Huge flight time drop

Discussion in 'Cinestar 8' started by Cris Olariu, Aug 7, 2013.

  1. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The current BL-Ctrl firmware should go into a BL Limitation error at 104C. Not quite sure you didn't get that.....but at that temp it will automatically start to reduce motor power to avoid melting itself.

    Andy.
     
  2. Gary Haynes

    Gary Haynes Administrator
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    Cris I went back through the string. I don't see it but have you ever answered the basic question of the all up weight of your copter, flying weight with batteries and camera? If you don't have a way of weighing it would suggest a digital fishing scale would be a good investment. Likely you have multiple items including the overall weight pushing the limits of props/motors/battery.
     
  3. Cris Olariu

    Cris Olariu Member

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    Steve, thank you for taking another look at the GPX file.
    The AUW is an approximate 13lbs (I don't have a fishing scale on hand, so I had to use a regular scale, and prop the copter on it. I'll look into getting one of those scales, or something similar in the next couple days, then repost the actual weight). That includes the copter, the gimbal, one 8000mAh Quadropower battery, and my Canon 60D with a 50mm prime on there (that is the lightest lens I have).
     
  4. Cris Olariu

    Cris Olariu Member

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    I should make a mention that I was also flying in direct sunlight and in about 85 degree (and rising) outdoor temperature. As opposed to the GPX files that I've uploaded initially, which were done in about 65-70 degree outdoor temperature.
    I saw somewhere on the forum that someone used a thin 120mm PC fan to cool off the PDB. What is everyone else using? Or should I just try to build something like that?
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I'm not using any additional cooling. I do have the heat sinks on the MOSFETs, but I was flying out in 95F weather and, provided I didn't hover for extended periods, the lateral motion of the copter kept the BL-Ctrls around 88-92C.

    The C8 has QC3329, MK boards, 3-Axis gimbal, and a Sony CX760.

    Andy.
     
  6. Cris Olariu

    Cris Olariu Member

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    OK Andy, I really need to get a ruling on the heatsinks. I had them on the old board, but when I got a new PDB and new BLs, I didn't install new heatsinks. It seems like most people don't notice a big difference on the BL temps when they add the heatsinks, so that's why I didn't add them on the second board.
    Did you notice a difference after you installed heatsinks? Also, do you have them installed on both sides? (on the old board I had them only on the top)
     
  7. Brad McGiveron

    Brad McGiveron Active Member

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    Cris... the heat sinks lower the heat from around 90 ish to 60 for all the MK setups I have run. A huge difference if you are running heavier weights or in warm climates where you'd easily go into meltdown without them on.
    Yes both sides.
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I think there may be some misunderstanding about what the heatsinks actually do, Cris.

    The heatsinks increase the amount of surface area in contact with the air. In still air (e.g. when the copter is hovering), you will not see a huge difference (lower temperatures) between having heat sinks and not having them.

    Where they really seem to make a difference is when there is airflow (either because of lateral motion of the copter), or using a fan as Josh and Dave have done. Then the heat transfer from the MOSFETs to the air is significantly better.

    The advantage to the fan is that it creates its own airflow even when the copter is hovering. Of course the downside is the increased weight and demands on the battery.

    So the heatsinks only work because of air flow, not because of direct radiative cooling (well, not much radiative cooling -- there's doubtless some!)

    And yeah -- put them top and bottom. You may find that you don't have the clearance under the PDB with the boom clamp screws sticking up too far. Either get 37mm machine screws or raise the PDB on slightly taller standoffs -- or even just put "washers" of neoprene tubing under the PDB on each of the standoffs.

    Hope this helps.
    Andy
     
  9. Jose Luis Ocejo

    Jose Luis Ocejo Active Member

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  10. Cris Olariu

    Cris Olariu Member

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    Brad and Andy, thank you for the explanations. I'll get some more heatsinks and add them to this board as well. My PDB is already raised up a bit with double the standoffs (I didn't like the wires getting squished in there).
    Jose, that's a great idea. I guess it barely adds any weight to the copter.
     
  11. Jose Luis Ocejo

    Jose Luis Ocejo Active Member

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    Yes its really very light and apart from keeping the electronics in the shade it helps in case you get caught flying and you get some rain it may give you that extra time to land and run for cover Home Depot sells a small sheet for $10 I think, they have only white I been trying to find a sheet that is B&W
     

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