One propeller cartridge is two propellers that spin in opposite directions, they are both powered by the same electric motor. Although they spin in the opposite direction they both push the air in the same way. They are nested in a small grill to stop the little propellers from hitting anything around them.
The device I have in my head would be a kind of rigid shirt that has propeller cartridges built into it that fold outward when flight mode it switched on. I dream of trying to make such a thing. Perhaps it could be a back pack with an umbrella type thing that folds out.
