Nowadays, various types of drones and robots are increasingly widely used. Brushless motors are small in size, light in weight, and fast in speed. These characteristics can be said to be very suitable for drones.
First: Why choose a brushless motor?
Brushless motors are basically selected for motors used in drones. More than 90% of the faults of brushed motors are caused by the carbon brushes, which is determined by its design. Dust, rust, and vibration may cause poor contact and cause problems.
2. Long life
The carbon brushes of brushed motors will wear out and need to be updated regularly. For the civilian product industry, this is obviously unrealistic; The brushless motor has no such concerns at all and is almost maintenance-free.
3. High efficiency
High efficiency refers to the conversion rate of energy. Brushless motors have no contact resistance and no heating elements such as carbon brushes. The utilization rate of electric energy is high, which can be as high as 90%; The brushed motor can only reach 75%, so compared to other motors used in drones, the running time of the brushless motor will have a clear advantage.
4. Heat dissipation
Since a large part of the electric energy is converted into heat energy, the brush motor must be designed for heat dissipation. This will affect the volume of the product and increase the weight of the product, which is not feasible for drones.
5. Control accuracy
Although the control precision of the brushed DC motor is high. However, with the popularity of sensors and perfect matching with brushless motors, the accuracy problem has been solved.
Second: How does the brushless motor measure the speed?
1. Hall effect principle speed measurement method
The rotating shaft of the brushless motor drives the magnetic steel on the shaft to rotate, thereby changing the size of the magnetic field. The change of the magnetic field is converted into a pulse signal by the Hall circuit, which is amplified and shaped to output a rectangular pulse signal. When the speed changes, the frequency of the output pulse will change, and the speed of the DC geared motor can be obtained.
2. Photoelectric speed measurement method
It uses a grid disc and photoelectric gate to form a speed measurement system. When the brushless motor drives the grid disc to rotate through the transmission part, the speed measuring photoelectric gate obtains a series of pulse signals. These pulse signals are coordinated by two timer/counters of the single-chip microcomputer, one counting and one timing. Calculate the number of pulses per unit time m, after unit conversion, the speed of the motor can be calculated.