Machine and Mechanical Design | Digital Adjustable Mannequin

Group Assignment

## Group Assignment -Design a machine that includes mechanism + actuation + automation + application -Build the mechanical parts and operate it manually -Document the group project Full group documentation can be found on our **[Lab Group Page](https://fabacademy.org/2026/labs/techworks/week12/week12.html)**.

## 1.0 Introduction For Machine Week, our team designed and fabricated a digital adjustable mannequin that can change its dimensions to accommodate different body sizes. The project combines mechanical systems, electronics, and digital fabrication techniques, using rack-and-pinion mechanisms driven by stepper motors to adjust the bust and waist measurements. Most components were produced through 3D printing and laser cutting, then assembled into a working prototype controlled through an Arduino-based interface. The project allowed us to explore the complete process of machine design, from concept development and fabrication to assembly, programming, and testing.

Digital Adjustable Mannequin / Waist Model and Prototype.

## 2.0 Design Rationale The project was inspired by existing adjustable mannequins, which rely on manual mechanisms to alter body measurements. We wanted to expand on this concept by exploring how digital fabrication, electronics, and mechanical systems could be integrated into a digitally controlled mannequin capable of adapting its dimensions more precisely and efficiently for garment fitting and prototyping.

## 3.0 Project Planning ### Project Management The selection process focused on finding a project that maximized the use of digital fabrication while solving a real-world design constraint. | Criteria | Mannequin Project | Alternative Idea | | :--- | :--- | :--- | | **Complexity** | High (Mechanical + Electronic) | Medium | | **Digital Mfg** | 3D Printing, Laser, CNC, PCB | 3D Printing only | | **Modelling** | High (Parametric & Kinematic) | Low | | **Scalability** | High (Modular segments) | Medium | | **Usability** | Professional Tailoring / Fashion | Hobbyist | > **Final Decision:** Digital Adjustable Mannequin. The project was divided between me and my team member Malak according to the main disciplines involved. I led the conceptual development of the project, including ideation, mechanism selection, mechanical design, CAD modeling, fabrication planning, and final mechanical assembly of the prototype. Malak however was responsible for the electronic design and automation aspects, including component selection, programming, motor control, and actuation testing. Throughout the project, design decisions were coordinated collaboratively to ensure seamless integration between the mechanical and electronic systems.

Project Work Breakdown Structure

## 4.0 Mechanical Design The mechanical design was inspired by the expansion mechanism. After studying existing manual models, the idea was developed into a motorized system capable of achieving synchronized and uniform dimensional adjustments. A single stepper motor was used as the primary actuator, driving an opposed rack-and-pinion mechanism that moves two links simultaneously in opposite directions. This balanced configuration ensures symmetrical force distribution and smooth motion, allowing the mannequin's outer panels to expand uniformly while maintaining stability and accuracy.

Iniital Sketching to draft the rack and pinion mechanism

Dense red triangular wireframe mesh of a MakeHuman torso model imported into the Fusion 360 canvas.

1. Importing the raw MakeHuman torso mesh as a geometric reference base.

Mesh Plane Cut tool active in Fusion 360, slicing the torso mesh horizontally near the lower section.

2. Sectioning the mesh with plane cuts to isolate targeted anatomy zones.

3. Reviewing the initial surface patch thickness and orientation from the isolated anatomy section.

A floating mesh strip segment divided into distinct yellow and pink highlighted face groups.

4. Isolating and partitioning specific mesh face strips to trace the shell profile.

A smooth, continuous grey surface strip converted from the faceted mesh geometry.

5. Converting the faceted mesh segment into a clean, smooth reference surface.

6. Tracing the precise anatomical curvature profile using a 2D spline sketch.

The final parametric solid body component, extruded with uniform thickness to form a clean crescent panel.

