I'm in the 10th grade and there are project activities in our school program. I have chosen the topic of physics and wrote about brushless motors. I would like to tell you about my project in this article.


Historical information:
The main problem of all engines is overheating. The rotor rotated in any stator and therefore heat didn't leave anywhere. The brilliant idea to rotate stator, which during rotation would be cooled with the air, but not rotor, came to people’s mind. When this engine was invented, it begin to be used in aircraft and shipbuilding, therefore it was named Valve Engine.

The electric analog of the valve engine was soon created. It are called the brushless motor because it had not collectors (brushes).

Brushless engine
Brushless electric engines came to us rather recently, in the last 10-15 years. Unlike brushed motors, they feed three-phase alternating current. Brushless motor effectively work in wider range of rotation rates and have higher efficiency. The motor design is rather simple, there is not brush assembly, which rubs with a rotor constantly and sparks. It is possible to say that brushless motors practically don't wear out. Cost of the brushless engines is slightly higher, than commutator ones. This is because all brushless motors are equipped with bearings and made with higher quality.

The brushless motors are divided into two groups according their design: inrunner and outrunner. Engines of the first group have the winding cases located on an internal surface, and the magnetic rotor rotating inside. Engines of the second group - "outrunner", have motionless windings inside, which round the case with the permanent magnets on its internal wall rotates. The quantity of magnets' poles in the brushless engines can be various. You can estimate torque and engine revs by the number of poles. Motors with bipolar rotors have the highest rotation speed at the lowest torque.



Work principle

Unlike the brush direct current electric motor (DC motor), the work principle of the brushless engine is based on the brushless engine's controller gives a pulse direct current on windings so that there was an alternate alternation of windings in which current is appeared.

The electrical machine are composed of motionless part — the stator and mobile part — the rotor.

Application

This type of the engine is created for the purpose of improvement of properties of direct current electric motors (DC motor). High requirements to executive mechanisms (in particular, high-speed microdrives of exact positioning) determined use of direct current specific engines: contactless three-phase DC motor.



Advantages and disadvantages of the brushless engines


Advantages:

- Rotation frequency changes in a wide range
- Possibility of using in explosive and hostile environment
- High reloading ability on the moment
- High power rates (efficiency more than 90%)
- Long service life, high reliability and the extended work resource due to lack of sliding electric contacts

Disadvantages:
- Rather difficult control system of the engine
- The high cost of the engine caused by using of expensive materials in a rotor design (magnets, bearings, shafts)

Building brushless motor (1)
Once I had already wrote about creation of the brushless motor from the old brushed motor: building brushless motor
Tests had showed:
Draft with the propeller 8х6 = 533 g,
Rotation frequency = 5433 rpm,
Power consumption is 120 watts (it only at idling!), and with the propeller is 330 watts. It is much bad indicators (Efficiency = 23%) and therefore it was decided to build the new brushless motor with the improved characteristics.

Building brushless engine (2)
Actually, it is impossible to assert that I have built the new engine completely because I have made it from old the broken and burned down brushless engine. It is possible to say that it was restored (I have repaired it and made triangular winding). It differs from the first in quantity of teeths (3 instead of 12), system of a winding and a design (more correct design with use of bearings).
I won't tell about ways of a winding of the engine, I give the reference: http://rc-aviation.ru/mtech/735-remont/1176-peremotka-dvigatelya, and also I will give advice: reel up not one wire, but a braid from several, thinner wires.



Tests had showed:
Draft with the propeller 8х6 = 754 grams,
Rotation frequency = 11550 rpm,
Power consumption = 9 watts (without propeller), 101 watts (with the propeller),

Power and efficiency
Power can be calculated in a way:
1) Power in mechanics is calculated by formula: N = F * v, where F - force, and v - linear speed. At measurements, the propeller has no linear speed. It has only rotation speed. If install this motor on an aircraft model, it is possible to measure the speed (it is equal 12 m/s) and to calculate the effective power:
N (effective) = 7.54*12 = 90.48 watts
2) The efficiency of an electric motor is calculated by formula: Efficiency = N (effective) / N (spent) * 100%, where N (spent) = 101 watts
EFFICIENCY = 90.48/101 * 100% = 90%
On average the efficiency of the brushless engines fluctuates about 90%, (the highest efficiency reached by this type of motors is equal 99.68%).

Engine’s characteristics:
Voltage: 11.1 volt
RPM: 11550 rpm
Maximum current: 15 A
Power: 200 watts
Trust: 754 grams (screw 8х6)

Conclusion:

The price of any thing depends on scales of its production. The number of producers of the brushless motors is growing quite rapidly. It's so tempting to imagine that price of controllers and brushless engines will fall in near future as it fell to the radio control equipment... Possibilities of microelectronics extends every day, the sizes and weight of controllers gradually decrease. It is possible to assume that controllers will start building in directly into engines in nearest future! Maybe we will live to see this day...

This is the translated version. You can read the original Russian article here.