Quadcopter Arm Joints

thingiverse

The included stl files illustrate some of my ideas on how the joints between quadcopter arms can be improved. In many commercial designs with separate arms, the arms are either sandwiched between two carbon fiber plates, or between a carbon fiber plate and an aluminium brace. The arms may either be completely separate, or be "joined" by a simple butt joint. This is mechanically weak, and also weighty because of the need for brace plates and normally at least two bolts per arm. The joints here interlock and so have higher inherent mechanical strength. This reduces the need for bracing - perhaps only one brace plate is required and fewer bolts can be used: three (or perhaps only two) for joining two arms together, and when four arms are joined only four bolts may be required. The joins are symmetrical, so all arms in either a two-arm or four-arm set are identical. The joints use various combinations of finger and lap joints. The half-fingered joints are probably in some sense optimal, they don't require a lot of CNC machining while they offer quite a lot of additional mechanical strength. The half fingered lap joints are probably strongest, but require the most CNC machining. Note that I have 3D printed and tested some of these joints, but I have not actually CNCed any of them. Note that these stl files are not intended to be used directly: the arms themselves are only for illustration and are very rudimentary. The bolt placing is also for illustration - the bolts are not necessarily placed in the position that gives optimal strength.