ADAPTS
Northeastern Unmanned Aerial Vehicles (NUAV) is Northeastern University’s Drone Club and I have the honor of leading it alongside two co-leads. In my first year as a lead, I helped progress the Autonomous Dynamic Airborne Payload Transfer System (ADAPTS) project. The objective was to have two drones exchange payloads in midair. After months of brainstorming, we decided to pursue a three-drone system.
From a high-level overview, one drone with a payload would hover above another. The top drone would release a tether that would have a small drone at its end. This small drone would be the end effector. It would hold the payload and control the position of the rope with respect to the bottom drone. This drone-rope assembly also called the active tether, would get close to the bottom drone and drop off the payload.
An assembly of the drone-rope mechanism onboard the test rig with the funnel mechanism below it.
OK… but what did I do for ADAPTS?
The three-stage payload swapping process uses a top drone (secondary drone), drone-rope assembly (active tether), and bottom drone (primary drone).
While leading the club, I facilitated brainstorming sessions, reviewed other members’ designs, and created some mechanisms for ADAPTS. During brainstorming sessions, I worked with our senior members to define our payload-swapping approach and each necessary subsystem. This involved high-level system designs and hardware-specific designs. I also designed a test rig to house the drone-rope assembly. I also designed a payload-securing mechanism that would embed inside the bottom drone. I also hosted design reviews for the active tether and the funnel mechanism, which were designed by other members. Additionally, I coordinated with the software divisions of the club to ensure the project was progressing.
Our payload volume was constrained to a cylinder that was 90mm in diameter and 200mm in height. Additionally, we wanted to be able to eject the payload from the bottom of the drone, as shown in the swapping process diagram above. So, my payload-securing mechanism had to wrap around this payload and apply a constant clamping force without expending energy or stalling the clamping motor. So, my initial design used carbon fiber plates to house a friction-reduction linear rail, a stepper motor, a threaded rod, and a large plate. The plate would move linearly and clamp onto the payload against a wall. The stepper motor would move this plate using a threaded rod, which would minimize any clamping forces from back-driving the motor.
Payload-Securing Mechanism V1
Payload Securer V1
Payload Securer V2
However, the V1 assembly used only one rail which increased the likely hood of a moment arm binding the linear rail. Plus, I needed to create housing for the payload. So, I modeled a carbon fiber plate frame that would house two rails. The addition of another rail would reduce bending moments about the rail’s pillow block and distribute clamping forces. I then designed more 3D printed components to interface between the clamping plate, rail, and threaded rod. The plate also included mounting for XT-150 connectors. This way the payload could charge the drone if it was a battery. Overall, the design became more developed, but there were still issues to solve.
Payload-Securing Mechanism V2
Eventually, one of the senior members noted that the length of my carbon fiber plates would be too flexible for the forces the assembly would experience. So, I used SolidWorks weldments to create a lattice structure made of 12mm diameter carbon fiber tubes. Using previously designed corner joints, I created a layout with the same linear rails and plate assembly. Furthermore, I replaced the hobby stepper motor with a servo that offered a greater torque output.
Payload-Securing Mechanism V3
Payload Securer V3
Assembling & Activating the Coupler
The active tether with a functional coupling mechanism onboard.