Overview

The mechanical system consists of a dorsal-mounted exoskeleton frame, four independent servo-driven finger linkages, and a forearm mounting platform. The design prioritizes lightweight construction, adjustability, and ease of fabrication using consumer 3D printers.

The chassis is 3D-printed in PLA (polylactic acid) for its balance of strength, printability, and low cost. Total printed mass is approximately 120g. Four MG996R servos provide actuation force, each capable of 11 kg·cm torque at 6V, sufficient to assist finger flexion for grasping tasks.

Each finger has a dedicated four-bar linkage that translates servo rotation into finger flexion. This mechanism maintains approximately constant moment arm throughout the range of motion, avoiding singularities and ensuring smooth actuation. Extension springs provide passive return force when servos release, reducing power consumption and heat buildup.

Design Notes

• •Material: PLA filament (1.75mm) printed at 210°C, 0.2mm layer height. Infill 30% for balance of strength and weight.
• •Linkage geometry: Optimized to avoid singularities; link lengths chosen to provide ~90° finger flexion from ~120° servo rotation.
• •Mounting: Three velcro straps (wrist, mid-forearm, proximal forearm) distribute load and prevent slippage during use.
• •Modularity: Finger linkages are separate STL files, allowing individual replacement if damaged.
• •Clearances: 0.3mm clearance for pin joints, 0.5mm for snap-fit features. Test prints recommended for dimensional calibration.

Bill of Materials (Mechanical)