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Setup & Getting Started (Ardupilot)
Various JST-GH cables are provided to attach to the UM982 10 pin JST-GH connector. Two are full 10 wire cables (short and long) for connecting to Pixhawk Standard Autopilot’s GPS1 connector, or similar, and provide full functionality including safety switch button and LED.
The 10Pin - 6Pin cable allows users to connect the UM982 to GPS2 port on Cubepilot and Holybro Autopilots.
The UM982 primary application is to provide compass-less YAW information to the autopilot (commonly called Moving Baseline Yaw). Using this as a yaw source prevents magnetic interference from the vehicle motors and electrical systems, and any environmental interference sources, such as metallic structures or equipment that can cause incorrect yaw reports to the autopilot. This works even if the GPSs are not receiving RTCM data from a fixed RTK station or NTRIP server (see “RTK correction data injection” section below).
The parameters for the serial port that the UM982 is connected to must be setup just like its use as a single antenna GPS in the above section, EXCEPT:
- Set the GPS_TYPE = 25 (UnicoreMovingBaseline)
- Set EK3_SRC1_YAW = 2 ("GPS") or 3 ("GPS with Compass Fallback") if a compass(es) is also in the system.
- EKF3 must be enabled and used. Check that:
- EKF3_ENABLE = 1 (EKF3 enabled)
- AHRS_EKF_TYPE = 3 (use EKF3)
In addition, both antennas (“Master” and “Slave”) must be attached and positioned at least 30cm apart. The location on the vehicle is flexible but their positions impact several parameters which must be set in order to obtain proper operation. These offset distances in the x/y/z directions must be entered for the following parameters:
- GPS_MB1_TYPE = 1 (GPS1 Moving Baseline master antenna offsets relative to slave antenna, also enables the next parameters to be shown)
- GPS_MB1_OFS_X: offset in meters from the "Slave" to "Master" antenna in the X axis (in direction of 0 deg yaw, positive offsets are if "Master" is in front of the "Slave".
- GPS_MB1_OFS_Y: offset in meters from the "Slave" to "Master" antenna in the Y axis (in direction 90 deg (right) of 0 deg yaw, positive offsets are if "Master" to the right of the "Slave".
- GPS_MB1_OFS_Z:: offset in meters from the "Slave" to "Master" antenna in the Z axis (in direction up and down, positive offsets are if "Master" below the "Slave".
This figure and photo illustrates these parameters and their settings:
The UM982 can also be used as a typical GPS for a vehicle, using a single antenna connected to the “Master Antenna Connector”.
For autopilots running ArduPilot. The serial port associated with the GPS connector to which the UM982 is attached must be determined from the autopilot’s documentation. For example, the Holybro Pixhawk6 GPS1 port uses SERIAL3, while the Cube Orange’s GPS2 port would be SERIAL4.
For this example will assume that its attached to SERIAL4:
- Set SERIAL4_PROTOCOL = 5 (GPS)
- If this is the only GPS in the system, then set GPS_TYPE =24 (Unicore Master), and set SERIAL3_PROTOCOL = -1 to prevent miss-detection of a non-existent GPS
- If this is the second GPS in the system (one is attached to the first GPS, SERIAL3), then set GPS_TYPE2 = 24, instead of 0 and both SERIAL3_PROTOCOL=5 and SERIAL4_PROTOCOL=5
For RTK Fixed operation with centimeter level accuracy, a source of RTCM correction data must be injected into the UM982 to allow its position reports to the autopilot to be correctly computed.
Using ArduPilot, this will be automatically accomplished via Mission Planner Ground Control Station telemetry to the autopilot, using either a fixed base GPS (UM982 can be used in this application, see below), or internet RTCM data via an NTRIP server, if the Mission Planner PC has internet connectivity. For more information on using NTRIP, see the ArduPilot wiki article : RTK GPS Correction (Fixed Baseline)
For ultimate positioning precision in the centimeter ranges, the offset of the "Master" antenna from the vehicle's CG can optionally be entered to compensate for attitude effects on GPS accuracy. The offsets from the CG are entered into:
- GPS_POS1_X: offset in meters from the Center of Gravity to "Master" antenna in the X axis (in direction of 0 deg yaw, positive offsets are if "Master" is in front of the Center of Gravity.
- GPS_POS1_Y: offset in meters from the Center of Gravity to "Master" antenna in the Y axis (in direction 90 deg (right) of 0 deg yaw, positive offsets are if "Master" to the right of the Center of Gravity.
- GPS_POS1_Z: offset in meters from the Center of Gravity to "Master" antenna in the Z axis (in direction up and down, positive offsets are if "Master" below the Center of Gravity.
This photo illustrates these parameters and their settings:
For guide on Advanced application with Unicore Uprecise Software, please see link below.
To reset to factory default setting, please see link below