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P2V found after a few months outdoors - need suggestions on repairs

Discussion in 'Phantom 2 Vision Help' started by Mo of Pocatello, Sep 28, 2015.

  1. Mo of Pocatello

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    Hi, there's good news (or at least better news than nothing)! Somebody just found my P2V in the sea of sagebrushes after it had been in the weather since July 4th weekend.

    I opened it up, cleaned it a little and put it back together (such as it is). I replaced all the rotors (one broke), the rotor guards (several broke) and epoxied the broken land gear back together well enough for a test flight (if it were to fly). The body was cracked, the camera tore off and wasn't found, and one landing gear was ripped up as well, and the compass cable (if I identified it right) was a little frayed. The P2V must have hit hard ground, because it wasn't flying fast at all.

    When I turned the P2V on, 3 out of 4 motors appeared to work great. However, the left front one moved jerkily and slowly. When I gave it some throttle, it of course tried to flip over. I pulled the throttle down quickly because it completely flipped over and broke even more!

    The question is: other than buying a new shell, landing gears and cable set, what else do I need? You think a new motor for the left front rotor would be enough to make it work again, or is some circuitry perhaps busted as well and need replacement? The P2V seemed to have spent its months outdoors upside down, because some screw heads were rusty. Three of the motors were probably protected because the quad was upside-down! There was some dirt inside before I cleaned it up, but not bad at all considering how long the quad was out there. The cables inside looked intact.

    I'll probably use it with a RunCam I already have, and forget feedback from the P2V to the transmitter, though I'd really miss the feedback! If I can find an inexpensive replacement camera, maybe from another P2V that's otherwise busted but still has a good camera, I'd buy it. But a new camera costs $300+, and since I already have a P3, I don't think I'd like to spend that kind of money on my P2V.

    Do you know of a good mount for a RunCam? Without a mount, it points horizontally forwards. I need it to point down. What about if I want to have any control over the RunCam, would that be hard to do? I don't think it has any WiFi. However, it has a cable with it.

    Thanks!!
     
  2. Ti22

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    I’m more of a P1 guy but I understand BLDC motors and controllers. One obvious check would be if the affected motor turns freely and feels like the others with no power to the bird?

    Further troubleshooting to determine if it’s, Motor, ESC (controller), signal wires and/or Naza - I’d start by swapping the motor over to a working ESC. Can you do solder rework?

    If the motor runs when connected to one of the known good ESC’s I’d next qualify signal wires and (Futaba) connector pugged into Naza by swapping around there to a known good motor/ESC.

    Basically, process of elimination coupled along with a little substitution to help narrow down suspect components.
     
  3. Mo of Pocatello

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    You are quite right about the procedure! I am an engineer, an academic one at least, and I should have known that. The only hitch is that I'm not sure my soldering technique is good enough for me to be soldering and desoldering repeatedly and to expect all the equipment to survive it! Maybe it's time to get better at it though! My solder joints won't look nearly as neat as the ones currently on those boards. But then again I'm not sure how automated their soldering was. Anyway, thanks a lot for your reply!
     
  4. Ti22

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    I was lucky to have a bench tech job outta school and mastered solder rework. Awesome skill to have. Practice makes perfect and there’s plenty of junk surplus gear out there for perfect practice.

    In your situation, whaddya got to lose? It doesn’t work now and if you somehow determine the components needed for repair, somebody’s gonna need to do solder rework anyway?

    Youtube is a wonderful resource of learning hands on techniques for rework, soldering, etc. Of course, ask around here for advice?

    Are you a local flight club member? Plenty of those members can easily perform this type work and could be affordable and convenient angle to hire repairs?

    Good luck!
     
  5. Mo of Pocatello

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    Hi,

    Well, yes, I could lose perfectly good parts due to lack of skill at this point. Earlier this evening I tried to remove the left front ESC from the NAZA and did not succeed. First I tried to remove the solder joints at the ESC and, who knows, I might have wrecked that capacitor next to the joints. Then, I tried to remove the joints at the NAZA itself, as shown in the photo. I messed that up too, and didn't remove the joints! Those wires must have been hooked up incredibly securely. Any suggestions would be appreciated! Thanks in advance.



    soldermess.jpg
     
  6. Ti22

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    Soldering can be a daunting task at first but at least you’re capable of knowing if/when something seems wrong.

    The main thing to understand about soldering is thermal conductivity.

    For a job like that you need about 25-40W soldering iron with a “clean” tip. Must be fully warmed up so that solder flows easily onto the tip to “tin” it.

    If the tip isn’t covered in shiny solder it won’t be able to “conduct” enough heat to the workpiece to melt and thus flow. If your tip looks like Charcoal you need another tip. Sometimes they can ground/scraped down and re-tinned but more often than not you should replace Charcoal tips.

