Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

78 system to power the ExoMars Rover vehicle. The solar panels on ExoMars will produce 1200 Wh, working in combination with Saft’s 1142 Wh battery system. This system is based on Saft’s MP 176065 Integration xtd cells that have been developed for low mass and to operate with fluctuations in temperature from -40 to +85 C, and Saft is due to deliver the battery system before the end of 2016 to meet the launch plans for 2018. Another company, SubCtech in Kiel, Germany, is also using Li-ion packs for its unmanned underwater vehicles (UUVs). It has developed its own electronics to monitor the 3.5 kWh, 52 V packs, and this links into the data system on the craft using the NMEA 0183 interface standard. The Li-ion batteries can deliver very high currents for the electric motors, and work at the low temperatures in underwater environments down to 6 km. For larger battery capacities of 10- 100 kWh, SubCtech uses Lipo blocks instead of Li-ion cells. The company has developed its own specially tuned chargers for the power packs that charge the batteries safely and gently without opening the pressure housing and mean its UUVs can therefore be charged while in the water. The batteries are also designed to be fully redundant so there is always 50% of the remaining capacity available if the craft needs to be recovered for any reason. The founders of Dutch battery producer Cleantron were part of a project by the steel industry to develop an electric vehicle. “We noticed that all the car makers were struggling with the batteries, and the global steel industry wanted a demonstration electric vehicle built in steel rather than carbon fibre,” says Maurice van Giezen, managing director and co-founder of Cleantron. “We led this in Holland as there was no automotive industry, so we were independent, and this became the e 13m [£9m/$14,071,100] FSV Future Steel Vehicle. We had close contact with battery suppliers but were disappointed by what they were producing, so we set up a battery-making facility.” The problems were also apparent in unmanned electric systems, where the system designers were struggling to get good batteries. “We have also discovered over the past two years that the main UAV producers are using pouch cells, which provide lower reliability as they don’t use battery management to ensure there is no overheating and over- discharge of the cells,” van Giezen says. Cleantron collaborated with LG and Samsung to develop the first battery pack specifically for UAVs. This has the same shape as existing battery packs but gives 20% longer flying time by having a more managed output. “The 3.5 V power cell we use is proven in the automotive industry by Tesla but can only be bought by professional users,” says van Giezen. “We investigate new chemistries all the time, and it takes around seven years to get volume production from a cell supplier, and only then do they start building up statistics about the performance, so it takes almost ten years to come to market. “We are looking at the statistics of each cell. We then choose which batch of cells we want based on the statistics, and each individual cell comes into our production line and is measured to make sure it is within our tolerance requirements, which are tighter than those of any other cell manufacturer,” he says. Cleantron is also automating the process of connecting the cells up into packs to get more balanced and reliable batteries. “The human factor is far too big in battery manufacture,” says van Giezen. “A lot is done by manual labour, even for producing the cells themselves, so we are doing battery manufacture in the same way as the automotive industry now makes cars. “We also have a much more robust starting point than battery pack makers. Our automation starts from when the cell is measured and then fully cycle- tested for 48 hours and measured again. Then we make the connections between the cells using a welding robot, which can be up to 100 cell connections, and correlate the performance of each cell after manufacture. Every pack has a unique code so we can track back for the complete history of each cell in the pack.” This approach has yielded some weight advantages as well, as the cylindrical cell is actually 10% lighter than a LiPo cell. This was a surprise to the team, but comes from the geometry of the cylindrical cell. Layers of air between the anode, cathode and electrolyte for thermal management that aren’t present in the LiPo pouches make the cylindrical cells less dense, so they are lighter. The battery pack also has a battery management system (BMS) that is missing in LiPo packs, and the company is planning an advanced BMS in 2017 that will allow even better control of each cell in the pack. This is important Autumn 2015 | Unmanned Systems Technology Sodium-ion battery technology promises a power source that is 30% cheaper than conventional lithium-ion (Courtesy of Faradion)