View Single Post
  #4   Spotlight this post!  
Unread 20-05-2014, 10:15
headlight headlight is offline
Registered User
no team
 
Join Date: May 2013
Rookie Year: 2012
Location: Rochester Hills, MI
Posts: 69
headlight is an unknown quantity at this point
Re: motor Ke and Kt Quiz

I'm not really an electrical guy, but this is my understanding.

The biggest point of ambiguity is the definition of an ideal motor. I think a more accurate way to state the problem is that the motor is "perfectly efficient". Its nice because efficiency actually has a definition that relates to the performance of the motor, as opposed to the word "ideal" which can mean a variety of things (inductance of motor is disregarded? heat effects are disregarded? I've usually seen "ideal" motors modeled as resistors).


If the motor is assumed to be perfectly efficient and linear, then only one datapoint is needed to characterize the entire motor (because the power transfer would be constant, meaning that any excess power that results from a loss in velocity must be made up with an increase in torque). You provided two datapoints, two datapoints that do not describe a perfectly efficient motor. The motor described by your datapoints operates most efficiently at halfway up the speed vs. torque graph (200rad/sec, 0.2 n-m).

If I understand correctly, the quiz is basically nonsensical because conflicting information is given. The statement is basically:
"this motor is perfectly efficient and the power input is constant, when it is going fast it outputs 60 watts, when it is going slow it outputs 40 watts. why is that?"