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First crash - lost an ESC mid flight

Discussion in 'Cinestar 8' started by Dan Coplan, Jan 23, 2014.

  1. Shaun Stanton

    Shaun Stanton Active Member

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    I always wonder how accurate their motor current readout really is. There is no feedback sensor sending data directly from the ESC to the system. My guess is that it is using a predictive model based on known parameters and that the system knows the pulse width and uses a model that formulates a readout of current and temp. Which I suppose could at least get you in the ballpark that something odd is happening. I suppose a stalled motor or a failing ESC will cause the system ramp up the PW and therefore give you comparative idea that one motor is being ramped higher than another.

    It would be cool if that info would be overlaid on the OSD itself for in flight monitoring at least get somewhat of an idea of what the copter is doing.
     
  2. Graydon Tranquilla

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    Correction to my previous post..... I don't believe the iOSD provides current historical trending.... just individual motor rpm....and overall battery voltage.... here is an excerpt from their website.... "FLIGHT LOG FUNCTION The DJI iOSD MARK II can record the flight log, which will help you to record the input and output information of every channel, GPS signal, power voltage, home distance and height, etc. (The current iOSD on the market will have flight log function after firmware upgrade.)"
     
  3. Dan Coplan

    Dan Coplan Member

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    Shaun - thanks much for that explanation. Given the circumstances of everything that led up to my crash landing, including previous flights, and the feedback from others on this thread, your comments seem to make the most sense. Moving forward I'll keep this in mind and operate less aggressively and see how things go from there.

    Along those lines, how best do you match up ESC's with motors? I'm using MT-3515's and DYS 40A ESC's which I believe are flashed with Simon K.

    Dan
     
  4. Graydon Tranquilla

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    Dan, Have you ever used eCalc for Multirotors? It will enable you to match motors, props sizes, escs with your battery capacity and AUW to give you all the info you need +- 10% before leaving the ground. Tiger makes several KV levels for their 3515?... so which or should we assume 400KV?..
     
  5. Shaun Stanton

    Shaun Stanton Active Member

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    I am not 100% sure if the simon-k can allow you to change the pulse timing. Oddly enough I used the simon-k turnigy ESC's on a smaller Supposedly if you have the most recent firmware on them they are supposed to sense the voltage better and be more synced. Having said that the creator of this firmware Simon had some issues early on when testing MT-3509's which would be similar to yours in stator/magnet ratios just a shorter bell. However the larger bell does change the inductance and impedance so it is hard to tell.

    It possible that the transient response may not be syncing correctly as if you read these issues here in open pilot forum they talk motor stalling.

    http://forums.openpilot.org/topic/25549-how-to-tell-a-motor-isnt-compatible-with-simonk-esc/

    It does not look like there is a way to change the timing or phase angle of these ESC's because they are supposed to do it for you.

    Doing a motor test with the props may show how much rapid throttle response can stall out the motors momentarily. Because you are using WKM, if you were in Atti or GPS atti, you would have had your altitude hold function on sense its permanent in these modes. As the copter changing flight deck angles their are two things happening. On is that you are getting rid of negative angle of attack on the entire rotor disc and are aerodynamically creating some Newtonian lift which the auto pilot would sense a climb and compensate for in addition you would be changing the thrust vector causing a reduction in required thrust to maintain the steady altitude. But then rapidly going back to the pitch angle in the opposite direction would have caused the system to require getting that thrust back. These changes are so abrupt that probably caused them to be lagged well behind the phase curve.

    So best thing to do is test the motors response. My guess is a little aggressive control will help prevent this.

    Shaun
     
  6. Graydon Tranquilla

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    HobbyKing sells a device that you can use with each motor and each ESC so that you can test the full speed/torque range of each individually without the radio and FC involved. I use mine for doing motor vibration and prop analysis and elimination. And ofcourse you can do so much more invasive diagnostics with an oscilloscope or an oscilloscope program for you PC.
     
  7. Dan Coplan

    Dan Coplan Member

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    Graydon - I have checked out eCalc but to be perfectly honest, I'm good with the techie stuff up to a point and then my brain starts to go numb which is why I take my more involved work to someone who understands all this stuff.

    That being said, what's the motor/ESC analysis device to which you're referring?

    For the time being I'll take Shaun's advice and tone down the aggressiveness of flight.

    Is there any chance that the other ESC's could have been compromised/weakened but not completely failed or is it safe to assume that if they didn't pop they're probably fine?
     
  8. Graydon Tranquilla

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    Look for the Turnigy CCPM Servo Consistency Master such as this one: http://www.hobbyking.com/hobbyking/store/__8296__Turnigy_Servo_Tester.html (costs about $7.00)
    If you ESC is properly configured and connected to a good motor, your motor speed will range from 0 to 100% with a simple twist of the potentiometer.

    Typically a simple device such as the following:http://www.hobbyking.com/hobbyking/store/__27135__Turnigy_Multistar_ESC_Programming_Card.html
    is all that is needed to configure your ESC correctly.... note the parameters that can be set as detailed in the literature by means of the simple jumper positions. The more precise method is via Simon K programming tools which I have not yet used.
     
