Table of contents
- SNAV IMU Position Relative to Robot
- SNAV IMU Rotation Relative to Robot
ModalAI maintains a fork of Snapdragon Navigator to support VOXL hardware.
1) Make sure you have an account at developer.modalai.com
2) Down the
snav-modalai IPK package from https://developer.modalai.com/asset
3) Make sure the VOXL factory and software bundles are installed.
4) Push the
snav-modalai IPK package to VOXL.
me@mylaptop:~$ adb shell mkdir -p /home/root/ipk/ me@mylaptop:~$ adb push snav-modalai_1.3.0_8x96.ipk /home/root/ipk/
6) Log into VOXL via ADB or SSH. Remove the ModalAI Vision lib (it conflicts) before installing SNAV.
me@mylaptop:~$ adb shell / $ bash # adb starts an sh shell, start a bash shell manually yocto:# opkg remove modalai-vl yocto:# opkg install ~/ipk/snav-modalai_1.3.0_8x96.ipk
1) While still logged into VOXL, run the configuration script. You will be prompted by the first question:
/home/root$ bash /etc/snav/configure_snav.sh Which camera channel is the tracking camera connected to? 0 for DFT-only configuration 1 for stereo configuration 2 for TOF configuration
The wide-angle tracking camera will enumerate as camera ID 0, 1, or 2 depending on what other cameras are connected. This not NOT the physical port the camera is connected to, this is the camera ID that it is enumerated as in software. The 3 most common configurations and their corresponding camera ID are listed in the command prompt and repeated above for reference.
If you are using another configuration refer to the Camera Configuration page. You can always check the cameras before this step with the camera-test app built into the VOXL image or with the voxl-cam-ros node. You can also go back later and change the camera channel used by the ModalAI Vision Lib by updating the “override_cam_id” value in /etc/snav/camera.downward.xml
2) Next you will be prompted with the second question:
Which physical configuration is this for? 1) 200_quad_2S_pack 3) voxlcam_upright_tracking_cam 2) 230_quad_3S_pack 4) voxlcam_upside_down_tracking_cam
This configures the position of the IMU relative to the wide-angle tracking camera for the Visual Inertial Odometry function. Most use cases will fall into these 3 options. For custom use cases refer to the camera imu coordindate frames page. This also sets up the orientation of the IMU relative to the drone and flight control parameters such as if it’s using a 2S or 3S lipo.
3) Now we need to calibrate the IMU. Set up your VOXL in whichever orientation you will consider roll/pitch to be zero. Ideally this will be done with VOXL mounted to the quadcotper/robot and sitting still with no vibration or human contact. For VOXLCam this orientation should be with VOXLCam upright and looking forward with no tilt. For a red tray mount this is with the tray level.
the next step is static IMU calibration Make sure the quadcopter or VOXLCAM is flat/upright (roll/pitch=0) be patient, this will take 20-30 seconds PRESS ENTER to start static IMU calibration
This process will take 20-30 seconds, be patient. You can ignore any systemctl warnings that show up. When it’s done you should see:
 Static accel calibration was completed successfully Restarting SNAV DONE
SNAV IMU Position Relative to Robot
In SNAV, the position of the IMU relative to the center of the drone/robot is set in /usr/lib/rfsa/adsp/snav_params.xml Note that this file is probably a simlink to another settings file and that these snav xml settings files often include other xml files.
For example, the base snav install has /usr/lib/rfsa/adsp/snav_params.xml link to /usr/lib/rfsa/adsp/200qc_runtime_params.xml which includes /usr/lib/rfsa/adsp/imu_offset.xml containing:
Position of IMU1 in red VOXL Tray for dragonfly quadcopter as distance from dragonfly center of mass to IMU1 in drone coordinate frame.
<SnavParameters> <orientation_params> <param name="vehicle_center_to_imu_x" value="0.050"/> <param name="vehicle_center_to_imu_y" value="0.0152"/> <param name="vehicle_center_to_imu_z" value="-0.023"/> </orientation_params> </SnavParameters>
These distances are in meters along the vehicle coordinate frame which matches the ROS convention with X forward from center, Y to the left from center, and Z up vertically from center. The measurements are to IMU0 not IMU1.
For Voxl-Cam, the IMU1 position is roughly:
<SnavParameters> <orientation_params> <!-- in VOXLCAM, center is centroid of VOXL PCB. -0.001, -0.344, 0.0155 is to IMU1 in corner of VOXL by camera ports --> <param name="vehicle_center_to_imu_x" value="-0.001"/> <param name="vehicle_center_to_imu_y" value="-0.0344"/> <param name="vehicle_center_to_imu_z" value="0.0155"/> </orientation_params> </SnavParameters>
SNAV IMU Rotation Relative to Robot
Orientation params also includes the rotation matrix from IMU to body coordinates. By default this is in /usr/lib/rfsa/adsp/eagle.xml which is included by /usr/lib/rfsa/adsp/200qc_runtime_params.xml
Rotation matrix for Voxl-Core in red tray:
<SnavParameters> <orientation_params> <param name="imu_R00" value="0.0"/> <param name="imu_R01" value="1.0"/> <param name="imu_R02" value="0.0"/> <param name="imu_R10" value="-1.0"/> <param name="imu_R11" value="0.0"/> <param name="imu_R12" value="0.0"/> <param name="imu_R20" value="0.0"/> <param name="imu_R21" value="0.0"/> <param name="imu_R22" value="1.0"/>
Rotation matrix for Voxl-Cam:
<SnavParameters> <orientation_params> <param name="imu_R00" value="0.0"/> <param name="imu_R01" value="0.0"/> <param name="imu_R02" value="-1.0"/> <param name="imu_R10" value="0.0"/> <param name="imu_R11" value="-1.0"/> <param name="imu_R12" value="0.0"/> <param name="imu_R20" value="-1.0"/> <param name="imu_R21" value="0.0"/> <param name="imu_R22" value="0.0"/>