What is an Outer Rotor Brushless Motor?
An outer rotor brushless motor (ORB) is a type of electric motor with no moving parts inside the body of the motor. Instead, it uses rotating brushes to generate electricity. They are usually made from aluminum or other metal materials and have a diameter smaller than the size of a human hair. ORBs can be used for many different applications such as:
1. Electric toothbrushes
2. Lawnmower motors
3. Air conditioners
4. Power tools
5. Space shuttles
In this article we will compare the inner and outer rotors of a makita ORB 5500A brushless outrunner motor with an electric toothbrush motor. We will see how they differ and what advantages each one has over the other.
The inner rotor of an ORB is very similar to the motor found in an electric toothbrush. It is a low-power motor that is sub-classified as an asynchronous motor. In this type of motor, the magnetic field does not change with the rotation of the rotor, meaning that when a voltage is applied to the coils, it will only push the rotor until it reaches a speed where the centrifugal force balances with the magnetic force.
The outer rotor of an ORB is more complex than the inner rotor and can be classified as a brushless DC electric motor. This means that it uses direct current instead of alternating current. The advantage of using direct current is that it allows for a more efficient and precise control over the speed of the motor via pulse width modulation.
How they are different from each other?
Both types of motors have their own unique features. While an inner rotor motor is more convenient for small-sized devices such as power tools, the outer rotor is better for large-sized vehicles such as boats and planes because it can produce more torque.
Advantages of inner rotor over outer rotor
Inner rotor motors are much smaller in size than their outer rotor counterparts because they consist of multiple magnets that rotate around a fixed coil. The fixed coils result in higher efficiency, increased power density and greater reliability when compared to an outer rotor motor.
It is also easier to cool an inner rotor motor since it has smaller fixed coils. Since the moving parts of an inner rotor are much smaller, it is also capable of running at very high speeds.
Advantages of outer rotor over inner rotor
An ORB can produce greater torque which is very important for applications that need to rotate heavy machinery. Since the magnets are not fixed, it can accelerate faster and reach higher speeds than inner rotor motors.
Outer rotor motors have more metal in them, which means that they are heavier than inner rotor motors. This makes ORB rotors less efficient but at the same time more durable.
What is the difference between an inner rotor and an outer rotor brushless outrunner motor?
The main differences between an ORB and a traditional outrunner can be found in the coils and magnets. Since ORBs don’t have a stationary coil and magnets attached to the inside of the casing, they are much lighter than their counterparts. They also produce more power for the same weight and have a higher power to weight ratio than other motors. The main advantage that outrunners have over ORBs is that they can reverse easily.
An outer rotor consists of the following parts:
1. Outer Rotor Blade: These are the blades attached to the outside of the motor.
These are usually molded plastic or carbon fiber composite material.
2. Thrust Bearing: This part is in contact with the propeller and helps transfer thrust from the motor to the propeller, which in turn propels your vehicle.
3. Bell: This is the oversized part that the fan blades are attached to.
It is held in place by the outermost circumference of the motor casing.
4. Stator: This consists of multiple cores and coils and is typically made of aluminum.
The magnetic field produced by the stator pushes and pulls on the magnets attached to the outside of the rotor which causes it to rotate as it spins.
5. Magnets: Neodymium magnets are attached to the outside of the rotor and interact with the stator’s magnetic field to cause it to spin.
6. Casing: The outer casing is composed of a light weight aluminum material and contains all of the other components listed above.
Some motors have a plastic fan shroud that goes over the outside of the motor to protect the propeller from damage in a crash.
7. Mounting Bolt Holes: These are holes drilled through the casing that are used to mount the motor to the airframe.
What is an outrunner and how does it work?
An outrunner is a type of electric motor that has its magnets on the outside of the cylindrical metal core (stator). They typically have high power to weight ratios and can produce large amounts of power in a small package. Outrunners are often used in model planes, helicopters, and other RC vehicles that require a large amount of thrust.
There are two main types of outrunners: forward and reverse. Forward outrunner motors have the leads coming out of the back and the revolving part in the front. This allows them to push rather than pull, making them better suited for airplane propellers. Reverse outrunners have the leads coming out of the front and the revolving part in the back. This backwards design causes them to pull rather than push, making them better suited for helicopter propellers.
Outrunner advantages and disadvantages
The main advantage of an outrunner is that they produce a lot of power for their size, which makes them perfect for model planes and other small vehicles that need a lot of thrust or power. Outrunners can also be “tuned” in the same sense that a car engine can be tuned. By attaching different magnets to the outside of the metal core (stator) of the motor, the strength of the magnetic field can be adjusted. This allows an outrunner to produce more power for a brief amount of time or less power for a longer period of time depending on what is needed by the user.
Sources & references used in this article:
- Design of a magnetic-geared outer-rotor permanent-magnet brushless motor for electric vehicles (KT Chau, D Zhang, JZ Jiang, C Liu… – IEEE transactions on …, 2007 – ieeexplore.ieee.org)
- A magnetic-geared outer-rotor permanent-magnet brushless machine for wind power generation (L Jian, KT Chau, JZ Jiang – IEEE Transactions on Industry …, 2009 – ieeexplore.ieee.org)
- Brushless direct-current motor of radial core type having a structure of double rotors and method for making the same (PK Kim, KH Jeong, HG Song, SH Lee – US Patent 6,992,419, 2006 – Google Patents)
- Comparison of coaxial magnetic gears with different topologies (L Jian, KT Chau, Y Gong, JZ Jiang… – IEEE Transactions on …, 2009 – ieeexplore.ieee.org)
- Development of a magnetic-geared permanent-magnet brushless motor (LL Wang, JX Shen, PCK Luk, WZ Fei… – IEEE Transactions …, 2009 – ieeexplore.ieee.org)
- Exterior vs. interior rotors in robotic brushless motors (JW Sensinger, SD Clark… – 2011 IEEE International …, 2011 – ieeexplore.ieee.org)
- Comparison of permanent magnet brushless motor with outer and inner rotor used in e-bike (W Chlebosz, G Ombach, J Junak – The XIX International …, 2010 – ieeexplore.ieee.org)