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# soln12c - The Hong Kong Polytechnic University Department...

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The Hong Kong Polytechnic University Department of Mechanical Engineering 2008/09 Semester 1 ME4204 Mechatronics Systems Assignment 2 Name: Student ID: Notes: 1. Please answer all the following questions. 2. Submission Deadline: 1 November, 2008 3. Marks will be deducted for late submission: –5% per day 4. Submission Methods: Either a. Hand in during lecture (Print-out), Or b. Email to [email protected] (PDF format). 1. A 50 V, d.c. shunt motor drives a constant-torque load at a speed of 1200 rpm as shown in Fig.1. The armature and field resistances are 2 Ω and 100 Ω , respectively. The motor draws a line current of 15 A at the given load. (a) Calculate the resistance that should be added to the armature circuit to reduce the speed by 25%. (10 marks) Consider Fig.1a and assume the operating 1 represents the motor without any added resistance, and point 2 is f , the operating point at 25% speed reduction. Since the motor is shunt type, the line current is equal to the armature current plus field current.

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