Cold temperatures

Discussion in 'Radian' started by Peter Eriksson, Jan 13, 2013.

  1. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    Will temperature shifting have any affect on the radians?

    I today noticed when i was gain tuning that after a while the roll radian has a hard time keeping the level correct (off by 10deg), i was flying sideways right to left with smooth movements. If i keep copter level after a while (5-10 sec) . it levels out again.

    I started the copter inside +20 c and went out flying in -20, my thinking that the calibration of the radian mismatch when "calibration" temo and flying temp differs?
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,369
    Likes Received:
    1,162
    Hi Peter:
    -20C? Wow. You're brave.

    My guess is that everything will be affected by the temperature but mainly the mechanical stuff, ranging from the gears in the servos (and the grease on the internal gears), to the drive belts getting stiff, and the vibration isolator rings getting more rigid.

    Of course, that kind of temperature also affects the LiPo's and their power output. Usually with electronics the problem is keeping them cool, so I suspect that the boards, and the Radian sensors electronics should be OK. What I don't know is how well nanoscale accelerometers adapt to -20C, though -- which is maybe the heart of your question.

    If JohnC sees this posting he will be able to answer more authoritatively than I can.

    Andy
     
  3. Tim Joy

    Tim Joy Active Member

    Joined:
    Aug 2, 2012
    Messages:
    405
    Likes Received:
    72
    I don't think it's the cold. I have been very impressed with the radian in the cold, and have seen no ill effects down to 0 F. My camera OP actually messed up the roll level because we were on the side of a mountain with many confusing angles. If he would've left it up to the radian the horizon would be level! LOL.

    I have noticed, like all the gimbal stabilizers I've tried, the radian will lean into the movement on fast motions. It's most noticeable with the roll on a tracking shot (camera sideways). This is why I allow my cam OP to slew the roll. (normally it's on low rates set at 0 so he can't accidentally move it, but he can flip to high rates and adjust)

    My question is- WHY does it lean like all the rest? How about an input command to "notify of upcoming angled gravity vector". :D
    If I knew what I was talking about it might be dangerous...
     
  4. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    I tried having the hexa sit out in the cold for 5 min and then starting it up and flying, same thing.

    I think what i´m seeing is what Tim Joy is talking about, the radians as you say tend to lean if going fast to the side, this is a big problem with MK stabilisation to.

    I never thought that this would be an issue with the radians also....this is not good when flying solo.
     
  5. Tim Joy

    Tim Joy Active Member

    Joined:
    Aug 2, 2012
    Messages:
    405
    Likes Received:
    72
    Peter, by keeping your starts and stops gradual and smooth it will help keep the issue to a minimum.

    It must be a tough problem to solve. The only ones that seem to have cracked it is DJI with the zenmuse, but they trade off short-term roll drifting for a roll that goes all over the place the rest of the time!
    I've noticed that my sensitivity to seeing an un-level horizon is less than a half of a degree.
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,369
    Likes Received:
    1,162
    Do you find that if you lower the roll gain a little bit (2% - 4%) that it helps with the "leaning?"

    Andy.
     
  7. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    I lowered gain from 130 to 125 but the difference is not noticable, i think even if i fly smooth and slow i see leaning. I havent measured the offset but it is quite noticable just bu looking at the gimbal when flying it, severel deg i guess, 10 deg maybe
     
  8. Tim Joy

    Tim Joy Active Member

    Joined:
    Aug 2, 2012
    Messages:
    405
    Likes Received:
    72
    Don't think so. I think that might make it worse.
     
  9. Philip Ellerbroek

    Joined:
    Oct 8, 2012
    Messages:
    139
    Likes Received:
    7
    Peter,

    As of two months ago, I have had you exact issue as well. Three changes may have contributed. I moved from a Canon T4i to a Mark3, which is much heavier. Also, day temps dropped about 30 degrees F as we have entered the winter months here in the desert. Third, I upgraded my Radian firmware. I can tell you that I just adjusted my o-rings to be more stiff. I changed half of them to blue from Red. I noticed this helped noticeably but I believe I may switch them all to blue.

    Regarding Andy's above suggestion of lowering the roll gain...... I left my Roll Gains at 120 because I saw no improvement going up to 135/155/175, as well as 80/100/115. Actually, I noticed this sway issue increased once I lowered the gains below 115. Maybe there was a change in the roll radian firmware settings that I uploaded that could be causing this?

    I also believe I could benefit from a more stiff gimbal plate, which is said to be coming out soon. Many on the forum have done their own modifications. This may also help.

    I personally believe that the underlying mechanical issue may be from the horizontal gimbal shaft that connects to the gimbal plate. (this would be the vertical carbon fiber shaft that the roll radian servo attaches to). It seems to me that if extra weight is added to the gimbal tray in the form of more electronics or bigger cameras, that the entire gimbal "swings" like a pendulum more due to the added weight. ( view this movement: http://en.wikipedia.org/wiki/File:Oscillating_pendulum.gif )

    This is magnified if the o-rings are older and stretched out or if the temps change therefore affecting the o-rings. Lastly, if the gimbal plate flexes and allows this shaft to swing (think of a pendulum on an old clock), what may be happening is if the gimbal tray swings or sways it may be affecting the sensory input/output of the roll radian. Another effect that has been mentioned has been "bottoming out", which is a term that refers to the gimbal swaying and the springs/dampeners reaching their maximum movement point. Once this occurs, the gimbal can not sway any more and there is a "flicker" caused due to the inertia that transfers down to the bottom of the gimbal.

