# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DXIKZXgj7bX
- **Gondola URL:** https://gondola.cc/posts/64172357-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/e097a2f725.jpg
- **Posted:** 2026-04-14T21:42:47.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

In motion control, the hidden variable that often dominates system behavior isn’t velocity or even acceleration—it’s jerk, the time derivative of acceleration. When a system follows a rectangular velocity profile, it implies instantaneous changes in velocity, which mathematically requires infinite acceleration over zero time. That translates to impulsive forces, effectively infinite jerk, which no physical system can realize. Instead, the result is broadband excitation of structural modes, fluid sloshing, and loss of control authority.

In the liquid payload shown here, the sudden acceleration step introduces a sharp inertial mismatch between the container and the fluid. The fluid resists motion due to its inertia, generating a transient free-surface deformation. This manifests as slosh dynamics governed by gravity waves and container geometry, with energy injected across multiple frequencies. The outcome is chaotic surface motion and eventual spill, not because the velocity is too high, but because the rate of change of acceleration is discontinuous.

Trapezoidal profiles improve this by bounding acceleration, but they still introduce discontinuities at the transitions between constant acceleration and constant velocity. These “corners” correspond to step changes in acceleration, meaning jerk is still theoretically infinite at those نقاط. While better, they continue to excite resonant modes in both mechanical structures and fluid systems.

The real solution lies in higher-order trajectory planning—typically S-curve or polynomial motion profiles—where jerk is explicitly limited and kept continuous. By distributing acceleration changes over finite time, these profiles reduce spectral energy at high frequencies, preventing excitation of structural resonances and minimizing fluid slosh. In practice, this directly translates to improved surface finish in CNC machining, reduced wear in actuators, higher positioning accuracy, and stable transport of sensitive payloads.

#STEM #Engineering #Robotics #MotionControl #CNC Automation

## Stats

- **Views:** 427,164
- **Likes:** 32,694
- **Shares:** 0
- **Comments:** 180

## Tags

engineering, stem, robotics, cnc, motioncontrol

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