Underslung Load Stabilization
One summer project involved lifting a ReadyMadeRC Anaconda aircraft several hundred feet in the air using one of our large quadcopters, and then dropping it into free flight. Though successful, the flights exposed a serious hazard: the underslung load tends to start pendulum-like oscillation when moved. This is both difficult to damp out through manual control, and dangerous to the lifting aircraft, as it ends up being dragged horizontally by its own load.
Using our school’s “VIP” program, which pairs undergraduate students with graduate researchers, I proposed a research project to develop active stabilization for underslung loads. With the help of some excellent students (Matt Gelber and Tay Blankenship), a system was developed that used a two-axis gimbal to measure the load angle (relative to the body angle, which can then be converted into an earth-frame angle). This goes through a lowpass filter and then feeds a pair of PID loops, which output to the aircraft’s horizontal velocity control.
The end result is that when switched on (as shown twice in the above video), the aircraft quickly brings the load under control. The aircraft still retains movement control as well. Movement is accomplished indirectly, by setting the target load angle to something other than zero. For instance: to move forward, the target load angle is set to be behind the aircraft.
This research has been documented in a conference paper, which has been submitted to the AIAA SciTech 2021 conference. Documentation of this research has also been submitted to the VCU Innovation Gateway for potential patent protection.
