Yaw problem before take off

Discussion in 'Cinestar 8' started by Patrick Weeden, Mar 13, 2013.

  1. Patrick Weeden

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    Hey guys

    I'm wondering if someone can help me, as soon as I increase the throttle on my C8, it yaws violently to the left, I then trim and it yaws to the right, it seems to be going crazy and won't sit still or react to the stick inouts when trying to control yaw. Does anyone have any suggestions? Attached is my is my gpx file
     

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  2. Brad Meier

    Brad Meier Active Member
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    Can you upload a photo of your CS8? One of the things we've seen in the past that can affect yaw.. are the motors/ props all level and on the same plane? Just a quick suggestion...
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Also, can you tell us what transmitter you are using and verify that you are not using Exponential on the Yaw stick?
    Check the Servo Monitor screen -- most transmitters have them and move the Yaw stick either side of the central position and see what response you observe.

    Also, assuming you are using MK boards, connect up MK Tool, use the Channels window, and verify that the response you get on the Yaw channel is appropriate for the amount of stick movement.

    Also verify that you have the Mixer set to octo2 (that's also in the MK Tool window).

    Andy.
     
  4. Patrick Weeden

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    I am using the Spektrum DX8 and the yaw is not on exponential, I already checked the values and they are showing correctly. Here are the pictures, the booms/props seem to be as level as possible. It was flying perfectly, I installed a new FC board, re-calibrated the compass and everything seems ok. On the GPX file, I am seeing the error 22 (Magnetic error) at some points, not sure if this would affect the yaw? Thank you
     

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  5. Patrick Weeden

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    Forget to mention, at about 10% throttle, the yaw can be controlled normally, it just seems as soon as I increase to the point right before lift off, it is yawing badly and cannot be countered. Thanks
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The Error 22 will definitely affect the yaw. If you have already correctly calibrated the compass you may have a problem with the NC board. Check that you don't have LiPo (heavy current cables) running near the NC board.

    Do you have the NC board on boom #1 (can't quite see from the photos) and is it correctly oriented? Both ribbon cables should be on the left side of Boom #1 when looking at the copter from Boom #5.

    To confirm that the yaw problem is the compass, use MK Tool -> Misc window and change the Compass effect to zero, thus disabling the compass' input to yaw stabilization.

    Hope this helps.
    Andy.
     
  7. Patrick Weeden

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    Hi Andy

    The NC board is attached under the FC board, with some spacers (I have taken a picture but quite hard to see), both ribbons are on the left side of boom 1 too- I had this exact setup before and it was flying perfectly for about 6 months, I had to replace the FC board and now it is playing up. Is it recommended to move the NC board onto boom 1? I will change the compass effect and see if that helps. Thanks Andy, really appreciate it!
     

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  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I would certainly move the NC board out under the GPS -- it's much further away from the batteries, cables, motor wires, etc. Photo3-jpg shows how close the main LiPo cable is. Also twist the LiPo wires to the Dean's connector or use cable ties to hold both wires together, the better to counteract any electromagnetic effect -- you've got 60 Amps going through those cables! :)

    I cannot explain why everything was OK for six months and now is not, but if you're getting compass errors, then I would move the NC board for sure. You can either make up your own ribbon cables, or get them from Quadrocopter (if you're in the USA or Canada).

    ANdy.
     
  9. Patrick Weeden

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    Thanks Andy, I'm finding it hard to understand the sudden change too. On MKtools, the MK3Mag tab says no connection, is that because I set the compass value to 0 or does that mean there is a problem. The EarthMagnet value is 105 (Which is within normal parameters). COuld that be the problem? The GPS receiver is fairly close to the battery, do you think I should move it further out on the Boom? Sorry for all the questions :/
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    On the later version of the NC board, the compass was integrated with the NC electronics -- that's all that you're seeing with MKTool.

