Assistive Arm Mobility Interface Design
Budget: £10 – £20 GBP
UAHI (Upper Arm Hanging Interface)
Design & Manufacturing Drawing Brief
⸻
1. Project Objective
Design a load-bearing upper-arm suspension device that enables a client with a congenital limb difference (left arm terminating just distal to the elbow) to safely:
* Hang from a pull-up bar
* Achieve controlled spinal decompression
* Maintain symmetrical shoulder elevation
* Load tissues progressively without joint stress
The device must provide a stable, repeatable, and safe mechanical interface between the residual limb and an overhead bar.
⸻
2. User Profile (Design Constraints)
* Male, ~15 stone (≈95 kg)
* Left arm ends just after elbow (no forearm/hand)
* Full shoulder function assumed
* Soft tissue tolerance unknown → must minimize pressure + shear
⸻
3. System Overview (Based on Concept)
Assembly Structure
Load Path (Top → Bottom)
1. Pull-up bar
2. Bar clamp with integrated eye bolt
3. Locking carabiner (≥25kN rated)
4. Swivel (360° anti-rotation)
5. Steel yoke bracket (load distribution)
6. Structural socket (carbon fiber or equivalent)
7. Silicone liner (interface layer)
8. Residual limb
⸻
4. Design Requirements
4.1 Load & Safety
* Design load: 100 kg dynamic
* Safety factor: ≥2.0 (target 200 kg ultimate load)
* Must withstand:
* Static hanging
* Minor oscillation
* Progressive loading cycles
⸻
4.2 Biomechanics
* Load must pass:
* Axially through upper arm (humerus region)
* NOT through elbow joint
* Must:
* Prevent rotation
* Avoid distal pressure concentration
* Maintain vertical alignment under load
⸻
4.3 Usability
* Easy to:
* Don/doff (ideally one-handed assisted)
* Secure under load (no slip)
* Comfortable for:
* 30–60 second hangs initially
⸻
5. Component Design Specifications
⸻
A. Upper Arm Socket (Primary Interface)
Type:
* Transhumeral-style socket (short version)
Geometry:
* Internal diameter: user-specific (approx. 100–130 mm)
* Height: 120–160 mm
* Slight conical taper (proximal wider)
* Flared edges (proximal & distal)
Trim Lines:
* Lower anterior (reduce biceps pressure)
* Higher posterior (stability)
Materials:
* Preferred:
* Carbon fiber laminate
* Prototype:
* Carbon nylon / reinforced polymer
Internal Interface:
* Silicone liner (medical-grade)
* Optional:
* Vacuum suspension OR pin-lock
⸻
B. Yoke Bracket (Load Distribution)
Function:
* Transfer load from socket to vertical rigging system
* Prevent rotation and lateral instability
Design:
* Triangular / A-frame geometry
* Two lower mounting points on socket rim
* Single apex connection to swivel
Material:
* CNC aluminum (7075) OR forged steel
Fixing:
* Through-bolted with:
* M5/M6 stainless bolts
* Load-spreading washers
* Reinforced inserts in socket
⸻
C. Rotation Control
Component:
* Inline swivel
Spec:
* Rated ≥20kN
* Low-friction rotation
* Compact profile
Purpose:
* Eliminate torsional load on limb
⸻
D. Rigging Stack
* Locking carabiner (≥25kN)
* Swivel
* Yoke
All components must be:
* Climbing-rated OR industrial lifting-rated
⸻
E. Bar Interface
Design Options:
Option 1 (Preferred):
* Clamp-on bar attachment with eye bolt
Requirements:
* Fit standard pull-up bar (28–32 mm)
* Anti-slip (rubber-lined clamp)
* Dual-bolt tightening system
Eye Bolt:
* Rated ≥20kN
⸻
6. Manufacturing Drawing Requirements
Designer must produce:
1. Assembly Drawings
* Full system exploded view
* Load path clearly indicated
2. Part Drawings (Each Component)
* Socket
* Yoke bracket
* Bar clamp
Each must include:
* Dimensions (mm)
* Tolerances
* Material specs
* Surface finishes
⸻
3. Fixing Details
* Bolt sizes and positions
* Insert locations
* Reinforcement zones
⸻
4. Interface Zones
* Padding thickness
* Contact areas
* Pressure distribution considerations
⸻
7. Testing & Validation Requirements
Phase 1 – Bench Testing
* Static load to 150–200 kg
* Inspect:
* deformation
* cracking
* anchor integrity
⸻
Phase 2 – Assisted Use
* 10–30% bodyweight
* Short duration
⸻
Phase 3 – Progressive Load
* Gradual increase
* Monitor:
* skin condition
* nerve symptoms
* joint response
⸻
8. Key Risks to Design Against
Risk Mitigation
Socket slip Conical geometry + liner
Skin shear Wide contact + silicone
Rotation torque Swivel
Anchor failure Metal reinforcement
Bar clamp movement Dual clamp + friction liner
⸻
9. Deliverables
Designer/Engineer must provide:
* CAD files (STEP / Fusion 360 preferred)
* Full manufacturing drawing pack
* Bill of materials (BOM)
* Assembly instructions
⸻
Final Design Intent
This device should function as:
A load-bearing prosthetic suspension interface adapted for therapeutic and performance use
It must feel:
* Stable
* Predictable
* Safe under load
If you have experience designing assistive devices, adaptive fitness gear or similar load-bearing products, I’d love to see relevant examples. Let’s create an interface that makes mobility work accessible to everyone.
