dodeca stability

Discussion in 'Cinestar 8' started by Geoffrey Bainathsah, Nov 19, 2014.

  1. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0
    Hi Guys

    I recently helped out a friend with a gryphon dynamics dodeca 1200 with retracts and Z arms.
    Using DJI wookong M, set up in y6 mode, cc40HV and scorpionM4015 and 18x6.1 props.
    The issue we had was that i did not have the stability we were used to, specially in high winds.
    It would wouble around before recovering on roll and tilt axis.
    Yaw stability was great.
    We are used to flying x8 systems.
    Just wanted to know if anyone has experienced this and maybe have solved this already

    Geoffrey
     
  2. Angus Benson-Blair

    Angus Benson-Blair Active Member

    Joined:
    Jan 23, 2013
    Messages:
    150
    Likes Received:
    25
    If the Gryphon frame you have is a folding frame the problem might be to do with the rigidity of the joint. I had a flat hexa and it looked like the joints were responsible for resonance issues. This resonance would obviously feed back to the IMU which either made the aircraft look as if the gains were too high or that there was a stability issue. Of course this is a theory that is hard to prove but it's funny that Gryphon have now produced 'reinforcement kits' for their folding frames.
     
  3. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0

    I fly a gryphon x8 1000mm, the system is amazing, i dont have any sort of play in the arm joint . its simply wunderfull.

    Now that you mention it, yes there was a bit of play in the joint on the dodeca, i dont think this could have caused the instability, but you never know.maybe some has experience with a different dodeca frame?
     
  4. Steve Maller

    Steve Maller UAV Grief Counselor

    Joined:
    Oct 30, 2012
    Messages:
    3,979
    Likes Received:
    807
    You said you were in "y6 mode", but what about the other 6 motors? Does the WKM support full 12 motor operation? If not, that might explain your instability.
     
  5. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0

    Dji wookong does not support 12 motors, but only 8
    the solution is to run it as a hexa and use Y-spillter to duplicate each individual motor output.
    please take a look at the manual for this http://gryphondynamics.co.kr/wp-content/uploads/GD-12-Motor-Set-Up.pdf
    Ofcourse you can also set this up as a flat hexa, maybe people are having more luck with that compared to Y6?
     
  6. Steve Maller

    Steve Maller UAV Grief Counselor

    Joined:
    Oct 30, 2012
    Messages:
    3,979
    Likes Received:
    807
    I sincerely doubt that can be anywhere near as stable as a FC that actually knows how to fly a 12-rotor machine. I'd be super careful. :eek:
     
  7. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0

    I fully agree with you steve, but that's the way all DJI dodeca systems are running.
    even the A2 controller supports only 8 motors.
    Anyways, im hoping there might be someone other there with dodeca experience that can tell me that they dont have any issues using DJI.
     
  8. Ryan McMaster

    Ryan McMaster Active Member

    Joined:
    Mar 8, 2014
    Messages:
    289
    Likes Received:
    40
    This right here is your answer to this:
    If the system wont support it it wont support it, does not matter what "hacks" there are. The combination of the Gyrphon frame (which sextuples the number of failure points in your rig) with a motor config that is not supported by the FC just is a disaster waiting to happen. Don't get me wrong, I think it's a killer idea but the risks being taken far out weigh the rewards to be had. That FC is over worked and will fail sooner rather then later. What motors/batteries/props are you running?
     
  9. Tim Gould

    Tim Gould New Member

    Joined:
    Nov 3, 2012
    Messages:
    19
    Likes Received:
    0
    Geoffrey, You may want to chat with the Kopterworx guys since they have more experience with the Dodeca arrangement and WKM. I have built a dodeca from a Cinestar 6 frame and have a Xaircraft SuperX controller on it using the y6 mixing. I have mixed feelings about the arrangement. The SuperX flight controller does not have separate gains for rate and attitude mode making it difficult to fine tune. I have reached a happy medium though. One thing I find with the dodeca arrangement is that because of all the motors and props, individually they are lightly loaded. I think this lends itself to the floaty feeling. It is also very quiet for this reason. My x8 using my NAZA v2 feels more locked in.

