DC steppermotors are type of dc motors which are used because of their accuracy. They canrange from simply designed motors with as little as 6 stator teeth and 4 rotorteeth to more accurate designs which have 48 stator teeth and 50 rotor teeth.In a simple stepper motor with 6 stator teeth, 3 external power sources areconnected to 3 pairs of stator teeth. When a current is provided, they formpositive and negative poles. A permanent or electro-magnet called the stator ismade up of a series of insulated layers called laminations. When a pair of therotor teeth becomes energised, the opposite poles attract and the armaturerotates.
When this pair is de-energized and the next pair is energised thestator gets attracted to the next one and in this case will rotate 30° eachtime. In another example of a stepper motor which has 48 stator and 50 rotors,a similar method is used but instead a step angle of 1.8° can be achieved. Ifeel that a quad-copter doesn’t require this kind of accuracy that the steppermotor would offer and that other motor types would be ideal for this reason.
One advantageof stepper motors is that they can be quite small which is required if it wasfor a small quadcopter. Size isn’t a reason why I think they shouldn’t be usedfor a quad-copter but the size may affect the characteristics of the motor. A steppermotor which has a higher step count tends to be larger and the speed and torquecan vary because of this. High step count motors top-out at lower RPMs. Thehigher step-rates needed to turn these motors results in lower torque than asimilar sized low-step-count stepper motor at similar speeds. Therefore thesize of the motor does not matter too much, as long as it has enough torque topower the given rotor blade size. A motor with higher torque will drive alarger propeller at lower speed when producing a given power output versus a motorwith higher speed. The higher speed motor’s smaller but faster propellers willbe less efficient than the lower speed one.
Efficiency is an importantperformance characteristic because it will mean the quadcopter can fly forlonger on one charge. A stepper motor is less efficient than other motors forthe use in a quad-copter so this is another reason why I do not think they arethe ideal motor for the job.