Part I - The Hardware

Defining Features

The intention was, in the first place, to have an arcade machine that uses several trackers as input method. In the first brainstorming session it was to decide whether to buy an existing one and extend it or to build an own one from scratch. The decision fell on the latter as it provided more freedom to design the arcade exactly for our purposes.

Furthermore we defined the desired features of the to-be-build cabinet. Besides an eye tracker other I/O devices should be included, such as a Kinect, an audio system, a touch screen as well as the classic game controls like buttons and joystick. The whole impression should have the look and feel of a classic arcade shell from the 80s. Besides that, the dashboard with the controls should be convertible so that other controls can be easily implemented.

The intention was to put the arcade into a public place as a pub or the foyer of the department. To adapt to persons of different sizes, the eye tracker has to be tiltable so that the eyes of the person can be properly tracked.

Choosing Material

Being put in a public place required the machine to be sturdy. We decided to construct a frame that carries the weight using Bosch Rexroth aluminium profiles with a cross sectional area of 45 millimetres. The outer material was chosen to be out of robust polypropylene laminate birch plywood with a thickness of 18 millimetres and to be attached to the Rexroth profile whereby the panels become easily exchangeable.

The inner frame

To have a reliable list of which things to order in which size or length, the whole machine was then designed with Autodesk Inventor. The program provides a frame creation feature with which the exact length of every frame part can be adjusted and put down on a list that can be used to order the frame parts from a supplier who also cuts it to the exact length. It has to be taken into consideration that there is a minimum length (which probably depends on the supplier) of 100mm in our case. To make the frame torsion-resistant more horizontal bars were inserted at the back (between bottom and top).

To make construction easy, most of the parts are orientated 90 degrees to each other, but this could of course not be applied to the screen front and the control dashboard. We chose a 75 degree angle for the screen front and and angle of 15 degrees towards the horizontalfor the control dashbord which is at a height of 1m. The exact values can be obtained from the construction drawings provided later in this document.

At all corners where three profiles met we chose 3-way cubic connectors for connection, all parts that are situated 90 degrees to each other are connected with either 90 degree brackets or double 45 degree connectors for the Rexroth profile.
We positioned two "feet" at the bottom front of the cabinet, which can be both used by the player for a comfortable stance or for future projects to be equipped with more sensors to track e.g. running, steps or similar actions.

The 3D model of the Rexroth profile can be downloaded via GrabCad and has to be imported into the Inventor Content Library. The final frame can be downloaded here. After making all the fine adjustments we came up with the following order list:

Aluminium Profiles

 ----------------

Quantity    Length  Purpose
-----------------------------------
24            100   45 degree connectors
4             110   feet
2            1760   back side
8             237   feet
4             458   horizontal side bars bottom 
4             510   horizontal side bars top
2             535   bars for the control dashboard
13            660   horizontal bars front and back
2             690   vertical bars bottom
2             735   vertical bars top
4             740   horizontal side bars middle part
1             750   horizontal front bar bottom
2             870   bars for the screen


Connection Elements
 -----------------
Quantity    Item                                    Comment
 -----------------

20          45x45 3 Way Cubic Connector
12          Tilting Bracket 10 to 10 Slot           bars for control and screen panels
22          45x45 Bracket with Fittings
2           M12x30 T50 Core Screw (10pk)
1           Inner Bracket with Fixings (10pk)       for attaching the feet
32          45x45 (45 degree) Connector & Fittings  
2           System Hinge 30, Nut 6 Slot 6,          for attaching the eye tracker
            with Adjustable Friction   

Designing the Wooden Shell

To achieve the look and feel of an 80s arcade cabinet we got inspiration from the original PacMan Arcade Cabinet. All parts were designed with Inventor to cover the aluminium shell completely which was important for ordering the correct amount of plywood. We decided to have green plywood for the inner parts and yellow plywood for the side walls. The sheets were available in the sizes of 3050 x 1535 mm and 1220 x 2440 mm. To make the interior easily accessible for maintenance work plans included a door inside the back panel.

