Out of whack motor currents

Discussion in 'Cinestar 8' started by Steve Maller, Sep 26, 2013.

  1. Steve Maller

    Steve Maller UAV Grief Counselor

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    I just replaced my power distro board with my backup because I lost one of my BL-CTRLs, and sent the board in for repairs. The copter's flying OK although it appears to be a little out of sorts. It seems to be a bit more wobbly in the wind than usual. But what's of great concern is the wide disparity in motor currents. My props are all in balance, and I replaced 2 noisy bearings. I think it have 2 more bearings that could do with replacing, and I'll do that tomorrow. Motors are all vertical, too.

    I know I answer a lot of these questions, but this one has me stumped. I'm hoping the bearing replacements (motors 6 and 7) will address this. But I'm wondering if I overlooked something. Any ideas? Thanks in advance!

    MK Version: FC HW:2.2 SW:2.0a + NC HW:2.0 SW:2.0a

    Flight date: 9/26/2013 2:56:56 PM
    Flight time: 2:56:56 PM - 3:03:54 PM (418 secs, 00:06:58)
    Batt. time : 417 secs, 00:06:57

    Elevation(GPS) : 0 10.17 30.988 m (min/avg/max)
    Altitude(Barom.): -1.25 10.96 32.3 m
    Vertical speed : -1.23 -0.04 1.51 m/s
    Max speed : 12.3 km/h
    Max target dist.: 10.5 m

    Sats : 10 9 11

    Voltage : min. 14.6, max. 16.2 V
    Current : 0.5 54 84.3 A
    Wattage : 8 852 1230.78 W
    Capacity: 6394 mAh

    Motor1: 0.0 3.1 6.6 A Temp: 35 52 69 °C
    Motor2: 0.2 6.7 12.8 A Temp: 31 51 69 °C
    Motor3: 0.2 6.6 16.0 A Temp: 30 53 70 °C
    Motor4: 0.0 4.1 6.7 A Temp: 32 62 78 °C
    Motor5: 0.2 9.3 15.7 A Temp: 32 73 89 °C
    Motor6: 0.0 8.4 15.1 A Temp: 31 67 81 °C
    Motor7: 0.0 8.3 13.5 A Temp: 38 68 87 °C
    Motor8: 0.0 6.2 12.9 A Temp: 36 58 79 °C

    Magnet Field: 99 103 112 % (ok)
    Magnet Inclination: 51 63 73 deg

    No errors found ;)
     

    Attached Files:

  2. Gary Haynes

    Gary Haynes Administrator
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    Perhaps the lack of consistency between various MK bits and pieces? Not trying to be funny but if all you changed was the PDB and on a similar flight, weight, etc. then I would suspect quality control of the components you replaced.
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Steve: How does the balance look if you suspend the copter by the battery plate?

    Also, bear in mind, that the the maxima are just that -- you only have to hit a new high briefly because a sudden manouver/gust of wind and the amperage will shoot up.

    I tend to look at the average currents more than the maxima, and then test what I'm seeing in the currents by looking at the average temperatures, just using the temperature as a proxy for the current.

    Based on that, the rear "half" of the copter seems to be working harder-ish (technical term). That suggests it might be a balance problem....the copter that is, not the pilot. :)

    Andy.
     
  4. Steve Maller

    Steve Maller UAV Grief Counselor

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    Is there any way to confirm the readings that the BL-CTRLs are sending back to the other electronics? I am concerned because the other motors are reporting higher-than-normal temps, too, so I tend to believe the data.

    What's causing it is another story. In my feeble brain, I'm imagining that motors 6 and 7 are fighting against their old bearings, and not generating enough thrust, and motors 1 and 4 are being limited in power to compensate for the lower-than-normal output.

    Or I could be completely wrong. Hopefully I'll know more tomorrow. If it doesn't improve, I'll move the motors to different booms and see if I can corroborate this theory.
     
  5. Steve Maller

    Steve Maller UAV Grief Counselor

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    Looks dead on even. I'm pretty diligent about balancing front-to-back and left-to-right when I put on my LiPos. I have a system of velcro straps and restraints that give me latitude to adjust the balance in small increments depending on whether I strap a GoPro or something else on the copter.