    Another thing to remember about soldering is that sometimes it takes a little solder to better conduct heat into the workpiece.

    What I mean is to use a chunk of fresh solder in-between the tip and part. As you touch the part the fresh solder melts and better conducts heat into the part. Thus readily flowing the intended solder on the wires/PCB pad.

    You can only hurt something if you leave the iron on the workpiece too long. Generally speaking, anything more than 3-5s and soldering isn’t melting/flowing, something isn’t right. Pull back, let things cool on the workpiece and try again.

    I’d suggest practicing on scrap materials until you get a pretty good feel for the process. Then go to work on the intended target.

    And don’t forget Youtube for many great tutorial videos regarding soldering rework.

    Good luck!
     
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  7. Mo of Pocatello

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    This is so helpful of you! Thanks so much. I'll see what I can do.
     
  8. Mo of Pocatello

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    Here's an update: the soldering problem turned out to be just not having had a good enough soldering iron. I bought a 140/100W soldering gun for $35, and suddenly it was easy to desolder/solder. I should have known that to begin with! Anyway, thanks to you all for the suggestions.

    However, now there's another problem. The motor I bought had the wrong thread direction! It was so confusing what they mean by CW and CCW. Anyway, so I ended up replacing the ESC but of course not the motor. Even though the motor looks perfect, I still have the same problem as before. The left front motor is catatonic! Actually, it turned but in a jerky way and not like the others. I could just order another motor, this time with the right thread. However, maybe it makes more sense to test the existing motor and see if it is really broken or not. Could you please suggest how? I have an Arduino on hand, and I wonder if I should just try to drive it using that, with an appropriate high-current power supply. What are the 3 wires on the motor? I would assume the black one to be GND. I guess one of the others is the power supply (How many volts? Is it 11.1V like the battery?) Is the 3rd wire supposed to be driven using pulse-width modulation? Anywhere online I could look this up? Thanks!!

    (I could just attach the good motor from the right rear and see if the left front now works. But instead of extra soldering/desoldering I thought I might as well learn how to test a motor!)
     
  9. Mo of Pocatello

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    I just saw somebody's post on the diydrones Web site that these motors basically take pulses on the 3 wires, and the order of the wires pulsed determines the direction of spin. That's fascinating! Does anyone know the size and duration of these pulses? How could I generate these pulses with enough current with an Arduino?
     
  10. Ti22

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    These are 3 phase BLDC motors and require ESC (electronic speed controller) to power them. Frequency, voltages, waveshapes can vary greatly depending on many factors. It's a fascinating and rewarding topic to study and learn about BLDC motor technology.

    Other than using a functional ESC simple tests involve shorting any 2 pairs of three wires and spin the motor by hand noting the difference in force required to hand turn the motor comparing shorted pairs. No power, completely disconnected from ESC.

    That can sometimes tell you if some motor windings happen to be open or shorted.

    Of course, more elaborate methods of qualifying motor windings and insulation, etc., involve applying constant current and some theory to go along with devising a test setup.

    You can electrically reverse any motor by exchanging/swapping 2 phase wire connections.
     
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  11. Mo of Pocatello

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    Thanks! So here's what I did: I removed the rotors, opened the shell up again. I armed the motors and left them running at idle. Then for each of the 4 motors I probed one of the 3 wires with an oscilloscope. For the left front one, which doesn't spin right, I believe it was the red wire that I probed. However, it probably doesn't matter which at this point. Anyway, The results were as follows: The signals coming in to the other 3 motors were all the same: a fairly nice-looking periodic signal, though the oscilloscope sometimes had a hard time getting triggered right. The signal from the one that doesn't spin right, however, is different. Its period is about thrice the period of the other signals, and it is also dirtier.

    I could desolder the motor and see if I still see the same problem with the left front signal, but at this point I'm suspecting the main flight controller itself. What do you think?

    It's hard to get a probe on to a signal wire that connects the flight controller with an ESC.

    If I have to replace the flight controller, I'm thinking of going for an open-source one if it would be compatible with the ESCs and motors I already have. The reason is that I'm going to be teaching a microcontroller class next semester, and this would be a great way for me to learn how to use a microcontroller to control a quadcopter! Any suggestions?

    In general, how do you know which flight controllers are compatible with which ESC/motor? Are there any standards for the communications protocol?

    Thanks!!!
     
  12. Ti22

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    I think Phantom ESC's are pretty much like most RC speed controllers. Basically, should be looking for a throttle voltage signal reference to ground.

    I would definitely swap motor/ESC around in order to verify before assuming bad FC (flight controller).
     
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  13. Mo of Pocatello

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    All right! Thanks!