Position control example in Ch 1 has confusing wording

[Richard Murray]

Contributed by Jason Rolfe, Jan 2019: On page 1-17, the first clause seems redundant and inconsistent with the last clause:

Since the motor velocity is proportional to the current, the dynamics relating velocity tothe input of the current controller is approximately an integrator, because force is proportional to current and angular acceleration is proportional to force.

[Richard Murray]

I think the first phrase is incorrect. It should say that the motor torque is proportional to the current (which is what it says at the end). Then, since we are regulating the current, the dynamics between current command and velocity can be modeled as an integrator. I suggest we change the sentence to read:

Since the motor torque is proportional to the current, the dynamics relating velocity to the input of the current controller is approximately an integrator.

OK?

[Richard Murray]

Change to: “Since the motor torque is proportional to the current, the dynamics relating motor velocity to the input of the current controller is approximately an integrator.”

[Richard Murray]

Fixed in commit e865523.