EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Mr.B on June 16, 2024, 01:55:48 am
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Hi all,
I am looking for some hints on how to determine the pole current for a couple of servo motors scrapped out of a Logitech Rally Camera.
They are both two pole servo motors (4 wire).
The pan motor is about 3 times the physical size of the tilt motor.
The pan motor is 39.2mm X 39.2mm X 24.8mm (1.54in X 1.54in X 0.98in) - Slightly smaller than NEMA 17.
The camera was:
Logitech Rally Camera
USB 3.0 powered.
One pan servo.
One tilt servo.
Multiple miniature 'servo like' motors in the zoom and focus mechanism.
The optional plug pack is rated 5V, 15w. Theoretically the device draws less than this. (i.e. < 3Amps )
Google has not been able to reveal any information based on the servo markings:
Larger one:
STEPPING MOTOR
39H023HM-0404-01
S/N: 200812090564
Smaller one:
STEPPING MOTOR
36H012HM-0504A-006
S/N: 200610030251
(I am a little surprised that such seemingly insignificant parts have individual serial numbers.)
Coil resistance of the larger servo is 27.28 ohms.
Coil resistance of the smaller servo is 16.8 ohms.
If the nominal supply voltage is assumed to be 5V...
This implies that the larger servo is ~183mA per pole and the smaller one is ~297mA per pole.
I must be making an incorrect assumption here, as I would have thought the larger servo would have a higher current requirement, or that this is not the correct method of calculation.
They will be driven by a cheap little A4988 driver in my project.
I have a little project that I can hopefully use these in.
Otherwise I will just buy a couple of NEMA 17 servos and get on with the job.
Any assistance on working this out is much appreciated.
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No gems of advice from the community?
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Larger motors typically handle higher currents, but if the tilt motor has a lower resistance, it can indeed draw more current for the same voltage. Using an A4988 driver will help you manage this by controlling the current directly.
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The real issue here is determining what current I should set on the A4988 driver.
Too little and I will not achieve much torque.
Too much and I will damage the servo motor.
Goldilocks needs the porridge to be just right... 8)