Anatomy of an FTC robot's electronics
Every component on a legal robot, what it does, and which ones you cannot compete without.
By the end you can
- Name every required electrical component on a legal FTC robot
- Trace the path power takes from the battery to a motor
- Explain what the Expansion Hub adds and when you need one
An FTC robot's electronics are simpler than they look. There are about seven things, and once you can name all of them, wiring becomes a checklist rather than a mystery.
The required parts
- 12V battery
- The only power source for the robot's control system and actuators. A rechargeable 12V NiMH pack from the Competition Manual's approved list, with a 20A fuse built into its lead.
- Main power switch
- An approved on/off switch wired between the battery and everything else. It is a plain switch, not a breaker: the over-current protection is the fuse in the battery lead. Required, and inspectors check it.
- Control Hub
- The brain. It is an Android computer with motor ports, servo ports, sensor ports, and power outputs built in. It runs your Java.
- Motors
- DC motors with encoder cables, plugged into the Hub's motor ports. Most robots use four for the drivetrain plus one or two for mechanisms.
- Servos
- Small positional actuators for claws, wrists, and flippers. They plug into servo ports and draw power from the Hub.
- Driver Station
- A phone or approved device the drivers hold, with gamepads attached. It talks to the Control Hub over a wireless link.
- Expansion Hub
- Optional. A second hub that adds more motor and servo ports, connected to the Control Hub. You need one only when you run out of ports.
How power flows
Power takes exactly one path, and understanding it explains most electrical failures:
- Battery — stores roughly 12V. Its 20A fuse is the robot's over-current protection.
- Main switch — everything on the robot passes through here. Flipping it kills the robot completely.
- Control Hub — takes battery power in through an XT30 connector, then distributes it.
- Motor ports — the Hub sends variable power to each motor based on your
setPower()calls. - Servo ports — the Hub supplies a regulated voltage to servos.
- Sensor ports — low-power connections for I2C, digital, and analog sensors.
The battery is not a suggestion
Everything the robot controls must be powered from the single legal battery through the main switch. A second battery feeding a motor, servo, sensor or hub will fail inspection. The Competition Manual has narrow exceptions for self-contained devices (such as a camera with its own internal battery), so check the current rules before adding any extra power source.
What the Control Hub gives you
A single Control Hub typically provides:
- 4 motor ports — each with a matching encoder input
- 6 servo ports
- 4 I2C buses — for sensors like an IMU, colour sensor, or distance sensor
- 8 digital channels — on four connectors with two channels each, for touch sensors and limit switches
- 4 analog channels — on two connectors with two channels each, for potentiometers and some distance sensors
- 2 USB-A ports — for webcams and vision sensors
- A built-in IMU — gives you robot heading without buying anything
That last one matters more than rookies realise: the built-in IMU means field-relative driving and heading-correcting autonomous are available on day one with no extra hardware.
When you need an Expansion Hub
Four motor ports go quickly: a four-wheel drivetrain uses all of them. The moment you add a motorised mechanism you need more.
An Expansion Hub connects to the Control Hub (usually with a 3-pin RS485 cable) and doubles your motor, servo and sensor ports. It needs its own 12V feed into one of its XT30 ports. Each hub has two XT30 ports, and REV's documented convention is to run power out of the Control Hub's spare XT30 port into the Expansion Hub, so both hubs still get their power through the one main switch. The Competition Manual currently allows one Expansion Hub alongside the Control Hub.
Plan your ports before you build
Write down every motor and servo you intend to use, and count. Discovering on build night that you are one motor port short is a bad time to learn this. The wiring simulator in this track will let you plan it visually.
Why more matches are lost here than in code
The failure modes are mundane and all preventable:
- A motor cable works loose from vibration mid-match.
- The XT30 power connector to a hub is not fully seated.
- The battery was not charged, and the robot browns out under load.
- A cable runs through a moving mechanism and gets cut.
- The main switch is mounted where a defensive robot can hit it.
None of these are clever problems. They are all fixed by careful routing, strain relief, and a pre-match checklist — which the rest of this unit covers.
Check yourself
Your robot suddenly goes completely dead mid-match — no motors, no telemetry, driver station shows a disconnect. What should you check first?
Next
Now that you can name the parts, the next lesson looks closely at the first three — battery, switch and fuse — because every other part depends on them. Then you wire the whole thing, in the correct order.
Sources and further reading
- REV Control Hub specifications — port counts and electrical limits
- REV: Adding an Expansion Hub
- REV: XT30 power cable — how power is passed from one hub to the next
- FTC Competition Manual — section 12, Robot Construction Rules
- Game Manual 0: Control Systems
Finished this lesson?
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