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MK IR Trigger goes catatonic in flight?

Discussion in 'Electronics' started by Andy Johnson-Laird, Aug 26, 2012.

  1. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I was flight testing the MK IR Trigger this morning. It works solidly with the Sony HDR CX760 on the ground -- and, for a while in the air. Then it appeared to wedge -- none of the zoom/record/shutter actions would work.

    When I next landed the C8, I power cycled the gimbal (which also powers a Recom 5 volt for Rx, servos, and MK IR trigger). That didn't fix it. So, just for lack of much else to waggle, I disconnected/reconnected the two servo connections to the Rx and, bingo, that fixed it.

    It happened one more time, so this time I unplugged/replugged just the servo connector with three wires, and that fixed it.

    It suggests a dodgy connection in the three-wire servo connector, so I'll remove the connector pins from the housing, cut them off, and re-crimp new ones on. Before I remount them in the housing I think I might try putting several turns through a ferrite ring to see if that makes a difference.

    Has anyone else seen the similar flakiness with the MK IR trigger?

    Thanks
    Andy.
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Tabb: I'm working through possibilities to explain this failure. I've changed out the servo connectors on the IR Trigger.

    The next thing I wondered about is the IR Trigger board's placement. Right now it is double-sided foam-taped to the side of the roll FF servo. Any reason (like EMI or RFI) that that would be a Bad Thing to do? I realize there's a stepper motor in the servo, but I figured the magnetic field was pretty self-contained.

    Thanks
    Andy.
     
  3. Jeff Scholl

    Jeff Scholl Distributor

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    Hi andy,

    I've heard of IR sensors having erratic behavior in direct sunlight. Any chance for this on your mount?

    Cheers,
    Jeff
     
  4. Adam Paugh

    Adam Paugh Distributor

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    Perhaps some feedback coming from the ext. pot. to the Rx? Is this your gimbal with the Radian, Andy?
    Greetings,
    Adam
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Jeff: I've eliminated that possibility, I think. Once the MK IR trigger is "wedged," I can pick up the C8, put it into the back of my SUV in the shade, and it stays wedged. I've also got the IR LED "shielded" behind the CX760's lens hood which does a pretty good job of blocking direct sunlight except from camera right.

    Incidentally, *all* functionality from the IR Trigger goes away, so it's not just a single servo channel.

    But I'm still wondering whether the problem is the Spektrum AR6210 doing the wedging. I've added a small piece of wire-wrap wire to the signal side of the IR LED connector on the IR Trigger so that I can push on the JST connector but also connect up a scope probe.

    When I can get it to fail in the field, I'll land the C8, but leave the QC 1200 battery connected up to the gimbal to preserve the failure mode, rush back to the shop, and put an oscilloscope on the output from the IR trigger to the IR LED and see whether or not it's emitting any kind of signal when I activate the digital still/record on-off. If not, then I'll work backwards and check the waveforms coming from the AR6210 and see if the pulse width is varying appropriately.

    Adam: Yeah. I'm running the Radian beta versions. They're working great. I only have mode control on the pan module (with gain at 80%), the roll is fully automatic, and the shooter can control pan and tilt. I've got a Futaba 8FG now, so I might just cut over to that, use S.Bus for the Radian modules and an S.Bus decoder to pull off conventional PWM for the two channels needed for the MK IR controller. (I can hear you saying, "yeah, I told you so...go Futaba!" :) )

    Thanks
    Andy.
     
  6. Jeff Scholl

    Jeff Scholl Distributor

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    You may ask Holger about this. Our original model/prototype would wipe its settings, but that required a fresh upload to get it working again. What voltage/supply are you using on the rx power again?

    Here's,
    Jeff
     
  7. John Cunningham

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    Hey Andy,

    The radian will put out a PWM signal from the SBUS for you : You just set the desired channel for the 'Aux' channel (using the PC software) and it will appear on the 'IN2' pin (connection 2 I think) as a normal servo pulse. You can have different ones for the roll and tilt radian modules if you need 2 outputs.

    It was put in for exactly this kind of thing.
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks, John. That's good news. Less wires!
    Just to clarify (I've not looked at any Futaba PC software that might exist) -- but by "the PC software" do you mean the Radian Configuration software or something from Futuba?

    Thanks
    Andy
     
  9. John Cunningham

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    Yes - the Radian software.
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    To give you the executive summary first: The evidence below shows that the MK IR Trigger board is latching up after an indeterminate period of flight time. I don't know what's causing the latch-up.

    To answer Jeff's question: I'm using a QC1200 LiPo to power the AR6210 Rx, and thereby all the servos connected to it (including, of course, the two servo leads that go to the MK IR Trigger, one of which provides power.

    Under normal operation, the +5v DC supply (which is from a Recom 7805, looks pretty good -- there is some AC ripple on top of the DC but that's noise from the servos).

    Today, I took my oscilloscope out to the field where I fly. Normally the failure occurs on battery #1 or #2. But (obviously) because I had the scope there, it didn't fail until battery #4. Here's what I found as a series of scope screen captures.

    The first set of captures show the normal state of affairs without the MK IR Trigger board latched up:

    01 Normal output to IR LED from IR Trigger TEK0004
    This shows the +ve side (red wire) of the pair of wires connecting the MK IR Trigger to the IR LED when everything's quiet. No IR signals being sent.

    02 IR Signal being sent to IR LED TEK0002
    This is what the same output pin from the IR Trigger to the LED looks like with a signal being sent to the LED (in this case, Zoom In). The signal's on the right hand side. The LED has a current limiting resistor to ground so is attenuating the signal. The next image shows what it would normally look like without the LED

    03 Signal being sent to IR LED (LED unplugged) TEK0003
    Same signal as above, but the IR LED is unplugged so it's not attenuating the signal.

