Alexmos 32bit Tuning Guide

Adjusting the mechanics

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.

NOTE : Good balance and low friction can scale down power consumption and keep good
quality of stabilization.

If you rewound motors by yourself, it’s recommended to check winding. Remove motors from gimbal, connect them to controller and set parameters P=0, I=0.1, D=0 for each axis and set enough POWER. Connect main power supply. Motors should spin smoothly, while rolling the sensor. Little jitter is normal due to magnetic force between rotor and stator (“cogging” effect). Pay great attention to sensor installation. Its axes must be parallel with motor axes. Pay attention to mechanical links. They must be a VERY RIGID and backlash-free. Sensor provides feedback data for stabilization, and even any little freedom or flexibility will cause delays and low-frequency resonances. This can complicate setting of PID, and cause unstable work in real conditions (frame vibrations, wind,
etc)
How to Balance DSLR Camera

[wp_lightbox_prettyPhoto_video link=”http://www.youtube.com/watch?v=ZzKYVKiNkWc” width=”800″ height=”600″ description=”Step by step guide to balancing DSLR and Larger Cameras” source=”https://aerialpixels.com/wp-content/uploads/2014/02/Matte.jpg” title=”Step by step guide to balancing DSLR and Larger Cameras”]

 

2. Calibrating the sensor

Gyro is calibrated every time you turn the controller on, and it takes about 4 seconds. Try to immobilize sensor (camera) as hard as you can in first seconds after powering on, while signal LED is blinking. After powering on you have 3 seconds to freeze gimbal before calibration starts.
If you activated option “Skip gyro calibration at startup”, gyro is not calibrated every time and controller start working immediately after powering up. Be careful and recalibrate gyro manually, if you will notice something wrong with IMU angles.

Calibrating Accelerometer

You must perform ACC calibration only once, but it’s recommended to recalibrate it from time to time or
when the temperature significantly changes.

  • Simple calibration mode: set the sensor horizontally, and press CALIB.ACC in the GUI (or menu button, if it’s assigned). LED will blink for 3 seconds. Try not to move sensor during calibration. At this step no matter how camera is leveled. You are calibrating the sensor, not the camera!
  • Advanced mode (recommended): perform calibration in simple mode as above. Then turn
    sensor in order that each side of sensor looks up (6 positions at all, including base one). Fix the
    sensor in each position, press CALIB.ACC button in the GUI, and wait about 3-4 seconds, while
    LED if flashing. The order does not matter, but the base position always goes first (because the
    simple calibration cancels a result of advanced calibration). You have not to press WRITE
    button, calibration data is written automatically after each step.
    NOTE: Precise accelerometer calibration is a very important for horizon holding during
    dynamic flying or YAW rotation.

Alexmos 32bit 6 Point Calibration

4. Tuning basic settings

  • Connect the main power supply.
  • Set POWER according to the motor configuration (see recommendations above)
  • Auto-detect number of poles and motors direction. Do not proceed to next step until proper direction will be detected!
  • Adjust PID controller. To check stabilization quality, use peak indicator in the control panel(shown by the blue traces and blue numbers). Incline the frame by small angles and try to

Minimize peak values by increasing P, I and D to its maximum. You may use gyro data from Real-time Data tab to estimate stabilization quality, too. Better to tune PID with the “Follow Mode” turned OFF for all axes.

 Suggested algorithm for PID tuning:

1. Set I=0.01, P=10, D=10 for all axes. Gimbal should be stable at this moment. If not,decrease P and D a bit. Than start to tune each axis sequentially:

2. Gradually increase P until motor starts oscillate (you may knock camera and see on the gyro graph, how fast oscillation decays). Increase D a little – it should damp oscillations, and decay time decreases. The lower is decay time, the better.

3. Repeat step 2 until D reaches its maximum, when high-frequency vibration appears (you may feel it by hands and see noisy line on the gyro graph). Current P and D values are maximum for your setup, decrease them a little and go to step 4

4. Increase I until low-frequency oscillation starts. Decrease I a little to keep gimbal stable. Now you found a maximum for all PID values for selected axis. Repeat from step 1 for other axis.

5. When all axes are tuned in static, try to move gimbal’s frame, emulating a real work. You may notice that cross-influence of axes may make gimbal not stable. In this case, decrease a little PID values from its maximum for axes that looses The result of good tuning – stabilization error is less than 1 degree when you slightly rock a gimbal’s frame.

6. Testing gimbal in real conditions

Connect controller to the GUI and turn ON multirotor motors, holding it above your head. Check the vibrations on the camera by using Realtime Data tab / ACC raw data. Try to decrease the level of vibrations using soft dampers.

 

NOTE: Brushless motors versus traditional servos provide faster reaction, but less torque.That’s why it’s hard for them to fight against wind and air flows from props. If you are developing multirotor frame by yourself, try to avoid this influences (for example, lengthen arms a bit, or tilt motors away from center or place camera above props in case of H-frame). Also bear in mind, when copter moves with high speed, an air flow is deflected and can affect the gimbal.

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