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How DOES the P3 gimbal work?

Discussion in 'Pro/Adv Discussion' started by jodyberry, Jul 27, 2015.

  1. jodyberry

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    Hi all,


    I'm loving our P3 and am totally amazed of the stability of the footage - especially when it can hover and sit there like it's on a tripod!
    Anyway, can anyone ELI5 how the gimbal is able to compensate so perfectly for the quad movement?

    I've been in the video industry for many years and have used and understand how larger steadicams work. But I'm still trying to figure out how this gimbal maintains steadiness. Does it use the GPS, or ground sensors, or neither? It looks like some sort of electromagnetic unit.

    Any links or info would be greatly appreciated!

    Thanks...
     
  2. loganboyd

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    It uses an IMU and then turns its brushless motors to counter the rotation in the Roll, Tilt and Yaw axis that is senses by the IMU (inertial measurement unit).
     
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  3. ianwood

    ianwood Taco Wrangler
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    It uses a combination of data from the flight controller, the compass and it's own IMU. Most gimbals only use standalone IMU data. When you bring in the additional inputs from compass and FC, you improve the stability of it.
     
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  4. taroh

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    The P3 gimbal is not so different from other usual R/C brushless gimbal, I think (actually I haven't disassemble the P3 unit, sorry). If you haven't have experience with usual R/C gimbal, start with SimpleBGC (Brushless Gimbal Controller): http://www.basecamelectronics.com/ . The technology is open, controller uses Arduino micro computer unit with 3 axis gyro sensors.

    In a simple term, the camera almost balances itself in 3-axis, like steadicam. The gyro sensor is attached at a point of the camera (few cm off the gravity center), and senses very slight moving. Then the microcomputer calculates which way to correct, and move brushless motors to opposite direction quickly. In principle, the moving is sensed after moved (off course :) ), so if the sensitivity of rotation angular is less than 1 pixel equivalent of the camera, the picture perfectly stands still (actually it allows few pixels moving, I think). The correction is not only on the big and slow movement (roll/pitch/yaw action of the copter), but also for motor vibration. I don't know about the P3 gimbal performance, but SimpleBGC 32-bit version can reacts 100-300Hz of the prop vibration, so does msec (100s of times per second) order correction, I guess. But P3 gimbal seems to absorb most of the vibration at the "white rubber" joint, and brushless gimbal does small.

    I've ever analyzed the P2 gimbal (Zenmuse 3D) signal, and knew DJI also uses body IMU as auxiliary sensor. If added the aux sensor "prediction" signal to the main gyro, the stability becomes better and quicker (IMU sensor signal is not the main one which absorbs moving, anyway). Also SimpleBGC has this function.
    The tuning of the microcomputer (PID control) is very important (and fun :) ) depending to the shape of camera, design of gimbal balance, prop speed, specs of aircraft, etc., and this decides the performance of the gimbal. P3 gimbal is specially designed for specially designed camera (also Zenmuse + GoPro), and the tuning is so adequate that everybody can turn on and get the super still picture.

    edit - P.S. Recently DJI becomes like camera maker :) , because the gyro + PID control technology is similar to the one for the helicopters stands still in the air. It's natural that the world's great helicopter maker becomes world's great steadicam maker.
     
    #4 taroh, Jul 27, 2015
    Last edited: Jul 27, 2015
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