A 1.8° stepper motor driven with 10 microsteps per step gives resolution

 Q151. A stepper motor has a step angle of 1.8°. The number of steps per revolution is

A) 100
B) 180
C) 200
D) 360
Answer: C
Explanation: $\text{Steps/rev} = 360° / 1.8° = 200$.

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Q152. A servo motor with a torque constant of 0.2 N·m/A produces 0.6 N·m torque. The current is
A) 1.2 A
B) 2 A
C) 3 A
D) 4 A
Answer: C
Explanation: $I = T / K_t = 0.6 / 0.2 = 3 \text{ A}$.

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Q153. In a stepper motor, increasing the stepping frequency increases
A) Speed
B) Torque
C) Accuracy
D) Resistance
Answer: A
Explanation: Each pulse corresponds to one step; higher pulse rate → higher rotational speed.

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Q154. The damping ratio of a servo system is 1. The system is
A) Overdamped
B) Underdamped
C) Critically damped
D) Oscillatory
Answer: C
Explanation: ζ = 1 corresponds to critical damping (fastest non-oscillatory response).

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Q155. A 4-phase stepper motor has 50 teeth on rotor. Step angle = ?
A) 1.8°
B) 0.9°
C) 7.2°
D) 3.6°
Answer: C
Explanation: $\text{Step angle} = \frac{360}{m \times N_r} = 360 / (4 × 50) = 1.8°$ (Correction → Option A).

Corrected Answer: A (1.8°)

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Q156. In a servo mechanism, steady-state error for a ramp input depends on
A) Velocity error constant
B) Position error constant
C) Acceleration constant
D) None
Answer: A
Explanation: For ramp input, $e_{ss} = 1/K_v$.

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Q157. The time constant of a DC servo motor (armature control) is determined by
A) L/R of armature circuit
B) Mechanical friction
C) Load torque
D) Feedback ratio
Answer: A
Explanation: Electrical time constant $T = L_a / R_a$.

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Q158. The pull-in torque of a stepper motor is measured at
A) Constant speed
B) Start and stop conditions
C) Maximum speed
D) Resonant speed
Answer: B
Explanation: Pull-in torque is torque available for starting/stopping without losing synchronism.

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Q159. In a servo control loop, tachometer feedback is used to measure
A) Speed
B) Position
C) Torque
D) Current
Answer: A
Explanation: Tachogenerators produce voltage proportional to speed.

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Q160. A stepper motor takes 200 steps per revolution. Each pulse advances the shaft by
A) 2°
B) 1.8°
C) 3.6°
D) 7.2°
Answer: B
Explanation: $360° / 200 = 1.8°$.

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Q161. Servo motors are preferred in CNC systems because
A) They provide continuous feedback control
B) They are cheaper
C) They operate at fixed speed
D) They are AC type only
Answer: A
Explanation: Servo motors offer precise closed-loop feedback for motion accuracy.

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Q162. The open-loop control system among the following is
A) Stepper motor drive
B) DC servo drive
C) CNC feed system
D) Automatic speed governor
Answer: A
Explanation: Stepper motor runs open-loop (no feedback) in most applications.

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Q163. The mechanical time constant of a servo motor is
A) $J/B$
B) $B/J$
C) $L/R$
D) $1/K_t$
Answer: A
Explanation: $T_m = J/B$, where $J$= inertia, $B$= viscous damping.

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Q164. The rated torque of a stepper motor is 0.5 N·m and the torque drops to 0.2 N·m at high speed. This is due to
A) Inductive reactance
B) Magnetic saturation
C) Friction
D) Poor design
Answer: A
Explanation: High frequency causes current lag in inductive winding, reducing torque.

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Q165. In a servo system, if feedback gain increases, steady-state error
A) Decreases
B) Increases
C) Remains constant
D) Becomes infinite
Answer: A
Explanation: Higher feedback gain improves accuracy (reduces error).

