Brushless DC Motors, are beginning to Spread the amateur markets in the manufacture of vehicles (RC car, Truck, and tank) and aircraft (RC airplane and helicopter). Controlling these great motors was a big obstacle until microcontrollers(like Arduino) were cheap and powerful enough to do the job easily. work is underway to develop faster and more efficient controls to unlock the amazing capabilities of these motors. These motors can provide more power while operating silently and quietly unlike Brushed DC Motor and no brushes need So don’t worry about it wearing or rising temperature. Most applications vehicles are now switching to brushless motors Like aircraft and electric cars.
DC Brushless motor Components
To understand the components of brushless motors and how they work, let us disassemble one. This type of motor is found in types of aircrafts.
It looks different from Brushed Motor Components But some things are similar but without any Brushes See description:
- Contacts – Brings power from the power source to Windings.
- Bearings – Ring to less friction for the axle.
- Windings – Converts electricity to a magnetic field that rotates the axle.
- Axle – Transfers the motion rotation of the motor to the applications.
- Magnets – Static magnetic field for the windings to stable motion.
- Can – Hard casing for the internal components of the motor.
In these motors, the stator contains the coil and the moving particle contains the permanent magnets (unlike brush motors).
The rotor contains the magnets which are only moving part is the motor current flow direction control The polarity of each winding. motor control method the Brushless DC motor becomes like an AC Motor each winding giving a push and pull. To keep the rotational motion going we must keep this process sync with the speed of the rotor.
the following Curve show performance torque IN-LBS motors with motor speed revolution per minute (RPM):
It’s amazing, isn’t it? RPM gives more than the DC motors we have already studied and its torque is very high. in addition to Universal Motor but This type of motors is usually used for industrial purposes.
Brushless DC Motor Standards
Now we will study the choice of Brushless DC Motor As per motor standards that fit your aircraft or any vehicle and we want Brushless DC Motor to become the ideal model for the construction of the airplane, helicopters, and Drone. These standards should be reviewed in order to determine the speed of any aircraft and the weight of the aircraft. As we said earlier, the choice of a LIPO battery depends on the type of your motor.
Generally, there is more than one way to choose the motor, there are criteria set by the companies to estimate the expected load weight of the aircraft (from weight we can choose motor), and also we can see the motor information, manufacturers put us how much this motor can raise the total weight (motor weight, Fuselage, LIPO-Battery and additional equipment) and we must take a safety factor for the weight of the aircraft so that we can fly in a fast and strong way, for example, if the aircraft motor can lift the weight of 2 kg, we design the weight of the aircraft so that it is 1 kg so that the aircraft in the best condition in flight and speed of flight. The standard:
- Voltage Constant
This is the number of motor RPM symbolized “Kv” When buying Brushless DC Motor you don’t see the number of rpm directly but you will find a number like 500 Kv The number of rpm is calculated when multiplying this number by the voltage value that incoming from battery, for example, motor with labeled 1500 Kv and we battery max voltage 12 V, How many rpm will give us?
from this basic formula we can calculate rpm from RPM = Kv * Volt so RPM = 1500 *12 = 18000 RPM but that’s just at 12V
In this table we will study the number of cycles according to different voltage values for 1500kv motor:
|Volt Inlet Motor||Equation||RPM|
When representing data we get the following linear curve:
That is, the greater the voltage, the faster the rotational speed. but of course, there is a limit to the increased voltage.
2. Torque Constant
For all Brushless DC Motor, Kt = 1355 / Kv means that the motor is rotating more quickly for a given voltage (Kv) The decrease in torque is Kt.
The power of motor can be measured in watts. Note that 1 hp = 746 watts. The number of watts can be determined by Watts=Volts x Amps. The power requirements of the RC aircraft can be found, using the total weight of the RC aircraft. It is a standard system represented in the following table:
|Power rang requirement||RC Aircraft type|
|50-70 watts/ pound||The minimum level of reasonable performance. Confined to lightly internal RC aircraft and small garden aircraft.|
|70-90 watts/ pound||Beginner RC aircraft and slow plane to the flight model.|
|90-110 watts/pound||Fast aerobatic sports aircraft.|
|110-130 watts/pound||Advanced aircraft and high speeds.|
|130-150 watts/pound||3D aircraft – those that resemble real but miniature aircraft.|
|150-200 and more, watts/pound||Unlimited 3D aircrafts performance.|
For example, we have a 6-pound plane that we want to use the second standard from the table so we use this formula power = pound * (watts/ pound). so power = 6*60 = 360 watt is average power we must use.
Most manufacturers of Brushless DC Motors It lists the typical weight that the engine can lift, in this example for GH2217-06 Motor We will see the contents of the specifications:
|Conversion Equivalent||480 Size Motor||480 Size Motor||480 Size Motor|
|Lipo Count||3s (11.1v)||3s (11.1v))||3s (11.1v)|
|RPM per volt||1500 kv||1200 kv||950 kv|
|Current Capacity||20A / 60 sec||20A / 60 sec||20A / 60 sec|
|Dimension:||27.5 x 34mm||27.5 x 34mm||27.5 x 34mmm|
|Weight:||73g / 2.59oz||73g / 2.59oz||73g / 2.59oz|
|Recommended Prop||(3S – 11.1V) – 8 x 4||(3S – 11.1V) – 8 x 4 or 9 x 5 with thorttle mangement||(3S – 11.1V) – 10 x 6|
|Recommended Model Weight:||(300g – 1000g) (10.5oz – 35oz)||(300g – 1000g) (10.5oz – 35oz)||(300g – 1000g) (10.5oz – 35oz)|
|Style of Flying||Warbird / Faster||Aerobatic||3D|
Manufacturers display all the details of the Brushless DC Motor, for example, GH2217-06 motor needs 250W power, 3S LIPO Battery, 1500 kV (which mean RPM=1500*11.1 v = 16650 max RPM), Recommended Prop and many important considerations, Thus we can choose a motor for aircraft.
Advantages and disadvantages of Brushless DC Motor
Brushless DC Motor due to its many uses but there is Advantages and Disadvantages we will mention the most important of them to be considered when you buy the motor.
- The high speed we can get huge Revolutions Per Minute (RPM).
- High efficiency because we exploit most of the power supply and Reliable.
- Lightweight so it is optimal in flight.
- Because there is no brush so not exposed to rising temperature.
- No noise, he is calm motor.
- Difficult to control without a controller so required some skills.
- It needs to supply power gradually so avoid speed in the throttle.
- High coast, Expensive compared to other motors.
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