> For the complete documentation index, see [llms.txt](https://docs.arkelectron.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.arkelectron.com/products/gps/ark-x20-rtk-gps/px4-instructions.md). # PX4 Instructions See also the [PX4 documentation for the ARK X20 RTK GPS](https://docs.px4.io/main/en/dronecan/ark_x20_rtk_gps). {% hint style="warning" %} 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 X20 RTK GPS is never assigned a node ID and will not appear on the bus. To update the node firmware, see [Firmware](/products/gps/ark-x20-rtk-gps/firmware.md). {% endhint %} *** ## Single GPS Configuration Connect the ARK X20 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](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_ENABLE) | 2 | Enable DroneCAN with dynamic node allocation (use `3` if also driving DroneCAN ESCs) | | [UAVCAN\_SUB\_GPS](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_GPS) | 1 | Subscribe to DroneCAN GPS messages | | [UAVCAN\_SUB\_MAG](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_MAG) | 1 | Subscribe to DroneCAN magnetometer messages | | [EKF2\_GPS\_CTRL](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_GPS_CTRL) | 7 | Enable GPS fusion (lon/lat + alt + 3D velocity) | #### Optional | Parameter | Description | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | [UAVCAN\_SUB\_BARO](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_BARO) | Set to `1` to subscribe to DroneCAN barometer messages | | [UAVCAN\_SUB\_IMU](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_IMU) | Set to `1` to subscribe to DroneCAN `RawIMU` messages. Requires `CANNODE_PUB_IMU` on the node | | [UAVCAN\_SUB\_BTN](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_BTN) | Set to `1` to use the safety switch on the ARK X20 RTK GPS | | [SENS\_GPS0\_OFFX](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_GPS0_OFFX) / [SENS\_GPS0\_OFFY](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_GPS0_OFFY) / [SENS\_GPS0\_OFFZ](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#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](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#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 with its default parameters. To terminate the bus, fix the node ID, publish IMU data, change the receiver's baudrates or constellations, or use `UART2` as a u-center diagnostic port, see [Node Parameters](/products/gps/ark-x20-rtk-gps/firmware.md#node-parameters). *** ## 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](/products/gps/ark-rtk-base/px4-instructions.md). The X20P also accepts [u-blox PointPerfect](https://www.u-blox.com/en/product/pointperfect) PPP-RTK corrections (SPARTN), which need no base station. On vehicles running ARK-OS, the [pointperfect service](/software/ark-os/services.md) streams them to the flight controller over MAVLink — see [pointperfect-client-mavlink](https://github.com/ARK-Electronics/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. *** ## Moving Baseline GPS Heading Configuration Two ARK X20 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. {% hint style="info" %} Moving baseline requires X20P receiver firmware 2.10 or later — see [u-blox Firmware Update](/knowledge-base/knowledge-base/ublox-firmware-update.md) to check and update it. {% endhint %} ### 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*. {% hint style="info" %} 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](#rtk-corrections-from-a-fixed-base). {% endhint %} {% hint style="info" %} 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. {% endhint %} ### Flight Controller Parameters Apply the [Single GPS Configuration](#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](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#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](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_GPS_R) | 1 | Subscribe to DroneCAN `RelPosHeading` messages, which carry the heading computed by the *Rover*. Enabled by default | | [SENS\_GPS\_PRIME](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#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](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#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, X20P 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 — X20P 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 X20P `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 4-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 | TXD2 | | 2 | RXD2 | | 3 | TIMEPULSE | | 4 | 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. *** ## 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](/products/gps/ark-x20-rtk-gps/hardware.md#leds), then confirm the flight controller has an SD card, that `ark_x20-gps_canbootloader` was installed on the node before `ark_x20-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](/knowledge-base/knowledge-base/st-link-flashing-guide.md#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, that the antennas are at least 30 cm apart, and that the X20P receiver firmware is 2.10 or later. * **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](/knowledge-base/knowledge-base/gps-placement.md) guide for mounting best practices, interference sources, and antenna positioning. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. 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