Kinematic Inverse Solution and Gait Planning for Quadruped Robot Using XR806

Using the RX806 serial protocol to communicate with the DJI A board’s STM32, we achieve the kinematic inverse solution of a single leg of a parallel quadruped robot and overall gait planning.

Figure 1 Physical Image

2.1 Single Leg Kinematic Inverse Solution

Control 2 brushless motors (each represented by a red arrow) to form a single leg in parallel, calculating the foot trajectory through angle closed-loop control, and creating a cycloidal trajectory at the foot end (the green part in the image below) to simulate the motion of animals like cats and dogs.

Figure 2

% Cycloid Equation (matlab) sigma=2*pi*t/(Ts);xep=(xf-xs)*((sigma-sin(sigma))/(2*pi))+xs;zep=h*(1-cos(sigma))/2+zs;x=[x,xep];z=[z,zep];

2.2 Gait Planning (Currently Mainly Using Walk Gait)

The Walk gait is a static gait, meaning that during movement, three legs are always in a support phase, with at most one leg in a swing phase. The most common rotation order of the four legs in the Walk gait for quadrupedal animals is 1→3→4→2→1.

Figure 3

2.3 Brushless Motor Angular Velocity PID Closed Loop

Using P proportional, I integral, and D differential through incremental PID to enable the brushless motor to stably control speed and angle, the pd control function is as follows:

int Balance(float Angle,float Gyro,int Middle,float Balance_Kp,float Balance_Kd){     float Angle_bias,Gyro_bias;  int balance;  Angle_bias=Middle-Angle;                         Gyro_bias=0-Gyro;                                balance=Balance_Kp*Angle_bias+Gyro_bias*Balance_Kd;   return balance;}

XR806:

Initializing serial port configuration:

static int uart_init(void){ UART_InitParam param;
 param.baudRate = 115200; param.dataBits = UART_DATA_BITS_8; param.stopBits = UART_STOP_BITS_1; param.parity = UART_PARITY_NONE; param.isAutoHwFlowCtrl = 0;
 if(HAL_UART_Init(UARTID, &param) != HAL_OK)  return -1; /* Enable DMA */ if (HAL_UART_EnableTxDMA(UARTID) != HAL_OK)  return -2; if (HAL_UART_EnableRxDMA(UARTID) != HAL_OK)  return -3;
 return 0;}

In the main function, the while loop sends the corresponding data using the following function.

HAL_UART_Transmit_DMA(UARTID, (uint8_t *)buffer,sizeof(buffer));

In STM32, the serial port 3 receive callback executes the corresponding forward and backward commands.

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart){     if(huart->Instance == USART3) {  HAL_UART_Receive_IT(&huart3,&RxBuffer_control,1);
 switch(RxBuffer_control) {  case 'W': Motor_Control( 1,  1,  1,  1); break;  case 'S': Motor_Control(-1, -1, -1, -1);  break;  case 'A': Motor_Control(-1, -1,  1,  1);  break;  case 'D': Motor_Control( 1,  1, -1, -1);  break;  case 'P': Motor_Control( 0,  0,  0,  0);  break; }}

4.1 Stationary

4.2 Omnidirectional Movement