A molecular mechanism can look convincing in a static structure and still fail when it moves. One common source of trouble is timing: a component is driven from one position to another so quickly that the simulated system cannot follow the intended motion. The result may be a failed interaction—such as a gripper closing without grasping its target—even though the geometry seemed plausible.
The Simulate animation in SAMSON lets you run multiple simulation steps at each animation frame. Combined with an animation that controls atom positions, it can be used to simulate a system while parts of it are being moved. The key is to set up the sequence thoughtfully, then examine what the trajectory actually shows.
Start with the order of operations
SAMSON’s Animator executes animations from the top down. That means the position-generating animation should come before Simulate: first establish the positions from which the simulation should start, then run the simulation. If the order is reversed, the simulation may not begin from the positions you intended.
To add the simulation, double-click the Simulate animation effect in the Animation panel of the Animator. Its keyframe is placed at the current frame. You can move that keyframe if the simulation should begin elsewhere in the animation. Keyframes can also be moved later, so you do not have to get the timing perfect on the first attempt.
Think in terms of motion over time
A displacement is not just a distance: it is a distance completed over a particular duration. In the documented gripper example, the actuated blue part moves 1.7 nm in 2.5 ps. That corresponds to 680 m/s. At that speed, the gripper fails to grasp the cylinder. The example is a useful reminder that a visually small movement at the nanoscale can represent very rapid motion when the time interval is short.
When a driven mechanism does not behave as expected, check the motion’s timing as well as its geometry. Ask how far the controlled component travels, over what interval, and whether the resulting motion is compatible with the behavior you want to study. The example does not establish one universally correct speed; it shows why the speed implied by a chosen displacement and duration matters.
Use the simulation settings deliberately
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 determine how the simulation is advanced as the animation plays. They are worth checking when setting up a run, especially when combining simulation with another animation that controls positions.
Changing these values is not a substitute for checking the motion itself. A useful troubleshooting sequence is to confirm the Animator order, verify where the simulation keyframe starts, review the imposed displacement and duration, and then inspect the resulting motion. If the mechanism still does not perform as intended, revise the animation timing or simulation settings and compare the outcome. Treat the trajectory as evidence about the setup, rather than assuming that a plausible starting structure guarantees a successful interaction.
Keep a record of what happened
For later inspection, combine Simulate with the Record path animation to save the trajectory generated by the simulation. Recording the path makes it easier to revisit the motion and compare runs. SAMSON also provides Play path and Play reverse path animations for working with recorded trajectories.
The practical lesson is simple: organize the animation sequence, pay attention to how quickly controlled parts move, and use the recorded trajectory to evaluate the result. For setup details, see the Simulate animation documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.