Strip and add back components

[arjo129]

This is a "live blog" of myself trying to strip the vehicle down and add components in to determine the cause of the oscillations in the vehicle. The rationale for doing this is to make sure that we can isolate the systems responsible for Hydrostatic instability. I will start with a rigid body with an off-center mass.

Right now only the buoyancy plugin is enabled.

Requires gazebosim/gz-sim#1211

The vehicle in cd7990a is stable with no oscillation.

[arjo129]

Adding the drop weight in 14f8267 leads to oscillations. :(

[chapulina]

Adding the drop weight in 14f8267 leads to oscillations. :(

The weight is centered on the model, so its CoM isn't aligned with base_link's CoM. Its inertia also has some off-diagonal terms. So maybe this is expected?

[chapulina]

The weight is centered on the model, so its CoM isn't aligned with base_link's CoM.

Here's the offset on the CoMs:

The model sinks for me on 14f8267 though, it doesn't oscillate

[arjo129]

That is correct. Are you using the branch in gazebosim/gz-sim#1211 which "solves" the sinking.

[arjo129]

Will need to tweak the center of mass of the main vehicle. Also our visual needs to be offset.

[arjo129]

So I moved the center of mass of the main body forward but kept the same center of buoyancy in 0f271f2. The craft is once again stable.

[arjo129]

Closing this PR in favor of #89