All motors perfectly level or FC level?

Discussion in 'Cinestar 6' started by Gary McCready, Sep 7, 2013.

  1. Gary McCready

    Gary McCready Active Member

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    Q: How important is it to get all the motors as perfectly level with each other as possible? Is it more important to get the motors or the FC level?

    I was having a bit of GPS drift with my CS6 after the last update, 2.0. I leveled the FC, recalibrated, but it didn't help. I leveled the motors, which I assume is more important (the way I usually do it).
    When I placed my CS6 upside down on some glass two of the motors bolts (3 and 5 I think) were 3-4mm above the glass.
    I'm thinking to adjust the arms to level I would have to remove the camera gimbal and loosen and re-tighen every arm. How critical is this?
    Thanks, Gary in Salisbury, MD USA
     
  2. Brad Meier

    Brad Meier Active Member
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    You need to have the props all on the same plane. If you fly the copter in a hover at about eye level you can easily tell if the motors/props are out of plane. This is fairly high up there on importance. If they are not on the same plane you can have in commanded yawing and drfting.

    A good way to level the FC is by bringing up 3D view in MK tools. There you can tell what the FC thinks level is and reset as needed. The FC should also be on the same plane as the props.

    All of this will help stabilize your flying
     
  3. Gary McCready

    Gary McCready Active Member

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    Thanks Brad, but I am sure I can't tell 3mm difference while flying. Part of the problem is that 3mm is too small to see and the other problem is my eye sight is not very good. I think I might just remove the Camera gimbal, loosen the frame nuts and retighten while the motors are all level on the glass.
    I do have Xbee and can check the 3d View too, but not sure how accurate it is?
     
  4. Brad Meier

    Brad Meier Active Member
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    Try the 3d view while on the ground without the motors running. Ive found that when I level the copter, sometimes my 3d view shows that the FC isnt level. From here I just do another ACC calibration and things are fine.

    Also, its fairly easy to see the difference if the plane of the propeller disc is off when flying. You could probably even tell while its idling on the ground and you wouldn't have to concentrate on flying and looking for the angle. Be careful and only run the motors outdoors if you attempt the idle method.

    I have also done your glass method and it works most of the time. Start there if you like and see if that helps.
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Just out of curiosity guys, the "glass table" method is more about ensuring that the tips of the prop shafts are in the same flat plane, right?

    I think the other thing Gary may be asking about is ensuring that the axis of each of the prop shafts needs to be pointing straight up when the FC board is level. Put another way, the thrust axis of each motor is normal to the FC board (and thus all motors' thrust is vertical).

    I'm not sure the glass table really shows that all the motor's prop shafts are truly vertically aligned with respect to the FC. What that really shows is that the tops of the prop shafts are all in the same flat plane (and therefore they'd all touch the glass). My concern is the glass table technique is measuring whether or not the booms, clamps, and hub plates are all absolutely true -- and not so much whether the prop shaft is normal to the FC.

    Brad's absolutely right about the hovering at eye level and you can quickly see if one of the motors is canted over -- the disk formed by the prop blades is very evidently canted over.

    On the ground, I sight along the side of each motor's bell, and move my head until I can bring one of the battery posts almost into alignment with the motor bell. If you focus your eye on the motor bell, and then on the battery post, you can see the sliver of light between the two and can quickly eyeball whether the motor is not parallel with the battery post.

    Hope this helps.
    Andy.
     
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  6. Gary McCready

    Gary McCready Active Member

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    Thanks for the input guys! I know my motor are pretty much perfectly vertical to the long axis of the arm, I used a level. Someone even suggested using a board with the middle cut out. That way you would know all the motor plate bottoms were level with each other and the motors were all on the same plane. I know you would need to be careful about tightening the brackets very evenly, but it might be easier than trying to level each motor with a level.

    I think I explained it poorly. I can get my FC level, but then the motors are not. Or the motors are level (except 2 that are a bit off) and then the FC is no longer quite level. I've tried leveling the motors and then adjusting the screws to also make the FC level but it seems it doesn't seem to stay that way. I think it is because of the slight flex in the nylon nuts and bolts.So I decided it was more important that eh motors were all perfectly level and THEN calibrate the FC to that.

    Maybe I'm over thinking/analyzing things? Maybe it just needs to be close enough. It all started when I noticed 3 Esc (2,4,6) were hotter than the others, and I figured out it was my motors (5) was tilted. Fixed the tilt, fixed the problem with the Esc. But then I noticed my GPS had much more toilet bowl than the previous firmware. I also figured out that Arm 5 motor got tilted because I was holding it by that arm and it twisted slightly, lesson learned.

