Technological solutions to societal issues must be simple, sustainable, and most importantly, connected. For advantaged populations there is already a thorough, predefined infrastructure of communication, transport and utilities that allows new solutions to grow. However, there are billions of people living in poverty, many doing without the fundamentals of modern society such as medicine, clean water, and food.
When basic transport infrastructure is incapable, an effective system with a minimal footprint must be designed and deployed. Physically detached from the remainder of the developed world, it must self sustain while simultaneously drawing relevant updates to its implementation from abroad.
This is the idea of the LUV (Light Utility Vehicle)
The LUV family of UAVs applies off the shelf "drone" technology to a worldwide problem of lacking transport infrastructure. Critical, 3 KG supplies will be autonomously delivered with a sub $3000 aircraft at a range of up to 100 km. The LUV leverages digital design and fabrication in order to make local, as well as distributed manufacturing possible requiring only a consumer 3D printer (MakerGearM2) and a hotwire cutter (For cutting wing cores). A long term project goal is to setup a volunteer printing and assembly network similar to what e-Nable has accomplished for prosthetics.
The LUV is broken into discrete system modules which are easily replaced/repaired/reconfigured/updated while also remaining completely independent. This means that a large group of volunteers can work on the project simultaneously and remotely in order to reconfigure the LUV for the specific mission at hand. This work can range from modifying payload fittings to integrating additional active components such as surveillance systems etc.
The system modularity of the LUV is especially important when it comes to assembling and testing of the aircraft. It is designed to be fabricated with limited tools by a layman, which means it is well suited for use in remote regions.
The largest dimension of the largest component is under 1 m so the LUV is designed to go where it is needed most.
Construction: Locally sourced and COTS components are used throughout. All of the flight surfaces on the LUV are made of hotwire cut foam. A wide variety of easily sourced foams are adequate. In order to support lifting loads the flight surfaces are reinforced with composite spars. The spars in the tail surfaces are CF rod embedded directly in the foam cores, while the primary spar in the wing is a combination of 3D printed hardpoints, Graphlite rods in the caps, and a wet layup fiberglass shear web that is performed directly on the foam core. The wing surfaces are reinforced and covered with fiberglass shipping tape. The remainder of primary structural elements in the fuselage and are FDM 3D printed.3D printed parts are used throughout because they are cheap and consistent form of manufacturing, while also putting no constraints on material location within a part. Together with control over variable infill, the parts are as mass efficient as possible. These FDM components are slid onto a broomstick handle and fastened. A large variation of broomstick diameters and materials are suitable.
Payload: As specified by challenge requirements the LUV carries a primary 450 mm X 350 mm X 250 mm 3 kg payload. To keep operational costs low the payload will be packaged in a cardboard box. There are 3D printed shrouds slid over either end and are then joined by a waterproof cover that fully surrounds the remaining exposed surfaces of the payload. By mounting payloads under the wing a variety of sizes and envelops can be accommodated. Large payloads are held to the aircraft with velcro hoops that are easily released on the ground.
Secondary 1.5 kg payloads are mounted under the power modules and can be airdropped independently. A 3D printed shroud is attached to the front of a plastic bottle and released from the aircraft via the actuation of a metal gear servo mid flight. After release the dual parachutes that are stowed in the payload shroud are deployed by static lines.
Alternative payloads could be developed and easily integrated thanks to the LUV's modular architecture. Active payloads ranging from gimbaled optics to refrigerated medicine are made possible by close proximity to power and control electronics. Underwing mounting puts the payload under the primary flight avionics while mounting under the power module puts the payload directly under the battery. A standardized payload adapter will be developed so that the LUV can accommodate a range of payloads on a hotswappable basis.
Propulsion: The vehicle is an SLT configuration which reduces complexity and leverages reliable COTS components. Vertical thrust comes from 4 3D printed motor pods each, with coaxial mountings of Tiger Motor 4014 motors with 18 inch propellers. There is a mechanical brake system which clocks and locks the propellers with minimized frontal area for horizontal flight. Thrust for horizontal cruise comes from two identical Dual Sky 3520C motors mounted on 3D printed pods. They are swinging folding propellers which are easy to stow for transport purposes.
Landing Gear: The LUV's landing gear is a simple tail dragger configuration made from bent wire which is friction fit into 3d printed channels in the Power Modules as well as the Vertical Stabilizer. The gear is flexible enough to effectively absorb landing impacts but still stiff enough to support the fully loaded aircraft. The geometry of the gear can be modified by manually bending the piano wire to provide additional ground clearance for varying payload dimensions. Various lengths of wire can also be used. The wire is easily sourced and replaced so that a variety of missions and payload configurations can be accounted for.
