The attached screenshot indicates that the sliding block is connected to the world frame using a "Planar Joint". Here are a couple of observations regarding this setup:
- Positioning the sliding block relative to the top surface of the base becomes more straightforward with a "Planar Joint".
- Further, using a "Planar Joint" results in the normal (contact) force being zero, as shown in the image below.
The presence of a normal force is essential for calculating friction. To address this, replacing the Planar Joint with a Cartesian Joint can be helpful. It is important to note, though, that the steady-state velocity will always reach a nonzero value, as illustrated in the following image.
According to the documentation for the Spatial Contact Force block: "The effective coefficient of friction is a function of the values of the Coefficient of Static Friction, Coefficient of Dynamic Friction, and Critical Velocity parameters, and the magnitude of the relative tangential velocity." The effective coefficient of friction changes as depicted below:
When the velocity is zero, the effective coefficient of friction is also zero and increases with velocity during the initial phase, up to the critical velocity. For a block sliding on an inclined base, this means there will always be a sliding velocity where the sliding component of the block's weight equals the frictional force.
To simulate a scenario involving simple friction—where the sliding block remains stationary up to a specific inclination angle—the frictional force can be calculated manually and provided as input to the Spatial Contact Force block. Here is a simple example for calculating the frictional force from the normal force:
I have attached the models for your reference.
For further details on the Spatial Contact Force block, the following documentation page offers comprehensive information:
