Dissecting Drone Technology (Part 2)
Part 2 of 3 where Symmetry Electronics Applications Engineer Cobus Heukelman dissects all the systems in a drone.
Most commercial drones have an onboard video camera. A drone can either just store this video onto removable memory, or it can also stream a live feed back to the user. This is handy in situations where the user needs to see from the vantage point of the drone. For real-time video it needs to send its frames to the user as quickly as possible. If the video lags or waits to load, the user may crash the drone. For a video to have a decent frame rate (> 30 fps) there are two main components of the video system that are required: a good compression solution to reduce the size of each video frame, and a good communication system to transmit the compressed frames.
The data requirements for video feeds are significant. For uncompressed 1080p video at 60fps the required data rate is around 1-3Gbps, depending on the pixel format. These are extremely high data rates. So how can we get a live HD stream from our drone? We compress each of the frames to get a data rate we can transmit in real-time. Averlogic offers some great SoCs for this purpose, like the AL582C and AL360A, which are small and provide a vast amount of functionality. Lattice Semiconductor also offers low-cost video FPGAs and development kits to get you started. Using these, the video system can encode the video stream using the H.264 compression standard and then transmit the compressed stream to the receiver, which could be another of the same module, a smartphone, or any other device capable of receiving H.264 encoded data. For anyone requiring a fast to implement solution, the GainSpan HD Video AEK is a good option. This provides a simple-to-use development board that can send a live video stream to a mobile phone, allowing for rapid development of the application.
GPS is another essential component of any drone which aims to be autonomous. Autonomous drones generally allow the user to define a set of waypoints that the drone will then follow. This is very useful for any sort of surveillance/monitoring, or to send the drone to a specific location. To make sure that the drone is heading in the right direction and has not strayed from the path, the drone needs to have a good GPS unit, which is accurate and uses minimal amounts of power so that the battery is not drained too quickly. To ensure that your drone gets reception in difficult areas, you may want to consider a GNSS component that not only uses the GPS constellation of satellites, but also GLONASS, Beidou, and Galileo. Telit supplies a whole range of GNSS modules like the SE873, which is only 7 x 7 x 1.85mm and uses an external antenna, and the SE868, which features an onboard antenna. GNSS location also enables safety technologies like Geo-, which can keep drones away from restricted areas such as airports.
Following GPS waypoints is quite simple, but what if the drone needs to decide where to fly based on its own video? This gets back to our examples of the DJI and Lily drones that can follow the user. Well then you will need a bit more intelligence, artificial intelligence to be specific. To run your artificial intelligence software, the drone needs a good processor. The AMD G-series SoC (Figure 5) offers the combination of a dual or quad-core processor, integrated GPU, as well as an I/O controller on the same die. Their small footprint reduces overall system costs and supports the development of small form factor designs. Choosing a processing solution can be tricky because you don’t know exactly how much speed you really need before the software development is done. You don’t want to end up having to change the whole hardware design because it’s too slow, but you also want to keep your costs down. This is where the G-series SoC really comes in handy. It offers a scalable platform of processors that allows you to trade up to a more powerful solution without having to change your board or software designs. It also offers advanced graphics acceleration, with support for OpenGL, OpenCL, DirectX, and open source Linux development. The latest addition to the G-series family has 4K hardware video support, dual channel DDR4/DDR3, and ECC support for high bandwidth memory access and integrity.
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