The fist step for creating the hero drone and its engines was making the blocked out models with collision hulls and testing their dimensions in-game. They had to be big enough to plausibly interact with the environment, carry common household items (like wrenches or cups) but small enough to comfortably navigate in human sized, furnished rooms.
Certain parts of the engines animate when the drone is moving around (rotor cages tilt, the thrust reverser opens, etc) so I rigged them right in Modo. The logic driving the rig was simple but helped the modeling a great deal as I was able to see problems right away.