PX4 Instructions

Find additional documentation at https://docs.px4.io/main/en/dronecan/ark_rtk_gps.html

The flight controller must have an SD card installed. PX4 uses it for dynamic node allocation and for CAN firmware update — without one the ARK RTK GPS is never assigned a node ID and will not appear on the bus.

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Single GPS Configuration

Connect the ARK RTK GPS to the flight controller's CAN port using a standard 4-pin JST-GH cable. The recommended mounting orientation is with the connectors pointing towards the back of the vehicle.

Flight Controller Parameters

Set the following in QGroundControl and reboot the flight controller.

Required

Parameter	Value	Description
UAVCAN_ENABLE	2	Enable DroneCAN with dynamic node allocation (use 3 if also driving DroneCAN ESCs)
UAVCAN_SUB_GPS	1	Subscribe to DroneCAN GPS messages
UAVCAN_SUB_MAG	1	Subscribe to DroneCAN magnetometer messages
EKF2_GPS_CTRL	7	Enable GPS fusion (lon/lat + alt + 3D velocity)

Optional

Parameter	Description
UAVCAN_SUB_BARO	Set to 1 to subscribe to DroneCAN barometer messages
UAVCAN_SUB_IMU	Set to 1 to subscribe to DroneCAN RawIMU messages. Requires CANNODE_PUB_IMU on the node
UAVCAN_SUB_BTN	Set to 1 to use the safety switch on the ARK RTK GPS
SENS_GPS0_OFFX / SENS_GPS0_OFFY / SENS_GPS0_OFFZ	GPS antenna offset from the vehicle center of gravity (meters). On PX4 v1.17 and earlier these are EKF2_GPS_POS_X/Y/Z
SENS_GPS0_ID	Device ID of the receiver the SENS_GPS0_* offsets apply to. With two receivers, use SENS_GPS0_ID and SENS_GPS1_ID to match each set of offsets — matching by instance index is only reliable for serial GPS

CAN Node Parameters

The node publishes GPS, magnetometer and barometer data and subscribes to RTK corrections with its default parameters. To terminate the bus, fix the node ID, publish IMU data, change the F9P baudrates or make UART2 a u-center diagnostic port, see Node Parameters.

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RTK Corrections from a Fixed Base

Centimeter-level absolute position requires RTCM corrections from a fixed base station on the ground. For the base station setup and the flight controller and CAN node parameters that carry the corrections onto the CAN bus, see ARK RTK Base > PX4 Instructions.

The F9P also accepts u-blox PointPerfect PPP-RTK corrections (SPARTN), which need no base station. On vehicles running ARK-OS, the pointperfect service streams them to the flight controller over MAVLink — see pointperfect-client-mavlink. They reach the node the same way as base-station corrections: UAVCAN_PUB_RTCM on the flight controller, CANNODE_SUB_RTCM on the node.

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Moving Baseline GPS Heading Configuration

Two ARK RTK GPS modules can provide compass-free yaw estimation using the GPS moving baseline technique. The relative position between the two antennas determines heading, so no magnetometer is required.

The L1L5 variant does not support moving baseline heading. For dual-GPS heading use the standard L1/L2 ARK RTK GPS, or see the ARK G5 RTK Heading GPS for a dual-antenna solution.

Hardware Setup

• Connect both modules to the same CAN bus. Each module has two CAN connectors, so the second can be daisy-chained from the first.

• Mount the antennas with a minimum of 30 cm separation — more is better for heading accuracy.

• Choose one module to be the Rover and the other to be the Moving Base.

Heading is only output when the Rover has an RTK Fixed solution. No heading is output in RTK Float. RTK Fixed here means the baseline between the two antennas is resolved, which is what produces the heading — the vehicle's absolute position is no more accurate than a normal 3D fix unless you also feed in corrections from a fixed base.

A moving base and its rover must run at the same navigation rate, and u-blox limits a moving base to 5 Hz. Node firmware 1.18 and later sets 5 Hz on both modules in the moving baseline modes, so leave GPS_UBX_RATE at 0. On earlier node firmware set GPS_UBX_RATE to 5 on both modules: a rover running faster than its base has no time-matched observations for the extra epochs and outputs no heading for them.

Flight Controller Parameters

Apply the Single GPS Configuration flight controller parameters above, then change/add the following in QGroundControl and reboot the flight controller.

Required

Parameter	Value	Description
EKF2_GPS_CTRL	15	Enable GPS fusion + GPS yaw (lon/lat + alt + 3D velocity + yaw). Overrides the value of 7 from the single GPS configuration
UAVCAN_SUB_GPS_R	1	Subscribe to DroneCAN RelPosHeading messages, which carry the heading computed by the Rover. Enabled by default
SENS_GPS_PRIME	node ID	CAN node ID of the Moving Base. It is preferred over the Rover, whose navigation rate and data latency can degrade when corrections are intermittent
SENS_GPS_MASK	7	Blend both receivers using speed, horizontal position, and vertical position accuracy. This is the default value

Antenna Mounting

PX4 version	Parameters
v1.18 and earlier	EKF2_GPS_YAW_OFF: clockwise angle in degrees from the vehicle forward axis to the Moving Base → Rover baseline: 0 if the Rover is in front of the Moving Base, 90 if right, 180 if behind, 270 if left
main	SENS_GNSSn_ID and SENS_GNSSn_OFFX/Y/Z (antenna position, meters in the body frame) for both modules, and SENS_GNSSn_HDG 1 (Moving base rover) in the Rover's slot

CAN Node Parameters

Set the following on each node and reboot it.

On the Rover:

Parameter	Value	Description
GPS_UBX_MODE	3	Heading — rover with moving base, F9P UART1 connected to the CAN node

CANNODE_SUB_MBD already defaults to 1.

On the Moving Base:

Parameter	Value	Description
GPS_UBX_MODE	4	Moving base — F9P UART1 connected to the CAN node
CANNODE_PUB_MBD	1	Publish MovingBaselineData messages on the CAN bus

Sending Corrections over UART

The moving baseline corrections can be sent directly between the two modules over the F9P UART2 link instead of the CAN bus, which keeps that traffic off CAN. Both modules still connect to the flight controller over CAN.

Connect the two 3-pin JST-GH UART2 connectors to each other — TX of one module to RX of the other, and GND to GND.

Pin	Signal Name
1	F9P_TXD2
2	F9P_RXD2
3	GND

Then set GPS_UBX_MODE to 1 on the Rover and 2 on the Moving Base. CANNODE_PUB_MBD and CANNODE_SUB_MBD are not used in this configuration.

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Troubleshooting

• Node does not appear on the bus — run uavcan status in the QGroundControl MAVLink Console to list the nodes PX4 has detected. Check that UAVCAN_ENABLE is set to 2 or 3 and that the flight controller has a working SD card installed.

• Blinking red status LED — see LEDs, then confirm the flight controller has an SD card, that ark_can-rtk-gps_canbootloader was installed on the node before ark_can-rtk-gps_default, and that there are no stale binaries left in the SD card root or in /fs/microsd/ufw/.

• Node is not detected at all, even by the DroneCAN GUI Tool — for example after a bad flash that erased the bootloader. Recover it over SWD with an ST-LINK, see Flashing DroneCAN Nodes.

• No heading in a moving baseline setup — heading is only output at RTK Fixed. Confirm the Rover shows a solid blue GPS LED, and that the antennas are at least 30 cm apart.

• Test outside — GPS modules need a clear sky view to get a good fix. Indoor testing will not produce reliable results.

• See our GPS Placement guide for mounting best practices, interference sources, and antenna positioning.