# [turtlebot4_gz/Create3] `/diffdrive_controller/cmd_vel` does not honor configured acceleration limits under safe `/cmd_vel` commands

[147258369ymc]

Robot Model

Turtlebot4 Standard

ROS distro

Jazzy

Networking Configuration

Simple Discovery

OS

Ubuntu 24.04

Built from source or installed?

Installed

Package version

ros-jazzy-turtlebot4-simulator: 2.0.2-1noble.20260616.091643
ros-jazzy-turtlebot4-gz-bringup: 2.0.2-1noble.20260616.085653
ros-jazzy-turtlebot4-gz-toolbox: 2.0.2-1noble.20260615.145933
ros-jazzy-irobot-create-control: 3.0.4-1noble.20260616.082318
ros-jazzy-irobot-create-gz-bringup: 3.0.4-1noble.20260616.083553
ros-jazzy-irobot-create-gz-toolbox: 3.0.4-1noble.20260615.161517
ros-jazzy-irobot-create-nodes: 3.0.4-1noble.20260615.161556
ros-jazzy-ros-gz: 1.0.22-1noble.20260616.074726
Gazebo: Harmonic / gz

Expected behaviour

When TurtleBot4 simulation receives safe `geometry_msgs/msg/TwistStamped` commands on `/cmd_vel`, the internally published limited command topic `/diffdrive_controller/cmd_vel` should respect the configured Create3/TurtleBot4 acceleration limits:

- `|d(linear.x)/dt| <= 0.9 m/s^2`
- `|d(angular.z)/dt| <= 7.725 rad/s^2`

If an incoming `/cmd_vel` sequence changes faster than the acceleration bound, the simulator/control path should ramp or clamp the command before publishing the limited command and before it affects wheel/odom motion.

The relevant installed control configuration has:

```yaml
linear.x.has_acceleration_limits: true
linear.x.max_acceleration: 0.9
angular.z.has_acceleration_limits: true
angular.z.max_acceleration: 7.725
angular.z.min_acceleration: -7.725
publish_cmd: true

### Actual behaviour

## Actual behaviour

```markdown
Under safe `/cmd_vel` inputs well below the configured velocity envelope, `/diffdrive_controller/cmd_vel` shows command-path acceleration ratios far above the configured limits, and `/odom` then shows downstream acceleration-envelope violations.

In a 1000-round automated TurtleBot4 Jazzy simulation run:

- max `/diffdrive_controller/cmd_vel` linear acceleration ratio: **11.76x** the configured `linear.x.max_acceleration`
- max `/diffdrive_controller/cmd_vel` angular acceleration ratio: **6.62x** the configured `angular.z.max_acceleration`
- max input command remained safe: `|linear.x| <= 0.150 m/s`, `|angular.z| <= 0.800 rad/s`
- configured velocity limits are wider: `linear.x.max_velocity = 0.46 m/s`, `angular.z.max_velocity = 1.9 rad/s`

Representative frame `1782640335.8862267`:

```text
TB4 linear acceleration envelope violated:
  odom accel = 2.600 m/s^2
  odom ratio = 2.89x
  limit      = 0.900 m/s^2

Supporting /diffdrive_controller/cmd_vel ratios:
  linear = 6.13x
  angular = 3.75x

Representative frame 1782642590.4508777:

TB4 angular acceleration envelope violated:
  odom accel = -10.506 rad/s^2
  odom ratio = 1.36x
  limit      = [-7.725, 7.725] rad/s^2

Supporting /diffdrive_controller/cmd_vel ratios:
  linear = 6.07x
  angular = 3.59x

The failure appears after the external command enters the TurtleBot4/Gazebo/Create3 command path, not because the user command is out of range.

### Error messages

```bash
## Error messages


TB4 linear acceleration envelope violated: accel=2.600 m/s^2 ratio=2.89 limit=0.900
TB4 angular acceleration envelope violated: accel=-10.506 rad/s^2 ratio=1.36 limit=[-7.725, 7.725]

To Reproduce

To Reproduce

1. Start TurtleBot4 Standard simulation on ROS 2 Jazzy / Ubuntu 24.04.
2. Record these topics:
   - `/cmd_vel`
   - `/diffdrive_controller/cmd_vel`
   - `/odom`
   - `/wheel_vels`
   - `/clock`
3. Publish a safe `geometry_msgs/msg/TwistStamped` command sequence.

Representative linear repro sequence:

| step | linear.x (m/s) | angular.z (rad/s) |
|---:|---:|---:|
| 1 | +0.019 | -0.650 |
| 2 | -0.120 | -0.384 |
| 3 | +0.136 | +0.111 |
| 4 | -0.097 | +0.416 |
| 5 | +0.030 | -0.358 |
| 6 | -0.054 | -0.691 |
| 7 | +0.030 | +0.657 |
| 8 | -0.030 | +0.325 |

Representative angular repro sequence:

| step | linear.x (m/s) | angular.z (rad/s) |
|---:|---:|---:|
| 1 | -0.123 | -0.171 |
| 2 | +0.050 | -0.553 |
| 3 | -0.018 | -0.250 |
| 4 | +0.112 | +0.261 |
| 5 | -0.050 | +0.141 |
| 6 | +0.130 | -0.127 |
| 7 | -0.050 | +0.407 |
| 8 | +0.005 | -0.650 |

All commands are inside the velocity envelope:

- `|linear.x| <= 0.150 m/s < 0.46 m/s`
- `|angular.z| <= 0.800 rad/s < 1.9 rad/s`

4. Compute adjacent-sample acceleration on `/diffdrive_controller/cmd_vel` and `/odom`.
5. Observe `/diffdrive_controller/cmd_vel` acceleration ratios above the configured acceleration limits, followed by `/odom` acceleration violations.

Other notes

This issue is about the TurtleBot4/Gazebo/Create3 command path, not invalid user input.

The bridge path maps ROS `/cmd_vel` to the Gazebo model command topic and remaps the model command topic back to ROS as `diffdrive_controller/cmd_vel`. One suspicious boundary is that the simulated diffdrive controller parameter has `use_stamped_vel: false`, while TurtleBot4 Jazzy exposes `/cmd_vel` as `geometry_msgs/msg/TwistStamped` and bridges it into the Gazebo command path.

Suggested investigation points:

- `turtlebot4_gz_bringup` / ROS-GZ bridge launch path
- `irobot_create_gz_bringup` command bridge
- Create3 diffdrive command limiting
- conversion between `TwistStamped`, Gazebo `Twist`, and the published limited command