MG996R Servo calibration notes

Some 4+ years ago when I decided to play with electronics DIY, I bought my first servo, for about hkd70.  I thought I would use it to build a robot.  But I did not how to test it.  So I went to a toy shop and asked the shopkeeper how to test it.  The shopkeeper was a bit puzzled, because very soon I realized that I did not own any remote controlled car or helicopter, and that I actually did not even played before.  He seemed to be annoyed and did not wanted to teach me, because I was ignorant, or looked stupid.  I told him I was a beginner and insisted to learn from the beginning. He reluctantly told me that perhaps I should buy a servo adjuster and showed me how to center the servo.  But I did not appreciate the need to center the servo, I only need something to turn the servo.

Anyway, I bought the adjuster home and googled a manual.  I eventually could turn the servo, but I did not go further.  Instead I bought a unipolar stepping motor and found it good for beginners to start learning something.

It was perhaps two years later that I realized that almost all guys going to a toy or remote controll car shop to get a servo is for RC hobbists, and very rarely to DIY a robot.  And for RC toys, keeping the servo to centre is very important, perhaps for steering the car or helicoper.

Later I played with stepping motor and DC motors controllers electronics and forgot servos.  It is only now that I think I could look into servo again.  One big reason is that at that time I did not have a oscilloscope to display the 1mS to 2mS signal.  But for stepping motors I could just use a multimeter to check if I applied power to a motor winding etc.

Now I have a scope, so I could check out what the servo center adjuster is doing.  I found that the adjuster can vary the output signal from 1mS to 2mS.   I don't know why the frequency is 45Hz only.  I thought it should be at least 50Hz or 20mS period as specified.  I guess perhaps the 20mS is only a spec, and the slower the steadier the servo perhaps.

Anyway, I used the servo adjuster to check that the servo swings from about 45 degrees from the vertical each side.

I remember that my Guzunty Pi signal could swing the same servo to about 90 degrees each side.  Perhaps I should check that out.

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