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Q166. A stepper motor with 4 phases and 100 rotor teeth has a step angle of
A) 0.9°
B) 1.8°
C) 3.6°
D) 7.2°
Answer: A
Explanation: $\text{Step angle} = 360 / (4 × 100) = 0.9°$.

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Q167. A servo system with 20% overshoot and settling time of 0.5 s has damping ratio ≈
A) 0.7
B) 0.5
C) 1
D) 0.2
Answer: A
Explanation: For 20% overshoot, $ζ ≈ 0.7$.

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Q168. Stepper motors are ideally suited for
A) Incremental motion control
B) High-speed rotation
C) Power drive
D) Alternating torque applications
Answer: A
Explanation: Stepper motors provide precise incremental angular movement.

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Q169. The error signal in servo control is obtained by
A) Comparing input and feedback
B) Multiplying input and feedback
C) Adding feedback
D) Differentiating output
Answer: A
Explanation: Error = Reference – Feedback.

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Q170. In servo systems, “hunting” means
A) Oscillation about final position
B) Slow response
C) Constant error
D) Sudden reversal
Answer: A
Explanation: Hunting = oscillatory motion around desired setpoint.

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Q171. If a 1.8° stepper motor receives 5000 pulses, how many revolutions does it make?
A) 10
B) 20
C) 25
D) 15
Answer: C
Explanation: 200 steps per rev → 5000/200 = 25 revs.

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Q172. For position control, the best type of motor is
A) Stepper motor
B) DC servo motor
C) Induction motor
D) Universal motor
Answer: B
Explanation: DC servo motors offer continuous accurate position control.

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Q173. The transfer function of a velocity control servo system is generally
A) Type 1
B) Type 0
C) Type 2
D) Nonlinear
Answer: A
Explanation: One integrator gives Type 1 → finite error for ramp input.

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Q174. The rated current of a servo motor is 2 A, armature resistance = 4 Ω, back emf = 16 V. The supply voltage is
A) 20 V
B) 24 V
C) 28 V
D) 32 V
Answer: B
Explanation: $V = E_b + I R = 16 + 2×4 = 24 V$.

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Q175. The rotor of a stepper motor is made of
A) Soft iron
B) Hard magnetic material
C) Aluminum
D) Copper
Answer: A
Explanation: Soft iron rotor enhances magnetic coupling with stator field.

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Q176. In a servo system, the integral control action
A) Eliminates steady-state error
B) Increases overshoot
C) Reduces damping
D) All of the above
Answer: D
Explanation: Integral term removes error but may reduce stability.

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Q177. A 4-phase stepper motor with 8 rotor teeth has step angle =
A) 11.25°
B) 7.5°
C) 3.6°
D) 1.8°
Answer: B
Explanation: $\text{Step angle} = 360 / (4×12) = 7.5°$.

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Q178. The frequency of pulses to a stepper motor determines
A) Speed
B) Torque
C) Position
D) Accuracy
Answer: A
Explanation: Step frequency controls rotational speed directly.

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Q179. The torque-speed characteristic of DC servo motor is
A) Linear
B) Parabolic
C) Exponential
D) Hyperbolic
Answer: A
Explanation: $T ∝ (V - E_b)$, and $E_b ∝ \omega$, hence linear relation.

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Q180. For zero steady-state error to a ramp input, the servo system must be of
A) Type 2
B) Type 1
C) Type 0
D) Type 3
Answer: A
Explanation: Two integrators → zero error for ramp input.

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Q181. Stepper motor torque decreases with speed because of
A) Inductive reactance
B) Magnetic losses
C) Voltage drop
D) Mechanical friction
Answer: A
Explanation: Inductive reactance opposes current rise at higher step rates.

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Q182. The servo motor feedback device can be
A) Encoder
B) Resolver
C) Tachometer
D) All of the above
Answer: D
Explanation: All are common feedback transducers for position/speed.

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Q183. Stepper motor “detent torque” is
A) Torque with no excitation
B) Starting torque
C) Holding torque
D) Maximum torque
Answer: A
Explanation: Detent torque = magnetic alignment torque when unenergized.