  9. Shaun Stanton

    Shaun Stanton Active Member

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    They're probably fine. If you are concerned you could remove the shrink wrapping and examine the capacitors and re-shrink them. This may or may not show anything. Sometimes a capacitor that is going bad will start to look bloated like a coke can left in the freezer, but not always. I would think if there issues a motor test in manual mode may show if certain motors are not responding as well by the tones they make. Without props on you can be a little abrupt with the throttles since the motors wont be loaded. Last test would be to do a accelerated climb test and see if at max throttle if the copter starts doing weird things like starting to yaw or gyrate a little that may show that the ESC's are not producing the powered required power anymore.

    It is possible that the ESC in question was week by not being as robust as the others, as sometimes we have seen things blow without provocation like Steve's new BL 3.0 Set where one ESC' just blew for no real reason.

    Here is a little tidbit I learned about ten years ago not just you for anyone reading this posting.

    The way I look at flying is you can be aggressive without being abrupt. This is something I learned many years ago in Air Force flight school. Being aggressive is a mindset. It basically means you control where the aircraft goes and not the other way around. There may be times when an abrupt movement is necessary, such as you are b-lining towards an obstacle like a tree and you need to really make sure it moves out of that path. The ideal way to fly is to be on top of the aircraft and move it in planned and purposeful manner. Then react as necessary if things don't go as planned, but this is now being in survival mode.

    I think your system is probably fine but a good checkout will alleviate any doubts.

    Shaun
     
  10. Shaun Stanton

    Shaun Stanton Active Member

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    Those look like worth while investments. I have the white turnigy card with the push buttons for my 20A Turnigy Plush ESC's. The motor tester is good little tool I have been arduino boards that I controlled with a POT and this is a cheaper option :)
     
  11. Dan Coplan

    Dan Coplan Member

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    I seem to be on a real winning streak. Went out today for a music video. Nice gentle takeoff, eased it into position, hovering...and then whoops! There it went again. At least this time I was more familiar with what happened and how to get it back without crashing. This all happened in about a minute. Same prop. Haven't pulled it apart yet but assuming the ESC blew again. So this points fingers at what? Short circuit on the center board? When I aggressively put on the brakes the first time, which we're assuming is what caused the problem, could that have generated enough heat to compromise the leads on the board?

    Prior to going out today, I ran 3 sets of batteries through the copter hovering in place until they were drained. No problems whatsoever so I assumed all was fixed and well.

    Dan
     
  12. Shaun Stanton

    Shaun Stanton Active Member

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    That sucks, it does mean that something else is wrong. You are probably correct about something shorting out. The same side ESC blowing again does suggest the PDB. What are you using for power distribution? Its hard to say as a matter of fact if the hard controlling caused it. It is possible that if solder joints were weak and not where the ESC power terminal is may have just eroded through time. The hard controlling probably did not cause it but may have helped accelerate an already weak component.

    Shaun
     
  13. Chris Fox

    Chris Fox Active Member

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    G'Day Dan, did you carry out the throttle calibration on the new ESC that you installed?
     
  14. Dan Coplan

    Dan Coplan Member

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    I had a custom distro board implemented into the copter for me by someone who came highly recommended, and I have been happy with his knowledge and quality of work but sh*t happens, I guess? Just dropped it off with him and he isolated the motor and ESC and said they checked out fine so it's gotta be something on the board, right? Still waiting to hear back his report after going through it. As for doing the throttle calibration, I did that initially when I first got the copter several months ago and have had many successful flights until that fateful day a few weeks ago but no, I didn't think to do it or ask about it when I got the new ESC installed, though I did hover test it with 3 sets of batteries and took off no problem at this last job and was just easing into place when it went down again. Maybe that doesn't prove anything, however.

    Will report back when I hear back. Thanks everyone for the support. This is frustrating. But educational!

    Dan
     
  15. Dan Coplan

    Dan Coplan Member

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    Got the copter back and my guy said he couldn't find anything wrong - he checked solder joints under magnification and cleaned the leads from the ESC connector to the distro board. When I picked it up he held on to it while I did a number of full throttle tests and everything checked out ok. Will do some actual flight tests before I go back on a job. The thing that concerns me is not knowing what the actual problem was. It's one thing to find the problem and fix it, it's another to have everything check out ok and have no idea what the hell happened - that worries me.
     
  16. Chris Fox

    Chris Fox Active Member

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    G'Day Dan,
    It sounds like something may be over heating? Have you done a smell test on the motors?

    I have had a couple of motors go bad over time, where they stopped in flight, I have then packed up and gone home to trouble shoot, and found that when I run them up on the test bench everything works fine. However the problem has been the motor insulation has started to fail, and it only becomes evident when the motor starts to warm up under load.

    If this is the case you won't always see the issue, however if you put your nose up to the motor (when the copter is NOT powered up) you can smell when the insulation is damaged .... and it is a residual smell that is on the motor for quite a while (i.e. if you hang on to a dud motor for a couple of weeks, you can still smell the burnt insulation)

    It takes all of about 20 seconds to sniff all the motors, and if this is the case then you will know it if you have this problem.

    Cheers

    Chris
     

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