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V3 MUST READ!!

Discussion in 'Phantom 2 Vision + Discussion' started by CapnBob, Jan 4, 2015.

  1. CapnBob

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    This was reported on another thread, but I think it deserves it's own.
    Very crucial info here.

    From na5n on the dji forum:

    http://forum.dji.com/forum.php?mod=view ... D1&lang=en

    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.
     
  2. Dirty Bird

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    Interesting. Curious what has changed in the new motor/ESC combo is causing this, as the original motor/ESC combo doesn't seem anywhere near as susceptible? More important, what is the solution? Some sort of current-limiting circuitry or beefier MOSFETs?
     
  3. Fplvert

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    :?
    Thankfully I'm not on this horse, but I am very concerned for those that are!
    Wouldn't it be prudent to go back to the old motors? From what I've gathered, some of the later V2s had the new ESCs installed with the old motors and this problem only manifested since they've "upgraded motors."
     
  4. MacCool

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    I'm guessing that the 2312 motors and their higher current draw exacerbate the circumstances where the MOSFET is trying drive what it perceives as a dead short, driving it with higher current, therefore more heat in the short and frying the MOSFET.

    Paul's theory above is very elegant and well-reasoned and I'm impressed that he blew and re-blew the MOSFETs 3 times. So, as I interpret it, the actual problem is frying the MOSFET, not shorting the wiring from failed insulation. It sounds like that happens after the MOSFET goes. I guess the question is whether or not bigger wiring would actually solve problem and protect the MOSFET. Doesn't sound like it.

    I wonder is different firmware on the ESC could ameliorate this problem. Unfortunately, I believe the ESC firmware can't be done by the end user if that's the case.
     
  5. MapMaker53

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    Just an FYI.. I've had a couple of non-modded P2V+v2 tip-overs (prior to hand catching) with props being forced to stop with motors still wanting to spin and haven't experienced the ESC burnout described.
     
  6. MacCool

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    Probably a matter of timing. The lower current draw of the previous-version motors likely gives a little more time leeway toward stopping the motors before the current get so high that it fries the MOSFET. I'll bet if you stalled even the previous version motors long enough, they'd do the same thing.
     
  7. MapMaker53

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    Yep. I agree. Seems like a total cluster F regarding the V3 motors by the DJI "engineers". Between this and the solid thinner wire in a vibrating environment... Jeeeez.
     
  8. MacCool

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    I agree that solid wire in a vibrating environment might not be a great engineering choice, but to be fair, that's a theoretical problem that isn't likely to prove or disprove itself for quite a while yet.

    Otherwise, I note Paul's observation that he couldn't see any way to improve the ESC to keep this from happening. IIRC, the ESC's I used to use in my R/C off-road race trucks had pretty massive heat sinks on them, for one thing. Or I wonder if some tweak to the firmware of the ESC might mitigate the situation.

    Supposedly, DJI will be addressing this issue "soon". It will be interesting to see their position, and whether or not they propose a fix.
     
  9. Prylar Bek

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    So what do you think? A 'company wide stand down''?
     
  10. MacCool

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    No clue, but I doubt that. I'd probably be better able to guess if it was an American company. A Chinese company....no way. They are under some pressure to provide a diligent public face, though, given upcoming CES and their struggles to launch the Inspire 1.

    What DJI knows better than us is the actual numbers. What percentage of sales of v2.0/v3.0 have actually had ESC failures, and is it a big enough problem to vigorously address with something as dramatic as "company-wide standown", or broad-based recall, or can they just simply issue some "common sense" flight restrictions (no tipovers, no "abrupt air manuevers"), or can they just ignore it?
     
  11. Prylar Bek

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    Actually I meant a 'stand down' for US!!! LOL Well,I'm going to fly today anyway. FYI. over on the Inspire forum some guy posted a video from Malaysia from his new Inspire...VERY weird shaking video from the buildings he shot. Odd. That Inspire camera has issues. go check it out
     
  12. MacCool

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    I think that the Inspire 1, once it's in a broad base of consumer hands, is going to have many issues as end-users uncover little (or big) problems with the unit that didn't show up in DJI's testing. All that isn't unpredictable, of course, given the complexity of the system, but those guys who are dropping $3500 on the Inspire are going to be pissed when their bird doesn't work perfectly. And it won't. You know it won't. Not at first.

