Robot Anatomy and the Control System

Lesson

An FTC robot can look like a confusing tangle of metal, wires and wheels. The trick is to stop seeing it as one big machine and start seeing it as a small team of subsystems. Each subsystem has one clear job, and together they let the robot drive, collect game elements and score them. Once you can name the subsystems, you can divide work, test parts separately and talk clearly about problems.

The main subsystems

Top view of a typical FTC robot with its main subsystems labelled.

Subsystem	What it does	Typical parts
Chassis (frame)	Holds everything together and protects the inside	Aluminium channel or extrusion, plates, screws, brackets
Drivetrain	Moves the robot around the field	Motors, wheels, gears, belts or chain
Intake	Picks up game elements	Spinning rollers, compliant wheels, a claw
Scoring mechanism	Lifts, carries and places game elements	Linear slides, an arm, a gripper, servos
Electronics	Provides power and runs the code	Control Hub, Expansion Hub, battery, switch, wires
Sensors	Tell the robot about itself and its surroundings	Encoders, IMU, distance, color and touch sensors

Thinking in subsystems is useful for three reasons. First, different students can own different subsystems at the same time. Second, you can test one subsystem without the others: a drivetrain can be driven before any intake exists. Third, it forces you to think about interfaces, the places where subsystems meet, such as where the lift bolts onto the chassis or where the intake hands a game element to the scoring mechanism. Many robot problems happen at these interfaces.

The control system

How the Driver Hub, Control Hub, battery, motors, servos and sensors connect.

Control Hub: the robot's brain. It runs the Robot Controller app and your OpMode, and it has ports for motors, servos and sensors. It also contains a built-in IMU and creates the Wi-Fi network the Driver Hub connects to.
Expansion Hub: adds more ports when the Control Hub runs out. It has the same kinds of ports but no brain of its own, so it is connected to the Control Hub with a cable and controlled by it.
Driver Hub (or a supported Android phone): runs the Driver Station app. The drivers plug gamepads into it, select an OpMode and press Init and Start.
Battery: a 12 V rechargeable pack that powers everything.
Main power switch: turns the whole robot on and off in one place.

Control Hub port	How many	What you plug in
Motor ports	4	DC motors (power only)
Encoder ports	4	The encoder cable of each motor, next to its motor port
Servo ports	6	Standard and continuous rotation servos
I2C ports	4	Smart sensors such as color and distance sensors
Digital ports	8 channels	Touch sensors, limit switches, LEDs
Analog ports	4 channels	Potentiometers and other analog sensors

Here is what happens when a driver pushes a joystick. The gamepad sends the stick position to the Driver Hub. The Driver Hub sends it over Wi-Fi to the Control Hub. Your OpMode reads the value, for example gamepad1.left_stick_y, decides on a motor power and calls setPower(). The Control Hub sends that power out of a motor port and the wheel turns. At the same time, sensors and encoders send readings back so your code can react. This loop repeats many times every second.

Power: battery, fuse and switch

All the energy on the robot comes from one 12 V battery. Current flows from the battery through a fuse and the main power switch into the Control Hub, which then shares power with an Expansion Hub, the motors and the servos. The fuse is a safety part: if something shorts out, the fuse breaks the circuit before wires overheat. The power switch must be easy to reach so anyone can turn the robot off quickly.

1
Check the switch
Make sure the main power switch is off before you plug in the battery.
2
Inspect wires
Look for loose, pinched or bare wires, especially near moving parts.
3
Clear the robot
Lift the wheels off the table or floor and keep hands away from mechanisms.
4
Power on
Plug in the battery, turn on the switch and wait for the Control Hub light to show it is ready.
5
Connect
Turn on the Driver Hub and check that it connects to the Control Hub before selecting an OpMode.

Key terms

Subsystem: A group of parts on the robot that together perform one job, such as driving or lifting.
Control Hub: The REV device that runs your robot code and connects to motors, servos and sensors.
Expansion Hub: A device that adds extra motor, servo and sensor ports and is controlled by the Control Hub.
Driver Hub: The handheld Driver Station device where drivers connect gamepads and start OpModes.
Fuse: A safety part that breaks the circuit if too much current flows, protecting wires from overheating.

Practical exercise

Map Your Robot's Anatomy and Wiring

1Lay out your kit or look at your team's robot and sort every major part into a subsystem: chassis, drivetrain, intake, scoring, electronics or sensors.
2Photograph or sketch the robot from above and label each subsystem on the image.
3With the robot powered off, follow the power wire from the battery through the fuse and switch to the Control Hub and note each connection.
4Write down which port every motor, servo and sensor is plugged into (for example, motor port 0, servo port 2, I2C bus 1).
5Power the robot on using the safe power-up steps and confirm the Driver Hub connects.

Deliverable: A labelled top-view photo or sketch plus a hand-drawn wiring map showing the battery, switch, hubs and every connected device with its port number.

Knowledge check

Answer every question, then check your answers.