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Secondary 3 · Technology
Computational thinking and robotics · Robotics

Robot Design and Construction

Before you start, make sure you know: Transmission mechanisms (Secondary Year 1)
Before you start, make sure you know: Control systems (Secondary Year 2)

At the science and technology fair, Ximena's team's robot drives straight for a few meters and then veers more and more to the left until it hits the table. Is a wheel failing, the battery, or the program? A robot is not just "a machine that moves": it is a complete control system, and designing it well means making decisions that limit everything it will be able to do. By the end of this section we will solve the mystery of the veering.

The Robot as a Control System

Closed-loop diagram of a robot: the sensor sends data to the controller, the controller sends commands to the actuator, and the actuator changes the environment that is sensed. sensor controller actuator the actuator changes the environment, which is sensed again
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The image shows an educational wheeled robot with its parts numbered. Identify each part and explain what function it serves within the robot (structure, movement,…

The image shows an educational wheeled robot with its parts numbered. Identify each part and explain what function it serves within the robot (structure, movement, control or perception).

Educational wheeled robot with its parts numbered

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Name the basic parts of a simple mobile robot and state which element of a control system (sensor, controller or actuator) each one corresponds to.

Name the basic parts of a simple mobile robot and state which element of a control system (sensor, controller or actuator) each one corresponds to.

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Explain the difference between a robot and a simple automatic machine such as a washing machine: what capabilities make a system "deserve" to be called a robot?

Explain the difference between a robot and a simple automatic machine such as a washing machine: what capabilities make a system "deserve" to be called a robot?

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Applications and Behavior: What Does a Robot Do?

Robots are designed for a task, and the task decides which sensors and actuators they need.

Task Typical sensors Actuators
Robot vacuum Distance, bumper, cliff (for steps) Wheels, brush, turbine
Factory welding Arm position, vision Articulated arm, welder
Warehouse delivery Camera, line follower, ultrasonic Wheels, platform
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The flowchart in the figure shows the program for an obstacle-avoiding robot. Describe the complete behavior of the robot in your own words and reason what it would do…

The flowchart in the figure shows the program for an obstacle-avoiding robot. Describe the complete behavior of the robot in your own words and reason what it would do if the distance sensor were covered with insulating tape.

Start Move forward Is obstacle < 20 cm? yes Turn no
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Name three real-world tasks currently carried out by robots (domestic cleaning, factory welding, warehouse delivery) and reason what sensors each one needs for its task.

Name three real-world tasks currently carried out by robots (domestic cleaning, factory welding, warehouse delivery) and reason what sensors each one needs for its task.

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An obstacle-avoiding robot must also avoid falling down a step or flight of stairs. What sensor would you add, where would you place it, and using what programming rule?

An obstacle-avoiding robot must also avoid falling down a step or flight of stairs. What sensor would you add, where would you place it, and using what programming rule?

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The Chassis: Structure and Center of Gravity

Side view of two robots with the same parts: with the battery on top the center of gravity is high and there is more risk of tipping over; with the battery low and centered the center of gravity is low and the robot is more stable. A. Battery on top B. Battery on the bottom battery high center of gravity: more risk of tipping over battery low center of gravity: more stable
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What is a robot chassis and what qualities must it possess (lightweight, rigid, with space for electronics)? Relate this to materials you know from the workshop.

What is a robot chassis and what qualities must it possess (lightweight, rigid, with space for electronics)? Relate this to materials you know from the workshop.

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Design the weight distribution of a mobile robot: where would you place the battery (the heaviest component) and why does its position affect stability and drive-wheel…

Design the weight distribution of a mobile robot: where would you place the battery (the heaviest component) and why does its position affect stability and drive-wheel traction?

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Actuators and Transmission

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Explain what a servomotor is and how it differs from a standard DC motor. Give a suitable use for each one inside a robot.

Explain what a servomotor is and how it differs from a standard DC motor. Give a suitable use for each one inside a robot.

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Many two-wheel drive robots feature a third, unpowered caster wheel. Explain its purpose and what support and balance issue it solves.

Many two-wheel drive robots feature a third, unpowered caster wheel. Explain its purpose and what support and balance issue it solves.

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A robot has two drive wheels, one on each side. Explain what each wheel must do (spin forwards, backwards, or stop) for the robot to move forward in a straight line,…

A robot has two drive wheels, one on each side. Explain what each wheel must do (spin forwards, backwards, or stop) for the robot to move forward in a straight line, reverse, and spin on the spot to the right.

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Locomotion, Battery, and Sensor Calibration

Top view of three robots: two drive wheels with a caster wheel on a smooth floor, four drive wheels on uneven terrain, and tracks on soft terrain. 2 wheels + caster 4 drive wheels tracks caster smooth floor uneven terrain soft terrain more complexity and consumption, more terrain capability

Battery Life

A robot that must work for hours needs to know how long its battery will last. Capacity is measured in ampere-hours (Ah): a 7 Ah battery can deliver 7 A for 1 h, or 1 A for 7 h. The battery life is:

$$t = \dfrac{C}{I}$$

where $C$ is the capacity (Ah) and $I$ is the average current the robot draws (A). The stored energy is $E = V \cdot C$ (Wh), and the power consumed is $P = V \cdot I$, so also $t = \dfrac{E}{P}$.

Why? If the battery stores a certain amount of charge and the robot uses it up at a certain rate, the time is the charge divided by the rate of consumption.

