The Falcon DS1 - BeagleBone Blue Drone (Part 2)

Control Wiring

The BeagleBone uses mostly JST connectors. We need the following:

• Four (4) of the 2-pin 1.5 JST ZH female connectors, with attached 150mm 28AWG wires, for the motors,
• Eight (8) of the 4-pin 1.0 JST SH female connectors, with attached 150mm 28AWG wires, for the encoders as well as the UART, I2C, CAN, and PWR busses, and
• Four (4) of the 6-pin 1.0 JST SH female connectors, with attached 150mm 28AWG wires, for the SPI, GPS, GPIO, and ADC busses.

These connectors are small but they are also fiddly to crimp and a bit delicate. Nevertheless this is what we are stuck with. Despite a LOT of searching, I was unable to find a complete diagram which indicated all of the correct connections for using the BeagleBone Blue as a flight controller for ArduCopter. The best I was able to find was the Imfatant version, which he provides as part of his description regarding how to get ArduCopter onto the BeagleBone. I have reproduced his image below in Figure 12.

Figure 12. BeagleBone Blue Connections (ref: https://github.com/imfatant/test)

I ended up doing my own drawing, to ensure I knew what connected to what. I needed this in order to work out the best layout on the airframe and what cables and connectors are required.

Figure 13. BeagleBone Blue Control Wiring.

Note that the front of the drone is towards the top of the diagram in Figure 13. The motor numbers match up with the nearest motor outputs on the QUAD ESC. The control wires for each motor (S1, S2, S3 and S4) then go to the corresponding servo/ESC connections on the BeagleBone Blue.

Now that we have the connections worked out we can load up some software and start testing our rig.

Loading ArduCopter on the BeagleBone Blue

The most comprehensive guide to loading the ArduCopter software onto the BeagleBone Blue is found at the Imfatant Github repository. There is also a summarised version of these instructions on the Mirkix Github repository (Mirko Denecke's port of ArduPilot).

Figure 14. Checking the BBB Connection to the Mac.

I don't intend to reproduce what has already been written in these guides but I will point out areas where things have changed or if I had difficulties.

PART 1 - Preparation

1. The first issue I found in the Imfatant Guide is that the recommended console image is no longer available at  https://rcn-ee.net/rootfs/bb.org/testing/. I used the latest version that I could find: https://rcn-ee.net/rootfs/bb.org/testing/2019-06-30/stretch-console/bone-debian-9.9-console-armhf-2019-06-30-1gb.img.xz Download this and flash it to a microSD card using Etcher (or equivalent). I used a Toshiba 16GB class 10 card so that I would have plenty of room and speed.
2. I inserted the SD card (it only goes in one way) and booted up the BeagleBone Blue (BBB from here on), by connecting it to my Mac via the micro USB connection. As suggested in the instructions I tried "ssh debian@192.168.7.2" but the operation timed out. It appears that there are two drivers that you have to download and install for this to work on the Mac. 
3. Download the two drivers: Network: https://beagleboard.org/static/Drivers/MacOSX/RNDIS/HoRNDIS.pkg and Serial: https://beagleboard.org/static/Drivers/MacOSX/FTDI/EnergiaFTDIDrivers2.2.18.pkg and then install them. The Serial driver may ask you to reboot your computer (it did for me).  The Beaglebone Blue creates a network connection and emulates an Ethernet adapter. Your computer will receive IP addresses 192.168.7.1 and 192.168.6.1. The Beaglebone Blue has IP addresses 192.168.7.2 and 192.168.6.2. You can check whether this has worked by looking at Networks in system preferences (ref: Figure 14).
4. You should now be able to ssh in ("ssh debian@192.168.7.2") without difficulty. Password is "temppwd" (see Figure 15 to view a successful first log in).  If you receive a “REMOTE HOST IDENTIFICATION HAS CHANGED” error, you have probably previously connected to a different computer on 192.168.7.2 (like another BBB). Remove the old ECDSA key with: "ssh-keygen -R 192.168.7.2".
5. Next thing you need to do is get WiFi up on the BBB. Follow the Imfatant instructions for this but I found that I had to power the device down and reboot before the changes would take effect. Make sure you "sudo shutdown -h now" before powering down. While you have the power off, CAREFULLY turn the antennas around so that they face off the board. They swivel so don't just try and bend them up and over. You can unplug and replug the antennas if you prefer. Once you power back up, you should have the central green LED lit to indicate a WiFi network connection (ref: Figure 16). 
6. To get the WiFi IP address of your BBB, I usually use "hostname -I" or "ip addr show wlan0". Alternatively, you can just have a look on your router. Terminate your usb connection and ssh back in using the WiFi IP address. The password is the same. Verify that you have an internet connection using "ping -c 3 google.com".
7. The remainder of the Imfatant Part 1 Preparation instructions went smoothly for me.

