youshuang ding
In robots, actuators are generally divided into two types: hydraulic drive and motor drive, of which electric Sierra Leoneans EscortMachine drives are the rarestSierra Leone Sugar. This article mainly discusses the selection of motors in general robot driving mechanisms.
Commonly used motors in robots are divided into brush DC motors, brushless DC motors, permanent magnet synchronous motors, stepper motors, etc. Among small and medium-sized robots (size 15cm-30cm), DC motors and brushless DC motors are the most common due to their low price and high positioning accuracy. This article mainly discusses the selection method of DC motor.
Part One: Motor Requests
Introduction to DC Motors:
In the market, there are a variety of DC motors. According to incomplete estimates, there are thousands of electric baby delivery stores in China alone. Not to mention Japan, Germany and other established powerhouses in electric motor production. Even for a small DC motor, it has Sierra Leoneans Sugardaddy a complex internal structure and a large amount of product materialsSierra Leone Sugar. Here, we only consider its requirements for motor performance from the perspective of the robot.
The choice of motor is often a compromise between our performance requirements for the motor Sierra Leone Sugar Daddy and the price we can accept. Therefore, during the motor selection process, we need to comprehensively consider the various parameters of the motor, select the parameters that are important to us, and select the appropriate motor based on our needs.
For a motor, it often has multiple operating characteristic curves. Here we will list some of the most important characteristics and then give some explanations of these characteristics. For a motor, from the perspective of robot driving, we are mainly concerned about:
a) Working voltage – for a motor, there may be multiple voltage parameters; the most commonly used one is the continuous operation condition High rated voltage; some motors can operate above the rated voltage and exceed the rated speed and torque, but local overheating problems may occur after running for a period of time; that is to say, partial overvoltage can only operate for a short time and cannot to lastOperation;
b) Speed - motor rotation rate, the common unit is revolutions per minute, sometimes SL Escorts also applies radians per minute Seconds or Sierra Leone Sugar Daddy many angles per second;
c) Torque – Motor TransformationSierra Leone SugarThe ability to change speed; for example, when a wrench is used to turn a screw, the torque of the wrench causes the screw to rotate; in the field of robots, torque is generally used It allows the robot to change its position or the robot arm to complete various actions; torque is equal to the result of force and arm, and its unit is Nm;
d) Current – for a motor, there can be multiple current parameters, such as empty Carrying current, additional current and locked-rotor current, etc.;
e) Physical parameters – such as motor size, motor shaft size, cross-sectional size and fixing hole sizeSierra Leone Sugar DaddyPosition, etc.;
f) Other parameters – some motors will also provide other components, such as encoders, brakes, gearboxes, bases, etc.;
DC acceleration Motor:
It goes without saying that the current supplied by a DC motor is DC, so it can be powered by a battery; this is also the case with DC motorsSierra Leoneans One of the reasons why Sugardaddy is widely used in robots; small DC motors can be different in size, but generally different in basic parameters; the direction of rotation of the DC motor can be changed by changing the sign of the supply voltage ;
Small DC motors generally operate in the high-speed and low-torque operating range, which is different from the motor drive in robots Sierra Leoneans Escort request It is against SL Escorts; the robot field usually requires the motor to operate in a low speed and large torque range; therefore, in order to reduce the motor speed At the same time, increase the motor speed, Sierra LeoneSugar Daddyusually adds a shaft system, that is, an accelerator, between the motor and the input shaft; by combining different accelerators, the motor can obtain different rated speeds and ratingsSierra Leoneans EscortTorque; Many DC motors currently purchased on the market already have accelerators when they leave the factory, so they often become DC acceleration motors;
The advantages of accelerating motors are: simple to use, The output torque is high, the speed is low, and the range of options is wide.
