Actuators & Control · Study deck

Servo Motors: Position, Motion, and Power

A servo tries to reach a commanded position.

Motor Max is your guide for this deck.

servomotors
Motor Max, the module guide, in a scene from this chapter.
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After studying this chapter

Learning objectives

You will be able to:

  • Explain: For smooth motion from 0° to 180° over 1 second at 50 Hz, you send 50 commands with angular step Δθ=180/50=3.6°\Delta\theta = 180/50 = 3.6°Δθ=180/50=3.6° per frame.
  • Explain: A bare motor can spin, but the useful story is angle, holding torque, travel limits, and evidence that the louver reached the intended position.
  • Explain: Pulse-width modulation means controlling a signal by changing how long each pulse stays on; it is often shortened to PWM.
  • Explain: The design still has to prove power margin, linkage geometry, calibrated pulse widths, and safe behavior at the ends of travel.
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Major section

Start With the Decision

A servo tries to reach a commanded position.

  • A position command names the target angle; the supply must provide enough current to move and hold the load.
  • A vent may be told to half open yet press against its stop.
  • Position commands need motion limits and enough supply current.
A servo repeats a 20 ms frame while high pulses of 1.0, 1.5, and 2.0 ms command increasing angles.
A servo repeats a 20 ms frame while high pulses of 1.0, 1.5, and 2.0 ms command increasing angles.
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Major section

Start With the Story

The command alone cannot show whether the mechanism moved safely or reached the requested angle.

  • An actuator means a part that turns an electrical command into physical action.
  • Pulse-width modulation means controlling a signal by changing how long each pulse stays on; it is often shortened to PWM.
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Major section

Start With the Story (continued)

This runway does not prove that one servo fits every load.

  • The deeper sections explain torque, pulse calibration, gearing, power margin, linkage geometry, feedback, and safe travel limits.
  • A bare motor can spin, but the useful story is angle, holding torque, travel limits, and evidence that the louver reached the intended position.
  • The design still has to prove power margin, linkage geometry, calibrated pulse widths, and safe behavior at the ends of travel.
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Major section

Servo Motor Fundamentals

Servo motors provide precise angular positioning (typically 0-180 degrees) using command pulses.

  • The package simplifies control but does not remove stall-current or load-margin checks.
  • The internal potentiometer continuously measures shaft position, and the control circuit compares this to the commanded position from the PWM signal.

Key terms

What changes
What changes is the high time within that frame.
Small blue SG90-style hobby servo with three-wire lead, output shaft, mounting tabs, and interchangeable plastic horns
Small blue SG90-style hobby servo with three-wire lead, output shaft, mounting tabs, and interchangeable plastic horns
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Major section

Putting Numbers to It

At 50 Hz, the period is T=1/50=20T = 1/50 = 20T=1/50=20 ms.

  • A 1.5 ms pulse for 90° means duty cycle D=1.5/20=0.075=7.5%D = 1.5/20 = 0.075 = 7.5\%D=1.5/20=0.075=7.5%.
  • For smooth motion from 0° to 180° over 1 second at 50 Hz, you send 50 commands with angular step Δθ=180/50=3.6°\Delta\theta = 180/50 = 3.6°Δθ=180/50=3.6° per frame.
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Deck summary

Key takeaways

A servo tries to reach a commanded position.

  • The command alone cannot show whether the mechanism moved safely or reached the requested angle.
  • This runway does not prove that one servo fits every load.
  • Servo motors provide precise angular positioning (typically 0-180 degrees) using command pulses.
  • At 50 Hz, the period is T=1/50=20T = 1/50 = 20T=1/50=20 ms.
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Retrieval practice

Recall check 1 of 3

Motor Max says: answer from memory, then check your reasoning.

Q1A smart air vent needs to move a louver to 30, 60, or 90 degrees and hold that angle against light airflow. Which actuator choice best matches the job?

ARC servo motor driven by calibrated PWM pulse widths
BBare DC motor connected directly to a GPIO pin
CRelay module switching the vent between open and closed
DPassive buzzer controlled with PWM frequency
Show answer

Answer: A Servo motors are the usual fit when an IoT device needs simple commanded angles with built-in feedback and holding torque.

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Retrieval practice

Recall check 2 of 3

Motor Max says: answer from memory, then check your reasoning.

Q2What signal change commands a hobby servo to a new angle?

AChange the pulse width within the servo's calibrated angle limits.
BChange only the supply voltage while keeping the angle pulse fixed.
CChange only the radio report rate while keeping the pulse fixed.
DSend the same fixed pulse and assume the shaft chooses a new angle.
Show answer

Answer: A Pulse width maps to the requested position.

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Retrieval practice

Recall check 3 of 3

Motor Max says: answer from memory, then check your reasoning.

Q3A servo jerks a loaded linkage between endpoints. What should firmware change?

AMove through bounded intermediate positions instead of jumping to the far end.
BCommand the far endpoint in one jump, keeping the loaded linkage jerky.
CRemove pulse limits so the servo can drive beyond the calibrated endpoints.
DHold maximum torque continuously instead of pacing the commanded movement.
Show answer

Answer: A Interpolation limits abrupt command jumps and mechanical shock.

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Print reference

Answers

Answer key.

  1. A · Servo motors are the usual fit when an IoT device needs simple commanded angles with built-in feedback and holding torque.
  2. A · Pulse width maps to the requested position.
  3. A · Interpolation limits abrupt command jumps and mechanical shock.
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