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Q184. The root-locus of a servo system helps to determine
A) Stability
B) Damping
C) Gain margin
D) All of the above
Answer: D
Explanation: Root-locus reveals effect of gain on poles, stability, damping.

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Q185. The output of a stepper driver circuit is typically
A) Square wave pulses
B) Sine wave
C) DC
D) Sawtooth
Answer: A
Explanation: Stepper drivers deliver discrete pulse signals for stepping.

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Q186. The servo amplifier power rating depends on
A) Required motor torque and speed
B) Feedback device
C) Signal gain only
D) Supply voltage only
Answer: A
Explanation: Power = torque × angular speed → amplifier must supply this.

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Q187. The accuracy of a servo system depends on
A) Feedback gain
B) Type number
C) Sensor resolution
D) All of the above
Answer: D
Explanation: All affect precision and tracking performance.

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Q188. Stepper motor torque is highest at
A) Low speeds
B) Resonance
C) High speeds
D) Mid-range speeds
Answer: A
Explanation: At low step rates, current fully builds per step → max torque.

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Q189. The position resolution of a servo system with 12-bit encoder is
A) 1024 counts/rev
B) 2048 counts/rev
C) 4096 counts/rev
D) 8192 counts/rev
Answer: C
Explanation: 12-bit encoder → $2^{12} = 4096$ counts/rev.

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Q190. The frequency at which torque starts dropping sharply in a stepper motor is called
A) Corner frequency
B) Resonant frequency
C) Cut-off frequency
D) Pull-out frequency
Answer: D
Explanation: Pull-out frequency = maximum step rate with synchronism.

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Q191. Servo motors used in robotics are generally
A) Brushless DC
B) Stepper
C) Universal
D) AC synchronous
Answer: A
Explanation: Brushless DC (BLDC) servos provide high efficiency & precision.

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Q192. The control-to-output transfer function of a type-0 servo system is
A) First order
B) Second order
C) Proportional
D) Integrating
Answer: A
Explanation: Type-0 → single lag (first-order) response.

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Q193. In a stepper motor, rotor moment of inertia affects
A) Acceleration and pull-in rate
B) Step size
C) Holding torque
D) Resistance
Answer: A
Explanation: Higher inertia → slower acceleration → lower pull-in frequency.

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Q194. A 1.8° stepper motor driven with 10 microsteps per step gives resolution =
A) 2000 steps/rev
B) 1000 steps/rev
C) 3600 steps/rev
D) 4000 steps/rev
Answer: A
Explanation: 200 steps × 10 = 2000 steps/rev.

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Q195. The main advantage of servo over stepper motor is
A) Closed-loop feedback
B) Higher torque at speed
C) Smoother motion
D) All of the above
Answer: D
Explanation: Servos outperform steppers in speed-torque & smooth control.

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Q196. The settling time of a servo motor increases when
A) Damping decreases
B) Damping increases
C) Gain increases moderately
D) Load decreases
Answer: A
Explanation: Less damping → oscillations → longer settling time.

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Q197. The torque of a servo motor is proportional to
A) Armature current
B) Field current
C) Voltage
D) Speed
Answer: A
Explanation: $T = K_t I_a$.

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Q198. Stepper motors are typically controlled by
A) Pulse train
B) Sine wave
C) Analog signal
D) DC voltage
Answer: A
Explanation: Step control via digital pulse sequence.

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Q199. The speed of a DC servo motor is directly proportional to
A) Armature voltage
B) Torque
C) Current
D) Back emf
Answer: A
Explanation: $ω ∝ (V - I_a R_a)$, approximately proportional to armature voltage.

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Q200. The steady-state error of a type-1 servo system for ramp input is
A) Finite
B) Zero
C) Infinite
D) Undefined
Answer: A
Explanation: Type-1 → finite error for ramp input ($e_{ss} = 1/K_v$).