Workshop: Wiring and Electronics

Most robot failures in a match are not broken code or broken metal: they are loose plugs, pinched wires and flat batteries. Good wiring is invisible when it works and very hard to fix in the two minutes before a match. In this workshop you will turn your chassis into a robot that powers on, connects to the Driver Station and drives each wheel on command, with wiring neat enough that anyone on the team can follow it.

Tools and parts

Build the power path

1. 1
   Mount the battery

   Hold the battery firmly with a bracket, strap or holder so it cannot slide or fall out in a collision. Place it low and near the centre of the robot, and where it is easy to swap between matches.
2. 2
   Mount the main power switch

   Fix the switch where a person can reach and see it quickly from outside the robot, away from moving parts, so it cannot be bumped off by accident. Check the current Competition Manual for rules about the switch and its position.
3. 3
   Mount the Control Hub

   Screw the hub to a flat plate or the frame with the ports facing where cables can reach them easily. Make sure its status light stays visible and that mechanisms cannot hit it.
4. 4
   Connect the power cables

   Run the battery cable to the switch and the switch to the hub's power input using the cables made for your parts. Use proper adapters instead of cutting and splicing wires.

Motor and servo cables

The Control Hub has numbered motor ports (0 to 3), each with a power connector and a separate encoder connector, plus numbered servo ports (0 to 5). Plug each drive motor's power cable into its own motor port and its encoder cable into the matching encoder port with the same number. Servo plugs have three wires; check the colour order printed next to the port so the plug is not reversed. Push every plug in until it is fully seated, then give it a gentle tug to make sure it holds.

• Label both ends of every cable with its name and port, for example frontLeft M0.
• Keep a written port map in your notebook showing which device is on which port.
• Add strain relief: zip-tie each cable to the frame a short distance from the plug, so a pull on the cable stresses the zip tie, not the connector.
• Leave a small service loop of slack near each plug so you can unplug it without stretching the cable.
• Route cables along the frame, away from wheels, gears, chains and sharp edges, and use cable wrap where they rub.
• Trim zip-tie tails flush so they do not scratch hands or catch on other robots.

First power-on and motor configuration

1. 1
   Pre-power check

   With the robot on a stand so the wheels are off the table, check that no bare metal is showing, no wire touches a wheel and every plug is seated.
2. 2
   Power on

   Plug in the battery and turn on the main switch. Watch the hub's status light and compare what you see with the REV documentation. If anything smells hot or smokes, switch off at once.
3. 3
   Connect the Driver Station

   Pair the Driver Station with the Control Hub over Wi-Fi as described in the official FTC Docs, and confirm that it shows the robot is connected.
4. 4
   Create a configuration

   Open Configure Robot, create a new configuration and, under the Control Hub's motors, choose the motor type for each port and type a name such as frontLeft, frontRight, backLeft and backRight. Save it and make sure it is the active configuration.
5. 5
   Test one motor at a time

   Run a simple test OpMode like the one below. Spin each wheel alone at low power and check that the correct wheel moves. Note which motors need to be reversed in code so all wheels drive forward together.

1package org.firstinspires.ftc.teamcode;
2
3import com.qualcomm.robotcore.eventloop.opmode.LinearOpMode;
4import com.qualcomm.robotcore.eventloop.opmode.TeleOp;
5import com.qualcomm.robotcore.hardware.DcMotor;
6
7@TeleOp(name = "Wheel Test")
8public class WheelTest extends LinearOpMode {
9    @Override
10    public void runOpMode() {
11        DcMotor frontLeft = hardwareMap.get(DcMotor.class, "frontLeft");
12        DcMotor frontRight = hardwareMap.get(DcMotor.class, "frontRight");
13        DcMotor backLeft = hardwareMap.get(DcMotor.class, "backLeft");
14        DcMotor backRight = hardwareMap.get(DcMotor.class, "backRight");
15
16        waitForStart();
17
18        while (opModeIsActive()) {
19            // Low power so the robot cannot run away
20            frontLeft.setPower(gamepad1.x ? 0.3 : 0);
21            frontRight.setPower(gamepad1.y ? 0.3 : 0);
22            backLeft.setPower(gamepad1.a ? 0.3 : 0);
23            backRight.setPower(gamepad1.b ? 0.3 : 0);
24
25            telemetry.addData("FL ticks", frontLeft.getCurrentPosition());
26            telemetry.addData("FR ticks", frontRight.getCurrentPosition());
27            telemetry.addData("BL ticks", backLeft.getCurrentPosition());
28            telemetry.addData("BR ticks", backRight.getCurrentPosition());
29            telemetry.update();
30        }
31    }
32}

Troubleshooting checklist

Charging and handling batteries

• Label each battery with a number and record when it was charged and how it performed.
• Check the voltage before every test; swap batteries early rather than testing on a nearly flat one.
• Carry batteries by the case, never by the wires, and do not drop them.
• Store batteries in a cool, dry place away from metal objects that could short the terminals.
• Use only battery types allowed by the current Competition Manual.