    IMG_7888.jpg
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

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    FYI, here's a nominal flight with the old MK power distro board (the last flight from the day before BL-CTRL #3 failed).

    MK Version: FC HW:2.2 SW:2.0a + NC HW:2.0 SW:2.0a

    Flight date: 9/16/2013 11:58:10 AM
    Flight time: 11:58:10 AM - 12:06:49 PM (519 secs, 00:08:39)
    Batt. time : 514 secs, 00:08:34

    Elevation(GPS) : 0 18.77 74.029 m (min/avg/max)
    Altitude(Barom.): -6.45 19.55 75.75 m
    Vertical speed : -2.22 -0.01 2.44 m/s
    Max speed : 34.3 km/h
    Max target dist.: 6.4 m

    Sats : 8 9 11

    Voltage : min. 14.3, max. 16.1 V
    Current : 0.5 58 84.7 A
    Wattage : 8 894 1237.08 W
    Capacity: 8505 mAh

    Motor1: 0.0 7.7 13.4 A Temp: 25 44 60 °C
    Motor2: 0.1 6.5 13.0 A Temp: 23 41 57 °C
    Motor3: 0.3 6.9 12.7 A Temp: 26 44 55 °C
    Motor4: 0.1 6.8 15.0 A Temp: 25 43 54 °C
    Motor5: 0.0 7.8 13.9 A Temp: 23 48 67 °C
    Motor6: 0.0 7.0 10.8 A Temp: 24 47 62 °C
    Motor7: 0.0 7.8 11.9 A Temp: 24 50 68 °C
    Motor8: 0.0 6.6 11.3 A Temp: 27 47 64 °C

    Magnet Field: 95 103 113 % (ok)
    Magnet Inclination: 46 59 75 deg

    No errors found ;)
     

    Attached Files:

  7. Adam Paugh

    Adam Paugh Distributor

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    Hello Steve,

    Maybe I missed it up there, but do you have ambient temps for these two data sets?

    Greetings,
    Adam
     
  8. Steve Maller

    Steve Maller UAV Grief Counselor

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    Ambient temp for first (most recent, anomalous) flight was 55F and second (earlier, normal) flight was about 70F, and both were near sea level.
     
  9. Steve Maller

    Steve Maller UAV Grief Counselor

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    More data here:

    i ran mktool's motor test, and set each of the motors to a level of 60 and ran it with the prop on it
    what i see in this graph, at least, is consistent with the theory that the BL Ctrl may be under-reporting the current for motor 4 and 1 (levels started at 8 and went to 1 in this trace).
    so my question is this: is this a matter of concern for the stability/safety of the copter?
    i don't have a way of testing the thrust or the RPMs, so I don't know what to do about this
    i obviously need to get this looked at, but like i said, my other PDB is in the shop

    image.png
     
  10. Steve Maller

    Steve Maller UAV Grief Counselor

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    I just spoke to Riley, and also did some poking around here, and I'm going to work under the theory that I have two BL-CTRLs that are under-reporting their currents. Riley says that he's tried on a couple occasions to remedy this situation, but that there have also been cases (with copters that Jeff and Casey had) where they just flew and flew with this condition, and it was fine. Evidently, the telling thing is the BL temps. so I'll watch those carefully (they're in my SmartOSD screen).

    I did find another thread where a couple guys reported similar issues.
    http://forum.freeflysystems.com/index.php?threads/another-bl-failure.2054

    I'll report back as I fly this more...thank you all for your help!
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah, temperature is a pretty good proxy for current -- and it tends to average out a little more just because of the thermal mass.

    Andy.
     
  12. Steve Maller

    Steve Maller UAV Grief Counselor

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    Well, just took her for an extended fly, and I think the results are OK. BL #4 seems to be running a bit hotter than the others, although still well within safe operating range. I flew for 9+ minutes with the GH3 on board at normal operating AUW (about 14.7 pounds) and consumed a decent amount of petrol. The copter's handling well, despite a pretty good breeze, and a fair bit of turbulence from the wind hitting the ocean cliffs about 50m away. Here's the header of the GPX file....I flew quite a bit with AH and PH on (both of which continue to work well) and spent a good deal of time just hovering, and at a decent altitude. Ambient temp was 62°F.

