Simulation Quick Start

What the Sim Covers

• Physics — collisions, bouncing, gravity, ramps
• Game pieces — intake, hold, shoot, score
• Full robot control — drivetrain + all mechanisms
• Limelight AprilTag simulation — simulated vision pose estimates for localization
• Limelight game piece detection — simulated fuel detection via 3D frustum sensor (publishes tv/tx/ty/ta)

Setup

git clone https://github.com/feds201/feds-central.git

Run the Sim

You can launch the simulator from VS Code or from the terminal.

VS Code (menu):

1. Click the three-dot menu (···) in the top-right of the WPILib sidebar (or the WPILib icon in the top-right corner)
2. Select “Simulate Robot Code”
3. Choose “Sim GUI”

VS Code (command palette):

1. Ctrl+Shift+P → type “WPILib”
2. Select “Simulate Robot Code”
3. Choose “Sim GUI”

Terminal:

cd robot/2026-rebuilt
./gradlew simulateJava

Either way, a WPILib simulation GUI window will open. Don’t close it — you’ll need it in a moment.

Set Up the Sim GUI

In the WPILib simulation GUI that opened:

1. Connect a controller:
   • Xbox / gamepad: Plug it in — it should appear automatically
   • No controller? Drag “Keyboard 0” onto “Joystick 0” (see key mappings below)
2. Click “Teleoperated” to enable the robot

Set Up AdvantageScope

1. Open AdvantageScope (installed with WPILib)
2. Connect via NetworkTables 4 (AdvantageKit)
3. Click the + button (top right) → select 3D Field
4. In the bottom-right Field section, select this year’s game
5. Add game pieces:
   • In the left panel, find RealOutputs → Sim → GamePieces
   • Drag the game piece type into the Poses section (bottom center)
   • From the dropdown, select the matching game piece model
6. (Optional — required for our robot models) Set custom assets folder:
   • In the AdvantageScope menu, select “Use custom assets folder”
   • Point it to the current year’s sim_models directory (e.g. for 2026: feds-central/robot/2026-rebuilt/sim_models)
   • Our robot models will now appear in the robot model dropdown
7. Add the robot:
   • In the left panel, expand RealOutputs → Sim
   • Drag RobotPose into the Poses section
   • From the robot model dropdown, pick one of these:
     • KitBot — no setup needed, but doesn’t look like our robot
     • FEDS (Static) — our actual CAD, looks like our robot but mechanisms don’t animate (requires step 6)
     • FEDS (Components) — our CAD with animated mechanisms like rollers and hood (requires steps 6 and 8)
8. (Optional — required for FEDS (Components)) Add component poses:
   • Drag Sim/ComponentPoses from the left panel onto the robot pose you added in step 7, so the component animations are tied to the robot

You should now see the field, robot, and game pieces rendered in 3D.

Drive!

• Note: In order for the robot to shoot fuel, the shooter wheels must be at speed AND the feeder/spindexer must be running at the same time. The gated fire command (Right Trigger / ]) handles this automatically when combined with hub aim (D-pad Right / [).

Reference

AdvantageScope Telemetry Keys

All sim telemetry is under RealOutputs in AdvantageScope. Values are split into two namespaces:

Sim/ — simulation-only values (don’t exist on the real robot):

Robot/ — values that exist on both sim and real robot:

Sim/Debug/ — motor and gate diagnostics (sim only):

Useful Flags

Save Log Files (simLogging)

By default, the sim doesn’t write .wpilog files. To enable logging (useful for SysID characterization or offline analysis):

./gradlew simulateJava -PsimLogging=true

Logs are saved to the logs/ directory.

Simulation Speed

The sim runs in real-time by default. The speed multiplier is set in RebuiltSimManager.java:

SimulatedArena.overrideSimulationTimings(Seconds.of(DT), 1);
//                                                        ^ change this

Change the second argument to 2 for 2x speed, 5 for 5x, etc. (There’s no command-line flag for this yet — see future improvements below.)

Adding or Updating 3D Models

To add new models or update existing ones, just treat them like any other file:

1. Export your CAD as .glb files (binary glTF — the only format AdvantageScope supports)
2. Drop them into your year’s sim_models/ directory (e.g. Robot_Components/ or Robot_Static/)
3. Update the config.json if you added/changed components
4. git add and git commit as usual

That’s it. Git LFS handles the rest behind the scenes — your .glb files are automatically routed through LFS so they don’t bloat the repo. To your teammates, pulling your changes works normally; their next ./gradlew simulateJava will download the updated models.

Troubleshooting

Git LFS Not Installed

If you see this warning when running the sim:

Git LFS not available — 3D models will not be downloaded.

You need to install Git LFS. The simulation still works without it — you just won’t see the robot model in AdvantageScope.

After installing, run ./gradlew simulateJava — the models will download automatically.

Models Not Showing in AdvantageScope

If the simulation runs but you don’t see the robot model in AdvantageScope:

1. Check that models are downloaded: Look in your year’s sim_models/ directory — the .glb files should be several MB each, not ~130 bytes. If they’re tiny, they’re still pointer files. Run ./gradlew fetchModels to download them.
2. Check AdvantageScope config: Make sure you selected “Use custom assets folder” and pointed it to the correct sim_models directory (see Set Up AdvantageScope step 7).
3. Check your network: The first model download needs internet access to pull from GitHub’s LFS servers. After that, files are cached locally.

Robot Model Has No Moving Parts

If the robot model appears but mechanisms don’t animate:

1. Make sure you’re using FEDS (Components), not FEDS (Static) (single static mesh)
2. Drag Sim/ComponentPoses onto the robot pose in the Poses section — the component poses must be tied to the robot pose, not added as a separate entry

Future Improvements

• More realistic AprilTag sim (currently reports perfect odometry with fake detections)
• Command-line flag for time speedup
• More realistic intake (game pieces currently just disappear)
• Better ramp physics (robot can’t “fly off” yet)
• Reduce ground physics jitter on settled balls