# Moment of inertia of a composite model

Hello, I am modeling a quadrotor using boxes and cylinders. Each box/cylinder is defined as individual link and has its own inertia. I know the exact inertia of the quadrotor and am trying fit the dimensions and masses of the links to the correct values using regression. However, I don't know how to calculate the combined inertia of the whole model.

I am wondering if anyone knows how Gazebo does it. When I start the simulation and print the model sdf as a string to the console I can see the combined inertia of the model. Or if anyone knows how to calculate it, it would be nice too. I am using ODE as my physics engine, if it's done within the physics engine.

Thanks!