1. Magnetic material: ferrite

Ferrite, also known as ferrite or magnetic porcelain, belongs to non-metallic magnetic materials. It is a composite oxide (or orthoferrite) of magnetic ferric oxide and one or more other metal oxides. Metal oxides with ferrimagnetism, the magnetic force is usually 800-1000 Gauss. 

In terms of electrical properties, the resistivity of ferrite is much larger than that of single metal or alloy magnetic materials, and it also has higher dielectric properties. The magnetic properties of ferrite are also shown to have higher magnetic permeability at high frequencies. Therefore, ferrite has become a widely used non-metallic magnetic material in the field of high frequency and weak current. Due to the low magnetic energy stored in the unit volume of ferrite, the saturation magnetic induction (Bs) is also low (usually only 1/3 to 1/5 of pure iron), which limits its use at low frequencies that require higher magnetic energy density. It can be applied in the field of strong electricity and high power.

2. Magnetic material: NdFeB

NdFeB permanent magnet material is a permanent magnet material based on the intermetallic compound Nd2Fe14B. The main components are rare earth elements neodymium (Nd), iron (Fe), boron (B). Among them, the rare earth element is mainly neodymium (Nd). In order to obtain different properties, it can be partially replaced by other rare earth metals such as dysprosium (Dy) and praseodymium (Pr). Iron can also be partially replaced by other metals such as cobalt (Co) and aluminum (Al). The content of boron is small, but it plays an important role in the formation of tetragonal crystal structure intermetallic compounds, making the compounds have high saturation magnetization, high uniaxial anisotropy and high Curie temperature. 

NdFeB is a high-performance rare earth material with high coercive force and high magnetic energy product, and the continuous improvement of this material in recent years has increased the use temperature and reduced the cost of the material. Applying NdFeB rare earth permanent magnet materials to the development of various motors can significantly reduce the quality of the motor, reduce the size of the motor, and obtain high-efficiency energy-saving effects and improve the performance of the motor.

3. The difference between the two

The advantages of NdFeB are high cost performance and good mechanical properties; the disadvantages are that the Curie temperature is low, the temperature characteristics are poor, and it is easy to pulverize and corrode. It must be improved by adjusting its chemical composition and adopting surface treatment methods. , in order to meet the requirements of practical applications.

Ferrite is a metal oxide with ferromagnetic properties. In terms of electrical properties, the resistivity of ferrite is much larger than that of metal and alloy magnetic materials, and it also has higher dielectric properties. The magnetic properties of ferrite are also shown to have higher magnetic permeability at high frequencies. Therefore, ferrite has become a widely used non-metallic magnetic material in the field of high frequency and weak current.

NdFeB belongs to the third generation of rare earth permanent magnet materials. It has the characteristics of small size, light weight and strong magnetism. It is the magnet with the best performance and price ratio at present. The advantages of high energy density make NdFeB permanent magnet materials widely used in modern industry and electronic technology. In the state of bare magnets, the magnetic force can reach about 3500 Gauss.

Ferrite, also known as ferrite or magnetic porcelain, belongs to non-metallic magnetic materials, and is a composite oxide (or ferrite) of magnetic ferric oxide and one or more other metal oxides. The magnetic force is usually 800-1000 gauss, and it is often used in speakers, speakers and other equipment in addition to motors.

The general differences between NdFeB magnets and ferrite magnets are as follows:

 ( 1 ) The magnet performance of ferrite is poor, and the magnetic performance of neodymium iron shed is about 3 times that of ferrite.

 ( 2 ) In terms of price, the price of ferrite is much cheaper than that of NdFeB magnets.

 ( 3 ) NdFeB magnets have good temperature resistance, but demagnetization will occur if the working temperature exceeds a certain level. Therefore, it is recommended to choose a grade with a higher coercive force in a high-temperature working environment.

 ( 4 )The stability of ferrite is very good. It is an oxide itself, which is very stable. NdFeB is an alloy, and it is easy to oxidize, so it must be protected by coating.