    04 Output to IR LED from IR Trigger -- Gimbal servos moving TEK0012
    This is the output from the MK IR Trigger board to the IR LED with no IR signal being sent, but with the gimbal servos moving. The noise spikes are caused by the servos (perhaps feeding back EMF back along the +ve servo power lead?)

    Now we move to a series of images showing the failure. To get to this point I was flying around, a cameraman was zooming in/out, taking digital stills, starting and stopping video recording. Suddenly, the MK IR Trigger board latched up. The cameraman could not long perform any of these actions, so I brought the C8 back to the landing site,

    05 IR Trigger not working - output to IR LED, signal not present TEK0014
    This captured was taken with the stick controlling the zoom in/out fully deflected to one side. The IR LED was still attached to the MK IR Trigger board. The IR signal pulse is absent. So, the MK IR Trigger board is not commanding the camera to do anything.

    06 Input to MK IR Trigger from AR6520 Rx (no deflection of stick)TEK0016
    So, moving backwards up the circuitry, I checked that the PWM signal to the MK IR was good. This screen capture shows it with the stick centered.

    07 Input to MK IR Trigger, stick fully left TEK0017
    08 Input to MK IR Trigger, stick fully right TEK0018
    These two images show how the pulse width is varying as the stick is deflected left and right.

    09 Output from MK IR Trigger to IR LED after power cycling gimbal TEK0021
    So I unplugged the QC1200 battery, waiting ten seconds, and plugged it back in. I then did the same stick deflection left/right, and, as you can see, with the IR LED disconnected, the IR signal is now being sent to the IR LED.

    I'm open to contradiction here, but it looks to me like, as I said that top, that the culprit is an MK IR Trigger that's latching.

    By the way, what's the best way to contact Holger, Jeff?

    Thanks
    Andy.
     
  11. Jeff Scholl

    Jeff Scholl Distributor

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    I'm curious if the recom is not up to the task for the radians/servos/ir control while in flight.
    Could you provide a 5volt source (ex. 4.8nicd pack) in addition to the rx and see if it behaves?

    Cheers,
    Jeff
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I was wondering the same thing, Jeff. Just to clarify what you're suggesting: Did you have in mind using a common ground, but alternative, isolated, independent +5volt supply for the MK IR Trigger alone.

    Reading what you wrote carefully (and perhaps too literally) makes me think you might be suggesting putting the additional 4.8v NiCd in parallel with the Recom's 5v output as a booster?


    Thanks
    Andy.
     
  13. Jeff Scholl

    Jeff Scholl Distributor

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    I would try the battery as a stand alone. If that works then i would replace the Recom with a bec that provides for higher amp draw.
    Sorry for the confusion.

    Cheers,
    Jeff
     
  14. Joe Azzarelli

    Joe Azzarelli Active Member

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    Andy
    Not that it solves your problem but sometimes a different solution is faster/cheaper than the diagnostics and correction. I am using a GentLed duo for the cx760. Not a full IR solution, but handles zoom and photo-snapping. I use the provided Sony remote to start recording just prior to takeoff. And, of course, no lock-up in flight experienced.
     
  15. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Jeff: Thanks for the clarification. Tabb mentioned last night that a BEC was the way to go -- I'd gone with the Recom 7805 as that was what was on the MK FC board. I'm going to put a 5v/5A BEC on today and try that. If I still get lock ups, then I'll try the separate battery for the MK IR Trigger, with a common ground. The noise from the servo's appears to be coming back on the +5v line, although with "floating" grounds you never really know whether the ground is waggling up and down or the signal line your measuring is doing the waggling.

    Joe: Thanks for the recommendation for GentLed. That's Plan B. :)

    Thanks
    Andy.
     
  16. Joe Azzarelli

    Joe Azzarelli Active Member

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    Additional battery, additional PC board, change the recom - or just plug these into the servo connections... Just sayin' ;-)
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    After some additional scope probing, here's what I found:

    1. The servo noise only exists on the output side of the Recom 7805. There is no servo noise whatsoever on the input to the Recom.

    2. Therefore, there appears to be no need to use a separate battery. I reserve the right to be wrong on this. :)

    3. I've added a 5v/5A BEC (http://www.dpcav.com/xcart/5VDC-5A-Voltage-Regulator-BEC-Switch-Mode-Type.html) to drive Rx, Radians and servos, using the original Recom 7805 for the MK IR Trigger.

    4. Now the IR LED output signal is devoid of any noise even when the servos are working really hard. My hope is that this fixes the IR Trigger latching up problem.

    I'll flight test the system tomorrow and report back.
    Hope this helps someone avoid the same pitfalls into which I fell.
    Andy.
     
  18. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    OK. That fixed it. A single QC 1200 mAH LiPo. One BEC 5v/5A for the RX and servos, and one Recom 7805 for the MK IR Trigger. Worked flawlessly for about 70 minutes total of flying.

    Thanks for all the help, folks. Much appreciated.

    Andy.
     
  19. Jeff Scholl

    Jeff Scholl Distributor

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    Thanks Andy for the follow up! For future Radian/Servo combos we will be offering the Castle BEC which should be good up the 10amps - plenty with room to spare even if the servos bind on something.

    Cheers,
    Jeff
     
  20. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks, Jeff. I'll keep an eye out on the QC web site for it.

    Regards
    Andy
     

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