A molecular mechanism can look convincing in a static model and still fail when it moves. One common reason is that an actuated part is driven through its motion too quickly: the surrounding atoms have little time to respond, and the intended interaction may not happen. For a molecular modeler, the useful question is not only “Where should this part end up?” but also “What happens while it gets there?”
SAMSON’s Simulate animation helps answer that question by running multiple simulation steps at each animation frame. You can pair it with animations that control atom positions, so the system is simulated while another animation supplies or changes positions. This makes it possible to examine a moving mechanism in context rather than judging only its starting and ending structures.
Turn a motion into a test
Think of the animation as a sequence of two jobs: first, establish the positions that define the motion; then, simulate the system as it evolves. The Animator runs animations from top to bottom. Therefore, place Simulate below the animations that generate the simulation’s starting positions. If the order is wrong, the simulation may run before the intended positions have been set.
To add it, double-click Simulate in the Animation panel of the Animator. Its keyframe is placed at the current frame, and you can move that keyframe if the simulation should begin elsewhere in the sequence. Keyframes can be moved later, so you can adjust the timing without rebuilding the animation from scratch.
Use timing as a design variable
Consider the documented nano-gripper example. The actuated blue part moves down by 1.7 nm over 2.5 ps. That corresponds to an average speed of 680 m/s. In that example, the gripper fails to grasp the cylinder when the motion is too fast; a successful grasp was shown at a different speed. The practical lesson is that a desired displacement alone does not determine whether a mechanism will work. The rate of motion matters too.
When a simulated mechanism misses an interaction, use the animation as a way to investigate rather than immediately changing the structure. Check how much displacement is being requested and over what interval. A simple distance-over-time estimate can reveal whether the imposed motion is very rapid. Then adjust the motion’s timing and run the simulation again to see whether the system responds differently. This is a diagnostic approach, not a guarantee that slowing the motion will solve every failure: the outcome still depends on the molecular system and the setup.
Separate animation timing from simulation resolution
The Inspector for the Simulate animation lets you change the number of simulation steps per frame and the step size for the simulator’s state updater. These settings are useful to understand alongside the animation timing: the animation describes when the simulation is applied in the sequence, while the Inspector controls how the updater advances during each frame. Change settings deliberately and compare runs, so you can tell whether a different result comes from the motion schedule or from the simulation update settings.
If you want to inspect or share the resulting trajectory, add the Record path animation to save it. The related Play path and Play reverse path animations can be useful when reviewing a recorded path.
The key takeaway is to treat motion as part of the molecular design, not just as a visual transition. Set the position-generating animations before Simulate, check whether the imposed movement is plausible for the question you are asking, and use recorded paths to review what happened. For the full setup details, see the Simulate animation documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.