Problem Framing
First-Principles Design Brief
The studio context: 3 sessions per day, ~100 participants per session, each using up to 3 watercolor brushes — totaling ~900 brushes per day. With only a 1-hour break between sessions, a throughput target of ≥300 brushes per break was established.
900
Total brushes per day · 3 sessions × 100 participants × 3 brushes
≤45min
Target completion per break window (with buffer) → 6–7 brushes/minute
~1 day
Staff workday consumed by manual cleaning — the problem this design eliminates
Batch
10–15 brushes every ~2 min strongly favored over single-brush automation
Key insight from observing manual cleaning: humans clean brushes by moving water through bristles, not by pressing on them. This dictated the mechanical approach — gentle, water-driven agitation, not scrubbing or abrasive contact.
Concept Exploration
Mechanism Evaluation
Four cleaning mechanisms were evaluated before selecting the final direction.
| Concept | Pros | Cons | Decision |
|---|---|---|---|
| Ultrasonic cleaning | Fast | Bristle damage risk · High cost | Rejected |
| High-pressure spray | Simple setup | Splits bristles · Inconsistent results | Rejected |
| Conveyor automation | Scalable throughput | Over-engineered · Costly · Fragile | Rejected |
| Gentle mechanical agitation | Controlled · Scalable · Brush-safe | Requires careful fixturing | Selected ✓ |
Design Principles
5 Governing Rules
These principles were locked in before any mechanism was detailed, and guided every downstream decision.
01
No rigid contact with bristles — all force applied through handles only
02
Water does the cleaning, motion enables it — no abrasion
03
Batch size over individual precision — 15–25 brushes per cycle minimum
04
Mechanism must be intuitive to non-technical studio staff
05
Deliberate exclusions: no sensors, no closed-loop control, no plumbing integration — keeps it cheap, robust, and understandable
Core Mechanical Design
Final Architecture
Before choosing motors or parts, the water flow pattern was established first — because water motion is what actually cleans watercolor brushes. The chosen approach: baffled axial circulation using a pitched-blade turbine impeller.
Flow Regime
Problem avoided: the "Big Tornado" — spinning water in a smooth cylinder creates a large vortex with strong center motion and weak wall motion, producing uneven cleaning across brushes. Solution: four vertical internal baffles break circular spinning, prevent vortex formation, and force water to move top-to-bottom — ensuring all brushes see similar water motion.
Impeller Design
Down-pumping pitched-blade turbine (PBT) selected: moves large volumes of water gently, works well at low speeds, simple/reliable/low-cost, produces smooth axial circulation rather than harsh jets. The impeller pulls water from the top and pushes it downward through the brushes, mimicking the natural swirl-and-rinse motion of hand cleaning. Runs in a forward → reverse → short pulse → settle cycle to break pigment adhesion, prevent flow stagnation, and ensure uniform cleaning without bristle bias.
Tank Geometry
Polycarbonate cylinder — clear, tough, water-resistant, easy to source. Cylindrical shape promotes smooth circulation, eliminates corners where pigment can collect, and simplifies cleaning and sealing. Fully detachable tank assembly with laser-cut silicone gaskets, O-rings at interfaces, and optional lip seals at rotating interfaces for redundant leak protection.
Wet/Dry Separation
System split into two independent sub-assemblies: wet module (tank + impeller + seals + brush holder) and dry module (motor + controller + power electronics). Connected via custom gear-like mechanical coupling — inspired by mixer-grinder architecture. Benefits: no motor shaft exposure to water, easy basin removal, tolerant of misalignment, high reliability.
Brush Fixturing
Detachable TPU brush holder — flexible material accepts wide range of handle sizes, holds brushes vertically, keeps bristles away from impeller, snaps in and out for cleaning. Vertical orientation prevents bristle bending, allows pigment to fall away from ferrules, keeps brushes separated, and enables batch loading without tangling. All mechanical loads applied to handles, never bristles.
Controls (Simple)
Single sealed button. No user programming. Fixed cycle: forward rotation → reverse rotation → timed cycle → short boost pulse. Appliance-like operation ensures consistent cleaning quality and minimal user error. Single-button operation matches the non-technical studio staff requirement.
User Workflow
Studio Integration
01
Remove tank, fill with water
02
Snap tank into base
03
Insert 15–25 brushes into holder (vertical, handle-registered)
04
Close lid and press button once
05
2-minute cleaning cycle runs automatically
06
Remove clean brushes — total user interaction <30 seconds
EOD
Remove tank, dump water, rinse, snap back — no tools required
Risk Analysis
Failure Modes & Mitigations
| Risk | Mitigation |
|---|---|
| Water leaks | Multi-layer sealing — O-rings + silicone gaskets + lip seals at rotating interfaces |
| Impeller stall | Motor torque margin sized above stall threshold; forward/reverse cycling prevents buildup |
| Brush damage | Gentle low-shear axial flow + vertical holding + no rigid bristle contact |
| Pigment buildup | Fully detachable polycarbonate tank with no corners; end-of-day rinse SOP |
| User error | Single-button appliance operation; no user programming possible |
CAD Renders
SolidWorks Design
Full SolidWorks model covering complete assembly, subsystem details, and internal cross-sections — developed to production-ready specification under $200 BOM target.
Assembly ViewsFull assembly with brush holder loaded, tank with impeller visible through polycarbonate body, and detached lid/base views
Complete SystemFinal appliance render — wet tank module seated on dry base unit with single-button interface and wet/dry mechanical coupling
Section & Detail ViewsCross-section showing PBT impeller, sealing gasket (red O-ring), drive coupling interface, and brushes in cleaning position
What's Next
Future Development Path
- Flow visualization testing — confirm baffled axial circulation pattern and identify any dead zones across brush positions
- Bristle fatigue testing — 100+ cycle endurance test on multiple brush types (flat, round, angled, natural, synthetic)
- Seal life testing — thermal and chemical compatibility validation of O-ring and gasket materials over extended operation
- Impeller geometry optimization — blade pitch and diameter sweep to maximize cleaning uniformity at minimum motor RPM
- Manufacturing cost-down pass — injection-molded tank tooling, assembly time study, component count reduction
- Modular brush holder inserts — geometry-specific inserts for unusually large or small handle diameters
Project Info
Type
Design Challenge · Consumer Product
Domain
Fluid Systems · DFM · Product Architecture
Target
Professional art studios
BOM Budget
Under $200
Throughput
>300 brushes/hr
Tools & Methods
SolidWorksDFMFluid SystemsImpeller DesignSealing DesignTPU Fixturing3D PrintingBOM AnalysisSystem ArchitectureFirst PrinciplesUser Workflow Design
Design Intent
Philosophy
Intentionally simple, robust, and production-ready under $200
Key Insight
Water does the cleaning, motion enables it — no abrasive force
Architecture
Proven appliance architecture (mixer-grinder coupling) applied to art studio context