Project files

MyoHand 로봇 손 V3 바이오메카닉 출력·조립 가이드

이번 버전의 목표

V3 keeps V2's printable fork-and-tongue joints and tendon channels, while redesigning the proportions that made the hand look too long and narrow, and the axes that made the fingers cross each other when bending.

• Palm printed outer width: about 80.9 mm
• Overall outer envelope in the open assembled state: about 110.66 × 185.65 × 69.98 mm
• MCP center spacing: index–middle 19.0 mm, middle–ring 17.5 mm, ring–little 16.0 mm
• Center-chain length from the middle MCP to the tip: about 83.8 mm
• The index, middle, ring and little fingers use different lengths, fanned spread, and dorsal arch.
• The MCP, PIP and DIP pin axes are aligned to the true transverse bending axis, perpendicular to each phalanx's long axis and to the palmar bending direction.
• The MCP tongue holes are hourglass-shaped, narrow in the middle, so together with the elastic return section they can allow about ±7–10° of passive abduction/adduction.
• PIP and DIP are designed for an underactuated configuration in which one tendon bends both; the DIP/PIP ratio in the key pose is roughly 0.70.

Thumb structure

Unlike the other fingers, the thumb uses two serial CMC axes.

• CMC-A: abduction/adduction, design range −10°~+35°
• CMC-B: an oblique axis combining opposition and pronation, design range −5°~+35°
• CMC axis center spacing: 14.0 mm, chosen with print safety in mind
• Angle from the A axis to the B axis: 120°
• Positive rotation of CMC-B moves the thumb toward the palmar side and into the palm; at the maximum position it produces about 24° of longitudinal pronation component.
• Minimum calculated moment arm of the CMC-B tendon anchor: about 7.44 mm
• Thumb MCP: 0°~+55°
• Thumb IP: 0°~+65°

The palm hollow in V3.0 is a static arch created by the fan-shaped arrangement and height differences of the metacarpals. The active cupping structure, in which the ring and little finger CMC joints are separated into independently moving wings, is not yet included. It is safer to validate this as a separate part in the next version after actual print testing.

File Contents

• ../../../cad/version3/Thing_V3.blend: The final Blender file containing the assembled state, controls, pins, and previews of the tendons and return elastomers
• STL_Individual_21/: 21 STL files, including 17 individual structural parts, 3 calibration coupons, and 1 full print layout
• Previews/: 4 PNG images for verification: open hand, thumb opposition, and power grip
• ../version3_demo.mp4: Demo video for checking V3 motion

To avoid duplicate storage, compressed STL archives are not included in the repository. When needed, compress the STL_Individual_21/ folder and distribute it.

Thing_V3.blend is stored in Zstandard compression format, so open it with Blender 3.0 or later.

STL files are in mm. All_Final_Print_Parts is an integrated layout unfolded for printing, not the assembly pose, so use the Blend file to check the assembly.

Viewing the motion in Blender

Move to the next frame on the timeline.

To view only an individual part, select the V3_PRINT_... object in the Outliner and press the numeric keypad /. To return to the full hand, press / again or press Home. The controls are organized under the name V3_*_CTRL, and the printable parts under the name V3_PRINT_*.

The cyan tendons and dorsal return lines are digital previews for understanding the motion. They are not included in the STL files.

Recommended Pins, Holes, and Tendons

• Recommended tendon: 0.8–1.0 mm Dyneema or low-stretch line
• General tendon guide hole: 2.20 mm
• End anchor hole: 2.40 mm
• Dorsal return: 1.5 mm elastic cord or torsion spring for the pin
• Wrist connection: 4× M3, center spacing approx. 36×26 mm, CAD through-hole 3.40 mm

Actual fit varies with printer, material, and shrinkage. Before enlarging any pin hole, select the reamer or drill size based on the calibration coupon results.

Print and Assembly Order

1. First print V3_CAL_BORE_LADDER, V3_CAL_CLEARANCE_SLOTS, and V3_CAL_HORIZONTAL_BORES.
2. Using the material and layer height you plan to use, check pin fit, side clearance, and horizontal hole sag.
3. Print only the thumb CMC yoke and metacarpal first, and test-assemble CMC-A/B.
4. Print one regular finger and insert the pins in the order MCP→PIP→DIP, then check that it moves smoothly without load.
5. Print the remaining parts and assemble them onto the palm. Do not force the press-fit; if needed, lightly ream only the holes.
6. Route the tendons starting from the 8-channel comb at the wrist, passing through each guide and the end anchor holes. CMC-A and CMC-B are independent paths, and the thumb MCP/IP share a common flexion path.
7. Install the dorsal elastic cord or torsion spring starting at low tension, and adjust it so the hand returns to the open posture.
8. Align the forearm housing using the wrist elliptical ring and alignment lips, then fasten it at the four M3 locations.

If the hole axes are printed horizontally, sagging and ovalization can become significant. Where possible, orient the pin hole axes vertically, or determine supports, layer height, and post-processing based on the results of your calibration coupon.

Verification scope and cautions

• 17 structural parts: each a single connected body, 0 non-manifold edges, positive volume
• Thumb CMC-A, CMC-B, MCP, IP independent angle sweeps: 0 collisions between the inspected parts
• Non-adjacent printed-part collisions at frames 1/30/60/90/120: 0
• Control transform at frames 1 and 120: returns to the same open pose
• 21 STL files: binary structure, finite coordinates, triangle count and file length checks passed

This verification is based on CAD and collision calculations and does not replace an actual print load test. Begin by testing with low tendon tension, and check the areas around the CMC yoke, fork ears and MCP tongue for whitening, cracks or excessive play.