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http://www.feetechrc.com/product/analog ... o-fs5113m/
this is the data sheet of my servo motor i want to calculate the current which the servo will draw

That will depend on supply voltage and load.

I'd measure it.

Also the peak current while moving will be higher than steady current while still and will depend on how fast you try to move the servo.
You will probably need an oscilloscope of some form to catch the transient current pulse as they will be too short (100s of mS maybe) to see on a meter.


PeterO

PeterO wrote: ↑

Mon Feb 19, 2018 8:34 am

Also the peak current while moving will be higher than steady current while still and will depend on how fast you try to move the servo.
You will probably need an oscilloscope of some form to catch the transient current pulse as they will be too short (100s of mS maybe) to see on a meter.


PeterO

Stall current is usually the max. At speed current reduces due to back emf (put another way, to get the stall current through the windings when the motor is spinning will take a much higher voltage than at stall.)

PiGraham wrote: ↑

Mon Feb 19, 2018 8:58 am

PeterO wrote: ↑

Mon Feb 19, 2018 8:34 am

Also the peak current while moving will be higher than steady current while still and will depend on how fast you try to move the servo.
You will probably need an oscilloscope of some form to catch the transient current pulse as they will be too short (100s of mS maybe) to see on a meter.


PeterO

Stall current is usually the max. At speed current reduces due to back emf (put another way, to get the stall current through the windings when the motor is spinning will take a much higher voltage than at stall.)

Yes, but that depends on the type of physical load you are moving. You assumed there is a static load to carry, I assumed there was not, so we're both right

Oh, hang on, You wrote "Stall current" and I though "Holding current". SO yes "stall current" is going to be the highest (i.e when the servo is trying to move but is physically prevented from doing so). Peak transients can approach stall current when trying to quickly move a load with lots of inertia.

My experience comes from model aircraft where servos moving control surfaces have odd dynamic load characteristics.

PeterO

Ah yes, you wrote "when still" which in the context of a servo will be a light load maintaining a position rather than accelerating a load.
So to measure a maximum current drive the servo against an end stop (or otherwise fix the shaft and try to move the position) and measure the current. That will be worst case.