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Your robot must follow a black line painted on the white classroom floor. Reason what sensor it needs, where you would place it, and what the program should do every…

Your robot must follow a black line painted on the white classroom floor. Reason what sensor it needs, where you would place it, and what the program should do every time the sensor strays from the line.

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Your robot must turn 90 degrees accurately using its two wheels. Explain why the command "turn for one second" is unreliable (battery level, surface, friction) and what…

Your robot must turn 90 degrees accurately using its two wheels. Explain why the command "turn for one second" is unreliable (battery level, surface, friction) and what additional information would improve the turn.

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Explain what sensor calibration is and write a short procedure to calibrate a robot's light sensor in your classroom (which two reference readings to take and how to use…

Explain what sensor calibration is and write a short procedure to calibrate a robot's light sensor in your classroom (which two reference readings to take and how to use them).

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A line-following robot skids and flies off course on sharp bends. Propose two improvements, one mechanical and one in the software, and explain how each one works.

A line-following robot skids and flies off course on sharp bends. Propose two improvements, one mechanical and one in the software, and explain how each one works.

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You must select the drive system for an inspection robot in a greenhouse with 60 cm wide aisles, zero-radius turns on its own axis, and damp soil with irrigation pipes…

You must select the drive system for an inspection robot in a greenhouse with 60 cm wide aisles, zero-radius turns on its own axis, and damp soil with irrigation pipes protruding up to 3 cm. The robot has a fixed 12 V and 7 Ah battery and must guarantee 4 h of continuous runtime. Analyze the physical behavior of three options: 1) Two drive wheels with a caster wheel, 2) Fixed 4WD (skid-steering), and 3) Continuous tracks. Predict which critical failure rules out two of them (in terms of traction, maneuverability, or consumption due to lateral friction) and justify what the optimal configuration is to meet all constraints.

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From Design to Finished Robot

A robot is built in stages, and each one depends on the one before it.

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Put these steps for building and programming a robot in order, and justify the sequence: upload the program to the board, assemble the chassis, test and calibrate,…

Put these steps for building and programming a robot in order, and justify the sequence: upload the program to the board, assemble the chassis, test and calibrate, connect sensors and motors to the board, define what the robot should do.

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Design a robot to distribute leaflets along the school corridors: describe the chassis, sensors, actuators and general movement algorithm, and justify each choice…

Design a robot to distribute leaflets along the school corridors: describe the chassis, sensors, actuators and general movement algorithm, and justify each choice considering the real environment (people, junctions, obstacles).

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Design a robot to collect tennis balls from the school court: chassis, sensors, actuators, and general search and collection algorithm. Identify the three most critical…

Design a robot to collect tennis balls from the school court: chassis, sensors, actuators, and general search and collection algorithm. Identify the three most critical design decisions and justify them.

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Programming and Behavior Around Obstacles

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A robot with a single front distance sensor gets "trapped" in corners, oscillating between two walls. Analyse why this behavior occurs and propose an algorithm…

A robot with a single front distance sensor gets "trapped" in corners, oscillating between two walls. Analyse why this behavior occurs and propose an algorithm improvement (recording recent turns, introducing turns of different angles).

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A team is programming a line-follower robot with speed control and ultrasonic obstacle detection. In a block-based programming environment, they have nested conditionals…

A team is programming a line-follower robot with speed control and ultrasonic obstacle detection. In a block-based programming environment, they have nested conditionals with fixed pauses ("wait 50 ms"), which causes the robot to react late and veer off the track if it exceeds 0.2 m/s. Explain technically why typical block-based sequential programming causes this latency and processor blocking issue. Justify what technical advantages migrating the program to text-based code (such as C++/Arduino) using non-blocking timing (with millis()) or interrupts offers, and reason how the control structure changes to resolve the issue.

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Fault Diagnosis and Safe Mode

Top view of a two-wheeled robot that veers to the left of its intended path, with the three areas where to look for the cause: wheels (mechanical), battery and motors (electrical), and controller (program). intended path actual veering mechanical electrical program

Back to the beginning: Ximena's robot was veering. With the wheel-swapping test, and by checking motors, connections, and program in order, the team isolates the cause instead of guessing.

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A robot moves forward in a straight line for only a few meters and then gradually veers to the left. Analyze at least three possible causes (mechanical, electrical, or…

A robot moves forward in a straight line for only a few meters and then gradually veers to the left. Analyze at least three possible causes (mechanical, electrical, or software-related) and explain what test you would carry out to rule out each one.

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Design the "safe mode" for a school robot: what should the program do upon detecting low battery, a persistent obstacle, or loss of communication? Write the rules and…

Design the "safe mode" for a school robot: what should the program do upon detecting low battery, a persistent obstacle, or loss of communication? Write the rules and reason why safety comes before the mission.

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In a search and rescue trial in a collapsed environment, a robot must locate and shut off a gas valve. The team debates whether to use RF teleoperated control with a…

In a search and rescue trial in a collapsed environment, a robot must locate and shut off a gas valve. The team debates whether to use RF teleoperated control with a camera or 100% autonomous control with sensors. The environment presents two critical problems: blind spots with link losses of up to 1.5 s and unforeseen obstacles that require braking in less than 0.3 s while moving at 0.4 m/s. Predict the failures that the exclusively teleoperated robot will suffer in the face of these limitations and justify why a hybrid architecture (teleoperation assisted by local safety routines on the microcontroller) is technically superior to both options, detailing what decisions the robot must make on its own without waiting for the pilot.

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Summary

See all the exercises in this section