mechanical

Overview

Given the high level of actuation produced by our PAL, a robust mechanical design was key to success. Our cat's body and arms were constructed primarily of 3/16" Duron with press-fit puzzle pieces cut into the parts so that assembly can be done with minimal use of fasteners and adhesives. We chose this mode of design in order to make it easier to open up the body and modify the electronics within. In doing so, we were able to make last-moment fixes and changes and easily access parts that needed to be refilled (such as the chocolate dispenser).

Model Assembly of Body and Arms

Model of Head

Mr. Resis-kers Fully Assembled

Body

Our PALs body was designed to be relatively compact and proportionally reflect a natural position of a sitting cat. This design choice required us to be smart with space usage, as the body is used to store our electronics board, all wiring, and the dispensing system. Duron (3/16") was used as the material of choice due to its material strength, ease of manufacturability, and low cost. To make up for Duron's lackluster appearance, the cat is covered in white fur. This allowed us to cut more slots into the body than absolutely needed since unused slots were easily covered in fur during final assembly. Our electronics board is mounted vertically along the side walls of the body. While vertical mounting makes modifications to the circuit more challenging, we were able to easily access the board by removing the upper back panel, whose puzzle piece cuts were toleranced to be less of a press fit.

Front View

Back View

The front panel of the body hosted our progress and status LEDs, which were press-fit into place and secured using glue. Additionally, the candy dispensing slot was designed to line up perfectly with the vertical position of the dispensing system inside so that candy would not become stuck. On the back of the body, the tail servo is mounted towards the bottom. The tail itself is composed of two 3D-printed pieces connected to the servo arm that act as a clamp on the tail. The tail itself is composed of 0.4" OD tubing covered in fur, with metal pieces placed selectively within the tube to increase rigidity.

Front Panel

Model of Tail Clamp

Fully Assembled Tail

Head

As our largest 3D printed part by far, the head hosts some of our most important electronics while adding personality to Mr. Resis-kers. The two square slots in the head contain our eyes, which are two 8x8 LED dot matrix displays. The head also has a built-in mouth slot with an IR emitter and receiver embedded within to check if food has been deposited into the mouth. Finally, two red LEDs are embedded next to the mouth to serve as an indicator to the user that the cat wishes to be fed. Since accessing fasteners within the head would be difficult to do, most electronic components are fixed in place using glue.

A close up of Mr. Resis-kers face

The mess of wires and glue within...

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He's watching.

Arms

In addition to making our PAL look more realistic, both of the cat's arms serve important roles in the context of our project's functionality. The left arm serves as our timer, with the cat's "hand" being an hourglass that is rotated by a servo to start the game. The left arm is fully rigid, and fixed to the left side of the body using M3 fasteners.

On the other hand, the construction of the right arm is substantially more complex. The right arm is a two-bar linkage supported by a bearing to create an oval path of motion with the bottom of the path being fairly flat to mimic a petting motion. The linkage is powered by a DC motor operating at a constant speed. The right arm is rather large, with most of the linkage fully encased to prevent the user's hand from getting caught during the arm's motion. Located beneath the arm is a hand-sized slot with an IR emitter-receiver combo embedded inside to detect the placement of the user's hand in front of it.

Dispenser

Our PAL's dispensing system serves as the reward after a challenging journey, encouraging users to make Mr. Resis-kers happy so that they themselves can receive a reward at the end. The dispenser is hidden, located within the body, and only being activated when nirvana is achieved. The dispenser puts out wrapped Ferrero Rocher chocolates using a rack-and-pinion system powered by a servo. The rack-and-pinion system is able to achieve 1.5" of linear actuation, which is just over the diameter of a typical chocolate. The rack is designed with an extended flat top at the tip so that the next chocolate in the storage stack falls onto it and is put in place as the rack retracts. This system is able to store 5 chocolate at a time, meaning that it needs to be refilled after every 5 times nirvana is achieved. Given that during the showcase nirvana was achieved roughly every 1 in 10 attempts, refilling occurs fairly infrequently.

Front View

Back View

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