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Tethered drones

Picture of Rodrigo Valdivieso

Rodrigo Valdivieso

Unmanned Aerial Systems Expert

Most people will surely have the typical image of a drone in their head. The usual image is that of a multicopter type model, that is, a device with a few arms each holding a propeller at its end that together keep the drone up in the air allowing it to fly while recording images for which they are so well known.

Let us now consider that same drone, but tied to the ground with a line of, say 50 to 100 meters, so that it can no longer perform the mission for which it was originally designed, which is to fly long distances while recording images with a camera. This would seem contrary to the logic of its utility. However, applying this restriction, the drone acquires a new dimension of use for which, at a first glance, one could not imagine that there would be any practical utility.

Tethered drones have already proven their worth and are used in numerous direct applications that are being widely exploited today.

Having a drone tied to the ground, thus impeding it from developing its full potential in the activities for which it was created may seem like a contradiction, but in reality, it does provide two characteristics that when analyzed in detail prove to be quite important and useful.

These two main characteristics are:

– It has a physical element that connects it to the ground.

– It has a great limitation of movement.

Indeed, if we strictly limit ourselves to that view, then the drone ceases to have practical sense. What would be the use that such a “disabled” drone could have?

Let us see in detail why those features turn into interesting utilities:

The element that anchors the drone to the ground is a wire that conducts electricity and, in the cases, where a normal drone has not been converted into a tethered drone (that is, the drone has been designed as a tethered drone from the beginning) the wire also serves as a transmission line for control signals and data from the sensor onboard the drone. Therefore, the main characteristic of being attached to the ground by a physical element brings two new unique and tremendously exploitable “sub-characteristics” to the drone.

The first: it allows the drone to be electrically powered indefinitely while replacing the weight of the batteries with that of the cable (which is much less than that of the batteries) and therefore acquires a more flexible flight characteristics than in its non-tethered configuration. Most tethered systems do keep a small backup battery that allow them to make an emergency safe landing in case there is a cable power outage.

Second, control and sensor data do not need to be spread on radiofrequency to be received by the operator. The data can be transmitted by the wire.

The immediate result of the first “sub-characteristic” is that the drone no longer has a battery limitation to fly. It can fly on a virtually unlimited supply of power and can therefore be kept in flight for as long as it is needed.

The immediate result of the second “sub-characteristic” is that it becomes practically immune to external data access or theft because it simply does not broadcast any signal that can be intercepted.

The second main characteristic (the limitation of movement) also has several “sub-characteristics” of interest:

The system is inherently safe as there is no possibility of flying out of control and causing harm to third parties. In principle, if the perimeter corresponding to the radius given by the cable length is limited or secured, then the operation is totally safe since it is not even necessary for the operators themselves to be within that perimeter.

Additionally, the operation is extremely simple. It is not necessary to plan a laborious three-dimensional route with waypoints that can cross sensitive areas or at risk of sudden obstacles. It is only necessary that it rises to the specified height and stay in that position throughout the operation.

With all the features mentioned above, tethered drones have already proven their worth and are used in numerous direct applications that are being widely exploited today. In general, all the applications for which they are being used have the common denominator of needing a fixed observation camera at high altitude (or with a privileged point of view) for a relatively long time and with a quick and easy deployment.

Among the most common and widespread applications are security applications such as traffic surveillance in high density road areas concentrated on specific days like weekends. With these systems, the traffic authorities have a much clearer image of the conflicts that are taking place, which allows them to act in advance for their prevention and / or mitigation.

In large sporting events or large concentrations of people they are employed by security services allowing a continuous observation of critical areas both throughout the event and in the moments before and after the gathering and dissemination of the public.

In industrial applications they have proven their utility for engineering, insurance, security and certification companies in damage inspections that require a relatively long time to gather data of structures that are difficult to reach such as high facades of buildings, bridges, wind turbines, etc.

In the defense sector, they are used to maintain an undetectable persistent surveillance from a vantage point in improvised areas.

In general, many other activities are receiving this new technology with good acceptance due to its great utility and adaptation to the peculiar circumstances of combining an unlimited time of operation with a highly safe and fast deployment.

The application of tethered drones is already so defined that the manufacturing sector has this specialty of products as a range of solutions clearly separated from those of regular flight drones due to its specialization.

But that is not all. We have just seen how non-obvious new applications and new uses emerge when drones are drastically limited in movement.

Now let us go one step further. Let us further limit the freedom of movement of the drone (instead of a cable of up to 100 meters, let us shorten it to only 10 meters) and also let us remove the video camera (which is another main attribute of these systems) … what could be the utility of a system that besides being lame is now blind?

It may seem incredible, but there are already ongoing explorations and work on applications that are only possible with this so “depleted” system … these super-tethered drones on a “short leash” and without a camera are already being used for sporting applications like towing surfers, wakeboarders, snowboarders and skiers with the advantage that, as before, the battery pack can be carried in a backpack when possible thus drastically increasing the operation time of the equipment. These creations are being used by surfers and wakeboarders to catch waves and jump without the need to paddle or being towed by motorboat.  Skiers and snowboarders are also using them to climb slopes without the need for a chairlift, to cross-country and to jump and overcome obstacles. Obviously, this is still a very incipient practice which is not regulated and as such it poses a relatively high risk, but patents have already been registered by large companies, there are numerous groups of enthusiasts testing variants and few initiatives have been launched to start making experimental demonstrations.


Tethered drones


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