Iterative Design | QuinLift

Iterative Design Log

Documenting how the stair-climbing wheel evolved from concept to spring-assisted, medtech-friendly hardware.

Because this device interfaces with patients and stairs, we explored multiple wheel configurations, spring placements, and mounting approaches. Below is a visual record of our main iterations — from initial tri-wheel inspiration to our smoother spring-assisted version.

Wheel iterations

Early CAD attempts, step-clearance tests, and spring positioning trials.

Version 1 — Base tri-wheel

Direct inspiration from warehouse dolly. Worked, but too “clanky.”

Version 2 — Added spring housing

Goal: make the upward rotation smoother and more patient-friendly.

Version 3 — 5-wheel test

A 5-wheel cluster proved more effective.

3-wheel vs 5-wheel cluster

Exploring stability, smoothness, and manufacturability.

3-Wheel Cluster (baseline)

Pros: simpler, smaller, closer to warehouse dolly, easier to mount on walker leg.
Cons: noticeable “step” during rotation → more vibration felt by user.

5-Wheel Cluster (exploration)

Pros: more contact points → smoother stair engagement, less per-step height.
Cons: larger diameter, more parts, potentially harder to print/assemble.

Design takeaway

For our patient's we decided to prioritize comfort and safety over cost. While more expensive to produce than the tri-wheel system the 5-wheel cluster was significantly smoother.

Other iterations & tests

Tested various wheel designs on standard stair CAD.

Spring 3 wheel test

Springs were meant to compress, shifting center of mass, and allow for smoother rotation. We deviated from the design because of durability concerns with the spring mechanism, and the steps getting stuck between the gaps formed by the mechanism.

Tri-wheel with rollers test

Building off the flaws of the spring tri-wheel design we created a system of varying wheel sizes. This would allow the wheel system to slide off the stair edges instead of getting caught and as a result reducing force required./p>

Quad-wheel test

Experimenting with more wheels in order to increase manufacturability by only having one wheel size. We reached the quad-wheel design which failed to fix the issues with the gaps.

Penta-wheel test

Increasing the number of wheels to five aimed to further smooth out the stair engagement and was succesful!