Figure 15. Logged into the BBB via USB.

Figure 16. Green WiFi LED on indicating a connection.

Part 2 - Installing ArduPilot

Follow the Imfatant instructions for setting up the ArduPilot environment configuration file, /etc/default/ardupilot.

The switch -A in the ardupilot config file maps ArduPilot's "Console" serial port (SERIAL0, default 115200) to a target IP address and port number of one's choosing. For example, this allows MAVLink data to be transmitted over WiFi for test purposes. This data stream is auto-sensed by ground control station software like Mission Planner (Windows) and QGroundControl (Windows, OS X, Linux, iOS and Android).

To get the IP address of your Mac, from the Apple menu pull down “System Preferences” and click on the “Network” preference pane. The IP address for your WiFi connection will be shown on the right (see Figure 17).

Figure 17. Getting your Mac IP address for WiFi.

For Windows, press the Windows Start key to open the Start screen. Type cmd and press Enter to launch the command prompt. Type ipconfig at the command prompt to check the network card settings. See Figure 18, you want the IPv4 address.

Figure 18. Getting IP address for Windows

The next tricky bit is getting the latest ArduCopter executable, built specifically for the BBBlue's Arm architecture, onto the BBB. The Mirko Denecke link no longer works but the Imfatant one will allow you to download arducopter v3.6.

Once you have the file downloaded, there are a few different ways you can copy it to the BeagleBone. You can use SCP, just copy it onto a USB drive and then plug that into the BBB, or you can use something like FileZilla. I took the last approach. Depending on permissions, this may be as easy as dragging the file across (Figure 19).

To check the current permissions on the file type, "ls -ld /usr/bin/ardupilot". My initial result was:

drwxr-xr-x 2 root root 4096 Aug  6 08:29 /usr/bin/ardupilot

Which is a problem because the directory's owner and group is root and we have FTP'ed in as debian. In the string displayed above, the first character indicates if we are looking at a directory (d), file (-) or link (l). After that, the folder and file access rights are divided into three categories:

xxxyyyzzz
xxx are access rights for the owner
yyy are access rights for the owner's group
zzz are the access rights for everyone else

The access rights symbols will indicate whether you can read (r), write (w), execute (x) or are missing a right(-). Based on our results, the only person who can write a file into this directory is the owner (i.e. root). We can use chmod to fix this. In terminal type: "sudo chmod o+rwx /usr/bin/ardupilot" The "o" switch applies this change to all users and we are adding (+rwx) read, write and execute rights for this directory. Check with "ls -ld /usr/bin/ardupilot". You should get something like:

drwxr-xrwx 2 root root 4096 Aug  6 08:29 /usr/bin/ardupilot

You should now be able to drag across the arducopter executable into the /usr/bin/ardupilot directory as shown in figure 19. Username and password is the same as for ssh. Use port 22.

Figure 19. Copying the arducopter executable to the BBB using FileZilla.

After this we "sudo systemctl enable arducopter.service" and rebooted the BBB. Job done! You can check that arducopter is enabled with "systemctl is-enabled arducopter".

In Part 3 we will start putting everything together.