The main drawback is that the accuracy is low. Even if the same batch of accelerator motors are produced by the same store and the same voltage or current is applied, the output of the accelerator motor may be different; therefore, in the use of robots, the acceleration of When controlling the motor, it is generally necessary to introduce speed closed-loop control, but open-loop control cannot be used;
The following are some common reasons that need to be considered when choosing an acceleration motor:
a) Versatility – Generally speaking, The more versatile the motor is, the cheaper it will be;
b) Working voltage – the working range of ordinary small acceleration motors is 6-24V;
c) Input torque – ordinary smallSierra Leone SugarSierra Leoneans Sugardaddy type acceleration motor input torque is 0.1-0.5 Between Nm; generally can be used to drive robots weighing 20-30kg;
d) Speed - the motor speed will determine the maximum operating speed of the robot together with the tire size; in ordinary wheeled robots, the tire size is between Between 5-20cm, of which 6-10cm is the most common;
Although most accelerating motors can rotate forward and reverse, some accelerating motors can only rotate in both directions. In addition, although the acceleration motor generally has many parameters, from the perspective of the robot, many parameters such as motor We generally don’t care about the moment of inertia of the axis.SL Escorts. The most important Sierra Leoneans Sugardaddy parameters for robots to use accelerating motors are motor speed, torque and additional voltage.
Discussing further stepsBefore accelerating the motor, we first determine the specific requirements for the motor parameters in the robot.
Motor parameter requirements:
First of all, we need to determine the conditions around the robot’s operation, such as whether the robot mainly operates outdoors or indoors, on smooth ground or rough ground, whether it needs to climb, etc. Secondly, we need to determine the specific mechanical parameters of the robot, such as size, weight, etc. Next, you need to determine some parameters of the robot’s operation, such as operating speed and torque.
The motor makes the robot move by driving the robot’s tires. The robot’s movement speed mainly depends on the motor speed and tire diameter. The motor’s twist rate depends on the output voltage and its load torque. Under the same power supply voltage, the motor rotation speed when no load is higher than the rotation speed when load. Under the same power supply voltage, the greater the output required by the motor, the lower the motor speed and the greater the motor current. When the output increases to a certain level, the motor will stop rotating, that is, it will stall. At this time, the motor current is the largest. If the motor is blocked for a long time, the temperature of the motor will rise, and in severe cases, it will cause damage to the motor.
The relationship between the robot tire speed and the motor rotation speed is:
V=0.02*pi*w*R/60;
Where: V is the robot running speed (m/s);
w is the motor rotation speed after passing the accelerator (rpm); R is the motor radius (cm);
Suppose we require the robot to run at an average speed of Vavg, then the required acceleration motor speed is:
w=60*Vavg/ (0.02*pi*R) (1)
Motor torque request:
Motor torque requestSierra Leoneans SugardaddyImportant There is no friction and slope related to the operation of the robot in the air.
Assume that the friction factor in the air when the robot is running is C, and the mass of the robot tool is m (kg). At this time, the required torque for the robot to run at a constant speed in the air is:
T=0.01Ff*R=0.01C* mg*R;
where Ff is the friction force (N), R is the tire radius (cSierra Leoneans Escortm);
In addition to constant speed movement, we may also specify the maximum climbing angle theta of the robot and the required maximum acceleration a, etc. At this time, the two can be equivalent to friction, at this time:
C=C0+sin(theta)+a/g;
Where, C0 is the inherent friction coefficient in the air, theta is the maximum climbing interpretation, a is the maximum acceleration, and g is the gravity Acceleration;
T=0.01CmgR; (2)
The above formulas 1 and 2 are the robot motor speed and torque selectionWay.
Part 2: Motor operating conditions
When the DC motor starts to supply power, the motor shaft has not yet started to rotate. At this time, the click is in a stalled state, and the motor currentSierra Leone Sugar is maximum iS, and the torque generated by the motor is also the largest; therefore, the motor begins to rotate. At this time, as the motor speed increases, due to the increase in the motor’s back electromotive force, the motor As the current decreases, the torque decreases. When the motor torque is equal to the load torque, the motor reaches a balanced state, which is the balanced motor speed.
Motor balance refers to the fact that the motor torque is equal to the load torque. In robots, load torque mainly includes friction, climbing, acceleration and other factors.
