Mechanical Engineer for Dual-Mode Retractable Reel (TNB System Redesign & Prototype)
Budget: ₹12,500 – ₹37,500 INR
Overview:
We're looking for a highly skilled mechanical design engineer with experience in precision mechanical systems, spring-based retractors, and low-tolerance plastic mechanisms to work on a redesign of an existing multifunction retractable reel (used for string-based badge holders and accessories).
The product is meant to operate in two modes:
Mode 1: Always retract
Mode 2: TNB mode (temporary lock + tug to retract)
We are starting with Phase 1.1 and 1.2, as described below.
Background:
Previous designs (TNB1, TNB5, TNB6) have known issues with:
Multi-position locking (we want a single locking point at ~75% pullout)
Wobble in reel affecting locking accuracy
Torsion spring balance complexities
Assembly difficulty
This new design should address those issues while staying simple and easy to manufacture.
Scope of Work:
This job will be split into Phase 1.1 and 1.2 (each paid separately), with optional Phase 2 for prototyping if successful.
Phase 1.1 – Concept Design (Target Budget: $450)
Deliverables:
Mechanical concept for a dual-mode reel mechanism:
Switchable between "Always Retract" and "TNB Mode".
OR includes an auto-sensing locking mechanism that activates only at ~75% pullout if string is slowly released (Moonshot Option).
Locking must only occur at one point in the reel's pullout range (~75%).
Drawings or diagrams showing:
How the locking arm works
Where it engages and how it resets
How the mode switch works (or how locking behavior is triggered)
Any necessary tolerances or material recommendations
Engineering explanation:
How the mechanism prevents multi-position locking
How force balance is achieved if using passive parts (like a molded torsion arm)
Feedback considerations:
Must account for “tug” release between 6”–12”
Easy to assemble (e.g. avoid fragile or ultra-precise torsion springs like TNB1)
Reel diameter ~30mm–34mm, string length ~30”–48”
Note: This stage is design-only. 3D CAD modeling or FEA is optional unless used to clarify the concept.
Phase 1.2 – 3D CAD + Exploded Assembly (Target Budget: $450)
To be awarded after successful Phase 1.1.
Deliverables:
3D CAD model of the proposed mechanism using SolidWorks, Fusion 360, or Inventor.
Exploded assembly views
2D mechanical drawings with tolerances and annotations
Identification of:
Power spring type and specs
Materials (plastic, molded parts, etc.)
Moving parts and how they interact
Assembly notes or animation (optional but preferred)
Design should be prototyping-ready by the end of Phase 1.2.
Optional Phase 2 (Prototype Testing – Not part of current contract):
If design is approved, a new milestone will be created to:
Produce a 3D-printed prototype
Test locking behavior
Evaluate real-world assembly
Requirements:
Mechanical engineering background
Proven experience designing compact mechanisms
Strong understanding of spring mechanics, locking mechanisms
Clear communication
Can deliver work in agreed milestones and budget
Tools Preferred:
SolidWorks / Fusion 360 / Inventor
Ability to export to STL/STEP
Optional: Simulation (FEA) if needed
To Apply:
Please include:
Examples of similar work
Short description of how you'd approach this
Availability for next 2–3 weeks
We're looking for a highly skilled mechanical design engineer with experience in precision mechanical systems, spring-based retractors, and low-tolerance plastic mechanisms to work on a redesign of an existing multifunction retractable reel (used for string-based badge holders and accessories).
The product is meant to operate in two modes:
Mode 1: Always retract
Mode 2: TNB mode (temporary lock + tug to retract)
We are starting with Phase 1.1 and 1.2, as described below.
Background:
Previous designs (TNB1, TNB5, TNB6) have known issues with:
Multi-position locking (we want a single locking point at ~75% pullout)
Wobble in reel affecting locking accuracy
Torsion spring balance complexities
Assembly difficulty
This new design should address those issues while staying simple and easy to manufacture.
Scope of Work:
This job will be split into Phase 1.1 and 1.2 (each paid separately), with optional Phase 2 for prototyping if successful.
Phase 1.1 – Concept Design (Target Budget: $450)
Deliverables:
Mechanical concept for a dual-mode reel mechanism:
Switchable between "Always Retract" and "TNB Mode".
OR includes an auto-sensing locking mechanism that activates only at ~75% pullout if string is slowly released (Moonshot Option).
Locking must only occur at one point in the reel's pullout range (~75%).
Drawings or diagrams showing:
How the locking arm works
Where it engages and how it resets
How the mode switch works (or how locking behavior is triggered)
Any necessary tolerances or material recommendations
Engineering explanation:
How the mechanism prevents multi-position locking
How force balance is achieved if using passive parts (like a molded torsion arm)
Feedback considerations:
Must account for “tug” release between 6”–12”
Easy to assemble (e.g. avoid fragile or ultra-precise torsion springs like TNB1)
Reel diameter ~30mm–34mm, string length ~30”–48”
Note: This stage is design-only. 3D CAD modeling or FEA is optional unless used to clarify the concept.
Phase 1.2 – 3D CAD + Exploded Assembly (Target Budget: $450)
To be awarded after successful Phase 1.1.
Deliverables:
3D CAD model of the proposed mechanism using SolidWorks, Fusion 360, or Inventor.
Exploded assembly views
2D mechanical drawings with tolerances and annotations
Identification of:
Power spring type and specs
Materials (plastic, molded parts, etc.)
Moving parts and how they interact
Assembly notes or animation (optional but preferred)
Design should be prototyping-ready by the end of Phase 1.2.
Optional Phase 2 (Prototype Testing – Not part of current contract):
If design is approved, a new milestone will be created to:
Produce a 3D-printed prototype
Test locking behavior
Evaluate real-world assembly
Requirements:
Mechanical engineering background
Proven experience designing compact mechanisms
Strong understanding of spring mechanics, locking mechanisms
Clear communication
Can deliver work in agreed milestones and budget
Tools Preferred:
SolidWorks / Fusion 360 / Inventor
Ability to export to STL/STEP
Optional: Simulation (FEA) if needed
To Apply:
Please include:
Examples of similar work
Short description of how you'd approach this
Availability for next 2–3 weeks