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.