Simulation Timestep

The amount of simulated time a physics engine advances per step, which trades off accuracy, stability, and speed.

The simulation timestep (often written dt) is how much time the physics engine's integrator advances on each step — 0.002 seconds, for instance, means simulating 1 real second takes 500 steps. A smaller timestep computes contact and fast motion more accurately and is less prone to blowing up, but it also needs more steps to cover the same duration, making it slower. MuJoCo defaults to a 0.002-second timestep, and its documentation calls it the single most important parameter for the speed-accuracy trade-off; Isaac Lab's SimulationCfg defaults to 1/60 second, though specific tasks often set it smaller. The simulation timestep is usually shorter than the policy's control period: for every action the policy outputs, the simulation keeps running for several steps, and that multiple is called decimation; some engines further split a single step into several substeps.

ExampleIsaac Lab's velocity-tracking task for legged robots sets sim.dt to 0.005 seconds (200 Hz) with a decimation of 4, so the policy outputs actions at 50 Hz.

Also called

dt, Physics Timestep, Physics dt, Sim dt

Related

Control Decimation · Substeps · Numerical Integrator (Semi-implicit Euler / RK4) · Simulation Instability · Control Frequency · Real-Time Factor

Sources

MuJoCo Documentation: XML Reference (option timestep)
Isaac Lab source: velocity_env_cfg.py (locomotion velocity task)
Isaac Lab source: simulation_cfg.py (SimulationCfg)

As of

2026-09