Mech Master

1. RoboMaster based on Liangshan School development board.
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DJI's RoboMaster gives us the best experience. Every big boy wants to own a car like that. But its price is astronomical for me. However, it is not difficult for me who studies electronics. If we can't afford it, we will build one ourselves. Then, my own RoboMaster was born. Finished product picture display.
![Car2.jpg] ![Car1.jpg]
2. RoboMaster function decomposition diagram
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![Mind map.png]
3. Function introduction
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(1) Wheels and control
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① The wheels use 5CM McLennan wheels, and the motor uses N20 motor with a speed of 80 rpm.
The control method of McLennan wheels is shown in the figure. When the wheel rotates in different directions, the direction of the car is also different.
![Wheat wheel.png] ② Wheel drive circuit

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![Wheel drive circuit.png]
The McLennan control circuit
uses DRV8833PWPR chip. DRV8833PWPR is a 2A low-voltage dual-brush DC or single bipolar stepper motor driver. The chip has two H-bridge drivers that can drive two DC brushed motors, one bipolar stepper motor, solenoids or other inductive loads. The output driver module of each H-bridge consists of an N-channel power MOSFET configured as an H-bridge to drive the motor windings. Each H-bridge includes circuits to regulate or limit the winding current. An internal shutdown function with a fault output pin provides overcurrent protection, short-circuit protection, undervoltage lockout, and overtemperature protection. A low-power sleep mode is also provided.
③ Wheel speed detection. The pulse signal is measured through the photoelectric feedback signal to obtain the speed to complete PID control (refer to the design of netizens). The signal acquisition principle is shown in the figure
! [Wheat wheel speed detection.png] Speed ​​detection circuit diagram
! [Speed ​​measurement circuit diagram.png] When the photoelectric switch KEY1 receives the reflected signal, the photoelectric switches 3 and 4 are turned on, giving the U1 Schmitt trigger inverter 2 pin low level, and the inverter 4 pin outputs a high level to the Liangshan School (microcontroller) IO. In this way, the pulse waveform can be collected through the IO port of Liangshan School (single-chip microcomputer) to obtain the wheel speed. The inverter is to ensure the integrity of the pulse waveform. In this way, the closed-loop control (PID) is completed by coordinating with the wheel PWM signal.
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(2) Turret and launch system
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The turret moves left and right and up and down through two SG90 servos. It is controlled by the PWM signals of Liangshan School's PA5 and PB8 ports.
![Servo turret.jpg] Servo interface circuit
![Servo turret circuit diagram.png] PA5 port is the original design port, and PB8 is an IO port using a camera. The original design H11 port is PB15 port. Since it is not driven in the program, PB8 port is used first. The servo on the top and the servo on the left are the main servos, and the servo on the right is only for support and fixing. The internal mechanism has been removed.
❷ Bullet launch system
![Friction wheel launch.png] Prepare to use the friction wheel to launch 6MM bullets. There are friction wheels on both sides and bullets in the middle. This is the basic principle, which is still under design.

(3) PS handle control
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PS handle receiver diagram


![ps receiver.png] ![PS handle connection.png]
The communication sequence feels very similar to SPI. It is also a pair of 8-bit serial data transmitted simultaneously with four lines DI and DO. During transmission, CS needs to be low and CLK needs to change from high to low. DO is the signal sent by the microcontroller to the receiver. DI is the signal sent by the receiver to the microcontroller. Due to the limited space on the car body, the PS handle receiver can only be attached to the bottom of the car chassis.
![PS handle receiver installation 1.png] PS handle interface circuit diagram
![PS handle interface circuit.png] The PS handle receiver is installed on the CN1 interface. This interface can also connect to a 2.4G wireless receiving module.
The control also designed a Bluetooth module, using HC-05 Bluetooth. The Bluetooth module has not been connected for debugging yet.
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(4) Power battery
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![lithium battery.png] Power supply circuit diagram
![lithium battery power supply circuit.png] The car has three voltages. The 7.4V lithium battery supplies the driver chip of the car motor. The 5V uses the U18 78M05 linear voltage regulator chip to stabilize the 7.4V to 5V, providing power for the car modules and Liangshan faction. The U18 voltage regulator chip can provide 500MA current, which is enough. The 3.3V is output through the Liangshan faction. The battery is tied to the back of the car with a cable tie.
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(5) Car lights
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The car is designed with front and rear LED lights, but the shell is added and it is useless. The WS2812 lamp head is used. The WS2812 lamp designed on the bottom of the car body is also useless. Directly connect the WS2812 car light head.
![WS2812 car light.jpg] WS2812 circuit diagram.
![WS2812 car light circuit.png] After the WS2812 is powered on and reset, the DIN terminal receives the data transmitted from the controller. The first 24-bit data is extracted by the first lamp bead and sent to the data latch inside the lamp bead. The remaining data is shaped and amplified by the internal shaping processing circuit and then forwarded to the next cascaded lamp bead through the DO port. After each lamp bead is transmitted, the signal is reduced by 24 bits. The lamp bead adopts automatic shaping and forwarding technology, so that the number of cascaded lamp beads is not limited by signal transmission, but only by the signal transmission speed requirement. The lamp head uses four lamp beads in cascade. Four colors are written in the program.
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(6) Laser cannon
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The car is equipped with a laser emission tube, which is turned on and off using the PS handle.
Drive circuit
![Laser head circuit diagram.png] This circuit is not designed on the car circuit board, but a small board is installed. LED24 is the laser emission tube, which uses a digital triode DTC143ECA. The laser emission tube is powered by 5V and has a drive current of 12MA. The car power supply can drive the laser head normally. Use the LED_L lamp pin to drive the laser tube on and off.
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(7) Turret installation
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![Turret and gun connection diagram.jpg] The turret and gun are connected with two 3*18 screws, which makes it easy to replace the gun.
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(8) PS handle operation instructions
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![PS handle usage instructions.jpg]
(9) Problem description
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![Internal photos.jpg] The car circuit board is not designed with screw holes, which makes it difficult to fix. This is the biggest defect of the car. It can only be fixed to the bottom shell with screws and a small plate. The red small plate is used to fix the circuit board. This is where the car needs to be improved.
Screw hardware description
24 sets of φ2*8 screws 6 sets of φ4*45 screws 2 sets of φ3*18 screws
3D parts display
![3D printed body.jpg]
3. Summary
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There are many functions of the car that have not been tested yet, and all ports are reserved. Such as Bluetooth, patrol, ultrasonic ranging, voice control, audio positioning, camera image recognition. There will be time to complete it further. First, set the basic functions on the PS handle and complete the test of the basic functions. In the design, the Liangshan School's module transplantation manual provided great help for development and improved development efficiency. My programs are all CV from the manual, which is really YYDS. If there is no manual, if you encounter a difficult problem, you will be stuck and you will not be able to complete it in such a short time (spare time). The bottom shell of the car is designed by Easy EDA, and the turret and lamp head are designed by SOLIDWORKS. This software is just for beginners, and the design is not very professional. Don't criticize if you don't like it. Haha... The design files are uploaded in the attachment. I hope the design process can help everyone.