    On my Cinestar (which seems to work fine), the closest part of the GPS shield is about 5/8" away from the nearest part of the popwer distribution board's corner -- if that answers your question?

    Andy.
     
  11. Patrick Weeden

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    Of course, I didn't think about the compass being integrated. I have just been for a flight with the compass effect at 0 (it was at 64 previously) and it flew beautifully, one thing I did notice was that the yaw was not as responsive though. Can I leave the compass value at 0 or will that affect come home, PH or AH at all? I don't fly in carefree mode at all but just wondering what the compass effect does in terms of stability?
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    As far as I am aware, the compass primarily affects yaw stability. I've not had a chance to look at the MK firmware source code to see whether it affects PH or AH (beyond maintaining a constant heading -- which is the yaw component again).

    Until you can get the NC board away from magnetic influences, try increasing the Compass effect and see if there is a "sweet spot" that makes yaw a bit more responsive without the original problem showing up.

    Andy.
     
  13. Patrick Weeden

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    Ok i will do that tomorrow and see what we get. I also have another question, I am getting fairly consistent BL temperatures (24-26 degrees) except for motor 6 which is running at 75 Degrees. I had a look at the GPX file and motor 6 is running really high compared to all the others that are fairly similar. Do you know what could be causing this? I can't seem to find any info on it. Thanks Andy
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Remember, those are the Brushless Controller temps you're seeing. is the motor #6 itself noticeably hotter after a flight?

    Either way, swap two motors over and see if the elevated temperature stays with BL Ctrl #6. If the problem moves with the motor, then that's the problem -- if it stays with BL Ctrl #6, then that's the problem.

    If it does stay with BL Ctril #6, then make absolutely sure that all the prop shafts are vertical (check that by making sure the prop blade tips of adjacent props are at the same level as prop #6 (spin #6 180 degrees to check both blade tips) and the copter is properly balanced (by suspending it from the battery plate). It could be that #6 is working harder to stabilize the copter.

    If all the prop shafts are absolutely vertical, chheck the BL-Ctrl #6 on the underside. The two cylindrical capacitors should be glued to the underside of the Power Distribution Board -- check that their electrical leads are solidly soldered to the PDB.

    Andy.
     
  15. Patrick Weeden

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    Hi Andy

    I noticed that I had not clicked on "Ignore Magnet error on start" and checked the box before I went for a flight today. It flew beautifully! When I am using position hold, the C8 moves around quite a bit trying to hold its position (About 2-3 metres) however, when I activate come home, it comes home and stays dead on the take off position. Is there something I can try in the parameters to get the position hold to be more stable or to hold a point without moving around so much?

    I checked the capacitors on BL#6 and they are fine, I have tried to line up the motor shaft as best I can and it seems to be straight up but still giving high temperatures :(

    Thanks for your help so far!

    Patrick
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    If it's "circling" on position hold, that's called "toilet bowling." Usually that's just variations in the GPS signal (it's a consumer grade GPS, remember. There's quite a lot written about it on the web, Google: mikrokopter toilet bowling
    and you will find it. There appears to be a relationship to how well the compass is calibrated....so you're back to that problem again! :)

    Andy.
     
  17. Patrick Weeden

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    I understand that it is the relationship to how well the compass is calibrated, but how does that explain the fact that the come home feature works so well (It sits dead above the take off point without moving much at all)That's what really confuses me...
     
  18. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I agree. Very good question, but not one I know the answer to.

    Andy.
     
  19. Patrick Weeden

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    Haha, it is driving me crazy, I will have a play around today and see what I can figure out, I'm going to recalibrate the ACC and compass and see if that makes any difference. Have a good weekend Andy!
     
  20. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Yeah. When in doubt, or when you have nothing better to do, recal the ACC, compass, check motor shaft alignment, balance the copter, and check the transmitter sticks are calibrated and trims are at neutral and, using MK Tool are sending appropriate signals to the MK Boards.

    Even if you have better things to do, still do the above!

    Andy.
     

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