What you will need

  • A drone that arms and whose motors spin in the correct direction

  • Safety goggles

What you will get

  • A throttle midpoint calibrated to your drone so it hovers instead of climbing uncontrollably

Throttle Calibration#

If your drone climbs uncontrollably on takeoff and triggers a Safety Failure: too high disarm, the throttle midpoint needs calibration. No two drones hover at exactly the same throttle value. Motor efficiency, propellers weight, and battery charge all affect it, so the default midpoint (1600) might be too high. Without tuning it to your build, the drone will shoot upward faster than the controller can correct.

Finding and setting your hover throttle#

  1. SSH into your drone and open scripts/pid_class.py:

    nano ~/catkin_ws/src/pidrone_pkg/scripts/pid_class.py

  2. Go to line 173. You will see:

    cmd_t = self.throttle.step(error.z, time_elapsed)

    Add a hardcoded test value on the line directly below:

    cmd_t = 1400  # test value

    Save and exit with Ctrl+S, then Ctrl+X.

  3. Restart the FC and PID nodes (`1 and `2), arm the drone (;), and press t to takeoff.

    Warning

    Keep your hand near spacebar to disarm the drone immediately if needed.

    Observe what the drone does:

    • If it climbs, the value is too high. Lower it by 25.

    • If it sinks or does not lift, the value is too low. Raise it by 25.

    Repeat until the drone hovers. For the DD24 with Kv 2300 motors, the hover throttle typically falls in the 1450–1475 range.

  4. Once you have found the hover throttle, note the value and remove the hardcoded line you added in step 2. The PID controller will take over throttle again.

  5. Now go to line 81 in pid_class.py. You will see:

    d_range=(-40, 40), midpoint=1600)

    Set midpoint to your hover throttle value. For example, if you found 1473:

    d_range=(-40, 40), midpoint=1473)

    Save and exit with Ctrl+S, then Ctrl+X.

  6. Open scripts/pid_controller.py:

    nano ~/catkin_ws/src/pidrone_pkg/scripts/pid_controller.py

    Go to line 310 and update the takeoff altitude setpoint:

    self.desired_z = 0.2  # was 0.05

    Save and exit with Ctrl+S, then Ctrl+X.

  7. Restart the nodes and fly. The drone should lift off and settle at roughly 20 cm. Some oscillation are normal and indicate the need for further PID controller tuning.