    I do agree with some that the complexity of the dodeca arrangement does create extra failure points with the number of electronic speed controllers and wiring complexity. I am not sure the positives outweigh the negatives. As far as the flight controller goes, I don't see any reason why the flight controller would fail because of the dodeca arrangement. It only knows the mixing is setup for a Y6 copter.

    I will also comment on the Gryphon frame. My experience with it so far has been fairly good. While I don't think the joint arrangement and locking pins are ideal, they have not been difficult to maintain. We have had them develop some play over hundreds of flights, but it is simple to replace the pins and tighten up the arms. I do like the idea of removable arms and the fact that the frame is roomy. It easily accommodates eight ESCs and the flight controller. I would like to see a more robust joint though. I worry about the pin threads weakening over time. It is also somewhat heavy.
     
  10. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0
    as requested by KW

    Props 18x6.1 tigermotor
    Motor Scorpion M4015-340
    ESC Castle Phoenix edge 40HV
    Battery 2x 16000 6S
    Flight controller DJI wookong M FW5.26
    Futaba 14SG and R7008sb using S-BUS.
    Take-off weight 16.6 kg (including 4 kg dummy weight)

    The DJI wooking is programmed in Y6 mode
    [​IMG]
     
  11. Steve Maller

    Steve Maller UAV Grief Counselor

    Joined:
    Oct 30, 2012
    Messages:
    3,979
    Likes Received:
    807
    Correct me if I'm wrong, but wouldn't it be better if you configured this copter as a flat hex and ran the upper/lower motors on each arm as a matched pair in the Wookong? That seems to me that it'd be a better match for the copter's geometry.
     
  12. Ryan McMaster

    Ryan McMaster Active Member

    Joined:
    Mar 8, 2014
    Messages:
    289
    Likes Received:
    40
    That is my thought as well.

    Any chance your motor timing is off or the ESC's have some bad firmware?
     
  13. Tim Gould

    Tim Gould New Member

    Joined:
    Nov 3, 2012
    Messages:
    19
    Likes Received:
    0
    Gryphon dodeca looks pretty cool. How are the retracts?

    I don't know if CC has made any recent changes to their firmware, but the last time I tested their ESCs, 75A Edge Lite back in March, they didn't always provide 100% motor power with fast throttle changes. The motors did not cog or lose sync, but the ESC would not provide full RPM. You could then back it down and ramp up slower to get the full RPM. This was with the ESC programmed in multirotor mode.
     
  14. Dejan Mugosa

    Dejan Mugosa Member

    Joined:
    Aug 21, 2012
    Messages:
    80
    Likes Received:
    26
    Well we did some stuff over email but what I would propose is that you try for start 16 top and 17 bottom cheap propelers.
    So you will be able to see what happenes when you overspin the motors to higher RPM. If this helps.
    But ofc this is test only since this will not be good for actual flying.
    Also if you have at least test the 17 top and 18 bottom propelers.
    And let us know what the results are.
     
  15. Dejan Mugosa

    Dejan Mugosa Member

    Joined:
    Aug 21, 2012
    Messages:
    80
    Likes Received:
    26
    I guess there was no proper research done.
    18 inch is not in even in spec so I guess it will draw too much for the motor to handle.
    Second the motors have an average off 1.4kg usable lift power.
    Lipo PROP V A RPM TRUST(g)
    TL2826 10*5.5 22.7 3.8 7525 600
    TL2827 11*5.5 22.24 6.25 7300 900
    TL2828 12*5.5 22.23 8.56 7175 1250
    TL2829 13*5.5 22.2 12.41 6925 1700
    TL2830 14*5.5 22.25 16.89 6700 2200
    TL2831 15*5.5 22.23 23.03 6325 2975
    TL2813 15*5.5 22.23 16.09 6725 2475
    TL2834 15*7.5 22.23 15.92 6675 2375
    TL2815 17*5.5 21.9 25.29 6150 3450

    I would try them with 15x5 top and 16x5 bottom.
     
