Series: FRC Technical Foundations Unit: 3 — Electrical and Power Session length: ~3 hours Prerequisites: Lesson 5
Lesson 5 was about what the components do. This one is about the part that separates teams: whether the wiring survives contact with a competition.
There is a visible correlation at any regional between the tidiness of a robot’s wiring and how often that robot is on the field. It is not superstition. A robot with a clean, labelled, strain-relieved harness gets diagnosed in two minutes when something fails. A robot with a bird’s nest gets diagnosed in twenty, which is longer than the time between matches.
Rule 6.1 — Wire for the person who will fix it in six minutes with a robot on a cart. That person may well be you, at 4 p.m., between quarter-final matches, with a queue official telling you to hurry.
The majority of electrical failures on FRC robots are bad crimps. Not blown controllers, not dead motors — connections that were never fully made.
A correct crimp:
Soldering has its place for small signal connections, but a soldered joint on a wire that flexes becomes brittle exactly where the solder wicks up the strands. For power connections on a moving robot, crimp.
Every connector needs the mechanical load taken by something other than the connector. A zip tie anchoring the cable to the frame 50 mm before the connector means that when someone snags the cable, the frame takes the force instead of the pins.
Label both ends of every cable. Use the same names as your CAN ID map and your code constants.
If the code calls it elevatorLeader, the label says elevatorLeader, the CAN map says elevatorLeader. Three different names for the same device is how a pit crew replaces the wrong motor.
Rule 6.2 — One name per device, used identically in the code, the map, and the label.
When a mechanism does not move, the temptation is to swap the motor controller. Resist it. Follow a fixed sequence.
Rule 6.3 — Change one variable per test. Swapping a controller and a cable and reflashing firmware at once means you will never know what was wrong, and it will happen again.
[ANECDOTE SLOT] — An electrical fault that took far longer to find than it should have. Intermittent faults make the best stories here, especially ones where the symptom pointed somewhere else entirely.
The source FTC curriculum omits pneumatics entirely, because FTC does not permit them. In FRC they are a genuine design option, and they are frequently the right one.
Compressor → storage tanks → pressure regulator → solenoid valves → cylinders
Safety: a relief valve and a manual vent valve are required, and the vent must be operable without tools. A pressurised system is dangerous even when the robot is off. Nobody works on pneumatics until the system has been vented and a gauge reads zero.
Pneumatics are binary, fast, and hold position without power. That combination is genuinely hard to beat for:
Pneumatics are the wrong choice when you need positional control — variable travel, controlled speed, feedback. A cylinder goes to one end or the other. If you need to stop halfway, use a motor.
The other cost is a fixed budget: compressor weight, tank weight, and plumbing, for a system that adds maybe 20 N·m of useful work. If you are only using one cylinder, that overhead is usually not worth it.
Rule 6.4 — Pneumatics for binary, motors for positional.
Time: 120 minutes. Equipment: A chassis or wiring board, wire, terminals, correct crimp tools, labels, zip ties, a multimeter.
Working in pairs, wire a complete drivetrain from battery to four motors: main breaker, PD board, four channel breakers, four motor controllers, CAN chain, roboRIO power, radio.
Requirements — this is scored, not just completed:
Then have a different pair inspect and score the harness against the checklist. Peer inspection is the point.
Evidence of learning: A scored inspection sheet, a wiring diagram matching the physical build, and a photograph of the finished routing.
Time: 60 minutes. Equipment: A working robot, prepared faults, a stopwatch.
Adapted directly from the source curriculum, and one of the best exercises in it.
A mentor injects a labelled fault while students are out of the room. Good faults:
Teams have a strict time limit and must narrate their diagnostic sequence out loud as they work. The narration is what is being assessed, not the time.
Evidence of learning: A written fault tree produced afterwards, mapping symptom to the checks that isolate it. Keep this document — it becomes your competition troubleshooting guide.
Time: 60 minutes. Equipment: Compressor, tanks, regulator, pressure gauges, a solenoid, a double-acting cylinder, tubing, safety equipment.
Build a complete legal circuit on a bench board. Then:
Evidence of learning: A plumbing diagram, an actuation count, and a force comparison between calculation and measurement.
The hardware is now capable of moving. Lesson 7 — WPILib and Software Architecture is about writing code that will still make sense in week five.
