I am building an skeletal upper-limb model of a monkey from a CT scan. For some steps, I compare my results to existing models (principally Hamner's full body model).
In the forearm, there are two bones (Ulna and Radius). In Hamner's model, both bones have the same weight and the same inertia tensor. I'm pretty sure that they weighted all tissues of the forearm (total=1.2kg) and divided its weight by two for each bone (0.6kg each). I am now unsure if they did the same for the inertias.
I wasn't able to find any documentation or intuitive explanations for this matter, this is why I'm asking here.
More details below on some exploration that I did, but the main question is:
- I computed the mass and inertia of all tissues of the forearm from the CT-scan. I will divide its mass by two and assign the result to both ulna and radius. Should I also divide the inertia by two or keep it fully.
Thank you already,
Alex
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More details on some exploration that I did:
I wrote a script to input inertia values and density, that outputs the shape and mass of a corresponding cuboid. As said earlier, the forearm of Hamner's model weights 1.2kg, so I tried to vary the density input to match that result, and observe the cuboid to see if it had the same shape as a forearm.
- When using the inertia values as given by Hamner's model, the input density is 2600kg/m^3 (close to granite density), and the cuboid seems too short. (See picture)
- When multiplying the inertia values by two (for the two bones), I can use a density of 1060kg/m^3 (correct value for human tissues density), and the cuboid seems to fit better. (See picture)
To me, it seems they divided the inertia by two for each bone, but I would love to hear your opinion. Thank you!