    I agree with you, I'm going to fly anyway too. Not today (it's -13F here right now) but next week when it gets back to 20's and 30's. I bought the thing to fly, not to sit at home looking at it and wringing my hands over what might happen if I put it into the air.
     
  13. Prylar Bek

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    Totally my thoughts. As for the Inspire, I WANT to buy one, and even would forgive the initial bugs that will show up...BUT its really unforgivable the quality and issues with the video footage (if the clip on the site are an indication) If that is not fixable and then it doesn't matter how good the thing flies. DJI (if its true) has done a great disservice to itself by allowing it to ship knowing these issues with that 'swaying effect' exists
     
  14. Morgon

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    DJI claims that the firmware wasn't updated on the camera. The author of the video claimed that it was. Who knows.
    I was a little sad by the jello, too, but it was the only video I'd seen that exhibited it to that degree. There's just too small of a sample size right now.

    Speaking of sample size, I'd really like to see more yay/nay reports of issues with the ESC in the V2/3 motors. Whether it's just a bad batch or a systemic problem.
     
  15. Luap

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    I just bought a P2 V3 (I already have a P2V since a year and tipped it at least 7 times with no issue except for the props) and from all I read the bad and good:
    Bad:
    -The P3 upgrade was all about being able to lift higher payloads as well as have that extra power - now with the ESC issue you have to manage your throttle and hand catch. I suppose a heavier Phantom V3 with gimmicks such as the Flytrex etc which adds weight will be a big no no as this adds even more load to the ESC. Same with propellers - you'll be better off flying the old versions as more flexible in case of a tip over as well as less load on the ESC.
    Seems the above is the result of cost savings from DJIs part but making it appear as an upgrade.
    i.e. DJI uses higher KV motors but the ESC hardware is the same (the PCB board has V2 on all ESC produced) and firmware doesn't solve the problem (at least two new versions)
    DJI use the winding wires directly from the motor to the ESC and spare themselves cost of stranded wires as well as placement.

    -The new compass is now integrated into the landing skid so you can't just remove it and place it on longer-wider aftermarket landing skids as you could have with the old version.
    The anti-static comment is supposed to mean nothing from what I read in some posts.
    Again, appears to be a cost saving measure from DJI.
    The good - remote has a nice wheel for tilting the gimbal. But this is also available on the old version you just need to add a lever. The new remote has Lipo batteries.
    The WIFI doesn't interfere anymore with GPS causing satellite losses whilst recording - but the issue was addressed and solved by users in the old version by simply adding an aluminum shield.

    Really annoying - I wonder what issues the Inspire will have - I certainly do not want to be flying a 3kg quad if they are having such issues/cost saving measures for such a small update as the V3.
     
  16. flyNfrank

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    The 1st time out the gate with na5n guy they were trying to get me to believe what he was selling. I said I didn't agree with him and what I did believe the possible problem was is now what he is saying except my word were "the software that drives the ESC's".

    Ok....so now the most important part of everything with this is, na5n base on what I read has properly tested the parts with the right tools. A Oscilloscope. I totally believe you gotta give credit where credit is due. And for the guy to actually step back and do the testing the right way is someone I will applaud all day long. One thing though. I would like to know at what voltage he thinks the battery will shut down at? I do have some Voltage data from the flight that

    So as the eventual question with so many will be,....are these motors really worth the upgrade? Here is what I said in another thread a little over an hour ago....

    My opinion is, dji should return to the old motor combo, and let the aftermarket mess with aftermarket parts. DJ should simply turn the quad's performance back up some closer to what we use to have before the vPlus came along. They restricted almost every area. The straight on speed was quicker. the ascent was quicker, the descent was faster, the tilt angle was greater. Not sure if I forgot about anything? But that's all they need to do rather then this mess they have now.