SimMechanics: Is it wrong to use joint Internal Mechanics Instead of a Spring Damper Force Block?

Hi everyone, I am new to SimuLink and I am trying to model a spring behavior between two Solids. If i place a Prismatic Joint block between the frames the assembly is fine and by using internal mechanics i can set a stiffness and damping coefficient between the two parts.

However, more intuitively this is the job of the Spring and Damper Force block... The problem is if I remove the prismatic joint and replace it with the spring and damper block, the assembly of the two rods goes out of alignment (one of the Solids rotates and translates away). I cannot for the life of me get it to come together as it should.

So, do I lose something by using a prismatic joint to model a spring. And, what might I be doing wrong that the spring damper block doesn't work?

Answer 1

[Nicolas Schmit]

There is nothing wrong with using the joint internal mechanics. In this case, you do not need the Spring and Damper Force block.

If do want to use the Spring and Damper Force block, you still need to have a Prismatic Joint block (with no internal mechanics) in your model. This is because the Spring and Damper Force block models only the force, and not the mechanical constraints imposed by the joint.

Answer 2

[sanjeev kumar]

Dear Sir, How do you have decided the Spring Stiffness and Damping coefficient value of prismatic joint in your model?

Thank you