Connected motors with frames

The right electronics are the first step toward creating flight, but a multirotor isn't going anywhere without good old-fashioned physics to propel it upwards. The choice of motors therefore plays a pivotal role in the success of the machine.

Nevertheless, this choice is made difficult because of the complexity of specifications. We must do some research before settling on the right configuration for the hexacopter. Motors used these days are almost exclusively of the brushless variety, equating to minimal friction. Brushless motors are somewhat similar to traditional DC motors in that coils and magnets are used to drive the shaft. However, they do not have brushes on the shaft—hence their name—for switching the power direction in the coils. Brushless motors have three coils on the inner center of the motor, which is fixed to the mounting.

Brushless motors are assigned various notations, the most substantial being the Kv rating. Confusingly, Kv does not refer to kilovolts in this case. Instead, it's a motor velocity constant denoting the revolutions per minute (RPM) that a motor will turn when a 1V potential difference is applied with zero load. This number is significant, as it defines a multirotor's flight characteristics based on specifications like battery voltage and takeoff weight.

Robotics Institute 

University of Michigan, Ann Arbor

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Updated on 8/21/2017