A multi-rotor self-propelled movable object (700, 800), the movable object comprising: (a) a first rotor assembly, comprising: a first hub coupled to a first plurality of blades; a first drive shaft coupled to the first hub by a mating connection of first and second fastening features, wherein the first drive shaft is configured to cause rotation of the first hub in a first direction, and the mating connection of the first and second fastening features is able to be tightened by the rotation of the first drive shaft in only the first direction; wherein the first plurality of blades coupled to the first hub are configured to rotate therewith in the first direction to generate a first propulsive force, and wherein the first and second fastening features comprise mating screw threads; and (b) a second rotor assembly, comprising: a second hub coupled to a second plurality of blades; a second drive shaft coupled to the second hub by a mating connection of third and fourth fastening features, wherein the second drive shaft is configured to cause rotation of the second hub in a second direction that is opposite to the first direction, and the mating connection of the third and fourth fastening features is able to be tightened by the rotation of the second drive shaft in only the second direction; wherein the second plurality of blades coupled to the second hub are configured to rotate therewith in the second direction to generate a second propulsive force. (a) a first rotor assembly, comprising: a first hub coupled to a first plurality of blades; a first drive shaft coupled to the first hub by a mating connection of first and second fastening features, wherein the first drive shaft is configured to cause rotation of the first hub in a first direction, and the mating connection of the first and second fastening features is able to be tightened by the rotation of the first drive shaft in only the first direction; wherein the first plurality of blades coupled to the first hub are configured to rotate therewith in the first direction to generate a first propulsive force, and wherein the first and second fastening features comprise mating screw threads; and a first hub coupled to a first plurality of blades; a first drive shaft coupled to the first hub by a mating connection of first and second fastening features, wherein the first drive shaft is configured to cause rotation of the first hub in a first direction, and the mating connection of the first and second fastening features is able to be tightened by the rotation of the first drive shaft in only the first direction; wherein the first plurality of blades coupled to the first hub are configured to rotate therewith in the first direction to generate a first propulsive force, and wherein the first and second fastening features comprise mating screw threads; and (b) a second rotor assembly, comprising: a second hub coupled to a second plurality of blades; a second drive shaft coupled to the second hub by a mating connection of third and fourth fastening features, wherein the second drive shaft is configured to cause rotation of the second hub in a second direction that is opposite to the first direction, and the mating connection of the third and fourth fastening features is able to be tightened by the rotation of the second drive shaft in only the second direction; wherein the second plurality of blades coupled to the second hub are configured to rotate therewith in the second direction to generate a second propulsive force. a second hub coupled to a second plurality of blades; a second drive shaft coupled to the second hub by a mating connection of third and fourth fastening features, wherein the second drive shaft is configured to cause rotation of the second hub in a second direction that is opposite to the first direction, and the mating connection of the third and fourth fastening features is able to be tightened by the rotation of the second drive shaft in only the second direction; wherein the second plurality of blades coupled to the second hub are configured to rotate therewith in the second direction to generate a second propulsive force.