Is a Human Sized Quadcopter Really Different from a Small Quadcopter?

Is a Human Sized Quadcopter Really Different from a Small Quadcopter?

Drone Taxi, large payloads, long range, long hover time... the advantages of increasing the size of a quadcopter are obvious. Large multi-rotors are more expensive to test and build, so it is tempting to test small scale versions first. While this is a valid strategy, designers have to be aware of the limitation of their models.

 

Figure from Edmonds and Stringer

For example, small quadcopters are controlled by changing the speed of each propeller, while larger helicopter changes the pitch of the blades. At what size does the inertia make variable speed propellers impractical? Kendy Edmonds and D. Blake Stringer from Kent State University investigated how the transient response is affected by size in their papers 'Unmanned VTOL Propulsion Research – Scalability of Quadcopter Rotor-Motor Configuration Outside the sUAS Regime'. They also studied thermal response. The study was completed using the Series 1780.

Their graphs and test results will allow you to make interpolations for your own motors. The coast-down process is more sensitive to the rotor and motor size than the ramp-up. According to our understanding, this means that the controller of a large quadcopter should take into account the asymmetric response. Another conclusion of this paper is that thermal management strategy may change with larger motors. When scaling up a motor, the area available for thermal dissipation increases with the square of the size, while the mass of copper increases by the cube of the size. There are multiple other variables affecting the performance when scaling up, especially regarding the aerodynamics, but this paper is a good start!

 

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