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Advantages of 3-axis over 2-axis for UAV?
  • abcharlie
    I'm experimenting with 2 and 3 axis gimabls on a quadcopter - it seems the Y-axis is only really important for handheld gimbals, not airborne - can anyone confirm this? Without Y-axis, the gimbal becomes significantly lighter, with it there's not much improvement on the image...
  • Garug
    Yaw stability of many multi copters is not that great and control not that smooth. Gimbal Yaw axis will help on this.

    Also it requires more skills to fly any Yaw orientation and if there is a camera man, having separate control for Yaw helps.

    I am currently using 2 axis cimbal for flying.
  • djmorgan
    3 axis has advantage on any UAV as they can be very twitchy and the ability to control the yaw is evident in videos.

    Not a requirement for FPV but if you are going to do AP then 3 axis will be superior (smoother) to 2 axis

    Does not negate the need to have a vehicle well set up in terms of vibration minimised.

    David
  • djmorgan
    ....
  • kikojiu
    djmorgan it is always useful to use a 3 axis gimbal even if you leave it in follow mode and don´t do any movements with the yaw...Everytime you upset the gimbal roll axis i.e., it always makes the yaw move and try to compensate...this is physics. How does this reflect in flight? You will have a very difficult time in flying with the camera stable on the yaw axis. Instead of the yaw axis "absorbing" some energy when the roll or pitch are upset the energy will be counteract by the multirotor making it slightly move side to side making the shot unusable. This is not theory this is practice. I also flys multirotor for a living and I can only have very stable footage with a 3 axis. Of course you might on a calm day and if you let the multirotor free to deviate from its path to get smooth footage, but you can´t tell when it will happen. How many times I started a shot and it was ruined by a 2xis gimbal...
  • djmorgan
    kikojiu
    I also fly 3 axis and my post was meant to say that 3 axis is better than 2 axis!
    Your response seems to be contradictory! Yes the biggest issue I face is the small side to side movement from the yaw axis reacting to vehicle movement and gimbals actions, this does not occur with a 2 axis system but there are other disadvantages to 2 axis especially in panning.

    Your response seems to indicate 3 axis produces unusable shots except on calm days, I'm sure you didn't mean that :-)

    David
  • abcharlie
    Thanks for all the input, most instructive, I guess I'll be putting that third axis back on...
  • kikojiu
    djmorgan...the side to side movement on the yaw axis on my rigs only happen with 2 axis gimbals...the 3rd axis always compensates the side to side movement.
  • Garug
    By "the side to side movement on the yaw axis" I guess you mean the actual multi copter Yaw movement showing on video.

    That can be controlled to some degree with Flight controller Yaw parameters, but it is always there in some conditions. I kind of have now 2.5 axis controller on one of my multi rotor gimbals. the .5 is a passive Yaw suspension about +- 5 degrees. That helps but does not make it perfect. I will continue trials with this 2.5 axis for two reasons:

    1. weight
    2. camera in front

    The camera in front makes it possible to tilt completely up or down without any parts of the multi copter showing, but having actual 3rd axis on it would require more advanced control of Yaw axis than today available on AlexMos boards. This is as the camera Yaw movements need to be limited to some +- 15 degree, so that propellers do not hit it. The missing functionality is that it would always start parallel to the multi copter and keep the average direction on parallel to the multi copter.

    But I think I will now build a true 3 axis multicopter gimbal too, camera at the centre of the multi copter.
  • kikojiu
    Garug yes. I mean the yaw movement when the path is corrected during flight. On a 3 axis gimbal the yaw movements are less noticeable as the 3rd axis corrects with to some extent. Also when the roll is upset on the gimbal i.e. wind or multirotor sudden movement there is a force applied to the 3rd axis which is partially absorbed by the motor of the axis to smoothen the roll movement. Anyway each one has its own experience and I use mainly the 3 axis gimbals when I am working with a dual operator rig. Flying and filming alone I wouldn´t use the 360º of the gimbal...but that´s me...
  • gtranquilla
    Another benefit of having the yaw axis working is that a straight line heading towards a target can be maintained aoutmatically even if the Multirotor tends to yaw during the flight due to crosswinds etc. Best example is a flight from a fairway teebox to the green. Having the camera suddenly aimed a few degrees to starboard or port really spoils the video. But with the yaw axis that is far less likely to happen. Ofcourse have FC tight heading control to target would be the better choice..... but good luck with that!
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