

[Andy W]

Loads in flight will vary, but the smaller servos all seem to pull no more than 100mA or so when operating.. Hitec, GWS, Cirrus, FMA, every one I've tested was the same.
..a

[Seared Ice]

Would a 1A BEC be acceptable for pico/naro servo operation. Well, at least for 3 servos. What about 4? Would a 1.5A BEC be better? (more expensive parts...but not much lol...just a few cents)
~John

[Andy W]

BEC regulators are usually rated by the number of servos they can support at a particular voltage - i.e. how many watts they can dissipate.
1.5A @ 10V would be good..
..a

[Bruce Abbott]

For what it's worth, here's the results of some tests I did on unloaded servos, exercised with a GWS servo tester:-

GWS Pico (STD,F-BB) 200mA
Naro (STD,BB) 200mA
Naro HP BB 250mA
Naro Pro BB 150mA
Micro STD 120~150mA
Micro2BB-MG 150~300mA
Mini L BB 100~400mA (1.5A peak)

Hitec
HS-55 150mA
HS-81 250~350mA

Multiplex
Super FL Digi 100~300mA

Futaba
S3101 150~200mA (400mA stall)
FP-S143 100~200mA (1A peak)


Where a range of currents is given, this is because the servo drew noticeably more current when changing direction. A servo draws the highest current when it is forced to change direction continuously.

A 1A regulator should be able to handle 3 GWS pico/naro servos with ease, provided that it can handle the heat generated. I tested an SOT223 size regulator mounted on a PCB with 1" square copper area. With the power supply at 10V and delivering 500mA at 5V, it reached thermal shut-down after only 1 minute!

[Andy W]

That's much higher than I saw. I recorded pulsing that was higher than my stated currents, but the average was much lower. Interesting..
..a

[Seared Ice]

Thank you very much everyone!
Mr.Abbott, would a TO220 fare better? (I'm not much of a PCB guy...yet) I could then even mount a heat sink if needed.
~John

[Bruce Abbott]

The thermal resistance of a TO220 package in still air with no heatsink is about 50ºc/W, compared to over 70ºc/W for an SOT223 package on 1in² of copper track. A nice finned aluminum heatsink can greatly improve heat dissipation of a TO220 package without adding much weight.

[tomp]

Here's some detailed tests I did back in '98 comparing an FMA S90, Airtronics 94461, and an Airtronics 94141, kindly hosted on Chuck Gadd's website.
Servo Tests (http://www.csd.net/~cgadd/eflight/servo.htm)

It all started due to a (silly) email thread on Eflight, back when Eflight was only an email list! (My, how we've grown!).

The point I want to make here is that current draw is not simply DC, so be careful about how you measure it. Your measuring device may not respond to the AC aspect of the waveform.

Have fun!

tom

[Andy W]

I measured with a shunt, and a recording digital oscilloscope..
..a