7. Final individual body shell component optimized to mount onto the adjustable mannequin skeleton.

#### The Waist Mechanism

Initial Waist Mechanism Model (Proof of Concept)

Second Waist Mechanism Model (Proof of Concept)

Final Waist Mechanism Model

#### The Mannequin Base and Column

Column Development

#### Bust Mechanism (Radial Expansion Mechnaism)

Bust Mechanism

### 4.4 Final Design

Final Design/div>

## Design and Manufacturing Human Model Generation: A baseline body model was created in MakeHuman using target body measurements and exported as a low-polygon mesh. Fusion 360 Conversion: The mesh was imported into Fusion 360 and converted into a solid body suitable for parametric modeling and mechanical integration. Parametric Chassis Design (Fusion 360): A central mechanical structure was developed using user-defined parameters to control expansion distances, gear dimensions, and clearances. Rack-and-Pinion Mechanism (Fusion 360): A radial rack-and-pinion system was designed to convert motor rotation into synchronized linear movement for uniform mannequin expansion. Body Segmentation (Fusion 360): The torso geometry was divided into separate shell panels and hollowed to create lightweight, movable sections connected to the mechanical system. Assembly and Simulation (Fusion 360): Joints and motion links were applied to simulate expansion and verify smooth synchronized movement of all components. Manufacturing Preparation: Structural components were prepared for laser cutting, while gears, racks, and shell panels were exported for 3D printing and final assembly. ### Sub-Assembly 1: The Base and Column The first components modelled and manufactured with minimal changes were the mounting base of the mannequin and the column. While the base (AM_Base) remained unchanged during the design and manufacturing process, the column went through two main iterations: the first was the column was laser cut to 70-75cm in total length which was oversized. Also, after assembling the bust sub-assembly, as-built modifications were made and reflected in the model:

AM_ Column_ Asbuilt by m.azizi2793 on Sketchfab

### Sub-Assembly 2: The Waist Mechanism Following the iterations explained earlier, the final waist mechanism sub-assembly consisted of two racks, one gear, one stepper motor (sunk into the column), and two 3D-printed right and left waist pieces.

Final_ Assembly_ File V1 by m.azizi2793 on Sketchfab

It can be seen in this model that the upper bust mechanism is still not in its final version, where it consisted of a central (long) gear controlling the motion of 4 racks, which basically failed. ### The Bust Mechanism This was the main challenge of this project as I spent a heavy amount of time trying to create a mechanism which needs to expand in a synced fashion to expand 4 separated pieces for the bust: left, right, front, and back pieces. To which I came to be inspired by the radial expansion mechanisms found in brake discs, with a modification to adapt the design to take the asymmetry of the mannequin and calculate the offsets and mounting positions for each link. The center/beating heart of this mechanism was a tower gearbox with leveled gears, actuated by a center gear; each gear is on a level all connected together as shown:

Asbuilt- Assembly V24 by m.azizi2793 on Sketchfab

## Manufacturing and Assembly The first phase was producing the 3D parts and the column (laser cut) - The Base - The Gears and Racks - The waist pieces

3d Printing the base , Material PLA, 0.4mm layer height/ 0.8 mm nozzle/ ultimaker s5

PLA and PETG / 0.2MM LAYER HEIGHT/ NUMBER OF WALLS 4-5

Material PLA, 0.4mm layer height/ 0.8 mm nozzle/ ultimaker s5

Assembky of the motor and waist mechanism

Front view of the waist mechanism

Back view of the waist mechanism

I utilized the laser cutter for the column instead of milling it to save time and to test multiple iterations quicker which i ended up with two versions

dxf preview of the first version of the long column

dxf preview of the second version of the long column

dxf preview of the first version of the long column

dxf preview of the first version of the as built column

first col assembly

laser cutting second version

mods to first column (as built modifications)

### 3D Component Testing I printed various gears and racks to test material durability. | Part | Material | Walls | Infill | Result | | :--- | :--- | :---: | :---: | :--- | | **External Shell** | PLA | 3 | 15% | Success (Lightweight) | | **Primary Gear** | PETG | 6 | 50% | Success (High Torque) | | **Rack Gear** | PLA | 4 | 30% | Failed (Brittle teeth) |

