Pelidrone

ENGR423 is an course that introduces students to the sciences and fundamental behind drones. Students then work in groups to utilize these lessons to either design and manufacture or develop computer vision algorithms for drones to meet an open-ended outcome proposed to the professor and decided on by the group.

The Pelidrone is water proof drone designed to safely fly over bodies of water, with capabilities of landing on and taking off from surfaces of water to allow for energy savings, as well as the ability to be retrieved and used again in the potential situation of a fall.

Throughout the semester long course, the Pelidrone was designed, manufactured, and tested, resulting in many lessons learned and the final project shown below. 

Parts List

• (1x) 3S LiPo 3000mAh 30C

• (1x) Pixhawk Flight Controller

• (1x) FrSky Receiver (any with ACCST protocol) and Transmitter (Taranis Q X7 ACCST)

• (1x) 8 Channel SBUS Hub``

• (4x) ESCs with Opto BEC or BEC disabled (30A continuous current)

• (4x) DJI 2312E motors

• (2x) CW 9x4.7 propellers, (2x) CCW 9x4.7 propellers

• (1x) Power Distribution Board (100A continuous)

• (1x) GPS

• (1x) Roll of Red PLA Filament

• (1x) 2’x3’ Acrylic sheet

• (12x) M3 - 16mm Screws for Motor Mounts

• (12x) #4 Flat Washer Plain Steel for Motor Mounts

• (20x) 10/32” x 1/4" Screws for Gasket

• (20x) #10-L Flat Washers for Gasket

• (20x) #10-32 x 0.225” Heated Inserts

• (20x) Male and Twelve Female Banana/Bullet Connectors

• (12x) 6” Wires of 16awg Stranded Core

• (Kit) Black and Red Heat Shrink Tubing

• (2x) Female XT60 and (2x) Male XT60 Connectors for Arming Plug

• (1x) 1/16” BUNA-N Sheet

System Description

When designing the Pelidrone, the team decided to target a thrust to weight ratio of at least 2:1 in order to be able to maintain a stable hover at most 50% throttle. The static thrust output of the DJI 2312E is ~1.6 lb with a 9x4.7 prop at full throttle when powered by a 3S LiPo battery. Multiplied by four motors, our system will produce 6.4 lbf of static thrust. Our drone weighs approximately 2.5 lb in total, providing us with a TWR of 2.56. This will be sufficient to power and safely maneuver our drone, and maintain a hover at 40% throttle. Further, a 3000mAh LiPo battery with a 30C rating was selected. The expected maximum continuous current draw of our system is approximately 60A. This will provide us with 6 minutes of flight time. 

With a total weight of 2.5lb and a 20% factor of safety, the drone body was designed to have a buoyant force of at least 3 pounds to maintain positive buoyancy. With this force, the drone is able to float above the water while the motors and wire connections. Furthermore the large base profile allows the drone to resist large waves and turbulent water flow.

Final Outcome

Overall, the novel unibody 3D-printed design with the gasket proved to be waterproof throughout multiple tests. Complete submersion tests demonstrated that minimal amounts of water entered the body. No water entered through the gasket interface, while a small amount of water seeped through the motor wire holes. Epoxy was used to improve the seal at these interfaces. However, the epoxy contracted and created small holes during curing, allowing a few drops of water. While a few drops of water were present, they were in the arms and far away from the electronics in the center, demonstrating the reliability of the design. One future work includes improving the motor wire to body connection by using more epoxy or creating a special 3D printed cover. 

The positive buoyancy of the drone was then tested on a moving body of water. The drone was connected to a fishing line and lowered into a stream from a bridge. The drone was able to stay afloat with the motor and wires persistently staying above the water. The stream water was very turbulent and had many waves. The drone was able to stay afloat and was never completely submerged, demonstrating the ability of its large profile to prevent it from flipping over.

The team faced significant challenges during the test flights. The drone presented consistent issues with ESC calibration. Specifically one of the motors failed to spin, causing the drone to yaw or flip over. This then led to overcurrent in the wires and significantly damaged the electronics. Future works include selecting more appropriate ESCs. Due to the ESCs being enclosed with reduced heat dissipation, higher maximum current ratings should be selected. An appropriate ESC for the DJI 2312E motor would support at least 30A continuous current with thermal cutoff. Further improvements can be made to physically separate electronic components to ensure the ESC or batteries do not overheat.