Iterating a Gumball-Dispensing Game Design

John Bordoni

John Bordoni

October 8, 2015

Kinoma team members created a gumball machine that served as the platform for Monster Match, a game showing the capabilities of two Kinoma Creates talking to each other. However, this gumball machine lacked an effective dispensing mechanism, and a bit of character. The Makers in Residence took on the challenge of reimagining the gumball machine to give it a unique identity. Thus, the brainstorming began.

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We knew how to make it work…

We set out to improve the dispensing mechanism, and to make it more sturdy so it could be more easily transported to events.  The dispensing mechanism was a rotating disk with a hole the size and depth of a single gumball, designed to select one at a time and drop it into the dispensing chute with the help of a servo. Initial sketches for improvement involved a metal base with a thicker wall of acrylic tubing on top. Simple enough, but not good enough.

…but we knew we could make it better.

Additional ideas batted around to really make this game engaging:

  • Build a Plinko-style dispenser.
  • Build upon the metal, cylindrical idea with a second, outer acrylic tube that houses an individually-addressable LED string that could illuminate to add eye-catching personality to the dispenser.
  • Make a simple reaction game, where a single light would race around the string of lights and the user would try to stop the speeding light with the press of a button to halt it within a certain zone, similar to a fairly popular arcade game.
  • Build a rectangular array of vertical gumball chutes, each designated a particular color. Turn the gumball machine into an infographic to show the popularity of a variety of different topics (for example, each column could be designated a presidential candidate, and a gumball would dispense when a Twitter hashtag is used related to that candidate). However, this infographic form factor seemed impractical for a machine dispensing an item the user would eat – there would be very little user control.

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The ideas kept coming until I finally decided to continue the “arcade game” theme. Having always been a fan of Skeeball, I wanted to make a Skeeball-like game that dispenses a gumball if you hit a certain target.

The first idea was to create a ramp. The player would shoot a ball using a pinball plunger into a horizontal playing field with holes through they could “win” and claim their gumball. I mocked up this idea in CAD and had a fully 3D-printable, handheld version of this game created in two days. It used a small, spherical magnet as its “gumball”, and would return the ball if you failed to get it inside one of the three holes. If you successfully launched the ball into the hole, your prize was dispensed through a series of chutes under the playing field. This small mockup was an interesting tool to see what kind of games might be intriguing to play and how they might look. However, I was still unsure how the ball would actually be dispensed into the playing field.

Simple is always best

Eventually, I wondered why we weren’t just building a Skeeball game? What happens if we just shrank the size of a skeeball court into gumball sized dimensions? So, we used a CAD program to model this scaled version so we could 3D print it. Since the max dimensions of the 3D printer we had were 6” x 6” x 6”, and the part was nearly 10” x 14”, the part had to be broken into six 3D-printed parts. After a day of printing, I glued the skeeball mockup on top of a sheet of cardboard for support, and cut holes in the cardboard to match the playing field.

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Next, a system of tubes was needed to return the gumball once a point had been scored. Originally, we planned to use PVC tubes, but the joints were too large to connect all the holes together. So, we designed a special system of tubes using CAD software to successfully return the ball. This system was designed with holes in each tube so that a small IR light transmitter and receiver could be installed to figure out which point value had been scored. We hot glued these tubes onto the back of the game board, and created a ramp out of cardboard to finish the basic gameplay prototype.

The prototype provided us with the angles of the backboard and ramp to mimic the actual Skeeball game, and the appropriate sizing necessary for easy transportation. The tubing allowed for testing of the sensors to establish how precise they were and how quickly they could recognize a hit.

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Addressing challenges

1. A big challenge was figuring out how the player would shoot the gumball. It would be unsanitary for them to handle a gumball, and a pinball plunger might not have enough power to shoot a gumball into the playing field. So we quickly designed a customized launcher using CAD software and 3D printed parts. We only needed four screws and nuts, and a thick rubber band. This provided plenty of power that could easily be added or removed with more or less rubber bands.

2. Another challenge was figuring out how the gumball would be dispensed. The original idea was to have all the gumballs underneath the ramp, providing a colorful background, and a small wheel powered by a servo to select a gumball and raise it into the ramp for play. However, this proved difficult due to the lack of a significant enough slope (and therefore gravity) to ensure a ball would be dispensed. Eventually, we decided to make the dispenser part a separate, vertical part so it could be easily removed and dispense without as many jams.

3. An additional goal was to figure out how to make the game easily extendable. What if you wanted to play a full game of Skeeball with your gumball instead of just a single roll? What if you wanted to play a game where you only get your gumball after hitting a point value greater than 40? To make this happen, a part was 3D printed to house a servo that could take a gumball coming from the gameboard and send it back into the playing field or back to the user, thus allowing numerous game possibilities.

Design: Pretty lights!

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We also wanted this Skeeball machine to be unique and attract attention. There’s no better way to do that than to add pretty, eye-catching lights. We gave each chute an individual ring of LEDs that would light up to celebrate getting the points from that chute. Different animations and colors could be programmed for different point values.

Since the final product was going to be made out of clear acrylic and the chutes were to be 3D printed, there were numerous options on where to place each hole’s LED strip. A series of chutes were 3D printed, and we experimented with different colored filament (white vs. semi-transparent to see how the light appeared in each), and placement of the LED strip (flush with the outside, flush with the inside, or inside the chute itself). We found it was possible to fit each strip inside the chute despite being only 1/8” thick. Soon, we printed each chute in semi-transparent filament, cut each LED strip to size, and embedded them with the proper wiring. We then created the code to show certain animations for certain actions.

Let the construction commence

At last, construction began on the final product. I laser cut and etched guidelines on 3/8” and 1/4” acrylic  to make assembly and placement as easy as possible. Then, I installed and 3D-printed each of the chutes and tubes along with their sensors for the gameboard. We used black filament for the chutes to eliminate the impact of ambient light on the receiver. Since each chute uses five wires for the transmitter and receiver of the IR beam sensor, a PCB was made to make organization easier for all 35+ wires. An addition of the three wires for each LED strip (nine total for 27 additional wires) made for a mess. To help, each set of transmitter/receiver wires were zip tied together, and all wires were labeled with PWR, GND, and DATA. We used and connected a separate power supply for the LED light strips.

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Next, we constructed the ramp. Each piece was cut to size and then put in place with acrylic cement. Two solid 1” OD acrylic rods were used to hold the rubber band launcher. The ramp was 3D printed in a variety of different trial angles before deciding on the best one. The ramp was supported with rubber foam and padded with cork to provide a more natural motion and dampen any impacts on the hard plastic. A holder for the dispenser was 3D printed, as well as return chutes for any ball going back into the playing field and for any ball coming back to the player. The housing for the servo that controlled where a previous played ball was going to go (either back to the user or back into the ramp) was then added.


The Skeeball Gumball Machine was full of its own unique challenges, each needing to be solved before continuing on to create the final product. The game was designed with extensions in mind, and these extensions could end up making the game even more special. Maybe a second Kinoma Create could talk to the Kinoma Create that is operating the board? Maybe this second Kinoma Create would be in the hands of an observer, who might have special powers to select a certain point value that would reward double the points if the player hits it on the next launch? Maybe you can be the one to make this extension?

We can’t wait to bring it to an event near you!

John is a Mechanical Engineering and Computer Science student at Stanford University with a background in content creation, manufacturing, and graphic design.