    The aim is then to have your setup (roll gains, o-rings, other dampener mod's) in a way that keeps the copter, plate, and gimbal in a aligned and sturdy structure so that the gimbal doesn't seem to sway. On the other hand, if you get everything to tightly connected, you will likely see vibrations transfer from the copter down into the gimbal and therefore your video will see vibrations. Its a delicate balance that equates to each copter being calibrated for temps, elevations, camera weight, flying style. You may need to also change setups if o-rings get too old.

    I've found that picking the copter straight up helps with not stretching out the o-rings and therefore adding life to them, and avoiding picking up the copter by a boom near the hex plate and lifting it up to where one of the booms points to the sky because this puts all the weight of the gimbal and camera onto on set of dampener springs and this can really stretch them out. For example, I used to always pick my copter up in this manner on boom #5. When I was removing all my red o-rings for replacement, I compared the springs from the dampener closest to the boom #1 position and could see that these springs were much more stretched than all the others because of the constant weight and stretch placed on them.

    Finally, it should be said that none of this should be altered until you can say you have properly balanced your entire gimbal and camera. If the servos are struggling to "move" the axis and camera, this could not only slow the roll movement thus causing a sway delay, you are also unnecessarily stressing the servos.

    This is my very unofficial two cents, but I've been struggling to solve this as well and have been reading a lot throughout the forum on this. Also, you should know that I have no vibration issues. This simply revolves around what I now call "horizontal roll". At this point I'm fairly satisfied with the end results having replaced some of my o-rings, although I think I need to strengthen my gimbal plate still and my also put all blue o-rings on. In the end, I think the biggest factor is flying technique that is smooth, slower, and level whenever possible.

    Phil
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,369
    Likes Received:
    1,162
    That's an excellent synopsis, Phil.
    As you say, the gimbal has to act as a pendulum -- it has no other choice.
    Andy.
     
  11. Joe Azzarelli

    Joe Azzarelli Active Member

    Joined:
    Jul 13, 2012
    Messages:
    210
    Likes Received:
    26
    Andy, is the 'choice' algorithm a part of the latest firmware update? ;)
    (Happy New Year)

    Joe
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
    Staff Member

    Joined:
    Jul 31, 2012
    Messages:
    10,369
    Likes Received:
    1,162
    Hi Joe:
    Nice to hear from you. And HNY to you too.

    Yeah, there's a new checkbox on MK Tool:
    Gimbal to act like pendulum or not: [ ]

    Andy.
     
  13. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    I actually made a mod yesterday to make my mount moore stiif, one of the mods covers the pendelum effect, i dont think this will affect the leaning issue but the overall behavior is better after this i think.
    I had firmware 1.03 so nothing done there.
    I have put zip ties around my orings and the mount it really solid.
    At the back of the horisontal boom on the mount a have put soft foam to stiffen the whole structure up.
    I could raisr my gain on roll to 140 after this with grear result. Also changed up my gyro settings on mk quite alot.

    The leaning remains but on set i dont think it will be a problem when i always fly ultra smooth, but for testing i will be visible.......
     
  14. Jim Swanson

    Jim Swanson Member

    Joined:
    Jul 13, 2012
    Messages:
    97
    Likes Received:
    6
    Hey Peter,
    I'm always curious what mk settings people are using. Sometimes I think the mk's over-react to wind and control inputs...this in turn can create little movements on the gimbal. Do you mind sharing?

    jim
     
  15. Philip Ellerbroek

    Joined:
    Oct 8, 2012
    Messages:
    139
    Likes Received:
    7
    Peter,

    In addition to Jim's question, what size camera/lens are you using? What is their combined weight? I ask because if you have similar weight I'd like to use your MK settings now that you have adjusted and are happy. This may help me with my issues.

    Phil
     
  16. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    Sure i can post my Gyros, just need to get the from the laptop, I use GH2 with 14-42mm and 20 mm lense. Xoar props 14x5

    I have always been a High Gyro D settings type and have always promoted it, but my latest findings is way from the settings that i used to have. I´ll post before and after...try to get some pics also of the mount
     
  17. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    When i fitted my radians i also changed my props to xoar and this got me thinking that maybe the stiffer props gets stiffer more responsive reactions on the copter.
    I have been seeing werry small shakes at times and this might be the props, i will try this and get back

    I think it is important to say that a copter with small twitches will never get good performing radians!
     
  18. Philip Ellerbroek

    Joined:
    Oct 8, 2012
    Messages:
    139
    Likes Received:
    7
    What are your gains? Try lowering them 10 to 20 %. They may be too excited (sensitive).
     
  19. Peter Eriksson

    Joined:
    Jan 10, 2013
    Messages:
    30
    Likes Received:
    0
    Well it was not the props, no difference. Looked at old videos and before the radians this shake was not there.
    Gain on roll @120

    Gyro settings
    P=140
    I=120
    D=25
    DynamicStability=75
    ACC_Gyro-Compensation=200
    Stability=6
    Main-I=5

    Also tried
    P=165
    I=60
    D=5
    DynamicStability=75
    ACC_Gyro-Compensation=200
    Stability=4
    Main-I=5
    This setting gets really loose flying
    Going for roll disable to limit out radians next flight.

    Now time for a cold beer :)
     
  20. Philip Ellerbroek

    Joined:
    Oct 8, 2012
    Messages:
    139
    Likes Received:
    7

Share This Page