Mechanical Wallet

This project represents my abilities in 2019

Overview

Possibly the most challenging project I've completed to date is that of my 3D printed wallet. I've been using this wallet ever since its design was finished in May, but it took a lot of trial and error to get it to the place that it's in today. I wanted as many of the parts of the wallet to be 3D printed, and I achieved this, save for a spring that is used to keep the wallet locked shut. Because I wanted this wallet to eventually be printable for anyone with a 3D printer, I designed the spring loaded mechanism to hold a standard pen spring, which should be accessible to anyone who wishes to make the wallet.

Final Wallet Functionality

The current version of the wallet is its 26th iteration. This numbering includes the constant iteration required to get the tolerance of the spring loaded mechanism functioning properly. In the five months I've been using this wallet, I've also included incremental updates based on the feedback I was getting from people who were intrigued by my wallet.

CAD Exploded View

Early Design

I first had the idea for my wallet in early May. I had gone on the 3D printing community website Thingiverse to download a wallet to print myself, as my actual wallet had recently broken, but all of the options each had glaring flaws. I saw this as an opportunity to create something better than the existing solutions.

The design constraint that I aimed for was a single motion to both unlock the cards and push them up and out of the body of the wallet. Also, I wanted the wallet to shut itself when the user let go of the mechanism, thus locking the cards inside the wallet and preventing them from falling out. With this in mine, I began to design a spring loaded mechanism.

The primitive first version of the wallet

This portion of the design process took the longest, with version 11 being the first functioning wallet with a spring mechanism to close itself. The main lesson I learned from this was that the spring needed to be within a set range of strength in order for the wallet to close properly. It seems counter-intuitive, as at first thought one might think that the spring should be as strong as possible, but in reality the spring needs to close the latch slow enough for the cards to be brought into the wallet by gravity. If the latch snaps back too quickly, it collides with the cards and loses its momentum require to snap shut.

This also notes on the other design constraint of the wallet. As I mentioned above, I designed an arm that extended out from the arm that pushes up the cards. This secondary arm provides a roof of the wallet that keeps the cards from falling out. These two arms were initially connected as one piece, which can be seen in the following video, but I eventually separated them into two pieces.

Version 11: the first successful spring loaded arm mechanism

A few of the past iterations of the wallet

The reason that I split the arm into two pieces is mainly due to ergonomics. With the old design, the arm that provided the roof of the wallet would contact the hand of the user when the wallet was opened, and also prevented the user from opening the wallet with one hand. Thus, I split the arm into two, which allowed for the supporting arm to only move out slightly, while the arm pushing the cards up could rotate the full 90°.

In order to split the arm in two but still retain all the functionality of the wallet, I needed to design an interfacing mechanism between the two arms. I achieved this by adding extrusions to each arm and slots in the corresponding location on the other arm. When the wallet was pushed open, the arm pushing the cards pushes the roof arm out slightly before the roof arm hits the wallet body. Then, the card arm continues to move while it pushes over the extrusion of the roof arm. Once the user releases the mechanism, the card arm rotates quickly back to its original position, colliding and locking in the roof arm as it does so.

The updated arm mechanism

Not much has changed in the design of the wallet in recent months as I completed v23 in May and am currently on v26. One major change that has been added is a money clip on the back of the wallet, as many people I talked to said that that was necessary for them in a wallet. I have also added bluetooth tracking of the wallet though a concealed TILE tracking device that I embedded during the 3D print of the frame.

An additional feature that I added was a tile bluetooth tracker embedded during the print for concealed tracking if my wallet were to be lost. (Plan is to change this out with an apple tracker once released)

For anyone more interested in the iteration of the wallet design, I have included my notes that I kept since I began this project:

For wallet v2:

Need to shorten arm to make it able to turn

Need to rework the threads to make them fit together

Need to move button inward on the wallet body for strength

Make tabs in the button holder of wallet bigger as they are too small of teeth to grip the button

Make the arm thinner as it’s hard to turn

Increase the size of the hole in the button for the spring

For wallet v3:

Make circle on back of arm smaller to fit in hole

Make button smaller to fit in arm and body

Make walls thicker for strength

Put fillet on exterior of button sheath for strength

For wallet v6:

possibly make the threads larger

For wallet v7:

Included tolerance in the back circular cutout of base

Wallet v11 is first working version

For v15

Make tab holding cards at top a little longer

Make arm offset so back card can’t fall out

Make hole for cards bigger

For v17

Make gap on side of body smaller so cards cant slip out side

Make cut on top of hole wider so the overhang of the arm can be larger

Make the extrude on back of wallet reach further down to keep cards pushed forward

Lesson:

It’s all about the balance of the spring being strong enough to keep it shut but not strong enough that the arm shuts faster then the cards can fall

V18 is first version of finished design

V19 is the beginning of the testing of a arm that doesn’t slide out all the way

Another key aspect: ease of assembly/disassembly

Need to make back part of arm have smaller hole as the tolerance is too large

Wallet print on 7/27/19 18% overhang form supports

Make button not able to go so far out for next version