22 "Wanli" Raspberry Pi car - mobile phone remote control motor rotation

lb8820265

22 "Wanli" Raspberry Pi car - mobile phone remote control motor rotation [Copy link]

This post was last edited by lb8820265 on 2022-1-30 11:55

After struggling for a long time on how to accurately control the wheel speed, I finally decided to use open-loop control without calibrating the speed.

We have introduced the motor control and the UDP communication between the mobile phone and the Raspberry Pi . By combining these two functions and formulating a communication protocol, we can use the mobile phone to control the motor speed. The goal is broken down into three parts: the communication protocol, the APP host computer, and the Raspberry Pi car.

Communication Protocol

Before writing the APP and car code, it is important to understand the communication protocol between the two. This does not refer to the UDP described above, but to the specific meaning of the control data sent by the mobile phone. Since the ultimate goal is to control the speed of the four wheels of the car, it can be simply represented by 4 bytes. Each byte represents the speed of a wheel. The value range is from -100 to 100. Negative numbers represent reverse rotation, and positive numbers represent forward rotation. The larger the value, the faster the speed. In addition, one byte is used as a backup, for a total of five bytes.

Location	Byte0	Byte1	Byte2	Byte3
meaning	M1 Speed	M2 Speed	M3 Speed	M4 Speed
scope	-100~100	-100~100	-100~100	-100~100

APP host computer

The main function of the APP host computer is to connect to the Raspberry Pi and send control data. I mainly refer to my previous open source car project for the production of the host computer . Over the past so many years, AS software has changed too much and many libraries are no longer supported, but this is not a problem. Use AS4.1 to create a new "lb_Wanli_Car" project, integrate the previous UDP communication project, add a joystick and four drag bars and four edit boxes to display the control amount. The effect diagram and source code are detailed at the end.

The joystick is not used for the time being. This time, a drag bar is used to control the motor speed. A timer is added. It is turned on when the connection is successful and turned off when the connection is disconnected. The value of the drag bar is read every 100ms and sent to the Raspberry Pi.

Raspberry Pi Car

The Raspberry Pi car is mainly responsible for data reception and motor control, that is, integrating motor control with UDP communication. Modifications are made based on the previous four-wheel control speed. A new Car_Control project is created, and the Socket_UDP.cpp file is added. A new thread is opened in the main function to specifically receive data. The received data is parsed in the receiving function and the motor is controlled.

The parsing of data requires extra attention. The value range is -100~100, but there is no negative number for char type data. However, data greater than 128 can be considered a negative number. Subtracting this number from 256 is equivalent to taking the absolute value. The processing code is as follows.

void Data_Process(char * Data){
	float gen=2.55;
	if(Data[0]>128){
		M1.Motor_out=(256-Data[0])*gen;
		M1.Direction=2;
	}else{
		M1.Motor_out=Data[0];
		M1.Direction=1;
	}
	if(Data[1]>128){
		M2.Motor_out=(256-Data[1])*gen;
		M2.Direction=2;
	}else{
		M2.Motor_out=Data[1];
		M2.Direction=1;
	}
	if(Data[2]>128){
		M3.Motor_out=(256-Data[2])*gen;
		M3.Direction=2;
	}else{
		M3.Motor_out=Data[2];
		M3.Direction=1;
	}
	if(Data[3]>128){
		M4.Motor_out=(256-Data[3])*gen;
		M4.Direction=2;
	}else{
		M4.Motor_out=Data[3];
		M4.Direction=1;
	}
}

Operation effect

First, connect the hardware and run Car_Control on the Raspberry Pi.

Open the APP and connect the Raspberry Pi on the connection interface. Drag the drag bar on the control interface to control the motor, and you can achieve different speeds and forward and reverse control.

[attach]586548[/attach ]

Now it is possible to use a mobile phone to control the rotation of four motors, but the car uses a Nam wheel, so it is still not easy to make the car move.

Source code

GitHub:

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Gitee:

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