Selection of DC Motor
For any robotic project, selection of motor is very important. But in market there are a lot of DC Motor available, so at the time of purchasing you might be confuse about selection. Here in this blog you will get a brief guide about DC motors and its selection process for your robotic project.
Understanding Direct Current (DC) motors
Before choosing any Direct Current Motor you should go through DC motor specification. These specifications are operating voltage, Motor No-load & full load current, motor speed characteristic & Motor torque.
DC Motor Operating voltage
For a robotic project we don’t need any high performance heavy duty DC Motor. Often we required DC Motors which can operate in voltage range from 1.5 to 24 volt.
What is operating voltage for DC Motor?
Operating Voltage or Nominal Voltage is a voltage range on which DC Motor provide maximum efficiency. Operating voltage is a design parameter and provided by manufacturer. Your battery voltage should be in the range of operating voltage of DC Motor. Try to avoid over voltage on DC Motor, It may damage your circuit board or may burn your DC Motor.
Operating Voltage is directly proportional to Motor Torque and Motor Speed.
DC Motor Operating current
Current of DC Motor is not constant during the operation it varies on different condition. It is clear that current is directly proportional to voltage. But here for DC Motor Voltage should be in operating range so it is like a constant value. Normally it may be 12 Volt DC or 24 V DC. But current of DC Motor will not be same under all condition. Here I will discuss three important condition of Motor, which you will face during competition of your robotic project. These are
Motor “No-Load” Condition:
In this condition Motor will draw very less amount of current because there is no load on motor. It means motor is running free. It is also called free running condition of motor.
Motor “Full-Load” Condition:
In this condition Motor will draw its rated current. It will generate rated torque and work as its characteristic. It is the best condition for any motor. Basically motors are designed for this condition.
Motor “Stall” Condition:
In this condition Motor will not perform rotation. Its shaft will stop. This condition will occur when we apply over load to shaft. Here in this condition will draw maximum current. It is not a healthy condition for motor because motor will draw maximum current which is higher than its rating. It may cause damage and burn in motor coil. So It is not recommended to operate motor in this condition.
DC Motor Torque
In easy word torque can be understand by a rotating force which is generated by motor shaft. Torque is very important parameter to measure motor capacity. If your robotic project is heavy so you need a high torque driving motor and if mass of your robotic project is less you can use a low torque Motor. In market Geared DC motors are also available which can provide a high torque but you have to compromise with speed because it will slow.
DC Motor Speed
Speed of DC Motor is also very important parameter because for any robotic project we have to consider it. Generally it is measured in RPM. RPM stands for “rotation per minute”. If you are going to design a “Drones” you need a high speed DC motor. Generally high speed DC motor didn’t require any gear box assembly. But if you need a 10 RPM motor for designing of “Robotic Jaw” definitely you have to go for Geared DC Motor.
Choosing a DC Motor for a Robotic Project
Choosing a DC Motor is very important for your Robotic Project because it is the base of your design. Here I will share some important points which will help you to choose DC Motor for your robotic project.
How to decide speed of your robot? This is a very normal question for any robotic guy. And its answer is also very simple, at least for simple robotic Project. Speed of your robot is depend on your application suppose if you are designing a autonomous racing vehicle you have to use high speed motor and if you are designing a robotic jaw you need low RPM motor. But remember one thing you can accelerate your bot function by using a good control mechanism because for accuracy on high speed you need a good microcontroller.
Size of motor will directly impact on your physical design. In fact I have seen many guys who has change his bot design on the basis of motor dimensions. Well it is not a good practice. In many robotic competitions size of bot is already fix so at that time you can’t change you bot size. For handling this situation you should refer catalogue of different motor vendors, here you will get all available motor and its dimensions.
Motor Shaft Diameter and wheel assembly
Same as Motor size you have to choose your bot wheel as per requirement, but it is better to use small wheel if your bot is heavy or there are any inclined surface in your bot task. Large wheels are better on uneven surface. You can also use a combination of large and small wheels. Here you will get a different speed by powering different motors. By operating small wheel drive you will get high torque and slow speed and by powering large wheel drive you will get high speed and low torque. But be careful you have to use gear less motor because in many geared motor shaft don’t rotate at power off condition.
Also you have to check fixing method of wheel on motor shaft, because if it will not fix properly you will not get straight movement of your bot.
Motor Voltage & Current
Before choosing a motor you have to consider your battery power. In any robotic project Motor consumes major part of battery power. If you have limited amount of battery choose motor wisely. To avoid this problem and for optimum use of battery, consider your bot weight and don’t use heavy duty motors.
Recommended article: Feedback control
And also refer this video for understanding working of DC Motors.