V7.2 - Mass Characteristics
With an unloaded total mass of 56.315 +/- 3.780 lbs (25.540 +/- 1.714 kg), the V7.2 drone is just outside of the FAA's 55 lbs upper limit. V7.3 significantly reduced the overall mass, and V8 will solidify the design scale. I'll make sure to create an new Mass Characteristics page in the coming months once V8 is complete. -Bryan 03/07/18
Percentage of Unloaded Mass
Electronics - 8.75 lbs (3.9690 kg)
Reliable Sensing and Computing
Designed to accommodate programmable microprocessors, the Electronics Bays in V7.2 are built for plug-and-play design with low development cost. The onboard processing receives and executes the flight data package after the user transmits it to the drone over a secure Bluetooth connection. From there, a GPS interprets the flight data. Payload door check, landing check, and other core features are performed by accessing local Ultrasonic Proximity data and simple continuity lines.
Active cooling maintains an operable environment for the batteries, even while the drone is in hover. Energy from heat-generating components is sunk to the aluminum frame, and hot component surfaces (including batteries) are exposed directly to atmosphere for in-flight cooling.
A integrated load cell transmits data over Bluetooth to the Touchdown Delivery Application allowing weight data to be displayed while loading.
Three small geared servos retract and extend the legs. This critical feature, often neglected by other drone designs, allows for automated landing with minimal instability due to rotor wash. Once airborne, the retracted legs are clamped with linear microservos, so the deployment servos aren't required to stay energized. The tucked legs improve aerodynamics.
Because our drones navigate solely using GPS data and Proximity data, we have no need for onboard cameras.
Once arrived over a destination, our laser sighting technology makes for a landing rendezvous that nearly any smartphone user can manage.
Battery - 19.404 lbs (8.8017 kg)
Deep Cycle LiPo - Designed for 40 Minute Operation
V7.2 was designed with 66 Ah of power. Ultimately, I've backed off this design because of the overall mass the vehicle ultimately reaches when all other systems are considered.
V7.3 featured a reduction to 44 Ah of power, and V8 will maintain this reduction. Part recombination, substitution, and elimination along with max payload reduction and structural member refinement means 40 minute flight times will still be obtainable with the reduced power.
Structure - 18.255 lbs (8.2803 kg)
Aluminum 6061 Frame
Waterjet cutting is used as the primary method of frame manufacture. Cut Al profiles are bent precisely, deburred and chamfered, and tapped. Only two sheet thicknesses are used throughout the design.
Right angle brackets are machined with minimal tool changes from extruded stock.
Polycarbonate sheeting is also used throughout the design. It laser cuts cleanly, comes in many colors, is chemically tough, and structurally predictable.
ABS and PLA prints are also used throughout the design for mounting components and for the shrouds. This speeds up prototyping and allows for local plastic component production.
Propulsion - 8.84 lbs (4.0097 kg)
Designed for Thrust and Stability
Counter-rotating electric motors balance the torque required to accelerate 6 propellers. The two largest propellers (29") are shrouded to reduce tip losses and provide clear visibility during nighttime flights.
The 4 control propellers (14") are positioned farther from the centroid to maximize their controlling influences on the craft.
All propellers are tilted 10 degrees forward, which lowers their frontal profile during forward flight, and reduces drag forces significantly.
The propellers are carbon fiber. The driving motors are IP55 rated. Each motor has a capable Electronic Speed Controller.
Upholstery - 0.64243 lbs (0.2914 kg)
The frame is designed to support two elastic mesh sport pouches - one in the front and one in the back of the vehicle. A thin layer of rubberized foam creates a backing for fabrics. The edge of the payload is designed to clamp down on several layers of fabric and stitching, as are the lights.
The interior is lit by an ambient light sensitive circuit which diffracts high-output LEDs through printed lenses.
Fasteners - 0.413 lbs (0.187 kg)
The V7.2 design is done with several ANSI sizes, and ISO where needed for component mounting. The thematic emphasis for fastening in my design has been bolt reduction, recombination, and elimination. Where possible, fewer, larger bolts are favored, and numerous small bolts are avoided.
Subsequent designs will focus on nut elimination, instead emphasizing positioning fasteners so there is always an aluminum panel to tap into before the bolt thread terminates.