> For the complete documentation index, see [llms.txt](https://carec.gitbook.io/carec-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://carec.gitbook.io/carec-docs/documentation/simulation/simulation-strategy.md).

# Simulation Strategy

Simulation is CAREC's shared engineering platform for component development, integration, fault injection, regression testing, contributor onboarding, and design review. It is especially important while contributors lack access to wheelchair hardware.

## Fidelity ladder

| Level     | Purpose                                               | Typical contents                                        | Exit signal                                    |
| --------- | ----------------------------------------------------- | ------------------------------------------------------- | ---------------------------------------------- |
| Interface | Validate messages, services, actions, and state logic | Stub sensors and drive                                  | Interfaces and failure states behave correctly |
| Kinematic | Fast navigation and mode testing                      | Footprint and motion constraints                        | Routes, takeover, and stop logic pass          |
| Dynamic   | Control and stopping analysis                         | Mass, inertia, friction, wheel/contact model            | Measured limits and timing are credible        |
| Sensor    | Perception and localization                           | Cameras, depth, LiDAR, IMU, encoders with noise         | Detection/localization cases pass              |
| Fault     | Safety and recovery                                   | Dropout, stale data, latency, brownout, process restart | Defined degraded states occur                  |
| HIL       | Driver, compute, and network behavior                 | Real selected hardware with simulated environment       | I/O and watchdog behavior is validated         |

## Core principles

* Use the lowest fidelity that can answer the engineering question.
* Keep one command and interface contract between simulation and hardware.
* Make every safety scenario deterministic, observable, and reviewable.
* Record assumptions; replace them with measurements as hardware becomes available.
* Separate pass/fail requirements from exploratory metrics.
* Treat simulation gaps as tracked engineering risks.

## Evidence chain

Requirements link to scenarios; scenarios link to software, configuration, world, seed, and results; failures link to issues and fixes; releases link to the passing evidence set.

Simulation does not prove real-world safety. Hardware progression requires documented gaps between simulated and physical behavior, conservative limits, and unoccupied testing.


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