Here's the list of all wooden parts:

A Top          600x750mm 1x

B Bottom Front 750x735mm 1x

C Foot Front   218x190mm 2x

D Top Bottom   750x196mm 1x

E Top Front    750x226mm 1x

F Front Dashbo 750x229mm 1x

G Keyboa Front 750x265mm 1x

H Bottom Dashb 750x264mm 1x

J Back         1868x750mm 1x

K Door         1550x550mm 1x inside J

L MonitorFront 750x693mm 1x

M Foot Top     218x300mm 2x

N Foot Side    282x190mm 2x

Being arranged like in the drawing above, it is is easily appreciable what amount has to be ordered. In our case one sheet of 3050 x 1535 mm was sufficient for the inner parts. There were two sheets of 1220 x 2440mm ordered for the two side panels which clippings were planned to be used as shelves for the interior.

 

Finding the Right Button Layout

Originally we wanted to use half the Standard Japanese Arcade Layout (so the first row only) but after testing this against some other button layouts with some simple cardboard prototypes we found a layout which was preferred by most people that walked through our office.

Finding the Right Hardware

• Arcade Controls: There are several arcade kits available on amazon and ebay in all colors and shapes. We decided for the red ball-top joystick with a long handle and buttons in yellow and red.
• Screen: Iiyama offers a frameless water and scratch resistant touchscreen that is specificially designed for being built into kiosks or other public appliances. We also decided for it because its measurements: it is 46mm deep so it fits perfectly between two profiles and the width of 517mm fits in the available width which is the width of the machine (750mm) minus the width of four Rexroth profiles (one vertical, one tilted, for each side: 180mm).
• Eye Tracker: As we already had good experience with the Tobii EyeX tracker, we decided to continue using it. To make it adjustable to different heights we decided to fixate it on a metal bar, that is attached to the monitor front with two friction hinges.
• Foot Tracker: Microsoft Kinect
• Hand Tracker: Asus Xtion Pro
• Audio Output: The intention was to build the speakers into the screen panel above the screen so simple car speakers that can be screwed into the panel seemed to be the solution. We decided two Pioneer TS-G1031i 10cm Dual Cone Speakers (190W) powered by a Cougar C300.2 2-Channel MOSFET Car Amplifier (800W) would do the job.
• Gaming PC: As there have three trackers to be controlled besides executing the games we had a PC custom-built with up to date hardware to ensure fluent graphics and minimal delay. The specs:
• Intel I7 4790 Haswell ( NOT K ) Quad Core 3.60GHz Turbo Core 4.00GHz CPU Processor
• Corsair 16GB DDR3 Vengeance 2400mhz Pro ( 2 x 8GB Sticks ) ( CMY16GX3M2A2400 )
• Gigabyte Z97M-DS3H Socket 1055 Motherboard
• GTX 970 4gb GDDR5 Nvidia Geforce Video Graphics Card
• Corsair CX600 BRONZE Series 80 Plus Bronze Certified 600W Power Supply Unit

 

Assembling the Frame

For assembling the frame the following tools are necessary:

• 13mm hex socket for connectors
• T50 Torx bit with long shaft for core screws
• electric drill
• hex wrench 6mm for tilting brackets or hex bit for drill
• rachet screwdriver
• jigsaw with metal saw blade
• file

 

Putting the frame together was pretty straightforward for the perpendicular parts. We had to improvise at the front bottom part where four bars come together. We drilled a hole through the middle of the profile that was big enough for the T50 torx bit to fit through so that a core screw could be drilled upwards into the vertical bar. 

The two bars for the control panel had to be beveled in the right angles (15 and 75 degrees) to fit between the two other bars. This was done using a jigsaw with a metal saw blade and a file.

The screen is mounted to two bars which are fixet with two 90 degree brackets to two vertical bars. The first approach was to mount the screen directly onto the bars and to only saw out a rectangle the size of the visible part of the screen. As this would make tapping on the edges of the screen more difficult it was later decided to position the screen in a way so that the screen surface is coplanar to the screen panel. To achieve this, the screen was mounted on a piece of plywood which was then bolted to the two bars that were intended to carry the screen in the first place.

 

Crafting the Wooden Shell Parts

Tools used for this step:

• circular saw
• jigsaw with wood saw blade
• sander with sandpaper sheets of granularity 60
• router with fitting cutters for straight and rounded edges
• file
• vaccum cleaner
• hammer and chisel

After we've been delivered the three (huge) plywood sheets, we started sawing out the different parts with a jigsaw. After the first part we realized that this is desastrously inaccurate and results in unsightly uneven edges and that this has to be done with a circular saw. Gladfully some people from the Engineering School were very helpful and crafted all rectanglar parts for us after we gave them the plans.

