UAV Hardware Setup

Doodle Labs currently offers four main hardware variants in its Mesh Rider Radio lineup. UART is available on all hardware variants. However, these hardware variants have different pinouts, and you should refer to the documentation package of your specific hardware for pinout information. The hardware versions can be differentiated by the model number. In all cases, the UART is implemented as one TX line, one RX line, and GND.

Please note that - 1. The legacy models (-2H-*U) have a USB host port on the auxiliary connector and have no UART port. For the UART port, you require -2H-*S model.

Connection Guide

• 1. The UART connector is a 3-pin connector consisting of TX, RX, and GND. The TX and RX wires should be coupled closely with the GND wire for good signal integrity.
• 2. Typically, when two devices are connected over UART, the TX wire of the first device should be connected to the RX wire of the other device and vice versa.
• 3. While most models use 3.3-V TTL signaling, the External Mesh Rider Radio (-2J-*E) uses RS232 signaling. Please consult the documentation package of your hardware before hooking up the UART.

Hardware Connection

By default, the Pixhawk 4 supports telemetry on serial ports TELEM1 and TELEM2. The Mesh Rider Radio UART pinout can be found in the Mesh Rider Radio Integration Guide. For details on how to setup a serial-to-serial bridge, please consult the Doodle Labs Technical Library.

Figure 2 shows the TELEM1 Pixhawk port to UART Mesh Rider Radio port wiring. UART_RX from the Mesh Rider Radio should be connected to MCU_TX on the Pixhawk 4, and UART_TX from the Mesh Rider Radio should be connected to MCU_RX on the Pixhawk 4. A ground connection is required to complete the loop. VCC_5V, MCU_RTS, and MCU_CTS can be left open.

Fig. 2 Mesh Rider Mini model UART to Pixhawk 4 TELEM1 wiring

Setup using the GUI

Open up a web browser and navigate to the IP address of the Mesh Rider Radio. The Serial Configuration GUI is found in the Services -> Serial Configuration page. Figure 3 shows a screenshot of the page. The px4 flight controller expects a baud rate of 57600, and you can use device /dev/uart0 as long as you don't have your own additional serial converter connected to the radio. You can either run the serial bridge as a client or a server. In client mode, you should use the IP address of the host running QGC, with UDP transport and port 14550. In server mode, socat will listen to an incoming connection on a port or your choice and you may use either TCP or UDP. After making your changes, click Save & Apply. Proceed to firewall configuration below.

Fig. 3 Serial Configuration GUI

Firewall setup

By default, port 2000 is open for serial port communications. Therefore, if you setup a unicast server with UDP transport on port 2000, then no additional setup will be required.

Otherwise, you will need to open up the firewall for your desired network port. Details can be found in the Configuration Guide. Navigate to Network -> Firewall in the web GUI, and click on the Traffic Rules tab. Under the Open ports on router section, add a new rule for the port you want to open (this will be port 14550 or 2000 in the examples above) and click Save & Apply.

Recommended Settings

We recommend using UDP transport for Command & Control as it does not establish a connection between the server and client. In the event that the drone moves in and out of range, a TCP connection will experience higher latency and significantly higher reconnection time should the connection break.

GCS Hardware Setup

Fig. 1 Generic UART hardware connection

Setup using the GUI

The GUI is strictly for configuring the UART port as a Serial to Network bridge. Open up a web browser and navigate to the IP address of the Mesh Rider Radio. From there, navigate to Services -> Serial Configuration. A screenshot of the GUI is shown in Fig. 2. For mobile applications, we recommend using UDP transport over TCP transport as it is more responsive.

Fig. 2 UART Configuration GUI

When configuring the serial to network relay using the GUI, the program, socat, is used in the background. For unicast traffic, the relay should operate as either a server which listens on a particular network port for incoming connections, or a client which attempts to connect to a particular IP address and network port. For multicast traffic, the relay can either send, receive, or operate bi-directionally. It will be necessary to open the firewall at the desired network port, and a link to the firewall page is provided. For multicast traffic, it is also necessary to update the routing table and a link is provided to the static route page. An example static route is shown in Figure 3.

Fig. 3 Static route configuration for multicast traffic

Choose the device /dev/uart0. After making your changes, click Save & Apply. If you are familiar with Socat and want to use your own arguments, then you can input them using the checkbox at the bottom of the page.

The remainder of this section discusses configuration using the CLI.

Android Setup

There are three ways to connect an Android device to a Mesh Rider Radio:

1. USB Reverse Tethering: This option is typically available on Smart Tablets, where it is expected that they do not have a dedicated internet connection and are getting their interconnection from another device. In this mode, the Smart Tablet acts as DHCP client, or can be assigned a static IP address. The Smart Tablet's USB port is in "host" mode and supplies 5-V to a connected device. Please make sure that the tablet is able to supply about 15W of power on its USB-C port. This mode is only supported by the Wearable and Helix Mesh Rider Radio form factors and not the Embedded or External form factors.

2. Wi-Fi: The Wearable Mesh Rider Radio includes an auxiliary WiFi radio and this is the recommended way to connect an Android device to the Mesh Rider network.

3. USB Tethering: This option is available on most Smart Phones, In this mode, the Smart Phone starts a DHCP server at a fixed IP address. The Smart Phone's OTG port is in "device" mode and requires a 5-V input. Generally it is not possible to turn off the DHCP server or modify the IP address of the Smart Phone without rooting the device.

The recommended setup is shown in Figure 6. The Wearable Mesh Rider Radio runs a Wi-Fi AP which is bridged to the Mesh Rider network that the Tablet can connect to. The next best option is USB Reverse Tethering as it doesn't impose any limitations on the IP addressing. Make sure to choose a Tablet which supports USB Reverse Tethering.

Fig. 6 QGroundControl MAVLink Verification

Mav link Test

In QGroundControl, add a new Comm Link as shown in Figure 7. Change the host address to the IP address of the Mesh Rider Radio connected to the drone, and the network port to the listening port used by the Mesh Rider Radio. Click OK and then Connect.

Fig. 7 QGroundControl Setup

Linux/Windows

You can verify the MAV Link connection is good by going to the tab shown in Figure 8, and inspecting the MAV Link heartbeat.

Fig. 8 QGroundControl MAVLink Verification

Mesh Rider Radio Optimization

The following optimizations apply to both Mesh Rider Radio 1 and Mesh Rider Radio 2 in Figure 1.

The Mesh Rider Radio Configuration Guide includes a section on Common Network Settings which we suggest you review for details on how to configure the Mesh Rider Radio. We recommend:

● For the RM-2450, 2.4-GHz ISM band radio, do not use 20-MHz bandwidth, use 5/10/15 MHz bandwidths instead to avoid interference from Wi-Fi devices.
● Use the C&C and Voice queue for telemetry (MAVLink) data. In the example above, you would map port 3000 (or 14550) to the CS6 queue. Enable "Optimize Command & Control for Voice and URLLC".
● Use the Video queue for Video. Enable "Optimize Video Streaming".

GCS Network Port Binding (Important)

Some GCS software (notably Mission Planner) do not allow the user to bind the socket to a particular network port when in client mode. Instead, the network port is assigned by the kernel. Therefore, every time Mission Planner restarts it's UDP client, it will restart from a new network port. Unfortunately, this confuses socat (on the Mesh Rider Radio), and it can lead to high MAVLink packet loss.

The suggested solution is to setup socat in client mode and input the IP address of the GCS. In that case Mission Planner will be in UDP server mode and listening on port 14550.

For Advanced Serial Configuration Refer to the Serial Guide Serial Interface Guide