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In order to understand the basics of multirotor motors, which will help you pick the appropriate motor for your quadcopter construct. There are some broad guidelines you can take after, and considerations to bear in mind while choosing the ideal and effective motor.
Where to Start? Decide on Motor Size First
Regardless, you have to answer these 2 questions:
- What’s your quadcopter’s arranged total weight?
- What’s the size of the frame?
The aggregate weight of the quadcopter can be your best guess, as you haven't constructed it yet. It ought to incorporate everything: Frame, FC, PDB, wires, motors, ESC's, battery, payload, (for example, HD camera and gimbals), and so on.
By knowing the size of the frame, you ought to recognize what the most extreme propeller size can be utilized.
By knowing these 2 things, you can compute generally how much thrust the motors need to convey to lift it noticeable all around, by utilizing propellers of restricted size.
Thrust to Weight Ratio
A general thumb rule is that you ought to AT LEAST have the capacity to give twice as much thrust than the weight of the quad. If the thrust provided by the motors are too little, the quad would not react well to your control, it may even experience issues to take off.
For instance on the off chance that we had a quadcopter that weights 1kg, the aggregate thrust created by the motors at 100% throttle ought to be no less than 2kg, or 500g for each motor (for a quadcopter).
It gives you better controllability, as well as the space for including additional payload later on (like heavier cameras, or possibly additional batteries to extend flight time).
Motor Size and KV
Brushless motors in RC is typically demonstrated by a 4-digit number – AABB. "AA" being the stator width, and "BB" being the stator height. Essentially, the more extensive and taller the motor is, the more torque it can produce.
KV is another essential parameter, it's the theoretical increase of motor RPM (rotation per minute) when voltage go up by 1 volt without load. For instance, while fuelling a 2300KV motors with a 3S LiPo battery (12.6V), the motor would turn at around 28980 RPM. This is only an estimation incidentally.
In any case, once you mounted a propeller on the motor, the RPM won't be that high because of resistance. Higher KV motors would endeavour to turn the propeller quicker, yet bring down KV motors regularly create higher torque. Bigger props are matched with low KV motors, and smaller props with high KV motors.
It's important to discover a balance amongst RPM and torque when picking motor and propeller.
By blending high KV motors with excessively large propellers, the motor will endeavour to turn it quick like they would do with smaller props, drawing a lot of current and producing an excess of heat.
N and P
You may infrequently observe something like "12N14P". The number before the letter N implies the quantity of electromagnets in stator, and the number before P implies the quantity of perpetual magnets in the motor.
Most motors have the same 12N14P arrangement, some lower KV motors would have more electromagnets and lasting magnets to expand torque all the more productively (and along these lines more costly). While it's great to recognize when picking motors.</p>
Frame Size => Prop Size => Motor Size and KV
The vast majority of the circumstances by knowing frame size, we can estimate what kind of motor we ought to utilize. This is on the grounds that frame size limits props size, and prop measure limits motor size and KV.
This table below gives you a few thoughts and accept you are running 4S LiPo batteries, you may see individuals utilizing slightly higher or bring down KV motors. Frame size is referring to wheelbase (otherwise known as aka motor to motor distance).
|Frame Size||Prop Size||Motor Size||KV|
|150mm or smaller||3″ or smaller||1306 or smaller||3000KV or higher|
|450mm||8″, 9″, 10″||2212 or larger||1000KV or lower|
Voltage and Current Draw
It's additionally essential to understand that voltage will largely affect your motor and propeller choice. Your motor will attempt to turn much harder when a higher voltage is connected, and drawing a higher current.
Understanding Brushed DC Motors
- Dimension: 8mm (Diameter) x 23mm (Length)
- Voltage: 3.2V
- kV: 13000+
- Terminal Resistance: 0.63ohm
- No Load RPM: 37850
- No Load Current: 130mA
- Constant Torque: 0.79mNm/A
- Weight of motor: 6.2g
Comparing between motors
After you have settled on the size and KV of the motors, you can pick the best motor for your application, you ought to consider the accompanying components:
- Current Draw
- Weight – Moment of Inertia
The choice here truly relies upon your preference, how you need your aircraft to perform.
Higher thrust gives you best speed, yet you additionally need to take a look at efficiency, ensuring it's not utilizing an enormous amount of power that is exceed what your equipment can support.
Likewise your choice of motor and propeller can influence your selection of batteries as well. In the event that your quad could draw a lot of current at full throttle, your battery's maximum discharge rate must have the capacity to keep up so as to give the power, and also they don't overheat and go buff (look at C rating).
Motor weight, it's more essential in racing drones. It doesn't just influence the aggregate weight of your quadcopter and thrust to weight proportion, it likewise influences the latency of your quad.
More tips on Motor Efficiency
- A multicopter is more productive when it's as light as could be expected under the circumstances and also more efficient. You can find the right balance when choosing LiPo batteries for your multicopter.
- Battery and weight are the key factors we have to consider with regards to general power effectiveness. At the point when picking motors, aside from motor KV and thrust, we likewise need to take a look at motor productivity.