We still had to do the side walls which was easier as the did not have to fit into other parts but just closed the shell from both sides. To stick to the planned outline the drawings were plotted 1:1 on three A0 sheets which were then cut out and sticked to each other so the outline could be drawn on the plywood. After cutting out the walls the round parts were straightened with a sander and the straight parts were straightened with a wood shaper.

To achieve a straight edge another wooden board with a clean edge was put on top parallell to the to-be-straightened edge and thereby used as a ruler for the shaper. This resulted in a pretty nice and straight edge. Short parts and parts that could not be reached by the router were processed with hammer and chisel. This practice was used on all other straight parts that had to be adjusted.

Important:

It is essential that a running vacuum cleaner has to be connected to the extraction nozzle of the shaper at all times (!). Friction causes the parts to get very hot and can cause sawdust to be inflamed very easily. Always have a fire extinguisher within reach. Also make sure that the machine stopped rotating before you remove it or put it into location. After you put it in the right position make sure to slightly increase the distance from the router bit to the edge so that it does not touch it during the start-up phase. The machine is unpredictable at low rotation speed and can not only screw up your whole workpiece but become a danger to your health.

Preparing the Control Panel

Items required:

• arcade joystick and buttons
• 6mm drill
• four M6 screws, washers and nuts
• shaper
• jigsaw with wood blade

For sawing out the holes for the arcade buttons we used a 28mm holesaw with a vertical drill. Keep in mind to drill shortly and then pull the holesaw up again to let the sawdust out. It's the same problem like with the shaper, if you saw constantly parts become to hot and there's the danger of inflammation.

The hole for the joystick has to fit very tight. To achieve this there were four holes drilled at the corners of a (see drawing)mm rectangle big enough in diameter so that the jigsaw blade fits in. Then the hole was extended more and more until the joystick fit in.

As the thickness of the plywood is higher than the thickness of the middle (blue) part of the joystick. A layer of 8mm was removed at the back side of the control panel to make space for the connectors and the nuts. 

Finally the holes for the four screws were drilled with the vertical drill and the joystick was fixated using four M6 screws in combination with washers and nuts.

The more difficult part was to bevel the long edges of the control panel, as they required to have 60 and 75 degree angles in order to flush with the front and monitor panels. As our equipment lacked the right router bits this was achieved by removing 10mm with the straight router cutter and bevelling the remaining 8mm with hammer and chisel. The results were.. adequate. 

Preparing the Monitor Front

The same applies for the monitor front which requires a 60 degree angle at the bottom edge. The hole for the screen was sawed out with a jigsaw and edges were straightened with the above mentioned method using the router. As I already mentioned plans had changed to sawing out the full screen area from the monitor front, space was no more sufficient to mount the speakers. 

Preparing the Top Front

Those were positioned in the top front panel according to the instructions supplied. Holes with a diameter of 106mm were cut out with the jigsaw and bumps were straightened with the router. The holes don't have to be too accurate as they will be covered by the speaker frames. 

Preparing the Door

Items used:

• 3x Forge 75mm Butt Hinges
• 18x 5mm Countersunk Bolts with nuts and washers
• Combination Door Bolt
• 10 x 8 x 21mm thick N42 Neodymium Magnet
• drill with holesaw
• router with straight routing bit

The door was cut out using a jigsaw. To have the edges as straight as possible there were small "control holes" with a diameter of 2mm drilled in alongside the outline of the door. Starting from the four corner points where the jigsaw blade was inserted and cutting from one "control hole" to the next the result was pretty good. The edges were straightened with the sander and a hole was sewed out using a holesaw in order to have something to grab into when opening the door.

After that the door was attached to the frame with three 3-hole butt hinges using 18 M5 bolts countered with nuts and washers from the other side. Finally the door lock was attached as we don't want our equipment to be stolen.

Preparing the Tilting Element for the Eye Tracker

Items used:

• metal saw
• file
• drill
• metal drill bits 6 and 2mm
• friction hinges
• 4 M6 screws with nuts
• 2 M2 screws
• aluminium plate (width: 8cm)

First a strip of 32cm was cut off the aluminium stripe using the metal saw. The size of the piece can be random but it has to be big enough that both the drill holes for the connection to the hinges and to the eye tracker can fit on it and that is is bigger in width and height than the eye tracker itself. Thus users don't have to grab on to the eye tracker itself to change the tilt of it and maybe damage it.