    MK Version: FC HW:2.2 SW:2.0a + NC HW:2.0 SW:2.0a

    Flight date: 9/27/2013 2:53:58 PM
    Flight time: 2:53:58 PM - 3:03:20 PM (562 secs, 00:09:22)
    Batt. time : 557 secs, 00:09:17

    Elevation(GPS) : 0 30.16 80.065 m (min/avg/max)
    Altitude(Barom.): -0.8 31.04 82.85 m
    Vertical speed : -3.04 -0.02 4.1 m/s
    Max speed : 29.1 km/h
    Max target dist.: 16.6 m

    Sats : 10 10 11

    Voltage : min. 14.5, max. 16.9 V
    Current : 0.5 53 110.3 A
    Wattage : 8 820 1676.56 W
    Capacity: 8240 mAh

    Motor1: 0.0 2.4 6.0 A Temp: 18 38 50 °C
    Motor2: 0.3 8.7 17.9 A Temp: 20 49 68 °C
    Motor3: 0.1 5.2 10.5 A Temp: 22 42 60 °C
    Motor4: 0.1 4.5 9.3 A Temp: 21 52 76 °C
    Motor5: 0.1 6.4 15.3 A Temp: 18 44 58 °C
    Motor6: 0.0 9.5 20.6 A Temp: 15 48 67 °C
    Motor7: 0.1 6.1 14.2 A Temp: 18 45 60 °C
    Motor8: 0.1 8.3 15.9 A Temp: 19 48 64 °C

    Magnet Field: 100 103 111 % (ok)
    Magnet Inclination: 49 61 73 deg

    No errors found ;)
    QuickTime-Player-snap007.jpg QuickTime-Player-snap006.jpg
     
  13. Steve Maller

    Steve Maller UAV Grief Counselor

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    Good news is I did a ton of flying today, and the copter flew well. I'm still suspicious of BL #4 (discussed above), as its temperatures were significantly higher than the others. I was sitting in PH and AH quite a bit on this flight, and my SmartOSD was showing the level at 90+ and it was blinking. I was able to turn off PH and fly around a bit to cool it off, but it seems as though it's definitely got an issue, maybe related to the lower current reporting, or maybe not. Here is the 6th flight I did (and the longest) and as you can see, the ESC temps are a little out of whack, too.

    MK Version: FC HW:2.2 SW:2.0a + NC HW:2.0 SW:2.0a

    Flight date: 9/28/2013 10:31:30 AM
    Flight time: 10:31:30 AM - 10:42:39 AM (669 secs, 00:11:09)
    Batt. time : 663 secs, 00:11:03

    Elevation(GPS) : 0 40.25 93.711 m (min/avg/max)
    Altitude(Barom.): -1.75 41.16 96.9 m
    Vertical speed : -2.95 -0.04 3.68 m/s
    Max speed : 35.1 km/h
    Max target dist.: 8.9 m

    Sats : 7 7 10

    Voltage : min. 14.1, max. 16.3 V
    Current : 0.5 57 89.3 A
    Wattage : 7 863 1268.06 W
    Capacity: 10656 mAh

    Motor1: 0.0 2.8 4.7 A Temp: 28 46 58 °C
    Motor2: 0.1 10.2 16.5 A Temp: 26 62 86 °C
    Motor3: 0.2 6.1 10.4 A Temp: 26 59 83 °C
    Motor4: 0.0 5.1 9.0 A Temp: 23 71 91 °C
    Motor5: 0.0 6.9 11.8 A Temp: 21 51 71 °C
    Motor6: 0.0 9.5 16.8 A Temp: 15 53 66 °C
    Motor7: 0.0 6.2 11.1 A Temp: 19 42 55 °C
    Motor8: 0.0 8.6 16.6 A Temp: 23 48 61 °C

    Magnet Field: 100 109 117 % (ok)
    Magnet Inclination: 49 58 74 deg

    No errors found ;)
     
  14. SteveWilson

    SteveWilson Member

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    If it were my bird, I'd replace BL #4 before I flew too much more. Having flown the old mikrokopters, slightly overloaded, I got very good at replacing BL's. Whenever the numbers on one motor consistently started outlying, in my experience that is a BL fixing to die on you. Next thing I'd expect to see is once in a while when you start engines, #4 won't start until the 2nd or 3rd try.

    Thankfully switching to the CS8 solved all those problems for us.
     

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