In the field of robot application, we often pay more attention to the maximum speed that the motor can achieve under different load conditions.
For example, under no-load conditions, the maximum speed that the motor can reach, the no-load speed is w0; under load conditions, the speed that the motor can produce when it is stalled is the maximum torque, and the stalled rotor The torque is Ts;
Under other conditions, the motor runs on the linear connection between the two;
That is, if the load torque is T, then at this time, the maximum speed of the motor is:
w=w0 *(1-T/Ts);
If the motor requires a maximum speed of w, then at this time, the maximum torque that the motor can generate is:
T=Ts*(1=w/w0) ;
The above figure reflects the linear relationship between the motor’s maximum speed and maximum torque, torque and current.
The maximum no-load speed of the motor is w0, and the no-load current is i0; as the load torque increases, the motor speed decreases linearly and the current increases; until the load torque reaches the maximum torque, the motor stalls. If the motor torque continues to increase, the motor will be in a power generation state.
When the motor torque is T, the motor current is:
i=i0+(is-i0)*T/Ts;
where i0 is the no-load current, is is the locked-rotor current; Ts is Stalled rotor torque;
After the above discussion, we can draw the conclusion that when selecting an acceleration motor, we should first consider the following parameters:
Motor operating voltage, no-load speed, certain speed The speed at a certain torque and the current at a certain torque.
1. Motor operating voltage: When selecting the motor operating voltage, we need to select a motor operating voltage that corresponds to the robot battery. The operating voltage of most motors is 6V, 12V, and 24V. For robots with a general size of 15cm-30cm, nickel-hydrogen batteries are generally used. For large robots, lead-acid batteries are generally used; nickel-hydrogen batteries are generally standard AA ,C,DSierra Leone Sugar Daddy size, voltage 3.6-48V variesSierra Leone Sugar Daddy. For 12V motors, 7.2V or 9.6V power supply is generally used; for 24V motors, 3*9.6V power supply is generally used.
2. Motor speed: For estimating the motor speed of Sierra Leoneans Escort, we usually choose the rated voltage and rated torque, The motor speed that can meet the conditions, for robots with ordinary tire sizes between 5-20cm, the motor speed range is generally from 40-300rpm;
3. Motor torque: When selecting the motor torque, we usually A 50% margin is left based on the calculation in the previous part; in addition, if there is more than one motor number, the motor torque request can generally be divided by the corresponding number.
4. Motor current: The motor current will determine the running time of the robot. Generally based on the motor current data, we can roughly evaluate its application range. For example, if a motor current is 0.01A, then for most robot situations , the motor will be too small; on the contrary, if the rated current of the motor is 1A, then the motor will be too large;
In addition, when selecting, you need to pay attention to ensuring that the electrical performance can be installed according to the size of the robot body. In addition, according to the control accuracy requirements, the appropriate position sensor-photoelectric code disk or rotary transformer, etc. must be selected.
Part Three: Examples of Robot Motor Selection
Here is a variable position robot platform that the author is developing as an example to explain in detail the motor selection process.
The robot platform weighs approximately 4kg and requires a maximum operating speed of 1m/s. Two motors drive it to walk SL Escorts , the maximum climbing angle is 5 degrees, the motor power supply voltage is 24V, and the tire diameter is 65mm.
1. Speed requirement: Speed=60*Velocity/(PI*d)=290rpm;
2. Torque requirement: Regarding the motor torque requirement, since the total system weight is 4kg, it is assumed that the friction coefficient is 0.03. At this time, the click torque is: T=Ff*R=(0.03+sin5)*4kg*9.8kgm/s^2*32.5*10^-3m=100mNm; SL Escorts is divided into two motors. At this time, the torque of each motor is 50mNm.
PreliminarySierra Leoneans EscortThe acceleration motor parameters are: torque: 50mNm, speed 290rpm.
The final motor selection can be determined based on other machinery or price reasons.
Reference Literature:
Piccirillo J. The art and science of selecting robot motors[J]. Unpublished draft paper.Sierra Leone Sugar Accessed: March, 2009, 1: 2013.
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