Control a vehicle directly

Paths. scripts/… and references/… below are relative to the directory holding this SKILL.md. Your working directory is the user's project, not that directory, so prefix them with its absolute path or the command is not found.

Drive one vehicle yourself: control input, Ackermann speed target, lights, doors, physics. It targets the ego (role_name = hero) by default, or any vehicle by --id / --role / --filter. This is manual control — control and ackermann turn autopilot off first; for autonomous traffic use the control-traffic skill instead.

Instructions

Progress:
- [ ] Step 1: Check prerequisites (bash scripts/check_env.sh), clear FAILs
- [ ] Step 2: Ensure a target vehicle exists (spawn-vehicles ego)
- [ ] Step 3: Apply the command (control / ackermann / lights / door / physics)
- [ ] Step 4: Confirm on a rendered server; `stop` to halt manual driving

Commands need CARLA_HOST/CARLA_PORT/TM_PORT from scripts/env.sh.

Step 1: Check prerequisites

bash scripts/check_env.sh

Step 3: Control

source scripts/env.sh

# drive the ego forward for 3 s, then it brakes
python3 scripts/vehicle_control.py control --throttle 0.5 --hold 3

# turn while creeping forward
python3 scripts/vehicle_control.py control --throttle 0.3 --steer -0.4 --hold 2

# hold a target speed (built-in controller does throttle/brake for you)
python3 scripts/vehicle_control.py ackermann --speed 8

# lights: headlights + brake on; position off
python3 scripts/vehicle_control.py lights --on LowBeam,Brake --off Position
# left blinker on a specific car
python3 scripts/vehicle_control.py lights --filter '*prius*' --on LeftBlinker

# doors
python3 scripts/vehicle_control.py door --open FL,FR
python3 scripts/vehicle_control.py door --close All

# physics: read, then make it heavier / draggier
python3 scripts/vehicle_control.py physics --show
python3 scripts/vehicle_control.py physics --mass 2200 --drag 0.4

# emergency stop
python3 scripts/vehicle_control.py stop

# what ROS 2 topics drive this vehicle (read-only)
python3 scripts/vehicle_control.py ros-info

Driving it from ROS 2

On a server started with --ros2 ([[run-carla-server]] ROS2=1), the hero vehicle exposes two command topics — the server subscribes, so the commands come from outside this skill:

Topic (DDS name)	Message	Maps to
rt/carla/<ros_name>/vehicle_control_cmd	carla_msgs/CarlaEgoVehicleControl	carla.VehicleControl (throttle, steer, brake, hand_brake, reverse, gear, manual_gear_shift)
rt/carla/<ros_name>/ackermann_control_cmd	ackermann_msgs/AckermannDriveStamped	carla.VehicleAckermannControl (steering_angle, speed, acceleration, jerk)

ros-info prints them for the resolved vehicle plus a ready-to-run ros2 topic pub line, and says so plainly when the target cannot be driven from ROS: only role_name = hero gets subscribers (the server tests that string in ActorDispatcher), so ordinary traffic never does. Spawn the hero with [[spawn-vehicles]] ego --ros-name <name>.

You need the message definitions to publish. Verified: neither type ships with a stock ROS 2 install, so ros2 topic pub carla_msgs/msg/... fails with an unknown type until you provide them:

Type	Where it comes from
ackermann_msgs/AckermannDriveStamped	sudo apt install ros-$ROS_DISTRO-ackermann-msgs
carla_msgs/CarlaEgoVehicleControl	not an apt package — build carla_msgs from carla-ros-bridge, or hand-write a one-message package (below)

A minimal carla_msgs is enough and takes a minute — this exact recipe was used to drive the hero from ROS (0 → 64 km/h) on a packaged server:

mkdir -p ws/src/carla_msgs/msg
cat > ws/src/carla_msgs/msg/CarlaEgoVehicleControl.msg <<'EOF'
std_msgs/Header header
float32 throttle
float32 steer
float32 brake
bool hand_brake
bool reverse
int32 gear
bool manual_gear_shift
EOF
# + a standard ament_cmake package.xml / CMakeLists.txt calling
#   rosidl_generate_interfaces(${PROJECT_NAME} "msg/CarlaEgoVehicleControl.msg"
#                              DEPENDENCIES std_msgs)
colcon build --packages-select carla_msgs && source install/setup.bash
ros2 topic pub -r 20 /carla/hero/vehicle_control_cmd \
  carla_msgs/msg/CarlaEgoVehicleControl "{throttle: 0.8}"

Field order is the contract, not the field names: CDR is positional, so the .msg must list exactly those eight fields in that order to match CARLA's POD. The package name and message name must be carla_msgs / CarlaEgoVehicleControl so the DDS type name (carla_msgs::msg::dds_::CarlaEgoVehicleControl_) matches.

