One of the key features of the DPV is that it uses a magnetic coupling to transfer power from the motor to the propeller. This eliminates an otherwise sensitive feature; the dynamic shaft seal.
I will use a plane magnetic coupling. Using finite element analysis I was able to determine the horisontal force on the magnets versus the horisontal displacement. The gap between the magnets will be 6 mm, and I will be using 10 5 mm X 10 mm x 15 mm N52 neodymium magnets. When the outer diameter of the ring that holds the magnets is 80 mm, the coupling is able to transfer a maximum torque of around 6 Nm.
Exploded view of the magnetic drive assembly. Note that this is not the final design for the tailcone, only a rough model to show the principle.
Finite element analysis of the magnets using the free program FEMM. I was able to automate the simulations using Matlab, saving a lot of time!
3D model of the steel ring that holds the magnets on the outside (driven side) of the DPV.
The motor that I will use (BLT-500 trike motor from Goldenmotor.com) is rated to produce 500W @48V and 1000rpm. This yields a theoretical torque of 4.8 Nm. The performance charts from their website states that the maximum torque is 8.2 Nm, meaning that the magnetic coupling will slip if the propeller becomes entangled, effectively working as a safety clutch.
Matlab plot of the torque vs. angular displacement.
It will be very exciting to see if the simulated results agree with the results I will obtain from the real prototype!