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Hydroponics

Floating Plate

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Summary

A printed plate that floats on the medium and holds thirteen Arabidopsis seedlings at one depth however much medium remains.

The plate floats on sealed air in two chambers inside the pontoons. Every dimension is measured, and every displacement computed, from the STL (stereolithography) files of the computer-aided design (CAD), which gives the plate a load line. Sixteen pieces print in polylactic acid (PLA) and assemble without adhesives or fasteners.

Seedlings
13
Sealed air
42.27cm³
Freeboard drawn
9.2mm
Sensitivity
3.5g per mm
Printed parts
16

Results

Hydroponics Floating Plate

Section02

Purpose

2.1 Standardized Hydroponics for Laboratories

Laboratories that grow Arabidopsis in liquid medium improvise with cut foam, taped mesh or fixed plates, which differ between laboratories and runs. The floating plate prints from four STLs on a standard fused deposition modelling (FDM) printer, so another laboratory can print identical geometry. The design is intended to give the same root depth, spacing and conditions regardless of operator.

2.2 Limitations of Fixed Plates

The first prototype was a fixed plate over a liquid chamber. The level had to stay within a narrow window below the platform: below it, the roots lost contact; above it, the platform flooded. The level fell through plant uptake and evaporation, so it was topped up by hand, and each top-up let conditions diverge between replicates.

end of a runwindownarrowtoo high:floodstoo low:roots losecontactFixed plate
Level inside the window
samedepthno matterhow muchis leftFloating plate
Same depth at every level
Medium level over a run. A floating plate falls with the level, so the roots keep their depth (schematic, not to scale).
Section03

Design Requirements

R1 · Constant root depth

Hold root depth constant for the whole run without manual top-up. Sections 2.2 and 4.

R2 · Thirteen seedlings

Carry 13 Arabidopsis seedlings. Section 5.

R3 · Integral flotation

Float on its own buoyancy, with no separate float attached. Section 4.

R4 · Standard printer

Print in PLA on a standard FDM printer. Section 7.2.

R5 · Assembly without adhesives

Assemble without adhesives or fasteners. Section 5.

Section04

Buoyancy Design

The plate floats on sealed air in a chamber inside each pontoon (). Sizing the chambers is a displacement problem: at the freeboard that places the roots in the medium and the crowns above it, the plate must displace its own mass, the seedlings and any water the print takes up. We repeated the calculation after every design change, because wall thickness and footprint change mass and displacement together.

massbuoyancybuoyancyfreeboardcrownsrootsmedium
  • MassPlate, seedlings and any water the print takes up.
  • BuoyancyMedium displaced by the pontoons below the waterline (hatched).
  • FreeboardThe height at which the two balance.
Plate afloat in section. Section A–A of the CAD at the drawn waterline, 6.0 mm below the slab, with 9.2 mm of freeboard and 54.2 cm³ displaced (; point 1 in ).

The displacement at each waterline defines the plate’s load line (). In water at 1.00 g/cm³, each cubic centimetre displaced supports one gram. Along the straight pontoon sides, displacement rises 3.51 cm³ per millimetre of draft, so every 3.5 g lowers the plate about 1 mm. No printed plate has been weighed, so the load line has not been checked on a real part.

  1. Waterline drawn in : 54.2 g floats at 9.2 mm of freeboard.
  2. Slab underside at the water: 79.4 g and 3.2 mm. Beyond it the whole slab displaces, so each gram lowers the plate less.
  3. Slab top awash: 111.9 g.
  4. Solid PLA: the sixteen parts would weigh at most 92.6 g and float at 1.9 mm of freeboard.
Load line of the assembled plate. Computed from the STLs through the seven waterlines in ; beyond point 2 the plate sinks about 1 mm per 10 g.
Displacement at each waterline7 waterlines
Displacement at each waterline
FreeboardDraftPlate aloneAssembled
18.2 mm6.9 mm22.4 cm³22.4 cm³
15.2 mm9.9 mm32.9 cm³32.9 cm³
12.2 mm12.9 mm43.4 cm³43.4 cm³
9.2 mm, as drawn15.9 mm54.0 cm³54.2 cm³
6.2 mm18.9 mm64.5 cm³65.5 cm³
3.2 mm, slab underside at the water21.9 mm75.9 cm³79.4 cm³
0, slab top at the water25.1 mm105.9 cm³111.9 cm³

Freeboard is the height of the slab top above the water; draft, the depth of the pontoon bottoms below it. Displacement is the volume of the printed shell below the waterline, including the sealed air, computed from the STLs. Assembled values add the submerged parts of the handles and seed holders. The calculation assumes no air is trapped under the slab.

