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

74 T he evolution of battery technology has been a key element in the development of unmanned systems. The latest lithium-based technologies provide an energy density that has allowed the flight times of UAVs to be extended from minutes to hours, and for driverless cars it has allowed an operational range of 200-300 miles for the first time. The key is the weight of the battery for the energy it produces. With lithium- ion technology this is up to 2.4 MJ/ kg, which equates to 700 Wh/kg. By comparison, TNT explosive has an energy density of 4 MJ/kg, although of course the energy stored in a lithium- ion cell is released slowly rather than all in one explosive moment. Similarly, the development of battery technology has been slow as well. Tesla, which is at the leading edge of the commercial technology for its electric cars, sees an 8% increase in battery performance per year, but that comes in steps. The lithium-ion cell currently in use at Tesla dates from 2008, as it takes more than four years to enter mass production before it can be used in a vehicle. That means the 2013 technology should be in mass production by 2017, offering a 40% – 5 x 8% – higher energy density than the cells in use now. This boost in performance can be used to reduce the size and weight of a battery of a given power output, or boost the performance of a standard-size battery cell. For some applications such as unmanned aircraft, this means longer mission times with existing batteries. However, reducing the weight can also boost the mission time, so there is a trade-off that changes with each new generation of battery to achieve the maximum time in the air. Formats Lithium batteries come in two main formats. A lithium-ion (Li-ion) cell combines the electrolyte between the anode and cathode, with a protective layer that is then rolled into a cylinder. The protective layer acts as a damper and spreads out any heat that is generated. Advances in battery technology can take years to appear in commercial products but, as Nick Flaherty reports, many of them are now coming into view Power to the Autumn 2015 | Unmanned Systems Technology