# DRCSIM: hand bits with too big moments of inertia

drcsim-2.0: There seem to be lots of parts of the Sandia hand which are quite light yet have the default moments of inertia:

inertia ixx="0.01" ixy="0" ixz="0" iyy="0.01" iyz="0" izz="0.01"

right_f0_base mass value="0.35" right_f0_fixed_accel mass value="0.001" right_f0_0 mass value="0.05" right_f0_1 mass value="0.05" right_f0_1_accel mass value="0.001" right_f0_2 mass value="0.05" right_f0_2_accel mass value="0.001" right_f1_base mass value="0.35 ...

When all the parts are combined, this gives a hand about double the moment of inertia of the pelvis or uleg, and second only to the utorso. This causes simulations with the hands attached to be quite unrealistic. Essentially the hands act as substantial flywheels. It would be useful to get a more realistic set of moments of inertia for the hand bits.

I realize this may be a disaster in terms of simulation stability, since the range of size of the parts will be much larger.

In case you are wondering, something with a moment of inertia of 0.01 which weighs only 0.001kg needs to be at least about 6 meters across.

Can you tell me the total weight of a Sandia hand?

Thanks, Chris