A molecular mechanism can look convincing in a static view and still fail when it moves. One common reason is that an actuated part is driven too quickly: the simulation may show a target moving through space, but the surrounding system does not have a realistic opportunity to respond. If a gripper misses its target, the first question may not be whether the geometry is wrong. It may be whether the motion is too fast.
A SAMSON example makes the scale of the problem concrete. The blue actuated part of a nano gripper moves 1.7 nm in 2.5 ps. That corresponds to 680 m/s, and the gripper fails to grasp the cylinder. The useful lesson is not that this speed is always inappropriate; it is that converting a small displacement over a short time into a velocity can make an otherwise easy-to-miss problem visible.
Make the motion part of the simulation
The Simulate animation performs multiple simulation steps at each animation frame. This lets you combine it with other animations that control atom positions, so the system can be simulated while a component is being moved. That is useful when you want to examine how a molecular assembly responds to an imposed motion rather than simply inspect the starting and ending structures.
In the Animator, add Simulate by double-clicking its effect in the Animation panel. Its keyframe is placed at the current frame, and you can move that keyframe if the simulation should begin elsewhere in the animation.
Animation order matters
The Animator executes animations from top to bottom. Therefore, put Simulate after the animations that generate the simulation’s starting positions. In practical terms, first establish the positions you intend the system to start from, then run the simulation. If the order is wrong, the simulation may not begin from the state you expected.
Keyframes are movable, so you can adjust where the simulation occurs in the timeline as you refine the animation. This is useful for separating setup motion from the interval in which you want to observe the system’s response.
Use speed as a diagnostic
When a mechanism fails to grasp, collide, or follow an intended path, estimate the motion’s speed from its displacement and duration. Keep units consistent: divide the distance traveled by the time taken, then check whether the resulting velocity makes sense for the behavior you are trying to study. In the gripper example, 1.7 nm divided by 2.5 ps gives 0.68 nm/ps, or 680 m/s.
This calculation does not by itself prove why a particular simulation failed, and it does not identify a universally correct speed. It does give you a concrete quantity to investigate instead of relying only on how the animation looks. If motion is too abrupt for the question you are asking, adjust the motion or the simulation setup and compare the result.
Adjust simulation detail thoughtfully
The Inspector for the Simulate animation lets you change the number of steps per frame and the step size for the simulator’s state updater. These settings affect how the simulation is carried out as the animation advances. Change them deliberately, and compare runs so you can tell which setting or motion change corresponds to a different outcome.
To save the trajectory produced by the simulation, use the Record path animation. The resulting path can be explored with Play path or Play reverse path. Keeping a trajectory makes it easier to review what happened across the simulated motion, rather than judging only the final frame.
When a nanoscale mechanism behaves unexpectedly, check the animation order, estimate the imposed speed, and inspect the simulation settings. These checks help turn a visual failure into a more testable modeling question.
For the complete instructions, see the Simulate animation documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.