open-manus

An open-source, 3D-printed, direct-drive, 1:1.5 scale bionic hand. Manus is latin for hand.

I'm almost done with the joint connecting the middle and distal phalanges (labeled and highlighted in blue below).

Table of Contents

1. Current Status & Logbook
2. Motivations
3. High-Level Milestones
4. Helpful Resources
5. Tools Used

Current Status & Logbook

Just wrote up a whitepaper on my MPC controller for impedance control using current sensing!

I have a joint with an embedded magnetic encoder working. Currently working on a custom transmission to rotate the motor 90 degrees to be inline to keep the finger compact and the joints serially composable.

Also, drafted a schematic for the transmission that will allow me to rotate the motor 90 degrees to be inline with the rest of the joint without jutting out (see schematic below). For the coupler between the motor shaft (1.5mm) and the transmission shaft (2mm) in the diagram, I was unable to find an off-the-shelf solution, so am going to 3d print my own coupler. Found a nice resource on YT on best practices to 3d print holes.

I am also considering a few design choices to reduce the width of the joint:

See the logbook for more detailed progress updates.

Motivations

I've previously made an open-source differential drive platform, quadruped, and star tracker, which all had interesting design, control, and mechanical challenges. My day job is currently a Machine Learning Research Engineer at a legal AI startup called Harvey where I work on composing large language models into useful legal assistants, but ultimately my passion (and foray into machine learning) has always been robotics. Currently, I'm most interested in machine learning/reinforcement learning in the context of robotics, and I feel that building and training models to control a bionic hand will function to keep me up-to-date with the machine learning literature and keep me connected to my first love (robotics).

There are many odes to Ismail al-Jazari throughout this project (e.g. the RL model being named Jazari). He was a Muslim polymath inventor from the 12th century known as the "father of robotics" due to his groundbreaking work in automata, and happens to be a personal inspiration of mine.

High-Level Milestones

Development Checklist for single interphalangeal joint

1. Mechanical Design

• Implement basic gearbox.
• Test out basic gearbox.
• Implement custom rotated transmission for compactness.
• Test out custom rotated transmission.
• Implement clean design for finger housing (and easy assembly).
• Compose the interphalangeal joints to make 2 joints in series.

2. Control System Design

• Derive MPC controller for impedance control via current sensing.
• Formalize MPC controller design in a small whitepaper.
• Calibrate MPC controller gains.
• Test out MPC controller on simple servo.
• Test out MPC controller on custom interphalangeal joint.

3. Hardware Design

• Implement basic end-to-end circuit (shunt resistor for current, encoder, microcontroller).
• Decide if I want to centralize all of the electronics and control or if they should be partially distributed via CAN bus for easier wiring.
• Design PCBs.
• Get PCBs made.

Helpful Resources

• Will Cogley's Bionic Hand - I found his videos to be deeply interesting, but felt conflicted about the wire-driven joints. I felt that a direct-drive hand would make assembly/control/maintenance easier, and posed some interesting challenges, so decided to make my own direct-drive design. Ultimately, this was a great project, and his videos are wonderful to watch, even if only for entertainment.
• Nice resource on best practices to 3d print holes.

Tools used

• [3D Printer] Slightly modified Prusa MK3 (reprinted all printer parts using Formlabs Fuse 1 SLS Printer).
• [Literature Review] Zotero.