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Normal physical limitations?
  • Hi, mates.

    I have a medium-sized gimbal for DSLR cameras that makes little shakes/vibrations/oscillations in roll axis in extreme situations like high wind when flying, sudden stops when in high speed, heavy stepping, or leaving it roughly in the floor/table. It's my first brushless gimbal, and I use it for aerial filming with multicopter and by hand, and the roll bounces a little bit in those situations both in flight and by hand, although the shakes can be lessened through a really good PID/power tuning, but not completely solved. And that bothers me...

    After months of testing and searching I finally I'm wondering if I'm asking too much of the gimbal, and maybe this is normal in most of gimbals (bigger ones). Maybe it's just a normal physical limitation or imperfection...

    So, does your medium-sized or big gimbal roll axis shake/bounce in extreme situations?

    It would make a big difference to me to know that this issue is somewhat normal...

    Big thanks.
  • It depends what is considered as extreem situation, a video would help to say if it is normal or not
  • @Garug
    Hi. I made this video:

    http://youtu.be/-YljYJZPgJs

    The gimbal is turned off, and this bouncing also occur when turned on.

    In the video I'm hitting hard the roll axis, but something pretty similar happens when the gimbal is shaken roughly, like when leaving it on the table/floor.

    So, is this bouncing normal? I'm guessing it happens because of the physical design and the flexibility of some parts.

    I don't think that would be the cause of my roll vibrations in the roll axis in extreme situations, mostly because it would make vibrations in the pan (the yaw of the camera), not in the roll, but I need to know if this bouncing is normal for a gimbal like this, and if a perfect stabilization can be achieved anyway.

    Any advice will be welcome.
  • Based on video I suspect camera is not firmly enough attached. How is the IMU attached, it seems to be on air.

    Battery on roll gage? I suppose it is there as counter weight for motor to balance the roll, but if so it should be evenly distributed around the roll axis, not above it. I.e. it should be on side, and really well fifed.

    Camera is really low to be balanced?

    Also it would be good to remove everything that is not firmly fixed, like the hand grip.
  • Thanks a lot for the reply.

    The camera is firmly attached, it doesn't move a bit from the plate.

    The IMU is fixed with screws at the same part the camera is attached, and it doesn't shakes by itself or anything, I've checked.

    The battery, the pitch motor and the camera seem to be perfectly balanced, I make sure everytime I put the camera.

    Anyway, the “bouncing” happens even without camera, battery, an all, it seems to be a normal physical condition of the design and the materials, but I'm curious to know if it's really that normal (something similar happens to your gimbals) or if it shouldn't be that way.
  • There is always flex on the structures, the question is just how much, that is just physics.

    Even a relatively small flex causes easily vibrations and it is vibrations we are seeing on the video. These could be PID tuned away, but if the structure is flexing too much, the result would not be good.

    Looking the microphone on the video in relation to gimbal parts, it seems that the microphone is vibrating much more than gimbal parts.

    About gimbal balance, I still have to ask, because on video the camera seems to be really low (But that might be the angle the video was taken causing that illusion)

    If you roll or pitch the camera power off, does it really stay in any position you put it into? I.e. not return to level position. No offence meant, but I have seen just too many times on the forums the definition of gimbal balancing misunderstood.
  • Thanks again for the response. It's very appreciated, really.

    Now that you mention it, when the gimbal is turned off (that is, disconnected from the battery), the pitch and the roll axes usually return to the original position, especially the roll, but also pitch if the angle is too different from normal. Is that good or bad? :S

    I thought that this is how it should be since I don't know how could the axes be left in the position. They naturally return to the original angle due to the camera weight, or even the weight of the axes' materials themselves. The motors don't have any torque if there's no voltage... Anyway, the camera always return to an almost perfect horizontal angle, which is what I think it's “balanced”. Any advice will be much appreciated.

    The camera is right in front of roll axis' motor (or maybe just a centimeter to the left, is that bad?), just at the same vertical level. I don't know if it's too low anyway... :S

    It's also true that the camera shakes more than the gimbal parts themselves, but I guess it's because the camera is just at the less rigid part, the plate that holds it in the pitch axis. But as I said, it's weird this bouncing doesn't seem to affect the video very much (just a little bit in the horizontal when hit too hard) since the camera has a couple of stabilization systems by itself, so the roll vibrations must be originated by something else.
  • That is exactly the general misunderstanding of definition balanced gimbal.

    A balansed gimbal should not return to any position when power is off, it should stay on what ever position the camera is set to.

    Unbalanced gimbal will just not work well.
  • About the gimbal balancing. The user manual does not do a great job explaining it, this is from the 32 bit users manual.

