Motors are used in all industries. In fact, everything that moves and turns is propelled by an electric motor. From small, standard motors found in fans, pumps and conveyors to (very) large motors that drive wind turbines, for example. Large motors usually require customisation, as smaller ones are mostly mass-produced and widely used. Selecting the right motor for your application is a meticulous process, in which a wide variety of criteria play a role. We will list the most important steps for you here.
What do you need the motor for? And in what kind of production environment will the motor be used? The answer to these questions will provide initial guidance on what kind of motor is suitable for the specific application. Power requirements, speed and where the motor needs to be installed are other determining factors. What steps should you follow when selecting the appropriate small, standard 3-phase motor for your application?
The first step in choosing the right motor involves determining torque and revolutions per minute. You need this to calculate the desired power. That’s because the motor inside an application needs a certain torque and speed to cause a turning moment. Therefore, the questions you should initially be asking are: what do I need to move, how fast do I need to move it and how heavy is it? To further specify the function of the motor, it is also useful to know whether the motor is just intended to run something, provide constant speed or put something in place. The more accurately you can determine the function of a particular motor, the better the choice of motor type will be. After all, some motors are more suited to a particular function than others.
The next important step in the selection process is to analyse the production environment in which the motor will need to operate. Will the motor be used in a laboratory environment where nothing much happens, or will it be running in a setting where it is exposed to one or more production factors? Choosing the right engine depends on, among other things:
The next step is determining the installation space for the motor. In some production environments, this space can be quite limited. An example might be AGV systems (Automated Guided Vehicles). Although these should all be able to lift pallets, the space underneath is very limited. In principle, some motors have a higher power density than others. And one type of motor might also be more compact and deliver more power with the same design than another. If space is indeed a challenge, you could look into applying separate parts of a motor, such as a rotor or stator, separately. The benefit of an electric motor is that it comes in different designs and can therefore be mounted in several ways:
The design (or mounting method) is indicated by a European IEC34-7 standard code. This standard defines the dimensions of a motor. These include shaft diameter, shaft length, shaft height and bore spacing. This is particularly valid for standard induction motors. Other engines either follow no or a different standard (NEMA). So, if you have a standard induction motor that meets the IEC34 standard, you should select from electric motor suppliers that are able to supply these IEC34 standard motors.
The frequency of movement produced by the motor largely determines its lifespan. Are we talking about an application that needs to go back and forth once a day, or is it something that runs 24/7? An example might be brush motors. Although these contain brushes for transferring energy, they wear out as they are used more often. Brush motors are nevertheless a great solution for something that needs to move back and forth occasionally, as the brushes will last between 3,000 and 5,000 hours. They are obviously less suitable for applications that run continuously.
A motor converts electrical energy into mechanical energy. The efficiency between electrical energy and mechanical energy represents the efficiency of a motor. For example, car engines have very poor efficiency. You have to put a lot of energy into them to get back a certain amount of mechanical energy. Efficiency classes range from IE1 to IE4, with the highest number representing the most efficiency.
Applications involving the integration of a new motor may no longer use motors with efficiency classes IE1 and IE2. And from 2025, you will only be allowed to buy IE4 motors. Although these engines are more expensive, the extra costs associated with them are recouped in two years at most, and from then on you can start saving on costs. Companies don’t often see this investment in the short term; however, they usually take action when the current motor needs to be replaced, at which point they see that it can also save them money in the long run.
Steps 1 to 5 deal with the characteristics of the motor itself. But how should you control the motor? What kind of interface should the motor have with your system? If you have a system with a controller, and you want to be able to turn it on/off based on a particular output, or you want to have the option of checking the various statuses, so that you can continuously monitor the performance of the motor, the options in these situations are quite wide. There is plenty of choice between different manufacturers, where some have the option of hooking up to an existing system while others don’t. Here, customisation plays a major role.
In this context, the power system also comes into play. What kind of power system do I have? Can the motor be connected to the mains (AC)? Or is it a battery-powered system? If so, this will entail different demands being placed on the motor. A major trend these days involves controls being increasingly integrated into the engine. The benefit of this is that the whole unit is coordinated and compact. As such, the user doesn’t need to buy a separate control box with cables, which reduces the risk of malfunction.
So far, we have mostly talked about the motor and controls. But that's not all. Most motors have high rotational speed and low torque. As far as most systems are concerned, you want the opposite: high torque and low rpm. Similar to your bike and car, there’s a gear somewhere in between, and this usually comes with the motor. The same goes for the reduction gear, where you again have the same choices. Depending on the application, you should also assess which one is most suitable for it. Lifespan and noise are important in this respect. You can also expand the scope of your search by including the drive in the selection process; after all, even if the motor lasts for years, it won’t be of much use to you if the drive unit breaks down within a year. Selection is certainly important in this respect too; with drive technology often coming without maintenance, it simply has to last for a number of years.
ERIKS represents a number of major electric motor manufacturers. As a result, our range consists of motors that meet current standards and have the necessary quality so that they can be used in any production environment. We make calculations and specialise in programming drive systems so that we can provide our customers with the best possible advice when it comes to choosing a motor that best suits their application. We also create and manufacture completely engineered solutions ourselves. By getting us involved early on in the selection or design process, we will be able to develop solutions with you that lead to cost savings and more efficient production.
