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ZED stereo camera for Non-GPS Navigation

This article explains how a ZED stereo camera can be used with OpenKai as a substitute for a GPS allowing position control modes like Loiter, PosHold, RTL, Auto.

Required Hardware

• Stereo Labs ZED camera

• NVidia TX1

• Auvidea J120 carrier board

Setup

• connect the autopilot and TX1 as shown on the NVidia TX1 as a Companion Computer wiki page

• flash the TX1 as described in the Setup the TX1 section of the above wiki page but use the apsync-tx1-openkai image from firmware.ardupilot.org

• mount the ZED camera upside-down and using vibration dampeners to the front of the vehicle. It can be mounted right-side-up after connecting with ssh and then modify ~/src/OpenKAI/kiss/apmCopter.kiss so “bFlip” is 1.

• in order to download the ZED camera’s calibration parameters from stereolabs.com, connect the TX1 to the Internet with an Ethernet cable during powerup (this procedure is only required once)

• disable APSync’s video streaming (so that OpenKai can use the camera) by connecting your computer to APSync’s access point (ssid=ardupilot, pw=ardupilot), then open a browser to http://10.0.1.128:8000 and click the red Disable Auto Streaming button (button should turn green) and reboot the TX1.

Configuration through the Ground Station

Example setup below shown for first proximity sensor:

• enable communication between the TX1 and autopilot using the Setup the Pixhawk instructions from the tx1 setup wiki page

• set AHRS_EKF_TYPE to 3 (means use EKF3)

• set EK2_ENABLE to 0 (disable EKF2)

• set EK3_ENABLE to 1 (enable EKF3)

• set GPS1_TYPE to 0 (disable the GPS)

• set VISO_TYPE to 1 (enable visual odometry)

• optionally set PRX1_TYPE to 2 (enable using ZED’s depth map for object avoidance)

Optionally you may also:

• set the VISO_POS_X, VISO_POS_Y and VISO_POS_Z to account for the camera’s offset from the IMU or vehicle’s center-of-gravity (more details here)

• mount the camera in other orientations and change the VISO_ORIENT parameter. Note: if you are using the ZED’s depth sensing you will also need to modify OpenKai’s configuration (not documented)

Ground Testing

• Plug in the vehicle’s LiPo battery so that both the TX1 and autopilot are powered

• Connect the autopilot to a ground station using a USB cable

• If you are using Mission Planner as your ground station, once messages are successfully passing from the ZED/TX1 to the autopilot: - a proximity viewer should appear showing the distance to objects ahead of the vehicle (if PRX1_TYPE was enabled above) - “Bad Vision Position” message should disappear from the HUD

• Set the home position from the ground station map (from MP’s Flight Data screen, right-mouse-button-click on the map and select “Set EKF Origin Here”). The vehicle should appear on the map.

• Pick-up the vehicle and walk it around checking that the vehicle’s position movements are shown on the map

Flight testing

• Setup the vehicle with AltHold and Loiter flight modes

• Setup an auxiliary switch to enable/disable object avoidance and move switch to the off position. Alternatively set PRX1_TYPE to 0. This helps ensure the vehicle will not backaway from objects in AltHold mode which could surprise the pilot.

• Attempt to arm and take-off in Loiter mode

DataFlash logging

• The ZED’s visual odometry information will appear in the VISO dataflash log messages.

• Distance to objects ahead of the vehicle will appear in the PRX messages.

• EKF’s visual odometry information will appear in XKFD messages