Simscape Multibody inertia sensor: include a subset of bodies

We are simulating two orbital assets in close proximity in Simscape Multibody, and would like to compute the position of the CoM of each one via the Inertia Sensor block.

Both satellites are linked via a 6dof joint to the World frame, thus Simscape sees them as a unique mechanism.

We were able to span the Inertia Sensor measurement to either all rigidly-connected bodies of each satellite, or to the whole mechanism composed by both of them. However, we would like to compute the CoM position for each of the two satellites including all non-rigidly-connected appendages and bodies (i.e., mobile solar panels, robotic arm or others), but not including the other spacecraft and related bodies.

Is there a way to include certain bodies in the computation (e.g., those connected via revolute joints) and exlude others? We would like to avoid having to perform the computation "manually" if possible.

Thanks

Answer 1

[Steve Miller]

You could:

1. Copy the relevant components to a separate model and perform the test with the Inertia Sensor block there
2. Model the satellites as two unconnected mechanisms (may require moving that 6-DOF joint block to connect to a separate World, Mechanism Configuration, and Solver Configuration block).

--Steve

[Davide Vertuani]

Hi, thanks for your answer.

Answer 1. would be a solution if the mass would be static. However, the system's mass could be subject to changes during the simulation, so it won't fit.

Will see if 2. works in our case. In this case I am not sure we will be able to have the two systems interact (?)

[Steve Miller]

Davide, the Inertia Sensor reports the mass and inertia of the Simscape Multibody model as it changes with time. Simscape Multibody has variable mass solids, too.

The two systems can interact. As long as they are unique mechanisms (not connected by joints) the mass and inertia values will only be included in the respective Inertia Sensor's measurement. They could (for example) be connected using Spatial Contact Forces or External Force and Torque blocks.

--Steve

[Matteo Cinelli]

Hi @Davide Vertuani.

I have the same problem: a mechanism composed by different bodies and I would like to attach an inertia sensor only to a some of these bodies.

I tried option number 1, it works but it is useful only as an "off-simulation" tool.

I would like to explore option 2 but I didn't get really well how it works.

-- Matteo

[Matteo Cinelli]

I have a rotating cylinder connected, with a joint, to another element I would like to measure only cylineder inertia and mass.