The structure of the DC motor
It should be composed of two parts: stator and rotor. The stationary part of the DC motor is called the stator. The primary function of the stator is to generate a magnetic field. The part that rolls during operation is called the rotor. Its primary function is to generate electromagnetic torque and induced electromotive force. It is the hub for the energy conversion of the DC motor, so it is usually called the armature. Constructor and fan, etc.
stator
(1) Main magnetic pole
The role of the main pole is to generate an air gap magnetic field. The main magnetic pole is composed of the main magnetic pole iron core and the excitation winding.
The iron core is generally made of 0.5mm~1.5mm thick silicon steel plate punching and riveting. It is divided into two parts: the pole body and the pole shoe. The upper part of the excitation winding is called the pole body, and the lower part is called the pole body. The pole shoe is wider than the pole body, which can not only adjust the distribution of the magnetic field in the air gap, but also facilitate the fixing of the excitation winding. The excitation winding is made of insulated copper wire and is sleeved on the core of the main magnetic pole. The entire main magnetic pole is fixed on the base with screws,
(2) Commutation pole
The function of the commutation pole is to improve the commutation and reduce the commutation sparks that may be generated between the brush and the commutator when the motor is running. It is generally installed between two adjacent main magnetic poles. composed of pole windings. The commutating pole winding is made of insulated wire and is sleeved on the commutating pole iron core. The number of commutating poles is the same as that of the main magnetic pole.
(3) Machine base
The housing of the motor stator is called the frame. The base has two functions:
One is to fix the main magnetic pole, the commutation pole and the end cover, and to support and fix the entire motor;
The second is that the base itself is also a part of the magnetic circuit, which constitutes the magnetic path between the magnetic poles, and the part through which the magnetic flux passes is called the yoke. In order to ensure that the machine base has sufficient mechanical strength and excellent magnetic permeability, it is generally made of steel castings or welded steel plates.
(4) Brush equipment
Brush devices are used to introduce or extract DC voltage and DC current. The brush device consists of a brush, a brush holder, a brush holder and a brush holder. The brush is placed in the brush holder and pressed by a spring, so that there is an excellent sliding touch between the brush and the commutator. Insulation is necessary. The brush rod seat is installed on the end cover or the inner cover of the bearing, and the circumferential position can be adjusted, and it will be fixed after adjustment.
rotor
(1) Armature core
Generally, the armature iron core is made of punched sheets made of 0.5mm thick silicon steel sheets and laminated to reduce the eddy current loss and hysteresis loss generated in the armature iron core when the motor is running. The stacked iron core is fixed on the rotating shaft or rotor bracket. The outer circle of the iron core is provided with an armature slot, and the armature winding is embedded in the slot.
(2) Armature winding
The function of the armature winding is to generate electromagnetic torque and induced electromotive force, and it is the key component of the energy conversion of the DC motor, so it is called the armature. It is composed of many coils (hereinafter referred to as components) connected according to certain rules. The coils are made of high-strength enameled wires or glass-coated flat copper wires. The coil sides of different coils are embedded in the armature slot in two layers. It is necessary to properly insulate between the iron cores and between the upper and lower coil sides. In order to prevent the centrifugal force from throwing the coil edge out of the slot, the slot is fixed with a slot wedge. The termination portion of the coil extending out of the slot is bound with a thermosetting weft-free glass tape.
(3) Commutator
In a DC motor, the commutator is equipped with brushes, which can convert the external DC power into alternating current in the armature coil
The direction of the electromagnetic torque is stable and unchanged; in the DC generator, the commutator is equipped with a brush, which can convert the alternating electromotive force induced in the armature coil into the direct current electromotive force drawn from the positive and negative brushes. The commutator is a cylinder composed of many commutator segments, and the commutator segments are insulated with mica sheets.
(4) Rotary shaft
The rotating shaft plays a supporting role in the rotation of the rotor, and needs a certain mechanical strength and rigidity. It is generally processed from round steel.
Selecting the correct DC motor or DC gear motor for a specific application can be a daunting task, and many manufacturers may only provide basic motor specifications. These basic specifications do not meet your needs. Below we list the specifications of the miniature DC motors and provide an approximation if possible.
The following is a very common specification, which is what a DC motor manufacturer might list. For most buyers, this basic information is enough to make a purchase or not.