Section05

Geometry and Mechanical Design

Render of the floating plate from its CAD, cut across the outer row of seed holders. A dark slab is carried by a pontoon along each long side; inside each pontoon is a violet sealed chamber that closes to a point. Brown seed holders sit in the bores, a grey handle stands at the far end, and nothing hangs under the middle of the plate.
Cutaway render. The CAD model cut through the outer row of seed holders; sealed chambers in violet.
  1. 1
    Teardrop pontoons, printed without support.
  2. 2
    Integral flotation: slab, pontoons and chambers print as one part.
  3. 3
    Clip-in handles, to lift the plate without touching the seedlings.
  4. 4
    Corner poles for washer ballast, first floating plate only (section 6).
AA117.5092.5021.59Plan6.9920.3210.16wall 1.59R3.81≈45° pointprints withoutsupportDetail · one pontoon25.083.18open underneathSection A–A
  • Sealed air chamber, hidden below the slab
  • Pontoon, hidden below the slab
  • Clip-in handle
  • Sealed air, in section
  • Printed plate, in section
  • Seed holder
Drawing sheet. Plan, section A–A through the outer-row bores and detail of one pontoon, sliced from the STLs, in millimetres.
Measured geometry10 dimensions
Measured geometry
FeatureValue from the CAD
The plate
Plate envelope117.50 × 92.50 × 25.08 mm
Top slab3.18 mm thick
Seed positions13 bores in rows of 4, 5 and 4; 21.59 mm apart along a row, rows 22.86 mm apart, outer rows offset half a pitch from the middle row
BoresTeardrop: a ∅10.39 mm circle extended to a point, 11.69 mm long; each seed-holder flange has the same shape
Flotation
PontoonsOne along each long side, 10.16 mm wide and reaching 21.91 mm below the slab, with 3.81 mm corner radii. Each turns inward at both ends and ends short of the handle pocket
Sealed chambersOne inside each pontoon, 114.33 mm long: a pentagon 6.99 mm wide and 20.32 mm deep, its lower sides chamfered at about 45° to a point, with 1.59 mm walls and floor and the slab as its roof. 21.13 cm³ each, 42.27 cm³ in total
Below the centreNone; flat slab, open underneath
Displacement117.0 cm³ with the plate, handles and seed holders fully submerged; the plate alone at each waterline is in
The printed parts
Handles12.34 × 25.40 × 32.89 mm, one at each end. The foot wraps the slab end and locates on a trapezoidal notch; the grip rises 26.51 mm above the slab
Seed holderAn 11.92 × 13.21 mm flange over a tapered basket, 12.07 mm tall
Section06

Engineering Cycles

The plate’s three prototypes, each as a design–build–test–learn cycle.

Prototype 1 of 3

Prototype 1: Fixed plate

  1. DDesignA plate held at a set height
  2. LLearnLevel falls as plants take up medium

Design

A plate fixed at a set height over a liquid chamber.

Learn

It worked only while the level was corrected by hand (2.2).

Prototype 2 of 3

Prototype 2: First floating plate

Started 6/25

  1. DDesignFlotation moved into the frame
  2. BBuildPrinted on 25 June
  3. LLearnPoles were the buoyancy margin

Design

We moved the flotation into the frame. Corner poles carried washers that trimmed the freeboard without reprinting.

Build

The first printed floating plate on a dark table: a white slab perforated with a grid of holes over a closed hollow frame, with a threaded pole and a washer stack rising from each of the four corners.
First floating plate. Printed on 25 June 2026.

Learn

The poles provided the buoyancy margin and were removed once the chamber volume was tuned (section 4).

Prototype 3 of 3

Prototype 3: Current design

  1. DDesignSmaller, with clip-in handles

Design

Smaller footprint, clip-in handles, no ballast poles; this design is reproduced in section 7.

Side views are schematic and not to scale; the CAD of the current design is in .

Section07

Reproduction

7.1 Bill of Materials

Render of the printed parts from the CAD, drawn apart: the dark floating plate with thirteen teardrop-shaped bores, thirteen brown seed holders lifted above them, and a grey clip-in handle lifted off each end.
Printed parts. One floating plate, two clip-in handles and thirteen seed holders, exploded from the CAD.
Printed parts4 parts, 16 pieces
Printed parts
PartQtyVolume, eachCost
Floating plate163.60 cm³
Handle, left and right22.76 cm³
Seed holder130.43 cm³
Total1674.72 cm³ in all

All four parts print in PLA. Volumes are solid CAD volumes; filament use depends on wall count and infill. No cost is recorded.

7.2 Print Settings

Print settings4 rows
Print settings
Material
PLA
Printer
A standard FDM printer
Infill
15% gyroid in the pontoon sections
Supports
None

Layer height, wall count and print orientation are not recorded.

Section08

Design Files

The four STLsone per printed part, millimetres, Z up
  1. 1
    Floating plate

    Print one.

    STL 820 KB

  2. 2
    Left handle

    Clips onto one end of the slab.

    STL 620 KB

  3. 3
    Right handle

    Mirror of the left handle.

    STL 620 KB

  4. 4
    Seed holder

    Print thirteen.

    STL 179 KB