The Bullet physics simulation is driven by the Maya timeline. To run a simulation, play the animation from the solver's start frame, which by default is frame 1 in the Maya timeline. To increase the duration of the simulation, increase the length of the timeline.

## Solve Process

Bullet operates in time (seconds) and has a fixed rate at which it takes simulation steps. The Bullet solver does not use frames as a time unit. The fixed rate determines the resolution of the simulation and is specified by the solver's

Internal Fixed Frame Rate attribute, which is set to 60 steps per second by default.

Note: You may want to change this to 120 Hz for improved solve quality. (Attribute Editor > Internal Fixed Frame Rate)

For example, if Maya is set to playback at 30 fps, there would be 2 Bullet sub-steps per frame. This design and implementation better supports real-time gaming applications where drawing and computation time per-frame must remain near constant. Limiting the number of simulation steps slows down the drawing speed required for an accurate solve.

Depending on the simulation, you may require additional iterations before you reach the desired solve effect. The solver’s
Max Num Iterations
option lets you set a maximum number of times the solve is iterated before the solver stops calculating and uses the last approximate solution as the final "good" solve. Setting a maximum amount of iterations lets you limit the time a simulation is processed. While this method may not provide as accurate results as more explicit solvers, this degree of accuracy is sufficient for most applications.

See Bake Bullet Rigid Body Simulations for information on how to bake a simulation.