# Building A Servo Tester To Measure Peak/Stalled Amp Draw

Since finding data on stalled and in use under load (not free) amp draw for servos seems impossible, I want to build/create my own servo tester.

All I really want to know is how much amps the servo is drawing at idle, at movement under load, and at stalled/full position. I think that should cover all the bases relative to amp usage on the servo but if not, please let me know what I am missing.

Here are my questions:

1. I am going to need a power supply for an exact 4.8V and 6.0V since that seems to be the standard measurement voltages.

2. I'll need some way to accurately measure the amp draw.

3. I'll need some way to control the servo movement.

Is that it? What am I missing and if anyone has any suggestions please let me know and thanks for the help. This seems to be uncharted waters for those in the RC hobby area but someone in the robotics field may have been down this path.

I just use a standard servo tester but put a multimeter in the loop on the +5v side by cutting the power line on a servo extension. Very simple but works fine. I suppose if you were after exact measures a precise voltage supply might matter.

• Welcome to R.SE... could you elaborate on your answer, to explain WHY you do what you do? Mar 16, 2014 at 8:23

I believe that is everything you need. As for the solutions:

1. http://www.ti.com/lit/ds/symlink/lm2576.pdf you can implement power supply both for 4.8V and for 6V with this circuit, there is application note in the datasheet which you can use to calculate the needed component values to get the desired output voltage.

2. https://www.digikey.com/product-highlights/us/en/allegro-acs710-current-sensor-ic/1030 ACS710 is a current sensing sensor, or you can just use a standard ampermeter.

3. You need a microcontroller to implement the control for the servo. Servos are usually controlled via pulse width modulation (PWM), where the signal period is 20ms, duration of logical "1" is 1ms (5% duty cycle) for the minimal angle position, 1.5ms (7.5% duty cycle) for the middle and 2ms (10% duty cycle) for the maximal angle position.

Regards