“People who like to watch small videos such as “Douyin” find that Internet celebrities are walking and taking pictures, and the picture does not shake and shake, and the effect is different from taking a selfie with a mobile phone. Why? It turns out that there is a tool to use here – a hand-held gimbal! The hand-held gimbal will sense the motion state, and the mobile phone will remain stable by running the motor, and the pictures taken will not shake.
People who like to watch small videos such as “Douyin” find that Internet celebrities are walking and taking pictures, and the picture does not shake and shake, and the effect is different from taking a selfie with a mobile phone. Why? It turns out that there is a tool to use here – a hand-held gimbal! The hand-held gimbal will sense the motion state, and the mobile phone will remain stable by running the motor, and the pictures taken will not shake.
The core algorithm of the handheld gimbal is to use the FOC motor scheme to achieve fine adjustment of the three dimensions of the gimbal. For the three-way BLDC, the MCU monitors the position status information of the motor in real time through the position loop, speed loop and current loop, as well as the safe operation of the motor. In order to ensure that the mobile phone remains level within a very low error range when the body is moving and the outside world is shaking. Therefore, the control frame of the handheld gimbal:
l Motion control: 1-3 MCUs with FPU, floating-point arithmetic unit, used to process FOC algorithm, one stepper motor for each channel of X, Y, Z dimensions, and one stepper motor for each channel The three-phase half-bridge driver chip, or the H-bridge composed of 6 MOSFETs, controls the motor speed and commutation.
l Feedback mechanism: When the motor position is detected, a Hall element or a magnetic encoder is generally required to realize the motor position detection, so as to adjust the motor state in real time. In order to ensure the normal operation of each stepper motor during the operation, it is also necessary to use the op amp to collect the current of the motor driver chip to ensure the normal operation of the motor, or stagnation, to prevent damage to the machine after failure.
l Human-computer interaction control: At present, three types are generally used on the market, wire control, BLE, and WIFI. Since the mobile terminal is equipped with BLE, most of the PTZ human-computer interaction control adopts the BLE solution, but the BLE data bandwidth is low, which is not suitable for high-definition High-speed data transmission. Therefore, some manufacturers use WIFI to achieve high-speed transmission of video streams.
l Power supply system: The power supply system of the gimbal: generally powered by lithium batteries, with a boost of about 24V all the way, providing voltage for the motor driver chip or MOSFET to ensure the operation of the motor, and boosting the voltage all the way to 3.3V or 5V to supply power to the MCU.
l Without further ado, it is more intuitive to look at the pictures.
Figure 1 PTZ frame
1. Main control unit:
Mainly complete three things:
(1) Motor control. Read the attitude sensor signal to determine the current attitude of the gimbal, that is, sample the stator current and current, and then calculate the parameters that need to be adjusted through Clark, Park operations, and PI operations. Compare, control the output PWM, and thus control the motor, the MCU needs to complete the FOC speed control mode algorithm and the PID algorithm.
(2) Wireless data exchange. The MCU needs to link the mobile phone and other platform camera devices through Bluetooth to control the camera and complete the human-computer interaction.
(3) Coordinate and control the PTZ system.
GD32F4XX series MCU, 200Mhz main frequency, 3MB Flash 256K Ram, at the same time comes with hardware FPU, it is very advantageous for the motor control system that requires larger RAM to process FOC, PID algorithm, and also has advanced motor control timer, quadrature encoding It can collect motor speed, position, and current to form closed-loop control, programmable PWM mode, and can flexibly control three-phase motors to achieve rapid motor response.
2. Motor drive
Motor drive: You can use integrated driver IC or discrete MOS to build your own set:
Integrated IC: Simple control, higher integration, IC has its own under-voltage protection, short-circuit protection, dead-zone control, but due to the internal integration of MOS, poor heat dissipation and general driving ability.
Discrete drive solution: low integration, discrete MOS generally has a large current, good heat dissipation, and good driving ability. MCU generally has its own dead zone control when outputting PWM, but the reminder is slightly in the state of short circuit, overheating, and undervoltage. insufficient
At present, the MPS product line represented by our company has a mature motor driver chip. The chip has optimized dead time and symmetrical performance for various load conditions, and the internal MOSFET is set to 5.5A current limit. When this limit is exceeded, overcurrent The bridge will enter a high bit impedance state, and if the chip temperature exceeds 160°C, all internal switches will be turned off to prevent overheating damage.
Table 1 Motor drive parameters
The inside of the handheld gimbal directly supplies power for lithium batteries, which requires charging management chips, BUCK, BOOST, LDO and many other power ICs. Not listed here, if necessary, you can contact ZLG sales directly and we will customize a complete power supply solution for you.
4. Wireless transmission
The current mainstream wireless method of the handheld gimbal is BLE. Compared with the traditional wire control, wireless is more convenient and faster, and each mobile phone is equipped with Bluetooth function. With the subsequent changes in the function and form of the gimbal, higher data bandwidth is required. And farther transmission records, WiFi is a better choice. At present, we recommend two BLE chips represented by our company:
Table 2 Bluetooth chip parameters
As shown in Table 2. Both ICs are BLE5.0. Compared with BLE4.0/2, the power consumption is lower, and the FOTA function is supported. For handheld devices, the battery life will be longer. Compared with other Bluetooth SOCs, the voltage range of RSL10 is wider. , For the handheld gimbal powered by lithium batteries, the power utilization rate is higher.