Modular H-frame Quadcopter Drone

thingiverse

I've spend the past few months considering, and experimenting with, various drone designs. For now I have arrived at this H-frame quadcopter. * Designs consisting of complex monolithic pieces mean that any damage requires you need to reprint/replace large sections. Instead this design is composed of small modular pieces. * X-frame copters with electronics sandwiched between the top and bottom plate are a real pain for accessibility/maintenance. This design uses a single-layer structure with accessible electronics (or protected only by a non-structural fairing). * In the early days I spent too many hours printing drone arms only for the print job to fail or for them to fail in flight or during a heavy landing or crash. Carbon fibre is a wonderful, rigid, strong, lightweight material so let's use it for the backbone! * Hexacopters do not really offer redundancy except in very specific situations. Traditional helicopters, bicopters or tricopters require flight-critical servos so you still have about the same number of critical actuators in the end. I've opted for a quadcopter, which is as good a choice as anything by most criteria. This modular H-frame quadcopter is designed around around 15mm square carbon fibre tube. I purchased my tubes from Hobby King. https://hobbyking.com/en_us/carbon-fibre-square-tube-15-x-15-x-800mm.html Why square tubing? Although a square section arguably has intrinsic weak points that circular tubing doesn't have, a square also has higher rigidity than a circular section of the same principal dimension. More significantly I selected square tubing because it avoids the need to 3D print clamps, which tend to be brittle points of failure. None of the STL files require supports to print. The bolt holes are sized for M3 or an imperial equivalent. I suggest M3x30mm bolts and nylock nuts. I opted to made my drone fairly large ~650mm square with 15" props, but of course the same STL files can also be used to make a smaller airframe. The mounting 'shelves' have little nubs/standoffs on the side, which can optionally be used to screw a 'fairing' to cover any sensitive components. A 6 gauge screw should be about right. The fairings have a slight groove at the right level for where you should drill the screw holes. For mounting the battery, I suggest using the 'shelve' STLs and/or my customisable battery box thing. https://www.thingiverse.com/thing:4817598 I've included an STL for demo battery tray here which is a reasonable size to get you started. Your battery can be secured with two velcro straps. Motors get hot, so I suggest using a material with superior thermal properties for the motor mounts, such as nylon or ABS. That STL can either be printed on it's rectangular end (which is better if you are having warping) or on its face (which is better from the perspective of interlayer weakness affecting the part strength). The choice of material other components are less critical. I used PETG but PLA or whatever else you fancy is also probably fine. H-frame quadcopters develop some torsional twist in the chassis between the front and back. Ensure you configure the copter as an H-frame in your flight control software (and set the motor spin directions appropriately) and that will greatly improve the flight dynamics vs. if you try to fly it configured as an X-frame.