Want to know more about how to choose the best electric motor for your application and how ERIKS can assist you in doing so? Contact us - we are happy to tell you more.
7 min read
The selection of the right powertrain plays an important role in a vehicle’s performance. The vehicle manufacturers need to review the characteristics like vehicle weight, speed requirement, gradeability, acceleration, loading capacity & any specific road conditions (e.g. Off-road conditions) for selecting the right powertrain for their electric vehicle. In this article, Varun Rai – Business Head at EMF Innovations, discusses how to go about selecting the powertrain parameters for an EV.
The electric motor used in an electric vehicle must produce the right amount of power required for traction purposes. The important factor is to select an appropriate rating of the motor based on the load to be carried. To arrive at the required motor power, we should first figure out the force required to move the vehicle as per desired specification/requirement.
The force required to drive the vehicle is known as tractive force.
Traction Force (Ftr) = Ftr = Fr + Fad + Fg + Fi
Fr = Rolling Force, Fad = Force due to Air-drag, Fg = Gravitation Force & Fi = Inertial Force
Image Source: ResearchGate.netRolling Force (Fr) = It is a resistive force in the motion of the vehicle. This is also known as the Rolling friction force.
Fr = m* g * Cr * Cos α
M = Mass of the vehicle
g = Gravitation Force (9.81)
Cr = Rolling co-efficient. It depends on the contact area between the tire and the road surface. If the coefficient of friction is high, then the force required to move the vehicle will be more.
Force due to Air drag (Fad) – The force which is faced by the vehicle as it moves through the air.
Fad = 0.5 * Ad * Cd *Af * V2
Ad = Air density
Cd = Coefficient of Drag
Af = Front Area of vehicle
V = Velocity of the vehicle
The formula above indicates that the Speed and the front area of the vehicle play an important role in Air Drag calculation. The front area of the vehicle should be optimised to reduce the Air drag force.
Gravitation Force (Fg) –
Fg = M*g* Sinα
M = Mass of the vehicle
G = Gravitation Force (9.81)
α = Gradient Angle
While selecting the motor power, we should consider the gradeability for which we are designing the vehicle. More gradeability has a higher torque requirement.
Inertial Force (Fi) – Force required to overcome the inertia of moving parts at a given acceleration.
Fi = ma
M = Mass of the vehicle
A = Acceleration.
Acceleration plays a major role in selecting the peak power of the motor. This is the force that major acts while we are starting the vehicle from 0 kmph and continuously once the vehicle comes into motion and catches speed. While cruising, this force becomes zero.
After calculating the Tractive force, we can calculate the torque on the wheel.
Torque on wheel = Tractive force * Radius of the wheel.
Torque of motor (T) = Torque on Wheel / Gear-Ratio
Rpm on Wheel = Vehicle Speed requirement / Circumference of the wheel.
RPM on motor (N) = Wheel RPM x Gear-Ratio
Motor RPM can be directly calculated from the speed of the vehicle.
In the case of the Hub motor, the RPM and Torque on the wheel are the same as on the motor. Whereas in the Gearbox/Chain-drive/Belt drive system RPM on the motor = Wheel RPM x Gear-Ratio.
After getting the torque and RPM required, we can calculate the motor power and Peak power.
P = 2πNT/60 [P = power]
Click here to refer to the calculations and also calculate the motor specifications for your use case.
Conclusion – We should select motor power based on vehicle characteristics like Weight, Front area, Maximum Speed requirement, Maximum Torque, Maximum Power, and Gradeability. Other parameters which we need to consider during the selection of a motor are Efficiency, Weight, Size, and Cooling requirement. Also, we should consider the operating temperature of the motor during the selection of the Motor for the vehicle.
Selection of the right controller for the motor is critical to derive efficient performance from the motor. Motor controller unit interfaces between the motor, Battery and other electronics (Throttle, Display, brakes etc) of the vehicle. It controls the speed and acceleration of the vehicle based on throttle input.
The selection of the controller is majorly based on the Motor power, System operating voltage, and Function requirement.
Controller Peak DC current = (Peak Power Requirement / System Voltage) x System efficiency during peak power.
The peak phase current of the controller is around 3 times the peak DC current. The battery operating voltage range should match with controller operating range.
There are other parameters which need to be considered during the selection of the controller, like control method – Trapezoidal or Field oriented control, Speed control mode or torque control mode, communication protocols, and operation control (Like manual or computer-controlled).
Battery voltage is dependent upon majorly vehicle manufacturers’ preference regarding the voltage. Generally, for a higher-power motor, a higher voltage is preferable. The selection of battery parameters is based on the range required for the vehicle and the capacity to provide peak discharge current and the duration for the peak current.
Battery capacity (Ah or KWh) = (Mileage Requirement / Avg speed) x Avg current or power consumption.
Peak Discharge current depends upon the capacity (C) of the battery and the chemistry of the battery or even the quality of the cell used. Other parameters like energy density, charging time, lifecycles, and operating temp range need to consider during the selection of the battery.
The author can be reached at varun@emf-i.com.
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