Assistive Arm Mobility Interface Design

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.

Project ID: 40416303