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Health tech2022–2026

Lifting-Assistive Device (LAD)

A wearable that helps people with limited arm strength lift, built as an affordable alternative to commercial devices. Four years of design reviews, from a resin cuff and a thread to a geared actuator that took 3rd place at the Engineering Expo 2026.

3rd place, Engineering Expo 2026

Client: James Lewallen, CO, UW Health Orthotics & Prosthetics
Years: 2022–2026
Area: Health tech
Result: 3rd place, Engineering Expo, spring 2026

The problem

Lifting your arm should not cost $20k

The client’s patients need help lifting their arm. The commercial option, the MyoPro, is described on the team’s project page as:

“Clunky, expensive (over $20k), and offers varying responsiveness.”

The goal from the first semester: a device that does the same job at a fraction of the cost, that is comfortable to wear and that responds when the wearer wants it to.

A man wearing a MyoPro arm orthosis while cutting food — The MyoPro, the commercial device the team set out to beat on price.

Labelled diagram of the MyoPro orthosis — MyoPro components, for comparison.

How it was built

Step by step

Fall 2022Design review

MK I: cuffs, a linkage and a thread

The first design wrapped the arm in two cuffs joined by an aluminum bar linkage. A motor pulling a thread would assist the lift.

Cuff

Printed in Elastic 50A resin

Firmware

Zephyr RTOS, written in C
Raspberry Pi Pico, debugged with a Picoprobe

Motor

L293D dual H-bridge
Bipolar stepper motor
Battery powered

Render of the first LAD design on a human model — MK I on a model of the arm.

CAD of two cuffs joined by a bar — Cuffs and the bar linkage.

CAD of two split cuff rings — The cuff, designed to be printed in elastic resin.

Schematic of the motor control circuit — Motor circuit: H-bridge and stepper.

Spring 2023Minimum viable prototype

“A tug on the thread was achieved”

The cuffs were attached with velcro and the motor pulled the thread for the first time. Cuff 2.0 used about 80% less material than the first cuff.

Goals set for the next semester: a pulley, enclosures and the motor software.

A student wearing the minimum viable prototype on his arm — The minimum viable prototype, worn.

CAD of the slimmer Cuff 2.0 — Cuff 2.0: about 80% less material.

Printed Cuff 2.0 held in a hand — Cuff 2.0, printed.

Printed cuff on a table with a thread attached — Printed cuff with the thread.

CAD of a pulley wheel — Next: the pulley.

CAD of a slotted enclosure box — Next: the enclosures.

Fall 2023MK II

Fixing what MK I taught them

MK I worked, and it showed what had to change. The team listed the problems and fixed them one by one. The electrical sub-team set a clear goal: “establish communication between the firmware and the motor w/out setting the device on fire.”

What was wrong

Uncomfortable to wear
Friction at the joint
Power supply not isolated from the user
Risk from the LiPo battery
Messy software; Zephyr was overkill
No battery monitoring

What changed

Flexible 80A resin → TPU, about 10% cheaper
Spool moved closer to the bar
Aluminum → PLA ($0.10–0.12 per gram)
Bearings at the elbow and the wrist
Motor enclosure removed

The new board

U1 at 3.3 V, H-bridge at 5 V
Li-ion battery with a protection IC
Buck converters and capacitors
LED test points

Render of MK II on a human model, the arm piece in red — MK II on the arm.

Printed TPU cuff on a table — Cuff printed in TPU.

Close-up of the printed TPU joint — TPU joint, printed.

CAD of the cuff with a bearing hole — Cuff with a bearing seat.

CAD of the thread spool — The spool, moved closer to the bar.

CAD of the PLA arm bars with a hinge — Bars in PLA instead of aluminum.

Black contact pads on a table — Contact pads.

Render of the MK II circuit board — The MK II circuit board.

Schematic of the microcontroller — Schematic: microcontroller.

Schematic of the H-bridge — Schematic: H-bridge.

Schematic of the battery protection — Schematic: battery protection.

Schematic of the buck converters — Schematic: buck converters.

Spring 2024Engineering Expo 2024

A working arm, driven by a PS4 controller

For the Engineering Expo 2024 the team overhauled the assembly, the motor type, the devices on the circuit board and the software. Visitors could drive the arm themselves with a PS4 controller: “Intuitive and fun for kids (and adults).”

Mechanical

ABS printed supports and joints
TPU contact pads replace the cuffs
Custom-formed aluminum plating
Semi-enclosed motor and PCB
Adjustable securement
12 V DC worm gear motor: more torque, and the motor locks in place

Electrical

Brushed DC motor with integrated gearbox, 12 V instead of 24 V
No backdrive current, lower temperatures, same control circuitry
Battery: 2400 mAh instead of 1000 mAh, with built-in charging
ESP32-WROOM-32E: Bluetooth, two I²C buses, PWM
Several boards merged into one

Software

Bluetooth PS4 controller for the Expo
Master MAC address changed to the ESP32
Right stick drives the motor up and down

The LAD arm mounted on the team’s Expo board — On the Expo board.

Visitors gathered around the Insight Wisconsin table at the Expo — Engineering Expo 2024.

The Insight Wisconsin booth on the Expo floor — The booth.

Team members standing behind the Expo board — The Saturday crew.

A student wearing the LAD on his arm — Worn by a team member.

The assembled arm with motor and wiring on a table — The assembled arm.

The main board and the IMU board merged into one board — Main board and IMU board, merged into one.

After Expo 2024Where it was headed

Sensors, a smaller battery and a 10 lb goal

After the Expo the team set the next targets. The benchmark: lift 10 lbs independently.

Electrical, next

IMU
Load cell
Smaller battery
Goal: lift 10 lbs independently

Next steps listed

Improve range of motion
Control method: bump switches, thread tension
Enclose the battery, the motor and the pulley
Potentiometer and velcro
Comfort

Later

Automatic input from force sensors and a potentiometer
Max and min bounds, with controller rumble at fairs
LCD display
Brainstorm interactivity for fairs

A student wearing the post-Expo version of the LAD — The post-Expo version, worn.

CAD render of the LAD with a worm gear motor — Render with the worm gear motor.

CAD with the load cell and potentiometer labelled — Where the load cell and potentiometer go.

2024–2025New mechanism

The drawbridge

The team explored new ways to move the arm, including a “drawbridge”: the wrist and the shoulder tethered by a thread, so the forearm rises like a bridge. The build aimed at the Engineering Expo in April 2025.

A student wearing the LAD with straps over the shoulders — Testing the fit.

2025–2026Engineering Expo 2026

Geared actuator, 3rd place

A geared actuator replaced the drawbridge, and backpack-like straps hold the device on the body. The team upgraded the motor driver and the battery, and added current sensing and rotation limits in software. After a design review the LAD went to the Engineering Expo and took 3rd place.

CAD render of the LAD with its geared actuator — The geared actuator.

Render of the upgraded circuit board — The upgraded circuit board.

Credits

Who made it

Client

James Lewallen, CO, UW Health Orthotics & Prosthetics

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