  16. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0
    Hey Guys

    I agree with steve about programming this as a flat hexa.
    Regarding loading of the motor, i understand that we are only loading each motor with 1.4 kg.
    But the amount of throttle input during hover was averaged around 49%.
    what is the recommended loading Dejan?
     
  17. Roman Bugovskiy

    Roman Bugovskiy New Member

    Joined:
    Mar 8, 2014
    Messages:
    13
    Likes Received:
    2
    Hey,

    Geoffrey did you get that problem sorted out?? Really curious as I'm running into the exact same issues with my gryphon dynamics dodeca. Feels very 'floaty' after a super solid X8.

    Found a few very worrying issues with the gryphon dodeca frame. There was way too much play at the folding joints and I wasn't able to get the gains high enough for stable flight before serious vibrations. Had to use the braces so the whole folding thing is out the window as it's just not practical to be mounting the joint baraces every time we set up. After that there was still flex at the Z arms and I could easily push the two arms together and move them by about 10mm back and forth. Not good! For such a powerful machine that carbon needs to be much thicker. Having 4 motors supported by one arm is revealing itself to be a serious design flaw. Got it much stiffer by adding carbon tail pushrods from a goblin heli between the motors. Made a big difference.

    I'm using kde 5215 motors with their 75 amp esc, wookong, 18 inch carbon props, 4* 10000mah batts, flying the ronin/F5/prime, takeoff weight around 23 kg. The mixing is set to Y6 as per gryphon website.

    My issues are slow and wobbly response to wind and other external factors like decending quickly or hard flying. It just isn't springing back to level flight like I'm used to with the X8.

    I thought the rig was way overpowered so I put 16 inch props on the top. Seems to have helped a bit but still not ideal.

    Getting worried now due to the substantial investment made to fly heavy payloads but the results aren't living up to pro standards.

    Is the hexa configuration more stable?

    Dejan, any advice??

    Best
    Roman
     

    Attached Files:

  18. Geoffrey Bainathsah

    Geoffrey Bainathsah New Member

    Joined:
    Jun 22, 2014
    Messages:
    7
    Likes Received:
    0
    Hi Roman

    I'm glad that i'm not alone regarding this issue.
    No i still have not solved this and to be honest i think we are going to give up on the Gryphon frame.
    Especially since you have some of my possible solutions monted on your drone.
    I was thinking it could be the flex in the folding arm joint--> you have supporting carbon plates.
    I was thinking it could be the motor not having a stable joint to the arm --> you are using the X motor mount.
    I do agree with Dejan about the 17 inch props on top and 18 inch on the bottom, which helpen on my Gryphon X8.
    Maybe you can give it a try?
    If not, i would say the Z arm bend is not rigid enough and gryphon has to work hard.

    One question, what size dodeca frame do you have?
     
  19. Dejan Mugosa

    Dejan Mugosa Member

    Joined:
    Aug 21, 2012
    Messages:
    80
    Likes Received:
    26
    Again in my opinion wrong motors. 330kv is not good. 500 would be good and 600+ would be perfect.
    Well the gryphon is a little soft for the power you have. This is why we have our own frame.
    And in all test kopterworx did the hexa clone setup is not good.

    330kv is just to slow to react to the wind changes. Too slow and too much power on signe rotation off the propeller.
     
  20. Roman Bugovskiy

    Roman Bugovskiy New Member

    Joined:
    Mar 8, 2014
    Messages:
    13
    Likes Received:
    2
    It's 1200mm frame. I have 16 inch props on the top and 18 on the bottom. Still no joy. Think I have eliminated all the issues caused by the frame. It's very slid now after the mods.

    I'm starting to think it might be the motor mixing in FC. Maybe there is a better solution then advertised by gryphon, ie Y6.

    Hoping to hear some solid advice on this since I seem to have eliminated all the other variables.

    The dodecas are sold by kopterworx and other retailers at a pretty hefty price so these guys must have figured out a way to make these machines work best. Otherwise I would be very unhappy if that's as good as a dodeca performance gets.

    Best
    Roman
     

Share This Page