Rotation in the plant frame
The FlavoRotor drum turns around a horizontal axis. Gravity remains vertical and close to 9.81 m·s⁻², while each plant module changes orientation relative to that vector. Rotation therefore produces a periodic directional stimulus, not reduced gravity. The encoder record links angle, angular speed and direction to every image and sensor sample.
Gravity direction during one drum revolution
Gravity remains vertical while the plant module completes a 360° orientation cycle.
Direction of gravityconstant in the room
Plant orientationθ(t) = θ₀ + ωt
Cycle periodT = 60/n
Values
| Series | Value | Note |
|---|---|---|
| Top position · 0° | Plant module upright relative to the drum | Gravity points vertically down while the plant-module radial axis points up. |
| Right position · 90° | Plant module rotated one quarter-cycle | The gravity vector is perpendicular to the plant-module radial axis. |
| Bottom position · 180° | Plant module inverted relative to its top position | This position also corresponds to root-zone immersion in the current drum geometry. |
| Left position · 270° | Plant module rotated three quarters of a cycle | The gravity vector is again perpendicular to the radial axis, with the opposite sign in plant coordinates. |
FlavoRotor horizontal-axis drum geometry; gravitropic sensing and signalling are described by Nakamura, Nishimura, and Morita (2019).
ExplanationRevolutions per minute are converted into angular speed in radians per second.
ExplanationA basket's angle equals its starting angle plus angular speed multiplied by elapsed time.
ExplanationOne complete rotation takes 60 divided by the drum speed in revolutions per minute.
How a plant detects reorientation
Gravity-sensing cells contain dense, starch-rich amyloplasts. After reorientation, the amyloplasts move towards the new lower side of the cell. That physical change alters gravity signalling and directional auxin transport. Unequal growth on opposite sides of the organ produces curvature: primary roots usually bend with gravity, while shoots usually bend against it.
| Stage | Root | Shoot | Measurement |
|---|---|---|---|
| Gravity sensing | columella cells in the root cap | endodermal cells | module angle and time after reorientation |
| Signal | asymmetric auxin transport towards the lower flank | directional auxin redistribution | organ angle and curvature over time |
| Growth response | positive gravitropic bending | negative gravitropic bending | root-tip angle, shoot angle and elongation rate |
The biological input depends on both orientation and exposure time. A slow cycle permits a longer dwell at each angle; a faster cycle changes direction more often. Drum speed is therefore reported together with acceleration ramps, stop duration and the complete angle-time series.
Mechanical acceleration
ExplanationCentripetal acceleration increases with radius and with the square of angular speed.
ExplanationThe plant experiences Earth's gravity together with the acceleration caused by rotation and any measured vibration.
| Speed | Cycle period | Radius | Centripetal acceleration | Fraction of g |
|---|---|---|---|---|
| 0.5 rpm | 120 s | 0.15 m | 0.000411 m·s⁻² | 0.0000419 |
| 2.0 rpm | 30 s | 0.15 m | 0.00658 m·s⁻² | 0.000671 |
At these example settings, centripetal acceleration is less than 0.07% of g. The dominant physical input is the changing direction of the gravity vector in plant coordinates. Vibration, airflow, liquid movement and start-stop transients are measured separately because they can also change plant growth.
Rotation and root-zone exposure
Drum angle also determines when each root module enters and leaves the nutrient solution. For every position, the run record stores immersion depth, immersed duration, drainage duration and retained liquid mass. A biological comparison must match average light and root-zone exposure between rotating and control plants; otherwise orientation, illumination and hydroponic contact change together.
Controlled rotation experiment
| Group | Variable isolated |
|---|---|
| Static plant with matched mean light and root exposure | baseline |
| Rotating plant | combined periodic orientation treatment |
| Static plant with matched time-varying light | light distribution |
| Static plant with matched vibration | mechanical vibration |
| Rotating plant with slow acceleration ramps | start-stop transient |
Primary endpoints are chosen before cultivation: root-tip angle or shoot curvature for orientation response, plus one growth or chemistry endpoint. Encoder angle, three-axis acceleration, plant images, light exposure, immersion and air velocity are synchronised by timestamp. The analysis uses the plant or independent cultivation cycle as the experimental unit.