New drone can fly, roll over land and sail

Conventional wisdom teaches that flying, boating and driving is usually easier with specialized vehicles. Cars that can sail or fly have been buzzing for decades. Large-scale commercial or military applications remain scarce. But does that also apply to drones? Your Amazon parcel drone probably won’t have to be able to do all three. However, the situation is different for specialist applications, according to researchers.

Rolling, flying and floating climate research

So we are talking about a UAV (unmanned aerial vehicle) that can move in those three environments. A team of researchers affiliated with the Arabian Center for Climate and Environmental Sciences (ACCESS) at New York University Abu Dhabi has developed such a drone. The purpose of this drone is to collect water samples in remote locations.

For environmental research you need quite a few samples. High in mountains, or in areas where hardly anyone ever comes, it logically entails the necessary challenges. According to doctoral candidate Dimitrios Chaikalis, this drone offers the solution. “Flying vehicles can easily navigate to such areas. While floating on water, it is best to take the necessary samples with minimal energy consumption, before flying back to base.”

Styrofoam, a computer and wheels from the 3D printer

But to make a drone that can do all that was not that easy. The final model has three pairs of rotors for flight and two propellers for water use. To be able to move over land, the drone has rubber 3D-printed wheels. These are printed directly around the wheel frame so no screws or bearings are required. These parts can easily rust during all the time that the drone has to spend in the water. The whole device weighs less than 10 kilos, because that has to be done according to the applicable regulations.

The drone has a Styrofoam housing to keep it afloat. The housing has the shape of a tripod so that the rotors can generate the necessary air flows. “The result is a vehicle capable of moving through any available medium, air, water, over the ground. This means that we will soon be able to deploy autonomous vehicles that are able to overcome increasing difficulties and obstacles.”

Not one, but two autopilots

But moving through the air is very different from moving over the surface of the earth. Therefore, the drone has two open source PX4 autopilots. So one for flying, and the other for moving over the ground and the water surface. An Intel computer controls the whole thing. It can itself switch between the two systems where necessary. The radio, receiver and GPS also work via this computer. All electronics are made watertight by means of plastic housing.

The latter is essential, especially for the motors that drive the wheels. Because these are completely submerged when the drone is floating. Integrating the waterproof motors was beyond commercially available autopilots. So the team had to develop its own hardware and firmware for this application. Nevertheless, the result does not lie. The drone can fly radio-controlled or autonomously on a pre-programmed path for 18 minutes.

The last horde

The fact that the prototype is not yet working perfectly came to light during a series of experiments. The styrofoam hull certainly helps the drone float, but it also absorbs water slowly. After thirty minutes in the water, the hull weighed 20% more. During the flight home, that water came out slowly, but it is not ideal. After 100 minutes, 20% of the new total weight had disappeared.

There is no solution to this problem yet. The weight gain is so significant that it must be taken into account when designing the autopilot. Then the researchers could take the loss of range that the extra weight entails for granted. Another option is to coat the hull in water-repellent material, but that also increases the weight, and then permanently.

It is essential that the trunk continues to function properly. The design is impressive, but can only be deployed as a submarine involuntarily. The drone is only protected against splashes and light submersion, i.e. floating on the surface of the water. Subsequent versions of the drone will therefore mainly be tinkered with on the fuselage. Subsequent iterations may become modular, says Chaikalis. The patent has yet to be approved, but the findings of the study have now been published.