Therefore, usually in the case of meeting the performance requirements of the motor, it is also necessary to consider better meeting the requirements of high cost performance. BG Motor's technical engineer team and business team will combine your requirements to customize and recommend suitable magnetic materials for you. Usually, brushless DC motors will choose high-performance NdFeB magnetic materials, and brushed DC motors will choose ferrite materials that are more economical; If some customers think that the control system of DC brushless motors is troublesome, we still The structure of the brushed DC motor can be customized, and the NdFeB magnetic material can be used, so that the torque of the motor can be larger, and it is easy to operate and use.

What is an air gap?

A simple way to define air gap is to say it is the air in the space between the stator and the rotor of the motor.

More specifically, we can have similar definitions for alternating current or AC motors and direct current or direct current motors.

In an AC motor, the air gap is the air space between the rotor core and the stator. On the other hand, it is said to be the space between the poles and the armature of a DC motor.

The flux gap is the distance between the high permeability material in the stator (stator "iron") and the corresponding high permeability material in the rotor (rotor "back iron"). This material is usually made from thin laminations of Fe-Si steel.

As we all know, in general, the flux gap should be as small as possible. 

Note that the flux gap includes magnets. Rare earth magnets (magnetized or unmagnetized) have essentially the same permeability as air. Therefore, from the stator point of view, the magnets are indistinguishable from air and should be included as part of the flux gap.

How does the air gap work?

To understand how air gaps work, first remember that electric motors and generators are rotating electrical machines.

This means that electric motors and generators work very similarly. The difference is that electric motors convert the supplied electrical energy into mechanical energy. Instead, generators take specific mechanical energy and convert it into electrical energy.

In both cases, the energy conversion process occurs when the stator and rotor work together to generate magnetic flux through their own copper windings. This is where the air gap comes into play.

A magnetic field is formed in the air gap, and one of the above-mentioned windings is responsible for generating the magnetic flux, which has to pass through the air gap twice for each pole of each phase of the motor.

Some of the key factors related to air gap operation are:

Magnetic force is inversely proportional to the square of the distance. As the air gap size increases, the magnetic attraction decreases and becomes more difficult to control.

Increasing the size of the air gap increases the magnetizing current, which represents the amount of current required to drive magnetic flux through the air gap.

The more poles a motor or generator has, the more times the flux must cross the air gap per revolution.

All these factors lead us to conclude that the smaller the air gap, the better. However, a smaller air gap means less separation between the moving parts of the rotor and the stator. This is why monitoring the air gap in motors and generators is critical, as the slightest variation in the alignment of the air gap with these characteristics can create operational problems in the machine.

The magnetic circuit consists of a soft iron ring, a copper winding (2A, 250 turns) represented by a green rectangle, and an air gap in the ring. Flux density (units of Tesla) is represented by the distance between the flux lines and the color, with red being the highest density and blue being the lowest. The flux density is clearly greatest in rings with small flux gaps. This ring also has the least amount of flux "leaking" into the surrounding air.

The reason for this difference is that the air gap increases the reluctance of the circuit. Reluctance is flux in a magnetic circuit, just like resistance is current in a circuit. Therefore, the magnetic flux in a circuit depends on the total reluctance and the applied magnetomotive force (number of turns times the current), just as the current depends on the total resistance in the circuit and the applied voltage.

Let's take a closer look at how the flux varies with the flux gap itself. We can do this by drawing a line across the flux gap and measuring the flux density at each point on the line.

Doing this for flux gaps of 1 mm and 4 mm it is clear that the flux in the middle of each gap remains the same. It can also be seen that the flux in the 4 mm flux gap is four times smaller than the flux in the 1 mm flux gap. So to produce the same flux density in a 4 mm gap we need to quadruple the windings at the same current, or keep the same number of windings and quadruple the current. This concept can also be applied to electric motors and explains why engineers usually go to great lengths to keep the flux gap as small as possible.

Influence of Flux Gap Size on Torque of Simple Motor

The torque produced by the motor depends on the flux density in the air gap, and as the size of the flux gap increases, the torque decreases gradually

From the above discussion it is clear that in general we want the flux gap to be physically as small as possible to increase the motor torque output, hence it is the motor constant. However, in addition to manufacturing tolerances, we also need to consider the thickness of the magnet. In general, if you make the rotor magnets longer, the flux density at their poles also increases. This will increase the torque output of the motor.

If you don't know much about the internal clearance of the brushless motor, you can contact our salesman, and they will give you a professional answer.