Publishing from a container? Add -e HOME=/tmp — with --user and no writable HOME, rcl aborts at startup with Failed to create log directory: //.ros/log.

The server side needs none of this: ros-info confirms the subscription exists (Subscription count: 1) regardless, and the type name resolves from DDS.

Two things that bite:

• Both paths write the same VehicleControl. A ROS publisher sending at 20 Hz and this skill's control fight; last writer wins. Pick one driver.
• Autopilot still overrides manual input. ROS commands are manual input, so the TM must be off for them to have any effect (control/ackermann here disable it for you; a ROS-only workflow must not enable it).

A ROS 2 installation is needed only to publish — nothing in this skill requires one ([[visualize-ros-rviz]] has containers if the host has no ROS 2).

Step 4: Verify

Watch on a rendered server. A VehicleControl persists — the car keeps the last input until you change it, so use --hold for a timed action or stop to halt. physics --show reads back the applied values; telemetry overlays live physics on screen.

On CARLA 0.10.0 (the UE5 line: 5.5 and 5.8)

Physics control is the one part of this skill that is engine-specific. UE4 builds (0.9.x) use PhysX; 0.10.0 uses Chaos, and VehiclePhysicsControl was replaced field-for-field. Verified live against a 0.10.0 server:

0.9.x (PhysX)	0.10.0 (Chaos)
forward_gears — list of GearPhysicsControl	forward_gear_ratios / reverse_gear_ratios — float lists; carla.GearPhysicsControl no longer exists
clutch_strength, gear_switch_time, use_gear_autobox	transmission_efficiency, gear_change_time, use_automatic_gears, differential_type, front_rear_split, final_ratio
moi, damping_rate_full_throttle, damping_rate_zero_throttle_clutch_engaged/disengaged	rev_up_moi, rev_down_rate, idle_rpm, brake_effect, inertia_tensor_scale
—	chassis_height, chassis_width, drag_area, downforce_coefficient, sleep_threshold, sleep_slope_limit

Wheels were renamed too: radius→wheel_radius, tire_friction→ friction_force_multiplier, position→location, max_handbrake_torque→ max_hand_brake_torque, lat_stiff_*/long_stiff_value→cornering_stiffness + spring_rate/suspension_*, plus new axle_type, abs_enabled, traction_control_enabled, sweep_type, wheel_mass, wheel_width.

Two gear fields are unreadable from Python on 0.10.0. forward_gear_ratios and reverse_gear_ratios are declared with no std::vector<float> converter, so reading either raises TypeError: No to_python (by-value) converter found for C++ type: std::__1::vector<float, ...>. Every other field on the struct reads fine, and physics --show reports gears=unreadable (0.10.0 converter gap) rather than dying. Writing and applying still works: a mass change round-tripped 1696 → 1750 kg.

mass, drag_coefficient, max_rpm, center_of_mass, torque_curve, steering_curve and wheels are spelled the same on both, which is why the --mass / --drag / --max-rpm flags need no version handling.

Examples

Example 1: nudge the ego forward

User says: "drive the car forward a bit"

control --throttle 0.4 --hold 2 — it accelerates for 2 s then brakes.

Example 2: hazard lights

User says: "put the hazards on"

lights --on LeftBlinker,RightBlinker (both blinkers = hazards).

Example 3: a heavier truck feel

User says: "make the ego handle like it's loaded"

physics --mass 2500 --drag 0.45, then drive and compare.

Troubleshooting

Problem: the car won't respond to control Cause: autopilot is still on (TM overrides manual input). Solution: control/ackermann disable autopilot automatically; if you set it via another tool, ensure autopilot is off. Sync mode also needs a world tick to move.

Problem: it drives off and won't stop Cause: VehicleControl persists (throttle stays applied). Solution: stop, or use --hold for timed inputs.

Problem: "no vehicle with role hero" Cause: no ego spawned. Solution: spawn one with the spawn-vehicles ego command, or target --id/--filter.

Problem: no door named Hood/Trunk Cause: 0.9.16 exposes only FL, FR, RL, RR, All. Solution: use those; not all vehicle models animate every door.

Outputs

Vehicle state on the server (motion, lights, doors, physics). No file. Verify on a rendered view; physics --show reads values back.

Detail (VehicleControl vs Ackermann, light flags, door set, the physics fields) in references/vehicle-control.md.