1. Rated voltage:
Voltage corresponding to high motor efficiency. Try to choose a battery pack that matches the voltage rating of your drive motor. For example, if the motor is rated at 6V, use a 5 1.2V battery pack to get 6V. If your motor runs at 3.5V then use 3 AA or 2 AAA battery packs. If the motor is operated beyond its rated voltage, the efficiency of the motor decreases, which usually requires additional current, generates a lot of heat, and reduces the life of the motor. In addition to the rated voltage, DC motors also have an operating voltage range, and the manufacturer does not recommend that the motor operate beyond this range.
2. No-load speed:
Assuming there is no connection, this is the fastest rotational speed of the output shaft (angular velocity). If the motor has slowed down and the speed of the motor is not displayed separately, the rpm of the motor is proportional to the value of the voltage input. "No load" means that the motor is not encountering any resistance (the hub or wheel is not mounted to the end). Usually, the no-load speed provided is related to the rated voltage.
3. Rated power:
If the power of the motor is not listed, it can be approximated. Power (P) is related to current (I) and voltage (V). The formula is: P=I*V. Use no-load current and rated voltage to approximate the power output of the motor. Use the locked rotor current and the rated voltage (not the maximum voltage) to get the maximum power of the motor (this can only be used for a short period of time)
4. Stall torque:
This is the maximum torque that can be provided when the shaft of the motor is not rotating. If the motor is locked for more than a few seconds, the motor will suffer irreparable damage. When choosing a motor, you should consider that it should not exceed 1/4-1/3 of the stall torque.
5. Stall current:
This is the current consumed by the motor at maximum torque. This can be very high, and if there is no controller to control this current, it will suffer damage in very large cases. If neither stall nor rated voltage is provided, try to use the rated power and rated voltage of the motor to estimate the current: power[watt]=voltage[volts]*current[Amps]
General Specifications:
General specifications for DC motors usually include weight, shaft length and shaft diameter as well as motor length and diameter. Other useful specifications include mounting hole location and thread type. If lengths or diameters are provided, refer to pictures, photographs, or scale drawings to get a feel for other dimensions.
Torque:
"Torque" is calculated by multiplying force by distance. A motor rotating at 10Nm stall torque can be within 1m
Hold 10N. Likewise, it also maintains 20N within 0.5m. Note: 1kg*gravity (9.81m/s2)=9.81N (10N is for quick calculation)
Ideal Specifications:
The additional information listed by many motor manufacturers can be very useful when selecting the correct motor. When searching for DC motors, some of the following information you may come across:
Voltage vs Speed
Ideally, the manufacturer might list a graph of the motor's voltage versus speed. For a quick approximation, consider using no-load speed vs. rated voltage: (rated voltage, speed) and the point (0,0).
Torque VS Current:
Current is a value that is not easy to control. DC motors only use the required current. Ideal specifications include, curves, and approximations that are not easy to reproduce. The stall torque is related to the stall current. A motor that is disabled from spinning will draw the maximum ("locked") current and produce the maximum torque possible. The current required to provide a given torque is based on many factors, including the thickness, type and configuration of the wires used to make the motor, as well as magnets and other mechanical factors.
Technical specifications or 3D CAD drawings:
Many robots like to draw a picture of the robot on the computer when purchasing the necessary parts. Although all motor manufacturers have CAD pictures with dimensions, they rarely publish them to the public. The ideal motor size includes the information above, as well as mounting hole locations and thread types. Ideally, the materials and dimensions used to make the motors, gears and windings are provided.
Reduction ratio:
When the manufacturer of the DC motor produces the corresponding geared motor for the motor, it must provide the corresponding reduction ratio. Deceleration is used to increase torque and decrease speed. The given no-load speed value is always the value of the output shaft after deceleration. In order to obtain the angular velocity value before deceleration, it is necessary to multiply this value (no-load rotation speed value) by the reduction ratio. Before deceleration, for the stall torque of the motor, divide the stall torque by the reduction ratio. The material used to make the internal gears is usually plastic or metal, and is chosen to bear the maximum rated torque.
Accessories: For geared motors, encoders are often used accessories. Finding the right encoder for your motor can be very difficult if you're not sourcing from the same company. An optical encoder allows you to find the direction of rotation as well as the rotational speed of the motor. Along with a suitable encoding, an optical encoder can also give you the angle of the shaft.
Hubs and Couplings:
Wheel hubs (which are used to connect the output shaft to other components) are gradually adapting to different sizes of output shafts. Only a few manufacturers offer native couplings. If you cannot find a suitable coupling, consider using spur gears to offset the shaft to another size.
The above is about the main parameters to be considered in the selection of miniature DC geared motors. I hope that the articles shared by the editor of Toho Motors can help you better understand miniature DC motors.
