Small DC Motors
DC motors are the engine behind many of the technological advancements that we rely on. They power everything from robotic movements to car seat adjustments.
Noise measurements without load on a small DC motor showed high response to structural excitation of the bottom cap and housing center, as well as to reconstructed particle velocity on the housing surface at 1360 Hz.
Stator
The stator is the fixed part of a motor that houses its field windings. These windings are made of insulated copper wire, which generates magnetic fields when current flows through them. This interaction between the rotor and the stator’s field creates electromotive force that turns the rotor.
The coils in the stator are distributed in a circular fashion. As a result, the voltages induced in each coil are somewhat displaced in time from each other. This phenomenon is known as phase delay and can be measured using a voltmeter to test the performance of a stator. In particular, one can test for a significant variation in the voltage across different coils that may indicate unequal winding resistance or shorted turns.
There are a variety of ways to wind a stator, including lapping or concentric winding. In general, lap winding connects adjacent coil sides in parallel, forming closed loops, and is common in direct current (DC) machines. Concentric winding, on the other hand, arranges coils in layers, with each layer covering the previous one, optimizing space and reducing copper consumption.
PCB Stators replace traditional copper wound stator designs in order to reduce costs and produce more efficient electric motors. This innovation in design technology allows for the creation of smaller and lighter electric motors, enabling their use in a range of everyday applications including consumer electronics like laptops and smartphones, automotive systems such as power windows and mirror control, and even robotic applications like surgical tools and regenerative drives.
Rotor
The rotor is the dynamic part of the motor that rotates Small DC motor to create the mechanical revolutions. It consists of multiple disks that are insulated from each other by laminated sheets. This design prevents the creation of a large eddy current which would waste power, and minimizes acoustic noise and vibration.
The fixed part of the motor is called the stator and has permanent magnets that provide a stationary magnetic field. To make the rotor spin, a sliding electrical switch is used to alternately attract and repel the rotor’s magnetic fields. This is known as commutation. The commutator is made of segments and fixed brushes that connect to the motor windings. When a control input is connected to either transistor TR1 or TR2, the commutator is switched “ON” and point A is connected to +Vcc and point B is connected to 0 volts (GND).
By continuously switching the rotor windings “ON” and “OFF” at a high enough frequency, the motor’s speed can be controlled between stand still (0 rpm) and full speed (100%). This is done by varying the mark-space ratio of the motor’s supply voltage, which can be achieved using a technique called Pulse Width Modulation. A more advanced control method requires a micro-controller that calculates the position of the rotor relative to the fixed field using back EMF measurements and other motor parameters.
Commutator
For a motor or generator to work, its rotor coils must connect with the external circuit, a source of current in a motor or a load in a generator. This connection occurs when springs press carbon brushes against a commutator. The commutator, in turn, transfers power from the rotor to the outside circuit.
In a motor, the commutator is made up of insulated copper segments that are fixed to the rotor’s winding coils. As the Small DC motor wholesale rotor rotates, these commutator segments selectively reverse the current direction through the coils to keep them turning and to convert alternating voltage into direct voltage (DC).
The sliding contact between the brushes and the metal brush holders keeps this electrical connection from breaking while the commutator changes directions. This switching of current direction prevents the rotor from shorting out because it is always receiving DC from a different position in the external circuit.
Early machines used hard copper wire brushes to make contact with the commutator, but these brushes quickly produced invisible scratches and grooves on the smooth surface of the commutator. These grooves acted as paths through which the current could pass, and created a significant increase in the resistance of the coils. A solution to this problem was found with gauze brushes or fine copper wire mesh that allowed a much more gradual contact of the brushes with the commutator segments and reduced the amount of wear on both.
Wires
Typically, small DC motors come with 3 thin wires attached to the terminals. The yellow and green are the phase wires and the blue is the fan / speed control wire. Adding some solder and heat shrink to these short wires makes them easy to connect to your project. If you want to bench test the motor, you can take a long cable and touch A1 to + and S1 to – (do not leave this on for very long as an internal NiMH cell will supply a lot of current). It should spin CCW, if you touch it the other way around it will spin CW.
The motor operates by magnetism. Magnets have polarities, so opposite ends attract while similar ends repel. If you put two magnets next to each other on a spinning shaft they will rotate in the direction of rotation of the shaft, just like the two coils of the motor.
If you have a unipolar motor (two effective coils, each with a center tap), it will have an additional three thinner hall sensor wires, U(Yellow)-V(Green)-W(Blue) or A(Yellow)-B(Green)-C(Blue). So the total number of motor wires on a typical brushless motor is 8 leads.
The bare metal connectors on the motor can be quite fragile, especially after being bent, so it is important not to pull on them too hard when working with them. It may be a good idea to wrap them in some tape to decrease the chance of damaging them.