The movement of the robot itself requires the use of motors. There are a variety of motors available for robotic applications. Each type of motor serves a different purpose. Motors aid in the movement of the robot and act as actuators in the mechanical design of the robot. Robotic applications may involve the following types of motion:

1) Vertical movement - usually by shoulder rotation to move part of the robot up and down

2) Radial movement - moving part of the robot in and out

3) Rotational movement - Rotation clockwise or counterclockwise around a vertical or horizontal axis or around a plane in a 3D frame

4) Pitching motion - up and down motion while rotating motion

5) Rolling motion - rotation of a part of the robot on a parallel axis relative to the rest of the robot's body

6) Yaw motion - right or left rotational motion of a part of the robot

7) Motion - the movement of the robot on a surface or medium

All these types of movements are achieved with the help of various motors or pumps assembled with the drive train and end effectors. In this tutorial, the use of motors to provide the main motion for the robot itself or its components will be discussed. This tutorial will examine different types of motors, their applications, motor selection, and robotic car design.

Motor type

There are many types of motors available in industry. For robotic applications, some type of motor is usually used. Motors commonly used in robotics applications can be divided into the following categories:

• AC motor

• Brushed DC motor

• Brushless DC motor

• Geared DC Motor

• servo motor

• Stepper motors

Today we will introduce three types of motors (AC motors, brushed DC motors, brushless DC motors)

AC motors are driven by AC current. They are typically used in heavy duty applications requiring high torque (high load or load capacity). That's why these motors are used in robotic assembly lines deployed in manufacturing cells. Mobile robots are usually powered by a DC power source (battery or series of batteries), which is why AC motors are rarely used for such robots.

Brushed DC Motor:

Brushed DC motors use brushes to conduct current between the power supply and the armature. There are several variants of brushed DC motors, but in robotics, permanent magnet DC motors are used. These motors are known for their high torque-to-inertia ratio. Brushed DC motors are capable of delivering three to four times more torque than their rated torque. A brushed DC motor consists of six different components: shaft, commutator, armature, stator, magnets, and brushes.

Brushed DC motors have two terminals. When voltage is applied to both terminals, proportional speed is output to the shaft of the brushed DC motor. A brushed DC motor consists of two parts: the stator including the housing, permanent magnets and brushes, and the rotor consisting of the output shaft, windings and commutator. Its stator remains stationary while the rotor rotates relative to the stator. The stator produces a stationary magnetic field around the rotor.

The rotor, also called the armature, consists of one or more windings. When these windings are energized, they generate a magnetic field. The poles of this rotor field are attracted by the opposite poles created by the stator, causing the rotor to rotate. As the motor turns, the windings are continuously energized in different sequences so that the poles produced by the rotor do not exceed those produced by the stator. This switching of the magnetic field in the rotor windings is called commutation.

Brushless DC Motor:

Brushless DC motors are similar in structure to brushed DC motors, but they are driven by a closed-loop controller and require an inverter or SMPS for power. These motors have permanent magnets that rotatably fix the armature. Compared to brushed DC motors, they have a closed-loop electronic controller in place of the commutator assembly. These motors are typically used in industrial robots that require precise control of motion and positioning. However, these motors are very expensive and involve complex structures and electronics.

To choose motors for the robot:

To choose the right motor, many different parameters must be considered, such as the load a particular motor can handle, the torque required to move the robot without overloading, the number of revolutions per minute the motor makes while under load, etc.

Since there are many types of motors, one should be selected based on the application. For example, to run a robotic arm, servos are often used. Wheeled robots are simple in design and use electric wheels to navigate the ground. Wheels are also easier to design and manufacture than tracks or outriggers. There are some drawbacks to using wheels, such as navigating obstacles or low friction areas that are not easy to use wheels.

The most commonly used motors in such robots are DC motors. DC motors provide high torque with high efficiency. By applying torque in response to a load, a DC motor can be characterized by a speed and torque curve. DC motors used in hobby robots are usually preferred with voltage ratings of 3, 6, 12 and 24 volts. If the voltage applied by the motor is lower than what is given in the datasheet, the torque will not be able to overcome the internal friction - mainly from the brushes. Also, if you apply a higher voltage to the motor than it supports, it can get hot and damaged.

If you are still worried about finding a motor, please contact the salesman of BG Motor, they will give you a very professional motor answer