Autodesk fusion plugins

I used GF Gear Generator plugin to model my racks and gears , the parameters i had are:

Module (m): 1 mm
Number of teeth (z): 9
Pressure angle: 20°
Pitch diameter: 20 mm
Tip (addendum) diameter: 22 mm
Root (dedendum) diameter: 17.5 mm
Addendum: 1 mm
Dedendum: 1.25 mm
Clearance: 0.25 mm
Face width: 10 mm
Bore diameter: ~4.95 mm
Hub OD: ~13 mm
Total part length: 42.9 mm

Matching Rack (GF Gear Generator)

Module: 1 mm
Pressure angle: 20°
Addendum height: 1 mm
Dedendum depth: 1.25 mm
Tooth pitch: π × m ≈ 3.1416 mm
Face width: ≥ 10 mm
Fillet radius: 0.38 mm
Number of teeth: as required by travel distance

The second phase was manufacturing the bust mechanism,as mentioned earlier my first iteration for this failed but this phase was a mix of live modifications and reflecting the outcomes on the model, below area few shots of this "Failed" phase which led to me to develope the radial expansion mechanism later on. this phase also covered the 3d printing of the motor vertical clamp base which remained unchanged during the project.

3D Printed bust front pieces/right and left

I 3d printed the front bust pieces alongside with red "guides" and holders

Here I did the assembly and you can see the open slots in the second column version what they served, in addition to some on the spot plates to hold the gear mechansim on top of the motor

Back view of the mechanism, the actuated gear rotates clockwise and the second gear also rotates in the same direction,ensurign both racks push outwards/inwards at the same time, the failure is this is only good if we only had front pieces for the bust,not 4

failing to realize this observtion earlier i proceeded and modified the gear to become longer here and created the first "two level" rack and pinion mechansim, the long gear turns to isolated top and bottom motion gears responsible for the top and bottom racks

I later on went to correct the design I shall explain in my next section, however I did prepare the necessary parts as shown below for it:

Final Part List

## 7.0 System Integration (Mechanical and Automation) ### Integrating the mechanical chassis required careful alignment to bridge the gap between static 3D printed components and motorized automation. I focused on building the centralized structural framework, ensuring that the tolerances of the printed gears and laser-cut plates accommodated the physical mounting of the NEMA 17 stepper motors and limit switches without causing structural binding. This involved meticulously routing internal spacing for the wiring looms and establishing solid structural anchoring points, allowing the physical mechanism to reliably translate high-torque motor rotation into fluid, multi-axis panel expansion.

The Final Pivot: During a final development sprint, I redesigned the mechanism into a Spider Radial Expansion system. This utilizes a multilayered rack and pinion mechanism for much higher reliability. This was the major issue I faced during the design of this project, below is a progress of the the first bust mechanism was and the final design sketch I developed.

This was one of the most major problems and iterations I had to work around with to acheive linear motion expansion movement for the bust

| System Component | Status | Action Required | | :--- | :---: | :--- | | **Motor Functionality** | OK | Proceed | | **Electronic Controls** | OK | Proceed | | **Mechanical Movement**| ISSUE | Redesign for smoothness | ## Final Results The transition to the radial expansion mechanism allowed for synchronized, smooth adjustments across all body segments. The prototype successfully responds to digital inputs to match specific anatomical measurements.However there is further room to improve the assembly and model for this central spider radial expansion mechanism by introducing guides, sliders and a more efficient design for the gearbox itself, however it was a successfull Proof of concept to produce and manufacture the components and test them outside of the full assembly. The waist mechanism was fully functional and achieved its target to proof it can be integrated in future iterations of digital mannequins.

Resources & Assets

Source Files

Mechanical Design, Machine Design

Resources & Assets