[jopcloud]

Had a bad ESC on one of my 250s, so bought a new set. One of the new ones was bad, so I ended up with two old (2,3) and two new (1,4).

During vehicle wizard setup, I noticed the beeps are out of sync when I plug in flight battery. It seems like one is behind the other three. I've tried the output calibration method as well, but impossible to time that first beep as the first peep of one ESC is well after the first beep of the others.

The output minimum speeds after wizard are:
1073 esc 1
1031 esc 2
1045 esc 3
1073 esc 4

Not sure how to fix this. I've always had problems with these Emax Simonk 12 amp ESCs. 

[f5soh]

Try setting the outputs to PWM-490Hz

[jopcloud]

That's how they are already set.

[jopcloud]

Confirmed the two old ESCs on 2,3 are beeping behind the two new ones on 1,4. These ESCs were purchased about 3 years apart. Could the different firmware on the new ones be the issue?

[f5soh]

If two Esc are 3 years old you can expect some differences.

Should work, whatever the values found for neutral.

[jopcloud]

Put the two new ECSs on so now it has 4 new. Escs are beeping together now but 2 and 3 still have lower minimums. Seems to fly smooth but wonder of that's OK?

[ernstock]

Some of my earlier builds had similar 'feature'.
They also flew well so I never worried .

[TheOtherCliff]

Did you try recalibrating the ESCs?  The ESC calibration is stored inside the ESC, so this will often fix a "bad ESC".
https://librepilot.atlassian.net/wiki/display/LPDOC/ESC+Calibration

[crof2003]

My quad lost an ESC not long after building it. Even though I rebought the same ESC from the same seller, the replacement ESC beeps later than the originals and the neutral setting is notably higher than the others.

However, it's not affected the flight of the quad.  I'm assuming that's the whole reason to go through the setting of the natural - so all the motors start at the same time on take off. Once it's in flight the FC takes care of adjusting the motor speed to stay level anyways.

I've always let the Libra pilot wizard config the ESCs, so after looking at the other Cliff's link I may try to manually recalibrate the ESCs just to be sure!

[TheOtherCliff]

That can even happen in the same batch of ESCs.

The CPU chip has a cheap clock (next instruction counter) that can vary a lot.  Also they sometimes change the fuses to wait longer for smooth power before boot up.  Changing ESCs can even change which ESC is supplying most of the FC power which can change which one is warmer which can change the clock.

If it were me, I would recalibrate all ESCs, and if it flies OK, I would not worry about it.