    "Mount the camera on the tray and balance the gimbal in all three axes. Stabilization quality strongly depends on balance quality. To check your balance, pick your turned off gimbal in hands. Make fast motions along all axes, try to catch resonance point and swing the gimbal. If it is hard to do - gimbal is balanced correctly."

    This is one good way of testing how well the balancing was done, but does not really explain how to balance.

    To balance the gimbal you should:

    1. Power off.

    2. Verify that angles between all axis are 90 degrees, and pitch and roll axis are in same level. verify that the gimbal fees solid and that everything is well attached to it (no loosely attached weight, that will cause problems) also verify that everything moves freely i.e that the gimbal is correctly assembled.

    note: Everything that is installed during normal use needs to be on place, for example if battery is installed above yaw motor, it needs to be there when preforming the balancing.

    3. Keep roll levelled, start from pitch. Set the camera to a location where the pitch orientation stays in any position it is set to. Do this by moving the camera up/down, back/front as needed.

    Note: To be clear, the camera must not return to level position. It must stay in any position it is set to, lens up, lens down, level. it must stay on that position after you let go of the camera.

    4. Now do the same for roll axis. it should not matter on what pitch angle the camera is as it is already balanced. There is couple of ways of balancing roll. Often camera can be moved left/right or the hole roll assembly from where it is attached to the roll motor. This depends of your gimbal.

    Note: it is important that the weight is evenly distributed around roll axis. some assemblies makes possible the roll arms rotating up/down, they should be on same level and direction with roll motor axis. Also now weight above or below roll axis.

    5. Balance the yaw: at this time it does not matter on what position the roll or pitch are as they are already balanced. To balance the yaw, first turn the gimbal handle 90 degrees left (or right). The yaw axis is now horizontal. Move the hole roll/pitch assembly front/back as needed so that it stays in any position it is set to. (There should be mechanism allowing moving the yaw motor position front/back related to other parts.)

    6. perform the above mentioned test and you are done. (that test work great with big cameras and gimbals, but maybe not so great with small cameras.)

    7. If you change camera lens, zoom the lens, add filter or any other accessory, the complete balancing needs to be done again. But often small unbalance is manageable, so you may be able to use the zoom like I do here.

  • " for example if battery is installed above yaw motor" above yaw motor (on handle) it does not matter I meant to say above roll motor.
  • Wow, thank you very much, Garug, it's really appreciated.

    The person who sold me the gimbal, and mounted it, didn't know a thing about gimbals, I'm more positive everytime. He didn't told me any of that, and the gimbal was wrongly mounted in many ways (for example, my camera almost falls...), and the software was awfully configured. I must fix everything myself searching, trying and getting help from you, mates.

    Also, it's too bad that the manual isn't as accurate or detailed as it should be in some matters... Like balancing and PID tuning.

    I'll try everything you explain to see if it improves. Although I don't think that pitch and roll will keep steady in some angles...

    So, isn't mandatory that the camera remains just right in front of the roll motor, it can be some centimeters right or left? Maybe I could move the center of gravity of the roll axis moving the tube as well as the camera position in the pitch to make that possible. Should the roll be balanced even without a camera, or the balance only really matters when the camera is there?

    The roll arms are a little bit upwards. I found that weird, but I though it was like that because the pitch motor should be at the same level as the roll one. Should the be horizontal anyway?

    Sorry for so many questions... I'll explain how it works as soon as I can. Best regards.
  • The Roll and pitch motors should be on same level and their axis cross, The gimbal only needs to be balanced when you have everything needed on it and you can/should use the camera positioning to balance the gimbal.

    8 bit controller with one IMU can operate in any angles if firmware 2.4 is used and 'estimate frame angles from motors' is used. I am currently testing 32 bit board with 2 IMUs and it provides much needed reliability when operating in non normal angles. like in this video (this is still with 8 bit controller)



    I will write a review later on about the 32 bit board when I have gained more experience on it. It has problems too, it is not easy to get everything working perfectly...
  • So I balanced the gimbal. Now the roll axis stay in level at every position, with or without camera.

    But since the gimbal is a CineStar 3 copy, the camera in the pitch axis can't be moved up and down (especially up as I would need), so the pitch never stays in level, but always returns to original position... I wonder if that too-low-position could be causing the roll vibrations by inertia or something.

    I'll keep testing and trying with this gimbal, but as soon as I earn some more money I'll buy a really good one. That is, if I can't achieve a perfect level of stabilization as I wish.
  • It should not stay level!

    Power off, it should stay in any position you put it into when the camera and lens is attached (if you change camera or lens it needs to be rebalanced.). This goes for all axis. Any gimbal part should stay in what ever position you put them, not return to any position.

