Deconstructing the AR.drone: Part 6

The other day the Free Flight app on my iPad told me that there was a new firmware release available for my AR.drone. I figured there was no better time to try loading new firmware using the diagnostic port on the bottom of the device.

Here is the bottom of my drone with the rubber plug with the USB symbol on it removed. You can see the port just to the lower left of center, and you can see the missing indexing pin of the eight-pin header in the upper left of the port.

Here's what I needed:

• a cable I built that has a USB Type A connector on one end and an eight-pin Molex connector on the other, wired up as described on the AR.drone reference platform web site;
• the AR.drone tools developed by user skorpion2k, which include the libplf library, the plf_inst_extract tool, and the usb_flash tool, the latter which includes the USB driver needed by the process;
• a copy of the USB boot loader ardrone_usb_bootloader.zip kindly provided by user MAPGPS on the RC Groups web site;
• a copy of the latest AR.drone firmware update file ardrone_update.plf from Parrot;
• a Windows system with the usual accoutrements.

Here's the cable I fabricated, with the eight-pin Molex connector on the left and the Type A USB connector on the right. You can see the blocked socket that will match the missing indexing pin on the port when the cable is inserted in the correct orientation.

Here's the diagram of the cable that was provided by Parrot.

I unloaded all of the AR.drone tool zip files into separate directories on my Windows laptop so that the README files wouldn't overwrite one another, but consolidated all of the sub-directories, dynamic link libraries, and executables, plus the ardrone_usb_bootloader.zip file, into a single directory. There was a drivers sub-directory with the P6_USB_Stage1 device driver.

I used the plf_inst_extract tool to extract the ardrone_installer.plf file from the ardrone_update.plf file. The README file that comes with the usb_flash tool says to use a command like this

plf_inst_extract -i ardrone_update.plf -o ardrone_installer.plf

but as usual I am incapable of following simple instructions. Here's a screen shot.

I omitted the -o ardrone_installer.plf option. The plf_inst_extract tool uses the name extract_installer.plf by default, but the usb_flash tool expects it to be named ardrone_installer.plf. So I renamed it. Here's what was in the directory after doing that.

The order of these next steps is important. I connected my laptop to the unpowered drone using the cable that I had made. The diagnostic LED on the bottom of the drone lit up as a portion of the digital logic in the drone was powered from the USB cable itself. Then I connected the drone to its battery. The USB interface in the drone enumerated on my laptop. I went through the Windows device driver installation dialog to point it to the drivers subdirectory of the AR.drone tools. Windows installed the P6_USB_Stage1 driver. Here's a screen snapshot of the Windows Device Manager following that process.

I ran the usb_flash tool without any arguments at all. The first time it failed to establish contact with the drone, probably because I botched the order of something, but it worked fine the second time. Here's the successful run split into two screen snapshots.

I disconnected everything, cycled power on the AR.drone, connected my iPad to it, and the Free Flight app reported that the drone was running the new version of firmware.

This is a great example of how this kind of hacking depends upon the kindness of strangers. From the wiring diagram provided by the AR.drone's manufacturer Parrot, to the software tools developed and provided by skorpion2k, to the boot loader binary provided by MAPGPS, it is a combined effort of an avid community of AR.drone enthusiasts.