Holes of 6mm diameter were drilled for the hinges using the vertical drill. Gladfully the tracker has two little threads at its backside that can be used to fix it to the metal. As the eye tracker cannot be positioned above the nuts of the hinge-screws the 2mm holes have to be drilled slightly below it. Due to the small size of the screws it is important to measure the distance of the holes very carefully. It is also possible to screw in the bolts at the back of the tracker, color their tips with a felt tip and "stamp" them onto the metal strip. For both the hinge- and the tracker-holes first draw lines parallel to the long edges onto the metal to make sure everything is at the same height.

Assembling and Wiring the Arcade

After constructing the frame and preparing all wooden parts it is now time to put them all together.

Attaching the Wooden Parts to the Frame

Items used:

• many M8 coutersunk screws with a length of 35mm
• as many M8 T-Nuts for Rexroth 10mm profile
• 8mm wood drill bit
• ruler
• drill with 6mm hex bit (fits the screws)
• 2x Round white flush fitting plastic air vent with insect mosquito net fitting the size of the
• 2x NON-PWM computer case fans

Depending on their position all parts were equipped with drill holes either at 22,5mm or - when they had to cover another edge - 22,5+18mm = 40,5mm distance from their edges. All holes were then pre-shaped with a countersink. Of course some of the parts didn't match exactly especially when they had to fit within other parts. This was taken care of by shortening e.g. the bottom front part using the router with a straight router bit until it fit in. All bolts of a part were inserted in its drillholes and the T-Nuts were screwed on the tips of the bolts. The part was then put into place and the T-Nuts inserted into the profile of the frame. The bolts were then tightened using the drill. It is important to make sure that the T-Nuts have turned by 90 degrees inside the profile so that the bolts can pull the board against the frame. If they don't turn they just eventually are trenched into the wood which is not of purpose.

Before putting in the inner bottom shelve and the top "roof" there were 120mm holes cut out for the fans which will ensure a constant airstream from bottom to top. After that the fans were screwed over them on to the board and the air vents were put into the orifices to prevent foreign objects from entering the inside. We intended to use Arctic F12 PWM 4 Pin 120mm fans which turned out to be a bad decision. Read about that in the next section.

Wiring the Audio and Cooling System

Items used:

• a computer power supply
• Cougar C300.2 2-Channel MOSFET Car Amplifier 800W
• wire
• wood screws to fixate the items against the shelve
• 70cm 4 Pin Molex Plug to Socket Extension Fan Cable
• Fan Splitter Cable for 2 Fans
• luster terminals
• external sound card USB stick
• punched and coated metal tape

The fan and the amplifier were both connected to a 12V power outlet of the power supply. There are many ways to do this but it has to be made sure that there are no blank wires open or loose. To achieve this use luster connectors, build your own plugs (most ideally) or use shrink hoses. The 12V outlet is normally a yellow (+) and a black (-) wire leading to a molex plug but use a multimeter to be absolutely sure.

The four molex pins:
yellow-black: +12V, red-black +5V,
yellow-red: +7V;
Source: http://www.everydayguide.com

Connect the minus pole to the "GND" labelled terminal and the plus pole to the "+12V" lerminal of the last one. To turn on the amplifier make a short wire bridge from the "+12V" to the "REM" terminal. In a car this is normally used to turn on the amp only when the engine is running but in our case we want it to be always on and therefore we just connect it to our plus pole.

A 4-pin fan connector:
black: ground, red: 12V,
yellow or white: speed control,
blue: PWM
Source: futureshop.ca

Connecting the fan basically works the same way if you use non PWM regulated fans. The latter use a pulsated control voltage according to which they regulate their rotation speed (Wikipedia entry). If you have spare ports on your mainboard use them and simply make or buy a 4-pin extension cord that is long enough and connect it to the fan.
If you want to use a PWM fan using an external power source you're going to have a bad time and be better off using a simple fan with a 3-pin connector.

The PC was stored lying on its side on a layer of foam. As the fan is situaded below it an "air channel" was sawed out of the material.  When it was first connected to the amplifier sound quality was terrible. As the internal audio output was poorly shielded from the other components every action of e.g. the graphics card was audible through the speakers. For this purpose we bought an external USB soundcard and connected it with an USB extension cord as far away from the PC as possible (see photo).