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Lab 08: Believer Comms and Firmware
This week in AT209, the communications and firmware systems of the Believer were examined in Group 4. Hardware such as the Blue Cube flight controller and the RFD 900x modem were used as well as software such as the PuTTY and RFD Tools applications. The goals of this lab were primarily to establish a connection between a ground and air pair of units to establish communications between ground control and the aircraft as well as to adjust the settings of the equipment’s software for proper operation.
RFD 900x Setup
The first activity was to set up the RFD 900x modem, which was done to ensure a good connection could be obtained in the future. The RFD 900x uses 902 - 915 MHz and 915 - 928 MHz frequencies, and this is because they are commonly used in North America for unlicensed long-range communication. They also provide a good balance between range and data transmission reliability. Before powering the modem, the antennas were attached. The antennas needs to be connected before powering it on to prevent it from getting damaged. Once power is established on the RFD900x the Radio Frequency has no where to go if there isn’t an antenna. This can cause the RFD900x to overheat. As another point to note, there is a unique plug on the object: a USB serial plug. The USB serial Plug is special because it can use 3.3v compared to the normal 5.5 volts for regulars USB serial plugs.
The USB serial plug has many pins, and it is important to take care connecting the pins properly. Pin one is denoted by the arrow marker on the connector, corresponding with modem pin 1. This is the bottom left pin of the modem pin header and is denoted by the square solder pad and white ‘1’ marking on the PCB. The black wire connects to pin 1. The below image shows this setup.
Modem and pins
Another important paramteter of these associated parts is the BAUD. A BAUD rate is the number of signal changes transmitted per second. A higher BAUD rate means faster communication speeds, and reduce latency between communicating systems. Below an image of Group 4 working together can be seen working on getting the activity together and labeling the modems and controller.
Group 4 at work
RFD 900x Settings
Obtaining the proper modem settings is just as important as the physical aspect of the configuration, and great care was taken to ensure proper setup. The RFD Tools software was downloaded on a personal laptop, and it was through this that the settings were changed. Two personal computers were used so that one could connect via USB to the ground modem and the other to the air modem. In the settings, the modem was connected, and the serial speed was set to 115. This allows for a faster rate of data transmission. The Net ID was set to 100, and this was done to differentiate the settings from that of other aircraft in radio communication. An image of the settings menu can be seen below.
RFD Tools settings
Testing commmunication
After the settings were finalized, both personal computers downloaded the PuTTY software in order to test if signals could be sent back and forth. For this to work properly, the proper COM port had to be selected in the device manager for each computer, and the speed was again set to 115. After this was established, a text box appeared on the screens of both computers, and the message “hello world” was able to be sent back and forth, signifying complete connection testing. An image of this message can be seen below.
Hello world test
Installing Firmware
The second of the two parts of the setup included the installation of firmware. For Windracers, it should be known that the file type is .apj. The .hex files are only meant to be used by DFU/JTAG/SWD methods. The .apj file has been tested by developers and in most cases been test flown. This means that it is an easily identifiable and proprietary model, which should be used to ensure proper operation of the aircraft. However, this file must be run through Mission Planner, a full featured ground station application. It can be used as a dynamic control supplement or a configuration utility. Other programs include QGroundControl, APM Planner, UGCS, Betaflight, PX4, etc.
Mission Planner
It is generally expected that the Windracers flight controller firmware will work with Mission Planner. Even if the default software is not built for specific vehicle types and firmware, ArduPilot (the umbrella creator) allows the user to build using a custom firmware server. Another hardware item used here was the Blue Cube flight controller, which has many functions including the use of 3 IMUs. It contains 1 megabyte of ram and 2 megabytes of flash memory. An image of this can be seen below.
Flight controller and modem
On an AIDA3 personal computer provided by Purdue University, the Mission Planner software was downloaded previously. An administrator account sign in was required from Professor Rose. The Ardupilot loading firmware guide for custom firmware was used, and it was very helpful for this process. Below an image of the confimation of completed firmware installation can be seen.
Complete firmware installation
Testing Firmware
After the firmware was complete installed, it was tested on the Windracers Ground Control app. This application was again opened on the Purdue University AIDA3 personal computer. The flight controller was then connected to the computer by USB cable, and a connection was made in the settings. The settings for this connection included the use of a serial connection, COM17 (the default and only available option), and a BAUD rate of 115200 (115). The aircraft was able to autimatically connect and appeared on the flight plan menu shortly thereafter. An image of this screen can be seen below.
Flight plan menu with aircraft return
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