I am in the process of creating a Power Prediction Model for [the Hubo Robot](http://en.wikipedia.org/wiki/HUBO).
The Robot has 38 Degrees of Freedom and has a computer some sensors and motor boards. The motors are powered through Motor Boards. All these boards are powered through a main power board that exists at the robots chest.

My model should be able to predict the power for any trajectory of the robot. Say for instance if the robot raises its hand from 0 degrees to 180 degrees my model should be able to predict the power.

Heres an idea I came across. My idea was to equate the electrical torque to the mechanical torque of each joint.

For instance if the Right arm pitch moves from 0 to 180 degrees I can do as follows ?
$mgsin(\theta)= Kt\*I$

However, I am not getting a proper prediction and the current value is way off than what we can read from a software installed in the robot. I know there are losses but even then its off. I was wondering if there are any other approaches or a fault in my approach.

And after I do this I can add all the joint currents for a specific trajectory and then give a estimate for total power consumption.