Solar

Project Albatross

The goal for the project was to create an autonomous plane capable of flying for hours off of solar power. Another big aspect is the ability to takeoff from water using a pontoon system mounted to a 4-bar linkage. The plane is going to be made from foam board and 3d prints. The wingspan is 90in and the length is roughly 6ft.

https://cad.onshape.com/documents/cb4d8119196719dc9005cd1f/w/a50220c0795171ae93763f3d/e/ee41d6fe8c21d3f854f1676d?renderMode=0&uiState=6aa1fe8d3db98abb8ad60905

Motivation

We wanted to explore the idea of multi-hour flight using solar power. Most rc planes have a relatively short flight time, but we wanted to try and expand on that. That is why we also added the pontoons, so it could recharge on the surface of water.

Design

Pontoons

The pontoon mechanism works by having two hollow 3D printed hulls swing out when landing. The reason we decided to put them on a swinging mechanism was that it would greatly reduce drag, and in turn air resistance. Just based on frontal area that's around a 25% increase in efficiency. They will be driven by a motor that will winch it up or down.

Solar Panels

The solar panels just sit on the wing and will be wired to an MPPT board. They each generate around 3.5W in full sun, and there will be 17. It should be enough to sustain flight, but it will almost never get perfect lighting, so we will see. These sit on a 90in wing that has an 7in chord (not including the ailerons). Panels measure 125mm, so roughly 5in.

Hull

Used a series of ribs inside to support a really thin outer shell of 3D print. These will slide down into their corresponding spots, making the structure much stronger. The front one also serves as the motor mount too.

PCB

Flight Controller

The flight controller was built with Ardupilot in mind, with multiple connectors allowing for different sensors to be modular and swapped out. It is designed to take a 3 or 4S battery, and runs on an STM32F405RGT6. We are planning on using a GPS and a magnetometer but we have extra connector for different sensors if we want to add them going forward. We also have an IMU and pressure sensor on the board.

MPPT Board

We made a full solar circuit, with a MPPT board and BMI. With this plane design we kept the wings relatively small. Only 17 solar panels could fit. With each solar panel proving roughly 0.6V the total voltage was roughly 10V. This is well below the standard voltage of a 4s battery, thus we needed a step up MPPT board. The market for this is miniscule and expensive leading our design to be useful as it functioned as both a step up and step down board depending on the solar array. However, our board also ended up being far to expensive to become justifiable. We decided to pivot to using a standard step down MPPT and increasing the solar area, as well as deceasing the battery voltage to a 3S.

Assembly

The Plane

Most of the planes assembly consists of techniques similar to other rc planes. The wings are made from foam board "wrapped" around a dowel spar. They are made by cutting 3 slits across a sheet of foam board spaced out at 7in, 8iin, and 17 from one end. Then the paper layer of the foam board is peeled off for the top of the airfoil to create a better curve. The foam board is folded over the wing spar and three sections of these are connected.

The body is made from a dowel as the main structure of the hull, with 3d printed shells for aerodynamics and part containers. The slide onto the dowel and will be hot glued into place. Then the electronics are wired and placed into the nose cone of the 3d printed hull. The pontoons can then be mounted on they're hinges, which will be connected to n20 motor to swing up and down. Solar panels will be mounted on the wing using a plastic wrap to hold them in place, while still allowing sunlight through.

The PCB

Both the pcbs, especially the mppt board, are rather complex and have a lot of smd soldering. The use of a hot plate will be need and following the design the components will be soldered on. These boards will then be wired and hooked up to the rest of the planes electronics.

BOM