Designing a miniature Skee-Ball machine that anyone can play
Individual Project, 3 weeks
Key Skills
3D Modeling in Fusion 360
Laser Cutting
Experimentation and Iteration
This is the fourth project in my DIY Design & Fabrication class at Carnegie Mellon University. Unlike the previous projects, this task was open-ended in subject matter and material choice, as long as it could fit on a table for demonstration. I chose to make a miniature Skee-Ball machine because I wanted to construct something that was recognizable and fun to use. Over the course of this semester, I met Ryan Bates, a fabrication instructor at Carnegie Mellon University and owner of RetroBuiltGames, where he develops DIY kits complete with the software and electronics to replicate arcade machines. He has a claw machine, pictured below, that fits on his desk, and this inspired me to make something else in this area to bring the arcade into a home setting. Additional design and fabrication inspiration is shown below.
Design and fabrication inspiration, including Bates' "Super Claw" on the bottom row and arcade kit on the top right
I started by sketching the individual pieces and modeling them in Fusion 360, with the intent to make a cardboard prototype to see how the ramp would have to be aligned once it was curved. I used duct tape to try out various alignments, which was faster than modeling the ramp on the computer and trying to get the bend to match the specific dimensions.
Fusion 360 model for cardboard prototype
The final material needed to be sturdier, so I decided to laser cut the pieces and fit them together. I revised the CAD model to have slots on the edge of each piece so that they would interlock in a specific orientation. I sent the parts to the laser cutter and used 1/8" plywood as the main material, as it is cheap, effective, and easy to cut and engrave. The ramp material and the return board behind it are made of a thin but sturdy cardboard. It is flexible enough to bend once pressed between a table and a ruler, yet sturdy enough to resist wrinkling unless the bend is too aggressive.
Updating the CAD model with interlocking edges; laser cutting and assembling the outer walls and ramp dividers
The most difficult part ended up being the alignment of the ramp and the return board behind it. The placement of these two parts determines whether the game will be enjoyable or impossible to win given the dimensions of the surrounding pieces. I had to prop the parts up with duct tape, place the point board, back wall, and top plate, and test the alignment to make sure that there was sufficient slope such that the ball would roll down from each hole back to the starting point. As the second picture below shows, I added flaps to the top of the ramp to cover the first barricade, which can only be seen in the third picture. Originally, I envisioned the bottom of the point board being flush with the top of the ramp, but I could not find a combination of part layouts, incline angles, and bend amounts that worked. As a result, it was too difficult to launch the ball up the ramp without hitting this larger barricade. If the angle of the point board were lowered, then the top of the board would hit the back wall. I ended up making the ramp and its flaps as one piece on the laser cutter and I redesigned the rail dividers to match the slopes of the outer side walls so that they could be covered with rectangular cover pieces. Additionally, I made the middle of the front plate flush with the ramp so that the ball could be rolled from the front without the player having to start further up or throw it. These changes are shown in the pictures below.
Testing the position of the ramp and return board;, adding the point board and redesigning the ramp and front plate.
Moving the ramp around caused some misalignment between the guide rail on the return board, pictured above, and then return hole between the return board and the ramp. This caused the ball to get stuck in this gap. I inserted a small piece to block this gap, and added a ramp divider piece diagonally so that the ball would not get stuck on the left side if it did not make it up the ramp. The left cover could be used to dispense tickets or collect arcade tokens.
Adding pieces to ensure that the ball will return to the player
I had wanted to put the point values on the barricades themselves, as they appear on the original machine; however, it would be hard to see them if they were engraved onto the strips. There also wasn't enough room around the middle holes to engrave the point board above or beneath each hole. I copied the layout of the board and engraved it into the top plate. I then added my name to the back plate and added those pieces to the assembly, finalizing the orientation of the ramp and the return board.
Engraving points guide and back plate; showing final product
In the future, I might add a scoring system via proximity sensors on the underside of the point board or buttons under each hole. I would also sand down a few spots where the wood glue that I used shows, followed by painting the wood. Still, I am happy with the result. It is recognizable, functional, and fun, and appeals to everyone from nostalgic arcade-goers to children and graduate students alike.
The project was not without its flaws. First, I had to change some of the CAD models to account for the fact that 12" x 24" plywood was unavailable when I began manufacturing the parts. The change to 12" x 12" boards affected the ramp side covers, ramp dividers, side walls, bottom, and back pieces. Second, although I modeled the pieces with a design around the edges so that they would interlock with the surrounding pieces, it turned out that the 1/8" thick plywood was still thin enough that I ended up having to glue the pieces together regardless of the edge design. If I were to redesign the parts and use them with thicker plywood, I would include a more complex interlocking pattern such as a dovetail design so that the pieces could slide together and resist coming apart on their own.
Ideally, I would also have a more reliable ramp, return board, and point board alignment method. Originally, I created alignment plates for the ramp to sit on. These plates had protrusions that were intended to go through holes in the exterior side walls and be flush with the outside of the wall. Due to the iteration of testing and realigning the ramp, point board, and return board, I was stuck in a position where I had to secure the side walls before it was worth putting holes in them, in case these holes did not line up with the eventual position of the ramp. A second version of the project might make new side walls once the position of the ramp is finalized. The alignment plates ended up being rectangular, connecting to the inside of the side wall. If I could make these changes, it would go a long way toward selling the product as a "DIY Kit" rather than a finished product.
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