7.1 Project Proposal for Dice Rolling Robot

Introduction

Shaking and throwing dice is an integral part of many board and casino games, and the act of rolling them is a behavior that can be modeled by an intermittent motion linkage. Dice rolling, in general, is a simple task when performed by a human but requires somewhat complex motion to properly execute. Translating this to a linkage system poses an interesting problem on how to make a robot that can shake and throw dice easily. An issue in some dice rolling games is shaking the dice and releasing it with enough force to get a random result, without throwing the dice elsewhere and voiding the result. Although it is not possible to cheat a dice roll, there is a need for a mechanism that can consistently shake and throw dice in a controlled manner.

Description of Problem

Rolling a single dice is easy, but it becomes difficult to shake and release multiple dice at the same time. When multiple (3+) dice rolls are required, players in casino and card games must choose between rolling each dice individually and rolling all dice at the same time. Individual rolls guarantee usable results but are cumbersome and time-consuming. Combined rolls save time, but the dice may be shaken and released with too much force, sending them away from their desired destination. These lost dice often demand a reroll, costing even more time. A dice-rolling mechanism aims to shake and release dice in a controllable way, so they’re properly shaken and always arrive at their desired destination. 

Desired Mechanism

This motion will consist of an intermittent shaking phase, and a throw/release phase to display the result. The challenge involved is combining both of these motions in one rotation cycle of the input. For this, we have narrowed our mechanism choice to be a crank-rocker mechanism, a slip gear, or a snail cam and follower. All mechanisms should give the rocking motion needed to shake the dice, but the slip gear will allow for more punctuated intermittent motion, while the crank-rocker would be more fluid. The throwing and result part of the motion is slightly tougher to implement. With the slip gear system, there can be a region of longer engagement that ‘drops’ the dice after the initial shaking. The crank and rocker would need an external component to drop the dice, since the motion cannot change during traversal. The snail cam and follower could shake the dice with the profile of the cam, and then drop the dice as the profile returns to the beginning.

Proposed Scope

A dice-rolling mechanism must (1) shake a chamber holding the dice with enough force to guarantee randomization and (2) release the dice onto the same destination every time. Our final design will at minimum complete both tasks. Before fabrication we aim to test the intermittent gear connection to see if it can shake the platform at high pace. We also must decide how the dice are released and if they’re released at a set time or “on-demand” by the user. The power source is one last consideration. While a motor would be simpler to use, a hand-crank is more practical for players since it doesn’t require an electricity source. 

Our initial design will accommodate 3-4 dice, but an additional challenge could be to accommodate an extreme amount of dice (10+). The shaking mechanism will stay the same, but a more specialized release mechanism is required to ensure the dice scatter evenly.  

Another direction to extend this design would be to repurpose the intermittent gear mechanism to other shaking tasks. This could include mixing a drink or stirring ingredients together for a dish. 

Preliminary Design Ideas

1. Cam and Follower

We know that we need to incorporate multiple shaking motions and then tossing the dice within a single revolution, so we thought of a cam and follower mechanism where the cam is custom made to have bumps (to cause the multiple shaking motions) before having a steep drop (tossing of the dice). When the follower drops after completing one revolution of the cam, the right side of the box containing the die will hit a ledge, tipping it to the left and causing the dice to tumble out. Then the box will return to an upright position as the revolution continues thanks to the spring shown in the diagram.

Degrees of freedom:

2. Intermittent Gear Motion

We considered an alternative design using a gear with a specific pattern of teeth and gaps to achieve the desired output motion. For three-quarters of its circumference, the gear features alternating sections of teeth and no teeth. As the toothed sections engage with a smaller gear to the left, the smaller gear rotates, pulling down one side of a platform above it. The other side remains grounded, creating a rotational motion.  

An elastic band, anchored above the platform, is attached to the side being pulled down. When the input gear reaches a gap with no teeth, the elastic band snaps the platform back up, producing a rocking motion to shuffle the dice. In the final quarter of the input gear’s rotation, all teeth are present, pulling the platform down far enough to launch the dice.  

As this design has 6 links, 6 full joints, and 1 half joint, it has a total of 2 DoF.