given the problem statement, we outlined two categories of design requirements.

USER-CENTRIC
- prevent shaking of pills with movement
- secure pill dispensing (no pills on the floor!)
- tactile or audible feedback
- pill tracking
- easy to slip in and out of pockets
- type of pill dispensed indicator

HARDWARE
- dispense a single pill at a time
- pocketable form factor (ideally lwh 4x2x1 in)
- reminders - vibrate, chime, light
- quantity of pills - store up to 7 days, 5 types, 35 total
- weight - 8oz maxmimum

we seek to design:
a pocketable, lightweight device that can store up to (7) 0-size capsules and dispenses (1) pill at a time. the dispensing mechanism uses a physical mechanism, not a motor, and has a button unlock feature to secure the device when pocketed. the device has small electronics that provide intake reminders to users and an indication light that indicates the remaining supply of pills.

given this statement, we narrowed our search down to three different mechanisms.

with the variants in mind, we began diverse sketching and exploration of form factors and mechanisms. ultimately, we decided on the self-inking stamp mechanism to be driven by a rack and pinion, with a cartridge and form factor closer to the candy dispenser (tall, rather than wide).

using an iterative design process assisted by FDM 3D printing, we designed five prototypes.

prototype 1 focused on the sizing of the chamber and barrel for a 0-size capsule.

prototype 2 focused on the minimum size of the total housing required and how parts should be printed to allow for snug, press-fit assembly.

prototype 3 focused on a spring-loaded rack and pinion mechanism to turn the barrel inside.

prototype 4 experimented with a more pocketable form, as well as side locking buttons for the rack and pinion mechanism.

the final prototype added structural guides for the "pusher" of the mechanism, which double as the mechanism for the locking buttons, now moved to the front and back. the side buttons now serve as the locking mechanism for the cap, which has a refill door.

our design totals 9 manufactured parts with two off-the-shelf springs to be placed on opposite stilts (only one is rendered above).

a finite element analysis was performed using ABAQUS. using a measured displacement of 0.935 in in SolidWorks, combined with McMaster-Carr's manufacturer spring rate (k) of 3.3 lbs/in, we calculated a load of 3.0855 lbs.

the analysis assumes a freeform part composed of an isotropic PLA-like plastic with Young's modulus (E) of 595669 psi and a Poisson's ratio (ν) of 0.38.

the part experiences highest stresses at the base of the stilts and the the face opposite the rack. in usage, these stresses are acceptable, as the stilts are guided by the enclosing shell, which forces only linear up and down movement.

a tolerance stackup was performed in SolidWorks, with the barrel slot length (the length of a 0-size capsule) being the driving dimension, and parts ordered from barrel to outer shell. overall, the tolerance analyst showed very tight overall tolerances.

nominal value
0.9 in

minimum value
0.89 in
maximum value
0.91 in

RSS minimum
0.893 in
RSS maximum
0.907 in