- The same applies to brushless motor, the higher proficiency the better. A 70% proficient motor produces 70% power and 30% heat. A 90% effective motor produces 90% power and 10% heat.
- With less effective motors not just considering measure of vitality in flight time, you can get little thrust on full throttle. It will take the motors longer to achieve desired RPM and this will have negative impact on stability and responsiveness.
Other Factors that Manufacturers Don’t Tell You
- Best props
Response – how quick the motor can change RPM. Most straightforward approach to get some answers concerning by measuring to what extent it takes for a motor to go from 0 RPM to full RPM. It can help you much more to distinguish the best motor for your decision.
Features of Motors
- Solid/Hollow shaft
- Type of Magnets (N52, N54)
- Arc Magnets
- Smaller air gaps
- Soldering tabs on motor
- ESC integration
- Cooling design
Difference between Brushed DC Motors and Brushless Motors:
A “brushed” DC motor has a rotating armature (a set of wound wire coils) which acts as an electromagnet with two poles. A rotary switch called a commutator reverses the direction of the electric current twice every cycle, to flow through the armature so that the poles of the electromagnet push and pull against the permanent magnets on the outside of the motor.
A “brushless” DC Motor does not use brushes. It uses a permanent magnet and accomplishes the switching by electronically switching the polarity. In order to accomplish this in a controlled manner a speed feedback mechanism and an electronic controller are required. The controller may be mounted on the motor or may be separate.
Brushless motor: it is widely used in the machine which requires high rotation speed and control power.
Brush motor: it is widely used in the motors with carbon brush, like fan motor, power tools etc.
- Life span
Brushless motor: the life span is more than 1 thousand hours
Brush motor: the life span is within 1 thousand hours.
- Energy saving:
Brushless motor is far more efficient and energy saving than the brush motors. While brushed motor, has to change carbon brush timely, otherwise, the motor might get damaged.
Brush DC motors are mechanically commutated motors that are good for high speed apps. Brush DC motors are easy to drive and cost effective when long life is not required.
Why a Brushed DC Motor?
The Brushed DC Motor is the classic motor that is used in applications like motorized toys, appliances, and computer peripherals. This type of motor is inexpensive, efficient, and useful for providing high speed and power in a relatively small package.
How Does the Brushed DC Work?
This type of DC motor has a split ring device called a commutator around the middle. When DC power is applied, the electromagnetic energy pushes the armature away, causing rotation.
Brushed Motor Pros
- Two wire control
- Replaceable brushes for extended life
- Low cost of construction
- Simple and inexpensive control
- No controller is required for fixed speeds
- Operates in extreme environments due to lack of electronics
Brushed Motor Cons
- Periodic maintenance is required
- Speed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torque
- Poor heat dissipation due to internal rotor construction
- Higher rotor inertia which limits the dynamic characteristics
- Lower speed range due to mechanical limitations on the brushes
- Brush Arcing will generate noise causing EMI
How Can You Find the Right Brush DC Motor for You?
There are many different types of brush motor that are flat, or rectangular for feeding and loading, and round ones are mainly used for spindles. You can also select a brush motor according to rated load/rotation speed, according to your required torque/speed characteristics.
Selecting by Rated Load / Rotation Speed
If you know the rated load (required torque) for the set you are using, you can select the optimum motor for the Speed and Torque characteristics. It is necessary to confirm that the motor characteristics can provide the required torque and speed for the expected operating range.
The typical torque/speed characteristics for each motor size are shown below for your reference when selecting a motor.
|Rated Voltage (V)||Voltage Range (V)||Rated Load (mNm)||Starting Torque (mNm)||Rated Load Speed (rpm)|
The motor and motor control markets are thriving in a number of areas, particularly medical and robotic applications. Also, there is a rich demand for small, efficient, high- and low-torque, and high- and low-power motors in the automotive sector.
These applications can choose from brush dc motors, brushless dc (BLDC) motors, or a combination of both.
Brushless DC Motors
Traditionally, many motor needs have been met using brushed DC motors. These motors use the brushes to move the commutator, which creates the rotational torque needed for it to work. In a motor that is brushless, the commutation is done electronically. There is no need for brushes, as the torque is a function of the electronic action of the brushless motor on the commutator.
Why Use a Brushless Motor?
With a brushless DC motor, also called a BLDC motor, there is never any need to be concerned about the condition of the brushes, which could require that the motor be taken out of service and restored. Brushless motors can be just as effective for high –speed operation as a brushed motor, if not more, but because there are no brushes to replace, a brushless can have a life expectancy in excess of 10,000 hours.
For a project where a motor is only going to be used for a short time, a brushed DC motor may be sufficient and cost effective. But if it is going to be in continuous use, especially if it’s going to be required to take on a lot of power, a brushless motor is a much better choice.
Brushless motors can be used in a wide variety of applications. Low power brushless motors can be used to power radio controlled model airplanes, while high power brushless motors can be used for electric vehicles and industrial machinery.
How Do I Choose a Brushless Motor?
Brushless DC motors provide high power density and long life for applications requiring speed control. NMB’s BLDC motors are available in 0.1W up to 1kW.
