Another A2 Crash - Pictures, Graphs, and Video

Discussion in 'Cinestar 8' started by Josh Lambeth, Aug 5, 2014.

  1. Dave King

    Dave King Well-Known Member

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    I personally don't care about the stats and data. I want my copter to be able to maintain hover with the joystick in the center for several reasons. It's harder to fly manually when you don't use altitude hold. If your not careful it can drop very quickly at 26 pounds. For me its more of an extra safety thing. Also as Andy has found, full throttle is actually achieved much closer to 3/4 throttle so there's a lot less headroom between maintaining hover and going full throttle. For me I don't want to be near full throttle, as the MK BL's are more limited than a KDE ESC. I have a feeling this is why Ozcan's board failed when he was trying to maintain a certain speed chasing the motorcycle.

    So to me it appears that you have 2 choices. You can go the route of running the new high resolution KDE motors but unless you run their ESC's they are not any really going to benefit a lot of other ESC's. You can either have higher thrust motors at the expense of using a more unpredictable DJI system or you can try to achieve the results by another manufacturer motor. Right now I am trying "the other mean" route using a Tiger motor. I know the Tiger motors are efficient with the MK electronics as well as the majority of just about every ESC out there. I have a good feeling that the combination of the new motors I am testing and the MK electronics will be a good alternative. I hope to test by the end of the weekend.
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Dave is referring some freely available research results that I'm starting to publish at http://rathergoodguides.com/document-guides/esc-motor-and-propeller.html -- there will be more research results available over the weeks ahead.

    See the Rather Good GuideĀ® to ESC, Motor, and Propeller Research Results document on that page and why I had to define the term "absolute throttle" to avoid the tar pit of what motor vendors mean when they say X grams of thrust at 60% throttle...

    Andy.
     
  3. Steve Maller

    Steve Maller UAV Grief Counselor

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    That is exactly my point. Assuming that 47% or 67% is actually that is dangerous. You really want to know how much of your drivetrain's potential you're using at any given point. If you're hovering at 50% of your drivetrain's potential (irrespective of the physical position of the stick), that's good. If you're at 65-70%, that's bad. But it really has little to do with the physical position of the throttle stick. That's easy enough to change in your radio's configuration. If all our throttles were calibrated and normalized, that'd be interesting. It's like saying you prefer a car that cruises with the gas pedal lightly depressed vs. depressed halfway. What actually matters is what the motor and the transmission and the wheels are doing and how well the car accelerates (or the fuel efficiency, or whatever).
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Several non MK flight control systems automatically adjust for hover through the FC at the 50% position of the stick on the radio. No direct feedback based on stick position to throttle percentage.
     
  5. Gary Haynes

    Gary Haynes Administrator
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    Several non MK flight control systems automatically adjust for hover through the FC at the 50% position of the stick on the radio. No direct feedback based on stick position to throttle percentage.
     
  6. Dave King

    Dave King Well-Known Member

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    OK I just went through my MK files with the X8. I don't have much logged data at full throttle (because thats not how I use my copter) but I do have a few GPX files that I can compare to when I first tested the X8 with 10 pounds of dummy weight. With altitude hold off hovering, the stick throttle measures at 64% and I am drawing 95 amps. At full throttle I am drawing 133 amps. So hover is using 71% of the full throttle power. So using your current measurement yardstick for motor performance it shows that the motor is underpowered even more than I originally thought. Again this is with the assumption that the current numbers the BL's report is "accurate". I"m not sure how each motor is only averaging 16 amps at full throttle at 26 pounds other than the fact that I was not at full throttle for more than 3 seconds. I guess its a good thing that I did not stay at full throttle very long which is another clue as to why Ozcan's board blew up with a very similar combination.
     
  7. Steve Maller

    Steve Maller UAV Grief Counselor

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    95 amps at hover is a lot. My X8 at ~23 pounds (5D Mark III) hovers at 68 amps with the KDE 4012 motors and 16" Tiger CF props. It hovers at 58 amps at ~22 pounds with the GH4 on board.
     
  8. Dave King

    Dave King Well-Known Member

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    One thing I noticed during tests with the U5's is that the copter hovers at 70 amps/62 percent throttle with a 10 pound payload but as soon as I add 2.5 more pounds it jumps to 70 percent 88 amps. So it must be that the motors characterisics can quickly change by a pound or two if they are on the edge of being too far overdriven and way out of its efficiency range for load.

