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The Robotics Primer: Chapter 4

Measuring a motor’s torque and speed

You could measure a motor’s torque by measuring the amount of electrical current the motor uses, since producing more torque requires more current. Since the amount of power produced by a motor is proportional to the product of its torque and its velocity, if you can measure the power produced by the motor then you can simply divide the power by the amount of torque to find the rotational velocity.

DOF in the human hand

As mentioned in the textbook, the wrist has three degrees of freedom, one each for up-down, side-to-side, and rotation. Each finger can open and close, move forward and backwards, and move side-to-side a little bit, resulting in three degrees of freedom per finger. Three DOF times five fingers plus three DOF in the wrist results in a total of eighteen DOF for the entire hand, making the human hand redundant as opposed to holonomic or nonholonomic. I initially wondered if the growth of fingernails could be a degree of freedom, but since we cannot consciously control their growth, I concluded that the growth of fingernails is not a degree of freedom.


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