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====== Z-ranger expansion deck ======

Adds the possibility to fly with precise height control. Using the ToF sensor VL53L0x the Crazyflie 2.0 can measure the distance from the sensor to a ground object at up two 2 meters.

{{:projects:crazyflie2:expansionboards:z-ranger-rendered.png?direct&300|}}

===== Specification =====
  * [[http://www.st.com/en/imaging-and-photonics-solutions/vl53l0x.html|VL53L0x]] ToF sensor to measure distance up to 2 meters.
  * 1-wire memory for automatic expansion deck detection
  * Designed for mounting under the Crazyflie 2.0
  * Mechanical specification:
      * Weight: 1.6g
      * Size (WxHxD): 21x28x4mm

===== Schematic =====

Z-ranger expansion deck {{ :projects:crazyflie2:expansionboards:z-ranger_rev.b.pdf|schematic}}

===== Default usage =====

To get started you can follow the [[https://www.bitcraze.io/getting-started-with-z-ranger-deck/|Z-Ranger getting started guide]].

The Z-ranger deck will be automatically detected when it is mounted. By default the range is available on the log variable "range.zrange" and is used instead of the pressure by internal algorithms.

The best way to use the Z-Ranger deck is to enable the [[doc:crazyflie:client:pycfclient:index#flightcontrol|Height-hold]] mode in the client. This requires at least client and firmware [[https://github.com/bitcraze/crazyflie-release/releases|2017.04]] so make sure to update your Crazyflie.


===== Usage with the experimental Kalman filter =====

The Kalman filter is a sensor fusion algorithm that is still experimental. You can try it by recompiling the Crazyflie firmware.

To enable altitude control using the Z-ranger with the kalman filter, the Crazyflie firmware has to be recompiled with the following config.mk:
<file make config.mk>
ESTIMATOR=kalman
CFLAGS += -DUPDATE_KALMAN_WITH_RANGING -DKALMAN_DECOUPLE_XY
</file>

Once the recompiled firmware, precise height control using the altitude-hold mode. To activate precise height control press the [[https://wiki.bitcraze.io/doc:crazyflie:client:pycfclient:index#creating_new_mappings|altitude hold]] button on the gamepad and release the thrust. This will "lock" the height as the Crazyflie 2.0 goes into automatic height control mode. The up and down commands will then control the desired vertical speed instead of thrust.

The sensor can measure distances up to 2 meters but often fails at distances above 1.5m. In case of unreliable readings the Crazyflie 2.0 will slowly drift. If that happens bring it down to the detection range.

**Note: Currently the mobile clients does not support this functionality!**
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