    It does not mater how it is balanced without camera. No need to balance without camera. Just to make sure that all axis are 90 degree to each other and that it is balanced with the camera and lens (+ filters etc.) you will use it with.
  • @Garug
    Thanks a lot for the reply.

    That's what I meant, not sure about the meaning of “stay level”. I'm not native English.

    Anyway, the axes stay in the position I put them, now even roll, except for pitch, as I explained. Pitch works well, maybe the best-working axis for my gimbal right now, so the unbalance of it only could slightly affect roll, maybe, if anything. Maybe if I get tired soon I try to change the pitch part to be able to move up and down the camera, and improve the gimbal performance before buying a new, more expensive one. It won't be easy, though. I don't know how to even start. But I'll figure out something.

    Apart from that, I'm still trying with different PID settings. I fear lowing P too much will be worse (especially for handheld), but maybe that solves the roll fast oscillations in flight. When P is high, the roll axis is much more stiff, but there are more oscillations in roll when speeding up. So maybe the question is finding just the exact amount of P and D... I guess it would be easier with fully balanced axes, but...

    Do you recommend me trying Gyro LPF, or it complicates things even more, or do you think it won't help with the roll oscillations?
  • Ok, sorry I misunderstood, I am not native speaker either.

    I have used the Gyro LPF on a much bigger gimbal and on that it helps, I am not sure how useful it would be on this small gimbal, but does not harm anything trying.

    When tuning Power and 'I' are equally important with P and D. They all need to be reasonably well set.

    It is good to remember that the axis do interact with each other, so everything needs to be balanced, everything needs to be tuned for the axis to work perfectly. Usually good to start getting Pitch good, then Roll and Yaw and return to Pitch (and Roll and Yaw) if necessary.

  • Thanks again.

    Yeah, I know. Software-wise it's pretty accurate now I think, just need to keep trying different P and D, maybe Gyro LPF. Power and “I” values are at their best, judging by the several tests I did. Not so sure about P and D, though. I can't get them to give me concluding-enough results, possibly due to the pitch unbalancing.

    That pitch balancing impossibility bothers me, because it could be the culprit of the roll occasional oscillations. I can't be sure, though.

    I'll keep searching and testing and I'll comment some more.
  • You absolutely should get the pitch balanced, if badly unbalanced it affects everything.

    On your gimbal you could rotate the pitch, lets say to 30 degrees and then rotate camera + IMU back to level. this would raise the camera and maybe help balancing it.

    Or maybe you could just drill new holes to the supports to get the camera raised. To balance pitch the camera needs to be up/down and front/back in correct position.
  • Do you mean raising the camera position changing the pitch axis start angle?

    I wonder, what if I just raise the roll arms to some higher level? I thought about that, but I don't think it would work too well, so I didn't even try it...

    Anyway, I guess I won't lose anything for trying...

    Thanks.
  • Do not think it as changing pitch angle.

    The camera + IMU is returned to level, so the pitch angle is not changed, only the geometry of the pitch assembly.

    You should use what ever means help to get the pitch balanced, it is really mandatory for the functionality.
  • I'll definitely try raising the camera center of gravity by changing or moving the pitch part, or by making new holes to it to lift the parts, or something, whichever works best.

    Thanks a million, Garug. You're of huge help, seriously. You explained useful and interesting things when nobody else seemed to know or care.

    I'll be commenting when I try something more. Best regards.
  • If you don't have enough room to adjust the camera plate up/down, I found the the pitch arms can be adjusted up/down to help balance the camera. In other words, the pitch arms do not need to be perfectly level to work well. Things I did find important are the distance of the pivot points from the roll arm, and if you adjust the pitch arms, they must be at precisely the same angle. Let me know if you understand this, I can post pics if you need.
  • @soulpatchfilms
    Thank you very much! I understand perfectly, I really appreciate the assistance. Some pictures could come in handy for further reference/details, though.

    I thought about doing that arm rotation fix, although I didn't think it would work too well since it wasn't so good balancing at all (the camera is still too low from the pitch motor) and I thought the arms should be horizontal anyway. But I'll definitely try it. I need to balance the pitch somehow to see if the roll oscillations disappear for good, so it's worth trying.

    Best regards.
  • After all this time I found using an adequate design, proper materials, good balance and achieving perfect firmware config/tuning, almost every brushless gimbal can be very stable when used correctly (the operator is very important as well).

    There probably will always be some little movement in some situations, but I think it's completely normal and it can be corrected if desired using image stabilization with a good lens, or even software. The most important thing here is getting the most stable footage right from the gimbal.

    I've learned a whole lot this year and a half... :)

    Best regards.