Under The Hood – 3DR SOLO – Part 3
This will be the final chapter in our SOLO Under The Hood series. For those that missed for the first two parts they can be read here:
Today we literally get to the heart of the 3DR SOLO, the all important flight controller. Here I will get into some computer architecture and how the SOLO differentiates itself from other manufacturers.
Yes all drones have some sort of computational flight controller, but 3DRs model is based on the Maker movement of DIY (makerfaire.com/maker-movement) and the Open Source Initiative (http://opensource.org)
Remove the compass sensor lead from the J2 connector. At this point there will be one screw remaining holding the main board to the drone shell.
Make note of the centering pin in the top right corner. This serves as an alignment for the main board and will assist you to make sure when you reassemble, the board fits correctly.
With the main board free, push it down towards yourself while slowly lifting up the top end to clear the drone shell. As you are tilting it up be cautious of the ribbon cable that is attached to the accessory port connector.
There are 13 wires of this cable that are soldered. There is not a lot of solder holding these wires in place so constantly flexing this cable will weaken those connections. Breaking one of the leads would not be the worst thing that could happen considering there are no external accessories out in the market place. However it would be a delicate soldering job to reattach this cable. Now remove the two screws holding the accessory connector to the bottom part of the drone shell.
Flip the main board upside down. The 2 antenna wires are still connected. Be careful you don’t pull them out. We now get our first look at the onboard computer. A second computer of the same design is located in the controller. This architecture is what differentiates 3DR from the others. As a software developer you have two full computers to meet your processing needs.
Taken directly from 3DR’s website is the Solo System Diagram:
The computer consists of a single core 32-bit 1GHz ARM Cortex-A9 processor running on Yocto Linux. What does all of this mean?
ARM architecture – Acorn RISC Machine (Reduced Instruction Set Computer). This is an embedded system processor design. Most of us have one of these in our phones. It offers significantly fewer transistors than standard processors which reduces the cost, heat, and power consumption.
The processor comes from the Cortex-A9 family. The data sheet can be found here:
Yocto Linux – What the heck is this? This is the operating system that all the applications are running on top of. Similar in nature to Windows or OS X found on your computers. Yocto Linux would be referring to a certain distribution incorporating the Linux kernel. The kernel being responsible for all your low level hardware interactions. Included with this kernel would be the middleware layer which helps to interface with specific apps running within the OS. There are many distributions of Linux. Some of the popular ones include Ubuntu, Debian, and Mint. This one is lightweight and specifically meant for embedded systems architecture.
In the future I may do a series on SOLO software development and what is possible. Most other drone architectures are closed source. DJI does offer an SDK to make mobile Apps for their systems but it is not nearly as open as 3DR. This is what 3DR is counting on. They are hoping the DIY community comes together to create new Apps and functionality. In fact just recently 3DR announced their “Made For Solo” program to encourage individuals and companies to create new applications.
Drones are the new mobile. Initially when mobile phones came out they served only one purpose – voice communications. Look where the software developers took that industry. We definitely use our mobile phones for more than talking these days. Some would argue we don’t even use them for talking anymore. This is where we are with the drone industry. Just imagine 10 years from now where software will drive it. Apps will be the future of this industry.
Back to our teardown make note of where the HDMI cable is attached. This is the same cable which is connected to your GoPro collecting the video signal.
To remove the Sololink processor board unplug the HDMI cable and remove 3 screws. Carefully pull straight up. Flipping it upside down will reveal the 2.4 GHz air data terminal (transceiver). This is a 2.4 GHz communications system with the controller acting as a WiFi base station. Googling the printed P/Ns of the transceiver did not reveal any manufacturing information. I’m assuming one of the 802.11 standards is in play here.
The transceiver can be removed from the processor board, but it’s not necessary unless you need to replace it.
This is the backside of the transceiver completed removed.
With the processor board removed the main board is now completely free. The only component left on it is the Pixhawk 2 flight controller. There are 4 screws holding this in place.
The Pixhawk 2 connector is revealed. It’s quite different than how the first Pixhawk was integrated into the Iris+.
Here we can see the Pixhawk 2 flight controller. There is a micro SD card and USB port on the side. There is not much info online about the controller itself but most likely has similar specs to the original Pixhawk. There are rumors in the near future 3DR will release a development version of the Pixhawk 2 for the DIY community.
Once you have everything disassembled you will have your very own SOLO kit. The real question is will it ever fly again! I’ve done the assemble/disassemble process now 3 times without incident. My SOLO is still flying, and yours will also.
3DR has designed their SOLO drone to be future proof. The technology will allow you to grow and adapt your SOLO. They have one of the strongest developer communities in the world (http://diydrones.com). There are many developers building products for the accessory bay. Dual 1 GHz computers allow you to do wireless updates and develop processor intensive applications (i.e. Computer Vision). No more USB cables to update your drone. Components that can be swapped out including the motor pods allows easy maintenance. Open source hardware and software along with their newly “Made For Solo” program will keep third party developers innovating for years to come. 3DR wants its users base to be creative and it definitely shows in the SOLO design.
“That’s what happens when you add ‘personal’ to a technology. It evolves into something new, often more powerful in the hands of regular people than it ever was in the hands of the few.” — Chris Anderson (Founder of 3D Robotics)