by Mike McNamee Published 01/02/2017
Graphene is proposed for reducing the internal resistance of the battery to improve the power density (and by-the-by, the battery's propensity to go on fire!). Despite these concerns and a general level of scepticism, the rumours are that military small drones are flying for quite a lot longer with graphene-based batteries. The batteries may not necessarily be using the same electrochemical couple – lithium-sulphur, for example, has been lurking in the wings for some time and is predicted to be capable of proving about twice the energy density (Tesla the electric car company are rumoured to be working on this type of battery). The theoretical energy-density is a whopping three times as great. All the reports we can find are a little coy about the actual electrode chemicals being employed.
The re-emergence of lithium-sulphur is something of a flashback for your editor – in his former life as an advanced battery scientist he was aware of the system developed by The Argonne National Laboratories in the 60s which was used in military applications but was a primary cell only (ie it was not rechargeable). Some of the designs were terrifyingly dangerous – in the wrong circumstances lithium is very chemically active (which is why it makes a good battery component in the first place). Not all of the problems have succumbed to modern technology as the recent demise of the Samsung Galaxy has so spectacularly demonstrated. It is a fundamental property of high-power batteries – when things go wrong they tend to go on fire! Graphene has been proposed as an electrically conducting support for the electrode materials to take both heat and electricity away from the polymer electrolyte – this is the most likely way in which it is being exploited.
The FAA guidance (for flying with batteries) at the time of writing is tabled opposite. You need to check the specifics of the country to which you are flying or you might not get your kit out! Also ensure that your information is up to date at the time of flying as it can change.
Collision avoidance is one of the newer drone technologies present only in the DJI Phantom 4 at the time of writing. There are two technologies, ultrasonic echo sounding and image recognition. For the latter, the drone builds an optical 3-D map of its surroundings at high speed and then uses the information to steer around obstacles (such as trees). Indoors, with the loss of GPS, collision avoidance becomes important as the drone will drift about more (for example, if surveying the stained glass in a church or cathedral).
Presently there are no drones capable of operating in heavy (or even light) rain although the military might have something up their sleeves – the large Predator drones are presumably all-weather operable. This is not much of a problem unless you wish to use a drone to survey for roof leaks on a high building; photography normally needs good light.
Currently we have drones capable of stable flight, with simple operation, a number of safety features and high-quality stills or broadcast-quality video, including automatic flight-path control. The latter also includes the technically tricky tasks of circling a moving target such as a boat or car with a camera locked on. Other camera technologies are employed for survey and surveillance work using other parts of the spectrum such as infrared and UV. Batteries are the one restricting issue both for safe transport and flight duration. The limits on flight duration are governed by the intrinsic properties of the battery electrode materials and are well established – getting them under control remains a potential problem. Drones are an example of the convergence of modern technologies and the willingness of creatives to exploit them – you need look no further than the latest Planet Earth II series to see just how good it can get!
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