Hello there! My robot is not moving in a straight line in gazebo. The robot consist of 4 caster wheels and 2 diffrential wheel. The contact of the two diffrential wheels and the 4 caster wheels are the same. But when i am giving a velocity to the robot, the robot does not move... When i checked the diffrential wheel, the wheel was rotating, but the robot wasn't moving forward. Static is False , so that isn't the problem. But when I increased the diffrential wheel radius a little, the robot moves, but not in a straight line. Please Help me!! I have checked the centre of mass, It dosen't have a problem there. Could you suggest me some explanation why the robot is not moving when the contact points of caster wheeel and diffrential wheel are same on the ground. Or how I can make the robot move in a straight line with the increased diffrential wheel radius.

Thanks for your time!