Dear Mina,

Yes, delete gravity as it is canceling some of the applied force on the rail.

Attached is a simplified version of your model with just one wheel on a rail with 100 N of contact force and an axle on a translation joint being accelerated at 1 m/s^2.

When the Coeff of Friction is 0.2, the force to accelerate the system is 4.26 N.

When the Coeff of Friction is 0.0, the force to accelerate the system is 3.65 N.

The force to accelerate the mass is less when there is no friction on the wheel because the wheel is not experiencing any rotational acceleration.

You can calculate the 3.65 N simply from the mass in the moving parts, excluding the rail = 3.65 kg * 1 m/s^2 = 3.65 N.

You can calculate the difference between 4.26 N and 3.65 N, which is the force at the wheel radius needed to create the torque on the wheel to rotationally accelerate the polar moment of inertia of the wheel to maintain the rolling relationship.

Between 0.2 and 0, there is a limiting COF when the wheel starts slipping. The normal force and the wheel radius also affect this limiting COF.

ANSYS 2020 R1 archive attached.