Enabling Extended Kalman filter (EKF) on IRIS+

IRIS+ runs the opens-oruce flight control software APM:Copter. With version 3.2 – which was released on November 7th, 2014 – an interesting new feature was introduced: Extended Kalman filter (EKF).

On your IRIS+ the EKF  uses rate gyroscopes, accelerometer, magnetometer, GPS and barometric pressure measurements to estimate the position, velocity and angular orientation of the flight vehicle. Taking all these sensor values into consideration at the same time allows the EKF to reject measurements of an individual sensor with significant errors. This way IRIS+ becomes less susceptible to faults that affect a single sensor, such as an accelerometer.

Unfortunately this feature is not turned on by default in version 3.2 of APM:Copter. But it is very easy to do so, if you are already using Droidplanner or 3DR Tower on your Android tablet as a Ground Control Station (GCS).

Required software and version

  • DroidPlanner / Tower: The current version of DroidPlanner2, available on Google Play or Tower (DroidPlanner 3), which requires 3DR Services as well.

How-to use
Power-up your IRIS and your Android tablet, then connect Droidplanner or 3DR Tower to IRIS+ via the wireless radio. This is basically the same procedure as getting ready to fly with your GCS.
There is no need to arm IRIS.

Open the “Menu” and select “Parameters” (See Figure 1).

Figure 1: Parameters screen

Figure 1: Parameters screen

Droidplanner / 3DR Tower will load the current APM:Copter parameters from your IRIS. This can take a few seconds.

In the list of parameters, scroll down until you find the entry “AHRS_EKF_USE”, which should have a value of “0” by default. Tap on the value “0” and change it to “1” (See Figure 2).

Figure 2: Change AHRS_EKF_USE parameter to 1

Figure 2: Change AHRS_EKF_USE parameter to 1

Now save your changed to IRIS parameter by tapping in the upper right corner on the three dots and then choosing “Upload Parameters” (See Figure 3) and power cycle IRIS.

Figure 3: Upload Parameters

Figure 3: Upload Parameters

That’s it. Now your IRIS will use EKF, making it less susceptible to faults that affect a single sensor, such as an accelerometer.

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3 comments on “Enabling Extended Kalman filter (EKF) on IRIS+
  1. Douglas says:

    Thanks for sharing your good and great knowledge, we do not know these things and they can cost much $$$.
    Thank you.

  2. Peter van der Pol says:

    Heads up,

    As I was reading some more documentation of the EKF, I’ve bumped into this:

    http://dev.ardupilot.com/wiki/extended-kalman-filter/

    IMPORTANT: Do not set AHRS_EKF_USE = 1 unless you have performed an Accel and Magnetometer calibration. Failure to do so may result in an erratic flight path due to bad sensor data.

    • Peter van der Pol says:

      Heads up,

      As I was reading some more documentation of the EKF, I’ve bumped into this:

      http://dev.ardupilot.com/wiki/extended-kalman-filter/

      IMPORTANT: Do not set AHRS_EKF_USE = 1 unless you have performed an Accel and Magnetometer calibration. Failure to do so may result in an erratic flight path due to bad sensor data.

      In Copter 3.3 this will be enabled by default, I expect with a firmware upgrade that you would be forced to do a accel and magnetometer calibration