Tray Bien

Technological advances are making autonomous aerial vehicles useful for more applications all the time. But the most practical use cases still involve videography, mapping, and other tasks that do not require a substantial payload to be carried. The simple fact of the matter is that today’s energy storage systems cannot sustain a drone in flight for long durations under a heavy load. And that means that long-promised services like drone-based package delivery may be little more than hype for some time to come.

There are some ways around this problem. The most straightforward is to build larger drones — however, these aerial vehicles are bulky and expensive, and crucially, they can be unsafe to operate in populated areas. Other options have also been explored, like implementing reconfigurable multirotor designs or creative placement of the payload, but such solutions tend to make the vehicle unstable in flight, which is again unacceptable from a safety standpoint.

A team of engineers at Macquarie University in Australia came up with a different idea that could help drones to lift heavy loads, while remaining safe, stable, and relatively inexpensive. This idea is centered on teamwork. Multiple lightweight drones cooperate to lift a weight that none could lift individually. This is not an entirely new idea — existing systems tend to carry the payload beneath the drones, however, which leads to a pendulum swing induced by downwash from the rotors. That, in turn, results in instability.

In contrast, the researchers’ approach places the payload on a tray that sits above the drones, with each supplying lift to get it airborne. This method eliminates the pendulum swing, but it does introduce a new concern, namely, that the tray has to remain balanced between independent aerial vehicles.

Working with a two drone setup, the team designed what they call a Self Balancing Tray (SBT) to deal with this issue. The SBT connects to each drone via magnetic attachment points. There are also sensors embedded within the tray to monitor its stability. Measurements from these sensors are forwarded to an onboard NVIDIA Jetson Nano single board computer, which calculates any adjustments that need to be made to get the SBT into a properly balanced state. Adjustments are then made via 3-degree end effector actuators that interface each drone to the tray.

Field tests of the SBT with a pair of drones showed that the actuation system was quite accurate, with just a 1.6 percent deviation from the target being seen on average. This accuracy enabled the cooperative drones to carry their payload at a speed of up to 4 meters per second, which could come in handy in real-world package delivery applications. When perturbed, the SBT could get the load re-balanced in just over 2 seconds, which proved to be effective in keeping the vehicles stable in flight.

To date, the lift system has largely been tested indoors, so it remains to be seen how factors like wind gusts might impact vehicle stability. But the initial results suggest that the SBT is a technology to keep our eyes on in the future.