[TheOtherCliff]

Motor sputtering is usually caused by one of the three motor wires being burned inside the motor.  It can also be caused by one of the three motor wires being burned inside the ESC (electronic components).  Infrequently it is caused by incompatibility between ESC and motor brands/types.

Disconnect motor from ESC.  Test for continuity from one of 3 wires to another of the wires.  Test each pair of wires this way (A-B, A-C, B-C).  They should all act like a straight wire with such little resistance that you can't accurately measure it on a normal Ohm meter.  If using a normal Ohm meter it should show between 0 and 1 Ohm.

Further tests:
Take props off.
Plug in USB to computer and also plug in flight battery.
Go to Output page.
Enable "Test Motors"
Run motor outputs sliders up one at a time.

Do all motors sputter? ... That sounds like ESC/motor incompatibility.  Too much coincidence that all are burned?  If it is an incompatibility, and you are using stock ESC firmware, and the ESC has "timing" adjustment in the "beep menu", you might get it to run by adjusting that.

A note:  I had similar issues with cheap SimonK ESCs from eBay.  It turns out that they had really old firmware on them.  I flashed new firmware on the ESCs and they worked fine.

Another note:  The problem I had with the old SImonK firmware was really just a startup issue.  The motors that were lower when sitting on the ground were the ones that would sputter because when starting, those motors would be commanded to run faster to level the quad.  I found that tipping the quad to slightly raise motors that wouldn't start would allow them all to start when I held it very level when starting the motors.  There was no problem during flight.

[JohnC]

Hi Cliff

I think the motors are ok.  This is based on doing the calibration.  When I do 4 at once and slide the bar they all move and sound right.  As I write this I think I should try one at a time and see if there are any differences. 

[TheOtherCliff]

If motors start up with sliders but not in Attitude mode, then it sounds like you have a startup problem.  In Attitude mode you must manually level the quad, just to get the motors started, by slightly raising the motor(s) that don't start (tilt the quad to raise those motors).

Another way to simply test this is to try to start the motors in Rate mode.  In that case leveling is not an issue and they might start up more easily.

Make sure your ESC/motor "neutral" settings are very low ... just 5 or so from being "off".

Always try to start the motors slowly with minimal throttle stick that will start the motors.

[karla]

Disconnect motor from ESC.  Test for continuity from one of 3 wires to another of the wires.  Test each pair of wires this way (A-B, A-C, B-C).  They should all act like a straight wire with such little resistance that you can't accurately measure it on a normal Ohm meter.  If using a normal Ohm meter it should show between 0 and 1 Ohm.

Cliff, that was a neat test.
First time I heard it.
Can the motors be tested the same way?
Should also ask if you say a motor 'Sputter' and a motor 'Stutter' is basically the same symptom? I have often run in to stuttering motors.

[TheOtherCliff]

Sorry I wasn't clear...  You test motors that way; not ESCs.

In my experience, it is usually the motors that get burned, not the ESCs, but it would be easy to burn an ESC by touching the 3 motor wires together, especially intermittently while running.

[karla]

If you are testing motors this way, then why disconnect them from the ESC?

[TheOtherCliff]

In at least some cases, ESCs are not switched off when the power is removed.  For instance, some ESCs short the windings together (drag brake) for a long time after the battery is removed.  It takes a while for the charge on the capacitance on the FET inputs to bleed away.

You can feel that the prop still has a drag on it even after the battery is removed.  Disconnect the ESC and the drag goes away.