Caution: LONG post, but will hopefully help save your P2V+.
I have the new style P2V+. Never crashed nor a hard landing, but have lost two ESCs: once from a simple tip-over when powering down motors, and I think when I clipped a small stand of desert grass. The ESC actually failed on my next flight trying to take off. Puff of white smoke.
I repaired one ESC by reverse engineering it for the schematic and replacing the MOSFETs. Then with oscilloscopes connected to pertinent motor drive signals, characterized ESC performance under various conditions, including a 20-minute full power tethered flight to having some interuption to the props or sudden change in load - just to see what it takes to blow the MOSFETs on an ESC. Turns out ... quite easy! I repaired and intentionally blew up the ESC three times to verify the cause.
ANY INTERUPTION TO THE MOTOR ROTATION, SUCH AS A TIP-OVER OR GRAZING A LITTLE TREE BRANCH *WILL IMMEDIATELY BLOW THE ESC.*
Recommendations below ... but here is what seems to be the failure mode.
The ESC delivers the 3-phase drive pulses to the motor windings. Two windings are energized, one is OFF at any given time. The winding that is OFF is momentarily used as a generator, producing the back EMF (BEMF) voltage pulses that tells the MPU where the stator is compared to the windings to make motor speed adjustments and proper commutation sequencing. All three BEMF windings are summed together to form the "common node" voltage. This is the reference voltage for the MPU internal zero-crossing detector for determining rotor position. If you have a tip-over or otherwise interupt the rotation of the motor, there is a sudden loss of BEMF pulses and the summed common node voltage goes to zero, and thus no zero-crossing rotor position. The MPU suddenly doesn't know where the rotor is compared to the energized windings. It doesn't know which windings to energize next to sequence the motor. As a result, the energized winding, instead of being energized for only a few milliseconds, remains energized for a second or two (waiting for the next BEMF pulse). The motor windings are a near short circuit, the reason they are "pulsed." Now you have the MOSFETs trying to drive a near dead short, which would be nearly the full capacity (+11v 5A) of the P2V+ battery. During this momentary short, the MOSFETs get very hot until they fail. MOSFETs generally fail by the substrate melting, shorting the MOSFET (drain to source). This extreme heat destroys the MOSFETs, as many of us have visibly seen. The short circuit also causes the P2V+ battery to turn off to protect itself.
I do not know what can be improved on the ESC board to prevent this. Once the battery detects a short and shuts down, it's pretty much over.
Thus, on a tip-over, as soon as the prop strikes even some soft sand and interrupts the motor rotation for a blink of an eye, the ESC will fail, a couple of MOSFETs go up in smoke, and you may find the battery has also suddenly turned itself off. Now, imagine if that happens while in the air - skimming some leaves in a tree or something. The blown ESC and battery shutdown will make your P2V+ fall from the sky like a rock that we have all read about way too many times.
During my full power tethered flights, the wiring temperature was monitored. It never exceeded 40C, below the melting point of wire insulation, though the insulation (actually, shrink tubing) was "mushy." The MOSFETs were very hot by the end of the flight; the motors just kind of warm. MOSFETs switching high current *do* get hot under normal conditions. Still, I didn't see any compelling signs of wire melting or any design flaws with the DJI ESCs. Basically, they're quite clever and well designed. I no longer believe the motor wires are too small and causing problems. And, inspite of intentionally blowing up some ESCs for these tests, it never damaged a motor.
RECOMMENDATIONS
(The ones I will follow myself from here on out)
1. Don't EVER, EVER, EVER let your spinning props strike anything. EVER. It will blow the ESC.
Trees, shrubs, grass ... anything that will come in contact with your spinning props.
2. From here on out, I will hand catch my P2V+ for landings. (I practiced today. After 2-3 times, it becomes duck soup).
3. I do not intend on getting prop guards (yet), but it does certainly add to the importance of having them.
Especially if you don't do number 2.
4. To avoid any possible rotation interruption while in flight, I will no longer conduct abrupt course or altitude changes (even though
I love watching my Phantom bank on a direction reversal!). There's the possibility that an abrupt change in direction, for
which the four motor speeds are suddenly changed and redistributed, combined with prop wash, *may* cause a temporary
stall in rotation triggering an ESC failure. We all know what happens then. I don't know that for sure, but I plan on being more
conservative and "smooth" in making direction, yaw and altitude changes. Remember, the new 2312 motors have 25% more
power and 25% more torque to make impressive direction changes.
5. This certainly implies to never fly your bird out of line of sight. There might be a tree out there to snag your prop.
6. I also recommend to separate the 3 motor wires going to the ESC board so they do not touch each other, AND ensure they
are above and away from direct contact with the six MOSFET chips. On my P2V+, the motor wiring was slightly twisted in
contact with each other and resting on top of a couple of MOSFET chips, causing excessive heating of the wires. Some
simple separation and avoid the heat from the MOSFETs will go a long ways keeping the wiring in good shape.
And lastly, I don't think I'll ever fly over water. Not an ESC issue, but it sure seems it raises the unlucky factor by a ton. :-(
Finally, the signs of blown MOSFETs on your ESC is when your props try to move in one direction, then the other, seemingly hunting back and forth, seldom or never making a complete revolution. If it does that, bad ESC, and likely not the motor.
I do not know how this issue might apply to all P2Vs falling out of the sky, but I am convinced it addresses the scores of reports of ESC failures following a simple little tip-over, including my own, or other inadvertent contact of something with a spinning prop.
I'd be interested in anybody who has also torn into the ESCs to figure them out, or your flight experience when you blew an ESC and if consistent with the above. Hopefully being a little more cautious about tip-overs and a little conservative on ambitious flight control maneuvers will keep your P2V+ and many others in the sky for many enjoyable flights to come.
Paul
In the New Mexico desert
PS - I will prepare a document with the reverse engineered schematic diagram and the oscilloscope waveforms for troubleshooting failed ESCs, and will post shortly for those wishing to repair your ESC at the component level.
