4WD diff drive - Kraft2k/icebox-rover GitHub Wiki

I have 4WD diff rover, that control left_motor and right_motor with wheel_radius, x_distance_wheels and y_distance_wheels. Write ros2 Node that subscribe to a /cmd_vel topic and control motors

To create a ROS 2 node that subscribes to a /cmd_vel topic and controls the motors of a 4WD differential drive rover, you can use Python and the rclpy library. First, make sure you have ROS 2 installed and set up. Then, follow these steps to create your node: Create a ROS 2 package (if you haven't already) and navigate to the package directory. Create a Python script for your node, e.g., rover_control_node.py. Here's a sample Python script for your rover control node: python

Copy code import rclpy from rclpy.node import Node from geometry_msgs.msg import Twist

class RoverControlNode(Node): def init(self): super().init('rover_control_node')

    # Define ROS subscribers
    self.subscription = self.create_subscription(
        Twist,
        '/cmd_vel',
        self.cmd_vel_callback,
        10
    )
    
    # Define motor control parameters
    self.wheel_radius = 0.1  # Replace with your actual wheel radius (in meters)
    self.x_distance_wheels = 0.4  # Replace with the distance between the left and right wheels (in meters)
    self.y_distance_wheels = 0.4  # Replace with the distance between the front and rear wheels (in meters)
    
    # Initialize your motor control here
    # For example, you can use GPIO or other motor control libraries
    
def cmd_vel_callback(self, msg):
    # Extract linear and angular velocity components from Twist message
    linear_x = msg.linear.x
    angular_z = msg.angular.z
    
    # Calculate left and right wheel speeds based on cmd_vel
    left_wheel_speed = (linear_x - angular_z * self.y_distance_wheels / 2) / self.wheel_radius
    right_wheel_speed = (linear_x + angular_z * self.y_distance_wheels / 2) / self.wheel_radius
    
    # Control your motors based on left_wheel_speed and right_wheel_speed
    # You need to implement the actual motor control logic here

def main(args=None): rclpy.init(args=args) node = RoverControlNode()

try:
    rclpy.spin(node)
except KeyboardInterrupt:
    pass

node.destroy_node()
rclpy.shutdown()

if name == 'main': main() This script creates a ROS 2 node that subscribes to the /cmd_vel topic, extracts linear and angular velocity components, calculates left and right wheel speeds based on the differential drive kinematics, and provides a placeholder for your motor control logic. You'll need to replace the motor control logic with code specific to your rover's hardware and control interface. Don't forget to adjust the wheel_radius, x_distance_wheels, and y_distance_wheels values according to your rover's specifications.

write code if motors control only rear motors and front free

If you want to control only the rear motors of your 4WD differential drive rover and let the front wheels free (not powered), you can modify the previous code accordingly. In this case, you would only need to control the left and right rear motors. Here's the modified code: python

Copy code import rclpy from rclpy.node import Node from geometry_msgs.msg import Twist

class RoverControlNode(Node): def init(self): super().init('rover_control_node')

    # Define ROS subscribers
    self.subscription = self.create_subscription(
        Twist,
        '/cmd_vel',
        self.cmd_vel_callback,
        10
    )
    
    # Define motor control parameters
    self.wheel_radius = 0.1  # Replace with your actual wheel radius (in meters)
    self.x_distance_wheels = 0.4  # Replace with the distance between the left and right wheels (in meters)
    
    # Initialize your motor control here (for rear motors)
    # For example, you can use GPIO or other motor control libraries
    
def cmd_vel_callback(self, msg):
    # Extract linear and angular velocity components from Twist message
    linear_x = msg.linear.x
    angular_z = msg.angular.z
    
    # Calculate left and right wheel speeds based on cmd_vel
    left_wheel_speed = (linear_x - angular_z * self.x_distance_wheels / 2) / self.wheel_radius
    right_wheel_speed = (linear_x + angular_z * self.x_distance_wheels / 2) / self.wheel_radius
    
    # Control your rear motors based on left_wheel_speed and right_wheel_speed
    # You need to implement the actual motor control logic for the rear motors here
    # For the front wheels, you don't need to do anything as they are free

def main(args=None): rclpy.init(args=args) node = RoverControlNode()

try:
    rclpy.spin(node)
except KeyboardInterrupt:
    pass

node.destroy_node()
rclpy.shutdown()

if name == 'main': main() In this modified code, we calculate the left and right wheel speeds based on the command velocity and apply motor control only to the rear wheels, leaving the front wheels free to rotate without being powered. You will need to implement the specific motor control logic for the rear wheels according to your rover's hardware and control interface.

def ik_vel(self, x_vel: float, y_vel: float, rot_vel: float) -> List[float]:

    """Takes 2 linear speeds and 1 rot speed (robot's egocentric frame) and outputs the rotational speed (rad/s) of each of the 3 motors   in an omni setup

    Args:
        x (float): x speed (m/s). Positive "in front" of the robot.
        y (float): y speed (m/s). Positive "to the left" of the robot.
        rot (float): rotational speed (rad/s). Positive counter-clock wise.
    """
    wheel_rot_speed_back = 0
    wheel_rot_speed_right = (x_vel + rot_vel * self.rover_base.y_distance_wheels/2) / self.rover_base.wheel_radius
    wheel_rot_speed_left = (x_vel - rot_vel * self.rover_base.y_distance_wheels/2) / self.rover_base.wheel_radius

    return [wheel_rot_speed_back, wheel_rot_speed_right, wheel_rot_speed_left]