Mechanical design · UW–Madison

Robotics and
mechanical design.

I'm Hao Chen, mechanical lead for the hand subsystem at UW Humanoid. I design tendon-driven robotic hands, build walking robots, and develop engineering tools.

Explore the hand project

Hexapod in the ME building

My hexapod walking through UW–Madison's mechanical engineering building.

Robotic hand in motion

My tendon-driven robotic hand prototype.

Tendon-driven hand

From working prototypes to the hand I'm building now.

Nylon 12Planned SLS-printed structure

25 DOFProposed architecture, including wrist and forearm rotation

50 tendons25 antagonistic pairs across the complete design

I'm developing a 25-DOF tendon-driven hand. For the next version, I plan to use SLS-printed Nylon 12 structures, custom brushless DC (BLDC) motors, and a custom PCB with current and position sensing. All actuators would be housed in the forearm.

The actuation targets full backdrivability and high torque transparency. With current and position feedback, I want the hand to estimate its joint state and infer contact from changes in load, working toward proprioception that lets the fingers “feel” contact.

Prototype demonstration

Hand strength

Hand and forearm assembly suspended during a strength demonstration.

Prototypes and process

Different hand builds, tendon routing, and assembly work. Select a photo to view it full size.

Overhead view of the robotic hand and forearm with exposed tendon pulleys and wiring.

Four white finger modules with joint bearings, servos, and tendon lines.

Assembled robotic hand and forearm with tendon routing, controller, and breadboard.

Close-up of finger joints, palm pulleys, and tendon guides in the black hand prototype.

Black actuator frame with mounted servos and a controller board.

Exposed forearm assembly showing tendon spools, guide tubes, and actuator wiring.

Several hand prototypes and disassembled finger parts laid out together.

Orange and black finger prototypes with joint bearings and loose tendon lines on a cutting mat.

Black robotic hand with tendon pulleys and fingers assembled on the workbench.

Full hand and forearm assembly on a cutting mat during tendon routing.

White hand prototype with partially assembled fingers and loose tendons.

Close-up of servo mounts inside an open prototype frame.

White hand prototype with exposed joints, actuator mounts, and tendon lines.

Robotic hand and forearm with black covers fitted over the palm and actuator assembly.

CAD motion study

Finger actuation

The finger moving at its joints in CAD. Each active joint axis uses an antagonistic pair of two tendons for motion in both directions. The complete design uses 25 pairs, totaling 50 tendons.

CAD section view

Finger cross-section

A cutaway view of the finger model, showing the internal geometry around its joints.

Built and tested

Working prototypes

I built and tested functional hand prototypes.

For hand control, I used OpenCV and a webcam to estimate joint angles and convert them into PWM commands for the servos.

Current development

25 independently actuated axes

My proposed architecture has 25 independently actuated axes: four per non-thumb finger, five in the thumb, one for palm cupping, two at the wrist, and a separate proximal forearm-rotation axis.

Paired tendons actively pull each joint in both directions. I plan to house all actuators in the forearm, keeping their mass off the fingers and providing space for cooling, electronics, and service.

The working servo prototypes and the proposed 25-axis system are separate stages of development. The paper presents the design and sizing basis; qualification testing is still to come.

Analysis

Design calculations

My paper follows the force path from the fingertip to the motor. It accounts for finger-joint geometry, the perpendicular distance from the tendon to the joint axis, spool radius, gear reduction, pretension, routing losses, and efficiency.

I built Actuation Lab to make force analysis and preliminary motor sizing interactive. The paper documents the equations, assumptions, worked examples, and input/output reference behind these tools, including gearing, winding choices, current, and copper heating.

Open Actuation Lab Read the paper & calculations

Design and Development of a Dexterous Tendon-Driven Robotic Hand
Hao Chen · 37-page design & calculation paper

Paper excerpt showing calculated motor torque increasing with tendon spool radius; the 5 mm example requires 0.670 newton-metres under the stated assumptions. — From my paper: calculated motor torque versus spool radius. Model results under stated assumptions; not measured actuator performance.

Walking hexapod

From leg geometry to a full robot in motion.

I designed and built a large walking hexapod, implemented inverse kinematics for its 3-DOF legs, and integrated onboard Wi-Fi, a display, and internal cooling.

Outdoor demonstration

Uneven terrain

My hexapod walking on grass across uneven terrain.

Inverse kinematics

Servo calibration, 3-DOF leg IK, coding, and testing.

About

I'm at the University of Wisconsin–Madison. I like working across the full process: understanding the mechanics, making the hardware, and figuring out how to manufacture it.

Mechanical designTendon actuationInverse kinematicsOpenCVMaterials testingManufacturing

Team leadership

UW Humanoid

Mechanical lead for the hand subsystem, with a focus on robotic hand design and development.

Product development

Goblin Gear

I work directly with the CEO on product development and materials testing in UW–Madison's mechanics of materials lab. My work also includes communications and supply-and-demand coordination.

Manufacturing

My product business

To support my engineering work, I started a business selling lifting belts and knee sleeves. I develop product improvements and work with overseas manufacturers, from communication through production coordination.

My product-development work includes a patent-pending design.

Contact

Get in touch

Email Hao

haochen2880@gmail.com +1 (913) 215-4365 Instagram @haowo.c

Robotics andmechanical design.