Select the proper size and maximum watts output from the Motor and then add the torque and no load speed to get a list of brushless DC motors that meet your parameters.
The Brushless DC (BLDC) motor is the ideal choice for applications that require high reliability, high efficiency, and high power-to-volume ratio. Generally speaking, a BLDC motor is considered to be a high performance motor that is capable of providing large amounts of torque over a vast speed range. The major difference between the two is the use of brushes.
Commutation is the act of changing the motor phase currents at the appropriate times to produce rotational torque. In a brush DC motor, the motor assembly contains a physical commutator which is moved by means of actual brushes in order to move the rotor. With a BLDC motor, electrical current powers a permanent magnet that causes the motor to move, so no physical commutator is necessary.
A BLDC motor is highly reliable since it does not have any brushes to wear out and replace. When operated in rated conditions, the life expectancy is over 10,000 hours. Although a BLDC motor may cost more than a brushless motor, it will often more than pay for itself in the amount of work time saved.
BLDC Motor Construction and Operating Theory
To understand why a BLDC motor is so effective, it’s important to have a good understanding of how it works. There are actually two different types, with different benefits and drawbacks. While either one will probably be effective for most jobs, you may wish to familiarize yourself with both types, just in case one would be more appropriate for your project or application than the other.
Any BLDC motor has two primary parts; the rotor, the rotating part, and the stator, the stationary part. Other important parts of the motor are the stator windings and the rotor magnets.
There are two basic BLDC motor designs: inner rotor and outer rotor design.
In an outer rotor design, the windings are located in the core of the motor. The rotor magnets surround the stator windings as shown here. The rotor magnets act as an insulator, thereby reducing the rate of heat dissipation from the motor. Due to the location of the stator windings, outer rotor designs typically operate at lower duty cycles or at a lower rated current. The primary advantage of an outer rotor BLDC motor is relatively low cogging torque.
In an inner rotor design, the stator windings surround the rotor and are affixed to the motor’s housing as shown here. The primary advantage of an inner rotor construction is its ability to dissipate heat. A motor’s ability to dissipate heat directly impacts its ability to produce torque. For this reason, the overwhelming majority of BLDC motors use an inner rotor design. Another advantage of an inner rotor design is lower rotor inertia.
BLDC Motor Advantages:
If you’re still not sure whether or not this motor is right for you, here is a basic breakdown of some of the primary advantages of the BLDC motor.
- High Speed Operation – A BLDC motor can operate at speeds above 10,000 rpm under loaded and unloaded conditions.
- Responsiveness & Quick Acceleration – Inner rotor Brushless DC motors have low rotor inertia, allowing them to accelerate, decelerate, and reverse direction quickly.
- High Power Density – BLDC motors have the highest running torque per cubic inch of any DC motor.
- High Reliability – BLDC motors do not have brushes, meaning they are more reliable and have life expectancies of over 10,000 hours. This results in fewer instances of replacement or repair and less overall down time for your project.
BLDC Motor Pros
- Electronic commutation based on Hall position sensors
- Less required maintenance due to absence of brushes
- Speed/Torque- flat, enables operation at all speeds with rated load
- High efficiency, no voltage drop across brushes
- High output power/frame size. Reduced size due to superior thermal characteristics. Because BLDC has the windings on the stator, which is connected to the case, the heat dissipation is better
- Higher speed range - no mechanical limitation imposed by brushes/commutator
- Low electric noise generation
BLDC Motor Cons
- Higher cost of construction
- Control is complex and expensive
- Electric Controller is required to keep the motor running. It offers double the price of the motor.
Life expectancy of a Brushed DC motor?
The brushes are the limiting component in a Brush DC motor’s life expectancy. The life expectancy of the brush is dependent on application parameters such as torque, speed, duty cycle and direction of rotation.
Advantages of using a brushless motor versus a brush style motor?
- No brush noise, efficient, durable, robust, easy to cool
- Linear current/torque
- Synchronous speed control
- Position and Speed Servo (open/closed loop)
- Customizable Performance
- Extended Life
Advantages between outer rotor and inner rotor motors?
The advantage of an outer rotor motor is torque. These smaller packages can produce more torque than there equivalent inner rotor size motors. This is accomplished by the larger moment arm of the rotating outer rotor magnet. One disadvantage is speed capability. If high speeds exceeding 6,000 RPM are required, it is recommended you utilize an inner rotor construction motor.
With more advanced programming, we can add braking torque, holding torque, alternate I/Os, extended temperature ranges, and stall detection. Each software request will be reviewed on an individual basis for feasibility and cost.
A sophisticated control system would be required to keep the speed regulated to a tight tolerance. Utilizing an encoder feedback, the customer’s control can monitor and adjust the 0-5VDC input can be controlled <1%. This will allow the closed loop speed regulation needed for tighter tolerance speed control. Current tolerance on speed regulation for standard integrated controls is <5%. This is a key benefit when comparing BLDC to brush motors.
The integral part of option for the 2.25” have a standard input voltage range of 12-48 VDC. If an external controller is used, customer controller will determine the voltage range of the motor. However, BLDC motors do not accommodate high voltage inputs (<48VDC) due to clearance requirements.