    After reading other threads I think the problem (GPS hold not as good) might be more with the firmware changes rather than my bird?? I have seen suggestions of GPS on 85 and Compass correction on "zero"
     
  7. Casey Van Nyhuis

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    Alright guys,
    Gonna have to throw a potential wrench into this whole thing ;)
    This is something i have been internally fighting for a while now but have finally chosen my new discipline. In theory you should have all of your motors perfectly level. But there is another strategy that has gone unmentioned which is to offset your motors in opposite directions 3 degrees. As most MK users know you can very often look at your GPX file and find that half your brushless controllers are drawing more amperage then the other half. I've found that with the 3 degree motor offset this can normalize those numbers almost completely in a lot of cases. It appears as though Mikrokopter has realized this already but for some reason it has always gotten put on the back-burner and is never talked about. To the point where MK even sells adapters to do this. http://www.mikrokopter.de/ucwiki/en/AngleAdapter
    It's a pain to do but i've started doing it on all my kopters. Download the app on your iphone called "angle meter" and it makes it a little less of a pain at least. For those that don't know, the idea behind this is that the 3 degree offset helps counteract the torque on the frame that the motor creates. This theory has already been tested and proven to work in airplanes to help counteract torque roll as well so the logic should still be sound when there are 5 or 7 more motors.
    I would love to have some other people test it and see if they all find the same thing as well though!!
     
  8. Gary Haynes

    Gary Haynes Administrator
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    Casey since there are lots of angle apps which one are you using?
     
  9. Casey Van Nyhuis

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    The one i'm using is called "angle meter". Looks like the seller of the app is "Jin Jeon" but i'm sure anything that gives you an angle will be sufficient. I'm sure it's not 1000% accurate coming from an iphone app but probably gets us as close enough.
     
  10. Steve Maller

    Steve Maller UAV Grief Counselor

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    Fascinating. Thank you, Casey!
     
  11. Brad Meier

    Brad Meier Active Member
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    Interesting idea but I'm not sure that torque on an aircraft with one engine or two spinning in the same direction is quite the same as an even number on out copters spinning the opposite direction. Each clockwise motor should be canceling out all torque effects of the counter clockwise. Unless of course you are in a yaw motion where odd and even motors are spinning at different rpms.
     
  12. Casey Van Nyhuis

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    That was my original thought as well which is why i never bothered. In theory they should balance each other out just fine. But in practice it seems that for most people they have half their motors/brushless controllers working harder then the other half and for whatever reason on kopters doing this, when i slant the motors in the way previously described it solves that issue completely. This is my theory- As of right now each motor has a list of jobs: giving enough thrust to maintain altitude, varying thrust to keep the kopter from yawing, and varying thrust to make attitude changes given by the pilot. It seems like this motor offset may relieve the motors of one of those jobs by counteracting some of that torque so that they can focus on their other tasks more efficiently. But i do realize this is an over simplification of something much more complex.
     
  13. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    One of the more interesting side effects is that angling the motors like that also means that thrust center line is no longer vertical.

    I'd be curious to know if one motor is producing an upward force of say, 1,000 grams (just chosen at random), and you lean the motor 3 degrees over from vertical, what is the new, reduced, upward force?

    I just did a quick back-of-the-imaginary envelope calculation (I wish I remembered trig better). I think the 1,000 gram lifting force will reduce to 998.63 grams. So, down 1.37 grams. If it's an octocopter, that's only 10.96 grams total. Doesn't seem like enough to worry about. Also, given, say, an AUW of 13 lbs (aka 5,896 grams), each motor is more likely to be producing 737 grams of lift to hover an octocopter, so the loss of thrust would be reduced.

    Anyone with a functioning math brain care to comment? :)

    Andy.
     
  14. Steve Maller

    Steve Maller UAV Grief Counselor

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    I think I'm going to give this a try. Which direction should the 3° be for CW and CCW props?

    [edit] Oops, just answered my own question. The MK site to which Casey linked above clearly shows which direction for which props...

    Safari-snap001.jpg
     
  15. Casey Van Nyhuis

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  16. Steve Maller

    Steve Maller UAV Grief Counselor

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    That's a lot of pressure. Not sure that's what I signed up for. ;)
     
  17. Gary McCready

    Gary McCready Active Member

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    Thanks for the input Casey. Obviously you are much more knowledgeable with your extensive experience. I was pleased learn that is was more important to get all your motors level, as opposed to the FC. That is the way I've been flying my CS for the past year. I have read about 3 degree tilt and was wondering why I never heard much about it on the CS.

    My son is somewhat of an expert on Multicopter "math". I'll ask him what he thinks the 3 degrees accomplishes? He did his Senior Electrical Engineering paper on it, and it (robotics) is still his current topic of study for his Masters.
    https://docs.google.com/file/d/0B4lHayyf4zkeLU1GVThzT1g0Tms/edit?pli=1
    PS He is super busy so I don't expect a prompt response.
     
  18. Casey Van Nyhuis

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    Well i'm certainly not qualified to talk about the physics of it all...but i can speculate and guess right? ;)

    I'm just going off of the numbers i'm seeing when testing and that's good enough for me :)
    Sometimes ignorance is bliss after all.
     
  19. Jim Swanson

    Jim Swanson Member

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    Gary,
    I downloaded you son's paper and read parts of it. I'm so confused and depressed, I don't want to fly anymore.
    Thanks for sharing.:eek:

    Jim
     
  20. Gary McCready

    Gary McCready Active Member

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    Your welcome Jim. Don't let it get you down, I don't pretend to understand any of it. I sure don't remember much of my college math, I became a dentist. (now retired)! lol
     

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