Looking for insight into LinearSpringMassDamper calcForceTorqueOnBody

[EpicIan60142]

Hello!

I'm currently trying to dive into how StateEffectors and DynamicEffectors work in order to implement them for my own models, and I've been looking at the LinearSpringMassDamper class as an example. I've got a solid handle on the back-substitution method and the energy/momentum contributions, but when I try to re-derive what's implemented for the body force, my expected answer doesn't match what is in the model. I've attached a set of slides with my conundrum, but my questions are as follows:

1. is calcForceTorqueOnBody still a required method to implement in StateEffectors? I was under the impression that the forces and torques are handled by the v_trans and v_rot back-substitution vectors respectively, but I can also see why we'd need to explicitly calculate them

2. How does my derivation differ from the official one? Am I forgetting some basic dynamics or a subtlety?

3. Is there anywhere else I can go to learn further about how StateEffectors are implemented? I've currently learned everything I know from the spacecraft model documentation, as well as the LinearSpringMassDamper documentation. I've also read the papers referenced in both sets of documentation.

Thanks!

Sandbox.pptx