# OpenBionics Prosthetic Hand A low-cost, 3D-printable, **fully functional anthropomorphic prosthetic hand**. The OpenBionics initiative (openbionics.org) publishes designs that cost **under $200** and weigh **under 300 g**, aimed at closing the gap between commercial prosthetics (often tens of thousands of dollars) and what an individual or clinician can fabricate themselves. ## How it works The standout feature is a **whiffletree-based differential mechanism**. A single actuator drives all five fingers — but because of the differential, each finger stops independently when it contacts an object. That one trick unlocks **144 distinct grasp poses** from a single motor, letting the hand conform to a wide range of objects (cylinders, pinches, key grips, hooks) without per-finger control. A set of small mechanical locks lets the user selectively block specific fingers, which is how grasp selection is done on the physical device — no complex EMG classifier required at minimum. ## What you get - Fully printable 5-finger right hand (mirror files for left also available in upstream repo) - HerkuleX DRS-0201 smart servo as the single actuator - Wire-driven tendons with a differential bar mechanism - Parametric CAD — scale the hand to fit different users using anthropometry tables - Optional body harness + breakout board for integration with EMG or button control ## Canonical printed parts - `palmDown`, `palmUp` — two-part palm shell - `index`, `middle`, `ring`, `pinky`, `thumb` — finger bodies (multi-phalanx each) - `baseHerkulex` — mount for the smart servo - `mainBar`, `barIndexMiddle`, `barRingPinky` — the whiffletree differential - `FlangePlate` — wrist interface The upstream repo contains ~280 STLs total covering left + right hands, the HDM variant, lockable mechanisms, and the wearable harness. ## What you can do with it - **Teleop grasping demos** — use the orobot cloud surface to command preset grasps (open, power grip, pinch, tripod). - **EMG or button-driven control** — the upstream Arduino code reads muscle signals or switches and triggers grasps. This program wraps that with a cloud-side trigger surface. - **Research platform** — anthropomorphic, under-actuated, fully open — a good baseline for grasp planning, tactile sensor integration, and rehabilitation engineering projects. - **Education** — the whiffletree differential is a genuinely elegant piece of mechanical design; students can print one in a weekend and understand underactuated grasping hands-on. ## Ethics note This is a research-grade design published for open study and community iteration. For clinical use as a medical prosthesis, local regulatory review, professional fitting, and ongoing care are required — 3D-printable ≠ ready to wear. ## Attribution & license - Initiative: **OpenBionics** (openbionics.org) - Upstream repo: https://github.com/OpenBionics/Prosthetic-Hands - License: **Creative Commons Attribution-ShareAlike 4.0 International (CC-BY-SA 4.0)** - Homepage: https://www.openbionics.org/ ## Links - Upstream: https://github.com/OpenBionics/Prosthetic-Hands - HerkuleX servo docs: http://www.dst-robot.com/robot/include/images/sub0202/HerkuleX%20Manual_DRS-0101_0201_eng_20140128.pdf - Project page: http://www.openbionics.org/
Category: Robotic Hands
| Qty | Part | Notes | |-----|------|-------| | 5 | Servo motor (MG90S or SG90) | One per finger | | 1 | Arduino Nano or similar | Control board | | 1 | Servo driver board | PCA9685 | | 1 | 5V USB power bank | Power supply | | 1 | 3D printed finger set | See STL files | | 1 | Elastic cord (1m) | Finger tendons | | 1 | Set of M2/M3 screws | Assembly |