Capstan Gear Drive

Capstan Gear Drive for a Shoulder Support

During my project Servo Shoulder Support in2025 I realised, from the feedback I received, just how much there is a need for specific mobility aids for older or injured people.

My siblings and I got my father a professional exoskeleton designed for workers, as he was no longer able to lift his arm due to a shoulder injury.

He was delighted, but there was one problem: he couldn’t put the device on by himself (like a rucksack). So I got a strong servo motor and designed my own lighter, easier-to-put-on shoulder support.

The aim of all this is to make life easier for my father, so that he can at least raise his hand to shoulder height again.

Although the servo motor was powerful, the support was only satisfactory. I find professional-grade solutions like industrial servos or cycloidal gearboxes either much too large and impractical—or much too expensive.

That's why I developed my own drive system:

the Capstan Gear Drive

The actual project isn't finished yet. But its centerpiece—the revolutionary, custom-designed CGD — is being built here.

Nema17

3D print equipment + filament (PLA)

Dyneema line 1.5 mm

ball bearings: 2x 22mm, 2x 7mm

ESP32

stepper motor driver HW-134

power supply (12V)

screws & wires

Experience with Arduino IDE is required.

A capstan drive is a mechanism that uses a rotating drum (the capstan) to move or control a rope, cable, or tape by friction.

Instead of gripping the line with gears or teeth, the line is wrapped partway around the capstan. As the drum rotates, friction between the surface and the line pulls it along. The more wraps you add, the more force it can transmit without slipping.

You can find capstan drives on sailing ships for hauling ropes, anchoring, and mooring lines.

Well, please visit the 1st Shoulder Support project to see how it would look like.

An ESP32 and a XIAO nrf in a wrist band are controlling the shoulder support.

Power is supplied by an 18V garden tool battery.