Weather Resistance: All of the LUV's control electronics are enclosed and protected from environmental conditions. All servos have aerodynamic covers over them which also provide water resistance. ESCs are contained in the two Power Module, in addition to being plasti-dipped for additional weather proofing. All of the foam surfaces are sealed with Fiberglass reinforced tape to prevent any water absorption while also providing structural stiffness and an aerodynamically clean surface finish. The payload is also fully encased with 3D printed covers on either end and a water proof plastic wrapped center section.
Modularity: All systems break down into less than 1 m max dimension packages. The primary structure is based on parallel broomsticks which allow for limitless aircraft configurations and additional mounting options. The limited unique parts are reused between configurations to maximize their effectiveness.
Because the parts are all discrete each can be updated individually, either for performance improvements or specific mission requirements.
Ease of handling: The LUV is designed to be as simple as possible on a systems level to prevent user error or confusion during operation. The entire airframe is assembled with limited metric hardware requiring only 3 tools and 16 identical bolts total. When in operation all necessary functionality is easily accessible without additional hardware. The four 6S 10 Ah batteries are hotswappable and clip directly into the Power Modules. There are dual arming switches located on the outside of each Power Module to safeguard against accidental arming and to help simplify the user experience.
From a design perspective the LUV is a standard vehicle configuration meaning its stability is easily configurable and predictable, making it a flexible platform for various missions. Adapting it is as simple as moving modules along the two primary broomsticks to achieve the required balance point and static stability.
Weight: The mass fraction of the LUV regarding airframe structures is below 30% thanks to its minimalist configuration. Overall weight is kept below 17 kilograms due to a simplified design and the primary weights are distributed between the central pod and the two outer Power Modules. This effectively span loads the spar so its structural stiffness can be reduced, in turn reducing structural weight.
Failsafe and Safety: As with all UAS flights, safe operation of the LUV depends on a team of responsible and informed operators. Any risks related to mission success are investigated early in the planning phase of any system deployment. This assessed risk is minimized by establishing no fly zones which inform and limit any planned flight paths. This determines virtual "keep out" areas to minimize injuries and damage in case of an improbable vehicle failure. When operators are in direct contact with the vehicle is will always be disarmed. To rearm the system two identical sets of safety interlocks need to be activated, with both mechanical and software definitions checking vehicle states. A rigorous preflight checklist with both manual and automated entries is used to verify system integrity before launch.
While there is no parachute recovery system on board due to weight restrictions, the LUV relies on fault tolerant system design to overcome flight anomalies.
Propulsion System Safety: As a coaxial X8 the vehicle has a motor out capability which is software stabilized. In addition the LUV has two redundant horizontal thrust motors for cruise guaranteeing that it will make it to the desired delivery location with as little risk as possible.
Control System Safety: While in forward flight all of the controls are at a mimimum single fault tolerant as there are at least two control surfaces for control on each primary axis: pitch, roll, and yaw. Depending on mission risk assessments flight control computer hardware and sensors could be made fully redundant with fail over features included. The same applies to the flight control code and flight critical data processing algorithms.
Power System Safety: The LUV and all on board systems are powered by 4 identical 6S 10,000 mAh Multistar 10C lithium polymer off the shelf batteries wired in parallel. Critical control systems can be powered by only one battery, so the odds of a complete power system failure leading to no available vehicle power are minimized. Dual voltage regulators are used for the power of all critical hardware. A BMS (battery monitoring system) is also used to check the health of all four batteries simultaneously and to limit vehicle consumption in the event of a partial battery failure. In these limited power modes the primary goal of the FCC would shift from flight plan navigation to risk mitigation. Depending on the instantaneous flight mode of the vehicle (vertical or horizontal) system responses could range from gliding to a known safe zone, returning to the launch point, or mechanically locking all motors and preparing for impact.
Mechanical Safety: Designed to be as low impact as possible, the LUV possess a variety of mechanical features which limit risk associated with direct contact with the vehicle. Primary structural components are 3D printed which means they are frangible in nature, limiting the injuries they can cause. A further example of this is that the 4 lithium polymer batteries are fully encased by a minimum of 8 mm of FDM plastic to absorb impacts and prevent cell punctures.
However, most importantly is the low total kinetic energy of the vehicle. By limiting vehicle size, and in turn mass, the LUV's overall momentum is kept low to reduce impact energies in all configurations.
Conclusion: Seeking a minimalist solution, I designed the LUV to fulfill universal requirements with as little material cost as possible. The key to solving fundamental problems like the lack of transport infrastructure is a self sustaining solution that connects a population external to the problem with those who need the solution. This is made possible with digital design and fabrication so that via a distributed network of volunteers, parts and designs are created and then shared with those who need them. Combined with locally sourced materials and assembly, a safe and sustainable solution can be achieved.