> 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/sensor/ark-flow-mr/px4-instructions.md).

# PX4 Instructions

## Mounting

Mount the ARK Flow MR as shown in [Mounting](/products/sensor/ark-flow-mr/hardware.md#mounting). This corresponds to the default value (`0`) of the parameter [SENS\_FLOW\_ROT](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_FLOW_ROT). Change the parameter appropriately if using a different orientation.

The sensor can be mounted anywhere on the frame, but you will need to specify the focal point position, relative to vehicle center of gravity, during [PX4 configuration](https://docs.px4.io/main/en/dronecan/ark_flow.html#px4-configuration).

## Flight Controller Setup

{% hint style="info" %}
The ARK Flow MR will not boot if there is no SD card in the flight controller when powered on.
{% endhint %}

Connect the ARK Flow MR CAN to the flight controller's CAN port, as described in [Wiring](/products/sensor/ark-flow-mr/hardware.md#wiring). Once parameters are set the module will be detected on boot. See [DroneCAN > Enabling DroneCAN](https://docs.px4.io/main/en/dronecan/#enabling-dronecan) for more detail.

### 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\_FLOW](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_FLOW)   | 1     | Subscribe to DroneCAN optical flow messages                                          |
| [UAVCAN\_SUB\_RNG](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_SUB_RNG)     | 1     | Subscribe to DroneCAN range finder messages                                          |
| [EKF2\_OF\_CTRL](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_OF_CTRL)         | 1     | Enable optical flow fusion in the EKF                                                |
| [EKF2\_RNG\_QLTY\_T](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_RNG_QLTY_T)  | 0.2   | Range finder quality time                                                            |
| [UAVCAN\_RNG\_MIN](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_RNG_MIN)     | 0.08  | Min reported range                                                                   |
| [UAVCAN\_RNG\_MAX](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#UAVCAN_RNG_MAX)     | 50    | Max reported range                                                                   |
| [SENS\_FLOW\_MINHGT](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_FLOW_MINHGT) | 0.08  | Min height for optical flow fusion                                                   |
| [SENS\_FLOW\_MAXHGT](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_FLOW_MAXHGT) | 25    | Max height for optical flow fusion                                                   |
| [SENS\_FLOW\_MAXR](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_FLOW_MAXR)     | 7.4   | Max angular flow rate (PAA3905 limit)                                                |

#### Optional

| Parameter                                                                                                                                                                                                                                                                                                                | Description                                                                                                         |
| ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------- |
| [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` to also be set on the ARK Flow MR |
| [EKF2\_GPS\_CTRL](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_GPS_CTRL)                                                                                                                                                                                                                    | Set to `0` to disable GPS aiding (e.g. indoor flight)                                                               |
| [EKF2\_OF\_POS\_X](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_OF_POS_X) / [EKF2\_OF\_POS\_Y](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_OF_POS_Y) / [EKF2\_OF\_POS\_Z](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#EKF2_OF_POS_Z) | ARK Flow MR offset from the vehicle center of gravity (meters)                                                      |
| [SENS\_FLOW\_ROT](https://docs.px4.io/main/en/advanced_config/parameter_reference.html#SENS_FLOW_ROT)                                                                                                                                                                                                                    | Sensor rotation if mounted in a non-default orientation (default `0`)                                               |

### CAN Node Parameters

The node publishes optical flow and range finder data with its default parameters. To terminate the bus, publish IMU data or change the distance sensor mode and rate, see [Node Parameters](/products/sensor/ark-flow-mr/firmware.md#node-parameters).


---

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