Team 7: Collapsible Crutches

George Richards, Lauren Kidman, Tristan Kunzle, Danny Will

“My crutches would always fall to the floor when I wasn’t using them”

“Getting into cars and public transport with them was a Herculean task – time consuming, exhausting, and so embarrassing”

“When I was recovering from meniscus surgery and had to use crutches, I found them bulky and hard to store."

“Leaning crutches against a surface definitely creates a tripping hazard for people walking by”

Problem Statement

For Dartmouth students in cramped classrooms, current remedies for foot and ankle injuries are bulky and difficult to store or transport. Students need a more compact mobility aid to reduce struggles and mitigate the chances of further injury.

Users/Purchasers

Original Proposed Users/ Purchasers

Initially, the scope of our project was targeting Dartmouth students specifically as we began designing our prototype

Modified Users and Purchasers

Upon completion of our project, we decided to broaden the scope of our project to include not just Dartmouth students, but crutch users as a whole

State of the Art

Products on the Market

Active Patents

Carex Folding Crutch

This crutch takes the typical axillary crutch and adds a folding component at the halfway point. While it is a simple and easy to use mechanism, it can only fold in half.

Ergobaum Folding Crutch

This crutch ergonomic, a less common but better long-term style of crutch due to its reduced effects on posture. Like the Carex, this design simply folds in half.

US8235063B2

This patent adds a sliding component to an axillary crutch. Upon applying enough pressure to the handles, the crutch slides down into a box shape. While this design is very compact, its sliding mechanism can be accidentally activated during use, which could be very hazardous for the already injured user.

U7434592B2

This patent a slightly simpler style while also staying true to the typical ergonomic crutch. Like the Ergobaum, this design only folds in half, leaving room for further collapsibility.

Looking at existing products and patents, we derived thoughts and ideas to apply to a prototype of our own:

For one, we believe we could design a more effective collapsing mechanism that shrinks the crutch smaller than half its size, rather than the traditional folding mechanism. Furthermore, we also agreed that the mechanism should not be pressure based to avoid any issue of the crutch user activating the mechanism while using the product.

Specifications

Below are a list of specifications we thought were critical to designing an effective solution for our problem statement

Prototypes

Stage 1: Foamcore Prototyping

For the first foamcore prototype, we used a simple telescoping method. The bottommost section has the largest radius, and the increasingly small sections above it slide down to fit into the bottom, compacting the crutch.

This is a flat prototype testing a ball-lock mechanism. Upon pressing a button, two pins go inward, allowing the pole of the crutch to slide easily. When you reach the desired length, you release the button, and the pins snap back into place, securing the height.

At this point, upon doing some research and inspired by hiking poles, we decided some sort of ball-lock system would be an effective collapsing mechanism for our crutch:

HikingPoleExample.mov

BallLockSystem.mov

However, we quickly received user feedback that the cost to create the complex mechanism would outweigh the benefits of an easier-to-collapse crutch:

"I can just throw them in the back of my car. I wouldn't pay a premium for a fancy mechanism."

Thus, we decided to pivot...

Stage 2: Drawings and Mechanism Analysis

Snap Button Alternative

We proposed a solution that utilized snap buttons to telescope the mechanism. Snap buttons are much simpler, and therefore are very cost efficient, and also more durable; however, they would be a bit of a nuisance for the user, who would have to snap the button through each individual adjustment until they reach their desired height.

Lever Pin System

Upon finding adjustable paint poles at home depot, we also designed a "lever pin" solution. The telescoping sections each have a lever that upon pushing, releases a button upwards similar to the ball-lock mechanism mentioned previously. The user can then easily slide the poles to the adjusted height they want. While it is more time consuming to adjust the crutch, it is much less of a hassle than the snap buttons.

Lever Pin + Foldable Component

This final design takes the lever pin system explained to the left and adds a folding component to the armrest portion. Being that this section is at an angle, it cannot be telescoped, and thus to further collapse the crutch this section would simply fold downwards.

Stage 3: Final Prototype

Our final prototype was adapted from one of the adjustabel paint poles, which makes up the section of the crutch from the yellow component downward. We then designed the same lever pin system used by the pole in Solidworks, this time with larger radii to account for the diameter of the next section, which was made out of aluminum 6601 from the mshop. We then welded on another piece of aluminum to act as the handle, covering it in foamcore and rubber padding, and then finally the arm support at an angle. We then 3d printed and attached an armrest.

Video Demonstration

IMG_1705.mov

Testing and User Feedback

Mathematical Analysis

We utilized Euler's Buckling Formula to predict the weight in which a long column with pinned ends can bear before it bends:

Euler’s Buckling Formula:

PCr<(π2EI)/L2

I = Moment of inertia

E = Modulus of elasticity

L = Length of column

Goal is to make PCr>250lbs

E = 1 * 107 PSI (aluminum), 1.05 * 107 PSI (fiberglass)
I = 1/64*π ((1.000±0.035 in)4 - (0.902±0.035 in)4) = 0.2655 (smallest tubing)
L = 51.00 in (4.25 feet)

Pcr = 629.7 ± 0.005590 lbs

Aluminum will bear weight

We could only do mathematical testing for the tubing, when another crucial component is testing the weight bearing capacity of the joints that allow the tubing to telescope. We brought our prototype to Dr. Cullen and used the Instron machine for testing. Our results:

A singular crutch can hold at absolute minimum ~140 pounds

Thus, a set of the crutches would hold at least ~280 pounds

User Feedback

We sent out a survey to students across Dartmouth who physically tried our crutch. While we only received 11 responses, these were our results:

If you had to use crutches, would you choose these over a standard pair of crutches?

How much more would you pay for these crutches than a standard set of crutches?

Q: How comfortable is the crutch compared to other crutches you have used?

A: Average of 4.3 out of 5 with 1 being extremely uncomfortable, 5 being extremely comfortable

Q: How easy is it to collapse the crutch?

A: Average of 4.4 out of 5 with 1 being not easy at all, 5 being very easy

We checked our prototype to our specifications outlines previously, as well as compared that to a standard axillary crutch.

*While we did not meet our specification regarding size, it is important to note that we still significantly reduced the crutch's size from the typical height.

Ethics and Sustainability

Some Ethical Issues:

Safe working conditions for laborers

Safety of product
- If joints fail, user could be further injured
- If crutch is not easily accessible, could pose further injury

Some Sustainable Fixes:

Make entire body in thinner secondary aluminum (56% old, 44% new)
- Okala Factor = 0.55
- CO2 equivalent in pounds = 0.5

Mold lever pins and handles using silicone

Armrest made of bamboo

Polyurethane cord instead of bungee cord

Business Plan and Economics

Clarifying Cost Structure:

Fixed costs: factory leasing cost, shipping contract cost (calculated using UPS shipment calculator)

Variable costs: materials used for creating crutch

Total maximum cost of producing a set of crutches: $68.52

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