Unmanned Systems Technology 038 l Skyeton Raybird-3 l Data storage l Sea-Kit X-Class USV l USVs insight l Spectronik PEM fuel cells l Blue White Robotics UVIO l Antennas l AUVSI Xponential Virtual 2021 report

39 Data storage | Focus configuration and expected workload. This uses the PCIe interface as the physical link. This is also where the way the speed is measured changes. Rather than bits or bytes per second, the interfaces are specified by transactions per second. PCIe is currently at 32 GT/s with version 5.0 and looking at speeds of 1800 MT/s in the next couple of years System development For larger unmanned systems, the increased performance of drives and interfaces means many data storage developers have moved from building their own drives to using COTS versions and adding the layers of reliability and security on top. That means implementing secure network file systems, sometimes with NAS and redundancy at the drive level. An NAS architecture can use a RAID (redundant array of inexpensive discs) architecture where data is stored across an array of drives, but it can compromise the balance of SWaP and data security, as the additional drives take up more space and power. The key challenge is the ruggedisation of commercial drives for unmanned environments, ensuring the drives meet the temperature, electromagnetic compatibility, vibration and voltage requirements of the system. This is a complex packaging challenge. Cooling options For the cooling, it is key to look at the system level, not just the power requirements of the storage, assessing how the recording computer is working and how the data is transferred. That can mean reducing the frequency of data acquisition to reduce the data flow; reducing the frequency reduces the temperature. Where the data is encrypted at the sensor, that would also reduce the power consumption throughout the system. Such techniques can reduce the power consumption from 150 to 90 W. Unmanned Systems Technology | June/July 2021 One UAV developer has tried using an SD memory card for data storage, but temperature and vibration issues gave problems in logging the data, so the team developed an internal memory device connected via a cable. It works alongside a datalink to the GCS, logging data at a high data rate. As a mission gets further from a GCS, there may not be a good wireless connection at times for the data feed from cameras and payloads, and key data may need to be stored locally. This applied both during a mission and during development of the UAV. In case of an accident, the flight recorder can also be used to reproduce the root cause by storing diagnostic data from the autopilot. In this case, the UAV developer found that the energy in UAV impacts is much lower than in manned aircraft, so the survivability requirements of the storage system was not as demanding as for the regulatory ‘black box’, so it was found that a Kevlar protective cover would suffice. One of the weakest points of an SD card is it takes too much time to record the incoming data to a non-volatile multi-layer cell flash memory. That means internal dynamic memory is needed as a buffer to provide time to write the data to the flash memory. The resulting data recorder, powered by an embedded ARM Cortex-A5 microprocessor running a custom, stripped-down version of the Linux operating system at 200 MHz, weighs under 70 g and fits into an IP66 10 x 5 cm box for small UAV designs. The RS-232 serial interface takes data from the autopilot at 115 bit/s. The storage automatically starts recording on power-up and uses a circular buffer in a 64 Gbyte drive soldered to the board of the recorder. This drive can accommodate 4000 hours of telemetry data before overwriting the first data that was stored. On top of managing the data recording though an intelligent file management that differentiates data from separate sessions, the Linux system has a maintenance application through a separate Ethernet connection to a web interface for easy download of the flight data and updates of the system. This simplifies the download process. Rather than having to disconnect the UAV’s flight recorder, operators can plug an Ethernet cable into it and transfer the data quickly and easily. The next step for the fight recorder design is storing raw video, which would require a specific interface such as MIPI to a camera. However, UAV operators may want to use or store specific parts of a video or a series of high-resolution stills of specific areas of interest. The next logical step is to use the data storage for a digital elevation model. These are large and impossible to store in the autopilot or send to the GCS, so storing them on board is a key request from UAV operators. However, that would need multiple serial ports on the autopilot for the data coming from the model. Designing a flight recorder This dedicated UAV flight recorder was developed to overcome the shortcomings of using an SD card (Courtesy of UAV Navigation)