CMU Mechatronics Spring 2011: Team H

This project was developed at Carnegie Mellon University as part of the Mechatronic Design (18578/24778) course.

Gambit - The name of our device

Main Design Concept

Connect Four is a two player game, in which each player chooses chips of different colours, and takes turns to then drop the chips from the top into a 6 row, 7 column grid. The chips fall straight down, occupying the next available space in the grid. The objective of the game is to arrange 4 chips of the same colour in a line - either horizontally, vertically or diagonally on the grid. Each player gets 21 chips.

Variations of the game

Pop Out starts the same as traditional gameplay, with an empty board and players alternating turns placing their own colored discs into the board. During each turn, a player can either add another chip from the top or — if one has any chips of his or her own color on the bottom row — remove (or "pop out") a chip of one's own color from the bottom. Popping a chip out from the bottom drops every disc above it down one space, changing their alignment with the rest of the board changing the possibilities for a connection. The first player to connect four of their chips horizontally, vertically, or diagonally wins the game.

We fabricated a mechatronic device to play the game against another device/human. The device is capable of thinking on its own using the game algorithm that is implemented in it, and intelligently drop chips into the desired column with the help of mechanical systems.

The device is also capable of playing the pop-out variant of the game. More of this game playing ability can be seen under System Overview and Subsystems >> Pop-out Mechanism.

Simple CAD model

System Overview

The design consists of five subsystems:
1. The chip sorter
2. The chip feeder
3. The chip dropper
4. The linear carriage
5. The Pop-out Mechanism

The complete system

The chips are initially dumped into a hopper, from where they get stacked into the vertical tube as shown. The disc then rotates and drops a single chip into the chip dropper. The explanation of its working can be found under subsystems >> chip feeder.
Once a single chip is present in the chip dropper, the linear carriage to which it is attached, moves with the help of a belt - pulley system. Once the desired position along the game board is reached, the chip is dropped from top, and into the column.
The device is also capable of playing the Pop-out variant of the game. A slider-crank mechanism attached to the bottom of the carriage 'pops' chips out of the last row when the pop-out variant of the game is being played. The slider, of the slider-crank mechanism pops the chips out of the last row.

Subsystems:
The device consists of the following subsystems:
1. The chip sorter
2. The chip feeder
3. The chip dropper
4. The linear carriage
5. The Pop-out Mechanism

Working of the Chip Sorter

At the beginning of the game, the chips are dumped into the hopper.

Chip Sorter

The hopper is a cylindrical, acrylic tube as shown above in the figure. A hole in the acrylic plate below (see figure), deposits the chips into the vertical tube. A blade, driven by a motor, tosses the chips about, which eventually fall into the vertical tube.

Working of the Chip Feeder

Once the chips are stacked in the vertical tube, the chip feeder helps in depositing the chips into the chip dropper.

The Chip Feeder

The chip feeder consists of a circular, acrylic plate and a rectangular, acrylic plate (see figure). The circular plate is rotated by a servo motor. This plate has a hole (HOLE 1 in the figure above) whose diameter is slightly bigger than the diameter of the chip. The rectangular plate also has a hole (HOLE 2 in the figure above) cut in it - diametrically opposite the tube. As the circular plate rotates, one chip falls from the tube and into the hole cut in it. The gap between the tube and the circular plate is approximately one half of the chip thickness. This vertical positioning of the tube prevents the other stacked chips from rotating along with first chip. Hence only one chip falls into the hole at a time. Once the plate rotates by 180 degrees, the hole in the circular plate is above the hole in the rectangular plate and the chip falls into the chip dropper.

The sequence of this operation can be seen in the figures below.

(a) Chip falling from tube into HOLE 1

(b) Chip being carried

Working of the Chip Dropper

The chip dropper is a box-like structure made of acrylic. The two main functions of the chip dropper are to act as a buffer for the chip, and finally drop the chip into the required column as the carriage moves along the game board.

Chip Dropper

The black acrylic plate has a rectangular cutout, through which the chips fall from the chip feeder. The chip dropper has an aluminum sheet that helps in orienting the chips in the vertical position. A stopper, operated by a servo motor prevents the chips from falling down and rotates by 90 degrees when the chip has to be dropped into the required column. The figure above shows the stopper preventing the chip from falling through.

Movement of the Linear Carriage

A stepper motor is used to drive the carriage. The motion of the stepper motor is transmitted to the linear carriage with the help of a belt and pulley mechanism. The belt is attached to the acrylic mounts (see Figure 2), which are in turn attached to the carriage with the help of screws. The acrylic mounts have two circular holes. Steel guide bars pass through these holes, and help in keeping the carriage in an upright position.

Figure 1. The Belt-Pulley Mechanism

Figure 2. Acrylic mounts and linear bearings

We have inserted linear bearings (see Figure 2) in between the mounts and the guide bars. This reduces the friction by a large amount, and hence increases the speed of the carriage, ensuring that a move is completed well within 20 seconds. The steel guide bars are lubricated to further reduce the friction.

The stepper is calibrated to ensure that the the carriage stops at the desired column while the game is being played.

The Pop-Out Mechanism

The Pop-Out mechanism was incorporated into our device as our coolness factor. The coolness factor is what helps in distinguishing one team from the other.
The Pop-Out variant of Connect Four enables a player to pop chips of his/her/(its) own colour only, from the last row of the grid. This causes the chips above to fall down one position, changing the alignment with the rest of the board and hence changing the possibilities of a connection.

The Pop-Out Mechanism

The Pop-Out mechanism is a simple slider-crank mechanism. It is attached to the underside of the carriage and is level with the last row of the game board. A servo motor screwed onto the carriage drives a crank. The crank drives a connecting rod, which finally causes the slider to move in a straight line. The slider pops the chips out of the last row.