hoverboard bldc motor 3 stage 6 steps 30 magnets 15 pole pairs and 3 Hall effect sensors 90 States
the combination of a 3-phase BLDC motor with Hall effect sensors in a hoverboard allows for precise control of the rotor's position and efficient commutation. The interaction between the rotor's magnetic field and the stator's windings, along with the feedback from the Hall sensors, enables the hoverboard to achieve the desired motion with high accuracy and responsiveness. The system's design, utilizing 30 magnets and 3 Hall sensors, provides a robust solution for effective motor control in hoverboard applications.
Hoverboard BLDC Motor Overview
In this video, we dive deep into the internals of a hoverboard BLDC (Brushless DC) motor, focusing on its components and functionality.
Key Components
Rotor
The rotor is the moving part of the motor, containing permanent magnets. These magnets create a magnetic field that interacts with the stator's magnetic field, producing motion.
Stator
The stator is the stationary part of the motor, housing the windings (coils). When current flows through these windings, it generates a magnetic field that interacts with the rotor’s magnetic field, causing the rotor to turn.
Hall Effect Sensors
In hoverboard motors, three Hall effect sensors serve as encoders. These sensors provide information about the motor’s position as it spins. The motherboard can set the position directly, allowing the controller to determine the next target position.
Resolution of Hall Effect Sensors
The resolution of the Hall effect sensors indicates the minimum degree the motor can turn before a position change is detected. Incremental encoders, like those used in hoverboards, provide higher resolution by generating multiple pulses per revolution (PPR). Common resolutions for hoverboard applications range from **600 PPR to 2400 PPR**.
Unique States
With 30 magnets (15 pole pairs) and 3 Hall effect sensors, we can achieve detailed position sensing. Each pair of magnets provides 6 unique states, leading to a total of 90 states for one full revolution of the motor.
#### Hall Sensor Combinations
With 3 Hall sensors, there are $$2^3 = 8$$ possible combinations of states. For each electrical cycle, the 3 Hall sensors will go through all 8 combinations.
Electrical Cycles
In a motor with 15 pole pairs, there are 15 electrical cycles per mechanical revolution. Therefore, the total number of unique states per mechanical revolution is:
$$
8 \text{ (combinations)} \times 15 \text{ (electrical cycles)} = 120 \text{ states}
$$
However, for commutation, we typically use 6 states per electrical cycle, leading to:
$$
6 \text{ (states)} \times 15 \text{ (cycles)} = 90 \text{ states}
$$
Position Detection and Commutation
As the rotor spins, the Hall sensors detect changes in the magnetic field and generate signals. The STM32F103C8T6 microcontroller reads these signals to determine the rotor's position based on the current state. It then uses this information to decide which motor windings to energize, enabling smooth and efficient operation.
State Combinations
With 3 Hall effect sensors, there are =8 possible combinations of states. Electrical Cycles and Mechanical Revolutions
For each electrical cycle, the 3 Hall sensors will cycle through all 8 combinations. In a motor with 15 pole pairs, there are 15 electrical cycles per mechanical revolution.
Total States: Therefore, the total number of unique states per mechanical revolution is calculated as: 8 combinations × 15 electrical cycles = 120
states
8 combinations ×15 electrical cycles =120 states
Commutation States
However, for the purpose of commutation, which is the process of switching the current in the motor windings to maintain motion, typically only 6 states per electrical cycle are used. This leads to: 6
commutation states × 15 electrical cycles = 90 states
6 commutation states ×15 electrical cycles =90 states
Thus, with 30 magnets (15 pole pairs) in the motor, there are 90 states available from the encoder for one full revolution.
Understanding the 90 States
The states can be represented as follows:
HALL_STATE_000: 0
HALL_STATE_001: 1
HALL_STATE_010: 2
HALL_STATE_011: 3
HALL_STATE_100: 4
HALL_STATE_101: 5
HALL_STATE_110: 6
HALL_STATE_111: 7
Each state corresponds to a specific configuration of the Hall sensors, indicating the rotor's position relative to the stator.
Magnet Energization
The Hall effect sensors not only provide position feedback but also dictate which poles of the motor are energized. The microcontroller (often an STM32F103C8T6 in hoverboards) reads the Hall sensor signals and determines the rotor's position. Based on this information, it energizes the appropriate windings to maintain rotation
Commutation Logic
The commutation process involves switching the current through the motor phases based on the Hall sensor states. As the rotor turns, the sensors detect changes in the magnetic field, and the microcontroller adjusts the current flow to the windings accordingly, ensuring smooth and efficient operation