Design & Manufacturing Drawing Brief
⸻
1. Project Objective
Design a load-bearing upper-arm suspension device that enables a client with a congenital limb difference (left arm terminating just distal to the elbow) to safely:
* Hang from a pull-up bar
* Achieve controlled spinal decompression
* Maintain symmetrical shoulder elevation
* Load tissues progressively without joint stress
The device must provide a stable, repeatable, and safe mechanical interface between the residual limb and an overhead bar.
⸻
2. User Profile (Design Constraints)
* Male, ~15 stone (≈95 kg)
* Left arm ends just after elbow (no forearm/hand)
* Full shoulder function assumed
* Soft tissue tolerance unknown → must minimize pressure + shear
⸻
3. System Overview (Based on Concept)
Assembly Structure
Load Path (Top → Bottom)
1. Pull-up bar
2. Bar clamp with integrated eye bolt
3. Locking carabiner (≥25kN rated)
4. Swivel (360° anti-rotation)
5. Steel yoke bracket (load distribution)
6. Structural socket (carbon fiber or equivalent)
7. Silicone liner (interface layer)
8. Residual limb
⸻
4. Design Requirements
4.1 Load & Safety
* Design load: 100 kg dynamic
* Safety factor: ≥2.0 (target 200 kg ultimate load)
* Must withstand:
* Static hanging
* Minor oscillation
* Progressive loading cycles
⸻
4.2 Biomechanics
* Load must pass:
* Axially through upper arm (humerus region)
* NOT through elbow joint
* Must:
* Prevent rotation
* Avoid distal pressure concentration
* Maintain vertical alignment under load
⸻
4.3 Usability
* Easy to:
* Don/doff (ideally one-handed assisted)
* Secure under load (no slip)
* Comfortable for:
* 30–60 second hangs initially
⸻
5. Component Design Specifications
⸻
A. Upper Arm Socket (Primary Interface)
Type:
* Transhumeral-style socket (short version)
Geometry:
* Internal diameter: user-specific (approx. 100–130 mm)
* Height: 120–160 mm
* Slight conical taper (proximal wider)
* Flared edges (proximal & distal)
Trim Lines:
* Lower anterior (reduce biceps pressure)
* Higher posterior (stability)
Materials:
* Preferred:
* Carbon fiber laminate
* Prototype:
* Carbon nylon / reinforced polymer
Internal Interface:
* Silicone liner (medical-grade)
* Optional:
* Vacuum suspension OR pin-lock
⸻
B. Yoke Bracket (Load Distribution)
Function:
* Transfer load from socket to vertical rigging system
* Prevent rotation and lateral instability
Design:
* Triangular / A-frame geometry
* Two lower mounting points on socket rim
* Single apex connection to swivel
Material:
* CNC aluminum (7075) OR forged steel
Fixing:
* Through-bolted with:
* M5/M6 stainless bolts
* Load-spreading washers
* Reinforced inserts in socket
⸻
C. Rotation Control
Component:
* Inline swivel
Spec:
* Rated ≥20kN
* Low-friction rotation
* Compact profile
Purpose:
* Eliminate torsional load on limb
⸻
D. Rigging Stack
* Locking carabiner (≥25kN)
* Swivel
* Yoke
All components must be:
* Climbing-rated OR industrial lifting-rated
⸻
E. Bar Interface
Design Options:
Option 1 (Preferred):
* Clamp-on bar attachment with eye bolt
Requirements:
* Fit standard pull-up bar (28–32 mm)
* Anti-slip (rubber-lined clamp)
* Dual-bolt tightening system
Eye Bolt:
* Rated ≥20kN
⸻
6. Manufacturing Drawing Requirements
Designer must produce:
1. Assembly Drawings
* Full system exploded view
* Load path clearly indicated
2. Part Drawings (Each Component)
* Socket
* Yoke bracket
* Bar clamp
Each must include:
* Dimensions (mm)
* Tolerances
* Material specs
* Surface finishes
⸻
3. Fixing Details
* Bolt sizes and positions
* Insert locations
* Reinforcement zones
⸻
4. Interface Zones
* Padding thickness
* Contact areas
* Pressure distribution considerations
⸻
7. Testing & Validation Requirements
Phase 1 – Bench Testing
* Static load to 150–200 kg
* Inspect:
* deformation
* cracking
* anchor integrity
⸻
Phase 2 – Assisted Use
* 10–30% bodyweight
* Short duration
⸻
Phase 3 – Progressive Load
* Gradual increase
* Monitor:
* skin condition
* nerve symptoms
* joint response
⸻
8. Key Risks to Design Against
Risk Mitigation
Socket slip Conical geometry + liner
Skin shear Wide contact + silicone
Rotation torque Swivel
Anchor failure Metal reinforcement
Bar clamp movement Dual clamp + friction liner
⸻
9. Deliverables
Designer/Engineer must provide:
* CAD files (STEP / Fusion 360 preferred)
* Full manufacturing drawing pack
* Bill of materials (BOM)
* Assembly instructions
⸻
Final Design Intent
This device should function as:
A load-bearing prosthetic suspension interface adapted for therapeutic and performance use
It must feel:
* Stable
* Predictable
* Safe under load
If you have experience designing assistive devices, adaptive fitness gear or similar load-bearing products, I’d love to see relevant examples. Let’s create an interface that makes mobility work accessible to everyone.