URDF File - robot jumps and makes small leaps

edit

Hello, I want to create a robot with two driving wheels and two caster wheels. As shown in this image :

I d’not know if it is well showen in the picture, the robot has two caster wheels (front and rear).

I have create the URDF file that describes the robot, unfortunately I have some small problems that I do not know how to fix them.

URDF file link : https://gist.github.com/hdd-robot/2d3...

The problem is that the robot jumps and makes small leaps, which makes the odometry imprecise and it is very unpleasant.

Thanks in advance.