    You know this also brings up another interesting point of discussion is that the current the motor draws is going to drastically change depending upon load or more specifically payload. With a 5D I"m hovering at 55 amps versus 78-80 with the Red camera. You wonder how the motor manufacturers are determining the current number at a specific thrust value. Obviously they are just putting a prop on the motor with it attached to a test jig of some sort but that motor only has the load of the prop on it. I guess the way to figure it out would be take the maximum thrust measured, mulitple it by the number of motors on your copter and convert it to pounds and that would give you a pretty close indication of the current draw at that weight? If there can be as much as a 30 amp difference at hover, imagine the current draw difference at full throttle at different payloads. So I guess the conclusion is that the Manufacturer numbers get you in the ball park, tread carefully.
     
  9. Justin Zattelman

    Justin Zattelman New Member

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    Just curious, do you think vibration has anything to do with the A2 failures? In the coaxial setup wouldn't the motors run harder than a flat 8 setup and would lead to higher vibration under load. Just a thought? It seems to happen more to the coaxial platforms... Could just be because there are more coaxial setups around?
     
  10. Steve Maller

    Steve Maller UAV Grief Counselor

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    I don't think X8 copters are any more susceptible to vibration/oscillation issues than flat 8s. They may even be less because of the two motors possibly canceling each other's vibrations.

    There are a lot of folks successfully running big X8 setups with A2 systems. The problem IMHO is that the A2 doesn't surface very much of its diagnostic information, so you sort of have to trust that DJI are doing the right thing. I've found with MK kit that you often find out about errors before they happen, or at least before they cause a crash. With the increasing amount of really expensive rigs up on these machines, you really have to have a lot of faith in the systems. Or a lot of info. Or both.
     
  11. Josh Lambeth

    Josh Lambeth Well-Known Member

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    Hey Guys,
    Quick update on everything. I have completely given up on DJI to make this right. They have just completely stopped responding to my emails (No surprise there). I went to the dealer I bought the A2 from (FPVNinjas.com) and they took the A2 back and replaced it with a brand new one. If you guys need to buy anything FPV related or anything KDE/DJI/ECT go there!

    I also filed an insurance claim and they wrote back today saying they are covering my crash repairs minus my deductable. I will be rebuilding with the following components since I won't use DJI again.

    MK 2.5FC
    MK Navi-GPS Stack
    Herkules III ESC system using 2x Quadro XL boards (They each have their own large heatsink which will keep it cooler than the single heatsink on the OCTO XL board).
    KDE 5215-435KV motors
    Tiger 18x6.1 props

    I have spoken with Andreas who builds the Herkules boards and he assures me I will be ok with the 5215 motors. His ESCS have a TRUE Amp rating. When it says it will do 30amps continuous it will without overheating. I have also spoken to another couple guys who use the Herkules boards and fly REDs all day long on the TMotor U7 motors and they don't even get hot. With the payload I will be flying I should be perfectly fine.

    Can't wait to get this back in the air again!
     
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  12. Ryan McCrae

    Ryan McCrae Member

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    Are there any images of the 2x Quadro Xl boards? Im running the QuadroXL, and its been great.
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Josh: Does the Herk III ESC provide any telemetry regarding temps and currents back to the ground via the MK FC?

    Thanks
    Andy.
     
  14. Steve Maller

    Steve Maller UAV Grief Counselor

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    I believe the Herkules has an I2C bus connector, and does communicate with the MK boards.
     
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  15. Gary Haynes

    Gary Haynes Administrator
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    Steve that is the beauty of Andreas's boards. Direct connect to MK system.
     
  16. Ozkan Erden

    Ozkan Erden Distributor

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  17. Josh Lambeth

    Josh Lambeth Well-Known Member

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    Ozkan,
    Are you using X8 setup? Very curious what you find since I am about to order parts. Don't want to if it's not going to work.

    Josh
     
  18. Dave King

    Dave King Well-Known Member

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    Thanks for sharing the info with us. Let us know what you find out.
     
  19. Ozkan Erden

    Ozkan Erden Distributor

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  20. Josh Lambeth

    Josh Lambeth Well-Known Member

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