The Mix Master 2000: How to Build an Automated Shandy Machine

When we were asked to whip up a special brew this July for a big Creative Confidence book-preview event featuring David Kelley, one of IDEO’s founders, and his brother, best-selling author Tom Kelley, we knew we had to kick things up a notch.

Challenge #1: Two guests of honor called for not one brew, but two! We heard Tom enjoys light, Japanese-style beers and that David doesn’t really drink, so we decided to make a Belgian-style wit for Tom and sparkling organic lemonade for David and then mix them together to create a shandy, a refreshing summer drink.

Challenge #2: Now that we had two beverages, we needed to come up with a unique way to dispense them. Luckily, we like tough build challenges with tight deadlines even more than we like beer. A few shop hours here and there between projects, and before we knew it, we said “cheers” to the Mix Master 2000 Shandy Machine!

Introducing the Mix Master 2000

How it works

The Mix Master 2000 Shandy Machine’s look was inspired by the retro-futuristic steampunk movement.

The machine sits on top of a standard, top-loading freezer replumbed to hold two kegs (one containing wit, the other sparkling organic lemonade).

Thirsty partygoers begin by turning the large hand crank on the front to select their preferred beer-to-lemonade ratio (from 0–100%). When the analog meter on top points to the desired proportions, they flip a missile switch to open the valves. The two glass vessels on either side of the machine fill with beer and lemonade, respectively, then send the home-brewed concoctions into their waiting pint via a dispensing tube.

Beer recipe

We wanted to brew a beer that would pair well with lemonade, so we decided on a nice, light, citrus-wheat ale. The goal: around 5% ABV, or alcohol by volume. We used 2-row pale as our main grain along with wheat and wheat malt with a bit of coriander, chamomile, and orange peel. You can find the complete recipe on Brewtoad.

Lemonade recipe

Making homemade lemonade is pretty straightforward. It only has three ingredients: lemon juice, sugar, and water. Batch-processing 10 gallons of the stuff, however, is a bit trickier, especially when you don’t have an electric juicer. In our case, we landed on a ratio of 1:1:8 (1 part lemon juice, 1 part sugar, 8 parts water), and ended up using 160 lemons, 2.5 gallons of simple syrup, and several man-hours of squeezing time. Yikes.

Early testing

After we figured out what we wanted our shandy machine to do, we found some glass vessels lying around the shop.

They looked straight out of a science lab, which was cool, but we thought we’d have some foaming issues because of their small openings. We hooked up a hose from the tap in our kegerator and tried filling them with beer. Sure enough, the beer started foaming immediately and it took several minutes to drain using gravity. Not good if you want a proper pour...

We needed to do something about the foaming issue in order to make this thing usable more than once. We did some experimenting and learned several things:

• There couldn’t be any kinks in the tubing.
• A colder vessel worked best.
• The first pour was really foamy, but subsequent pours were better.
• Filling the glass from the bottom via a tube prevented overflow and allowed any foam that did bubble up to dissipate quickly.
• Adding some back pressure to the vessel made the biggest difference in preventing foam. (To give you an idea of the really rough type of prototyping we love, we used the finger of a rubber glove to make a makeshift balloon on top of the vessel.)

Architecture

The basic plumbing layout of the system is pretty simple. We have three-way ball valves that direct flow from the keg to the vessel, from the vessel to the dispenser tube, or block flow entirely.

To control the valves, we 3D-printed some gears to fit onto the lever controls. To drive the valves, we fitted stepper motors with smaller, 3D-printed gears.

Inputs

For the main shandy mixture-control system, we settled on a large hand crank.

We machined a shaft and attached an encoder to the end. We added some detents to the wheel to make sure the crank had a nice hand-feel and gave solid feedback so people could precisely dial in their desired mixture ratio (the detent mechanism is equivalent to putting a baseball card in the spokes of a bike tire).

We used a 3D-printed gear and flexible plastic leaf to engage the gear. We had to play around with some adhesive foam in order to damp the vibrations and get just the right sound and feel we were looking for. We added a covered, mission control-style toggle switch to start the cycle and a cancel button to round out the inputs.

Feedback

The main source of feedback on the machine is the large analog meter on the top of the machine. We searched online in vain for a large meter that would fit our steampunk style, have an appropriate measuring range, and could be controlled by Arduino. In the end, we found an old automotive meter that measured voltage from 0-16v.

We replaced the scale with one designed by our colleague Joe Graceffa and added a custom housing around it.

When we were testing the Mix Master 2000, we found ourselves staring at the Arduino serial output a lot to figure out where the machine was in its cycle. To make this easier, we added a small OLED display with an onboard SD card slot. Simple serial commands trigger bitmap images that signal Startup, Ready State, Beer Filling, Lemonade Filling, Pouring, and Error State.

Electrical layout

An Arduino Mega controls the shandy machine. This diagram shows how all of the components are connected:

To drive the meter, we needed to boost the 0-5v PWM output of the Arduino Mega to 0-16v. We built a simple, non-inverting amplifier circuit to increase the voltage. A fine-adjustment potentiometer allowed us to fine-tune the maximum voltage and made the meter read full scale.

Code

When the Mix Master 2000 is first powered on, we can’t be sure that the valves are in the correct position. Each motor is stalled against the valve hard stop to establish a home position (the valve hard stop is in the dispense position so there’s no risk of keg leakage). Once the machine’s ready, the crank encoder state is polled and the meter PWM is updated to reflect changes in the shandy-mixture percentage. As soon as the start switch is thrown, the pour cycle begins. During our early testing, we figured out how long it would take to fill a glass with each liquid (the times turned out to be different because of varying carbonation levels). The parameters for beer and lemonade fill times are used to calculate the on times for both valves using the selected shandy ratio.

The cycle sequence starts by opening the beer valve and filling the beer vessel for a predetermined amount of time. When the beer valve closes, the lemonade valve opens for a predetermined amount of time. Finally, both valves move to the dispense position to allow liquid to flow from the two vessels and into the person’s glass. A built-in wait time prevents the start of another cycle, ensuring all the liquid is dispensed.

If necessary, a cancel button throws an interrupt, immediately moving both valves to the safe home position and halting program execution until the Arduino reset button is pressed.

The final touches: steampunking & aging

We’re big fans of steampunk, so from the beginning, we knew we wanted the Mix Master 2000 to look quasi-Victorian. First, we used as much copper and brass as possible, then, drawing on John’s background as a Hollywood set designer, we “antiqued” it using various scenic techniques.

We started by stripping everything off the main body of the machine and painting it all silver. After that dried, we sprayed it again with black paint. While that was drying, we took Scotchbrite pads and scratched the corners, edges, and anywhere else we thought needed a little character. After the black paint layer dried completely, we started to reattach all the other pieces. We painted them copper or brass and scratched them up here and there to add wear and tear.

Once the whole machine was reassembled, we decided it should look a bit dirtier. To do this, we mixed different brown-toned acrylic paints with denatured alcohol. We brushed this onto key places like the corners of the motors so it looked like dirt had accumulated and it was streaked with rain (we wiped off the paint before it dried so the effect didn’t look too heavy handed). For sanitation purposes, we didn’t paint the drain tray or the stainless tubes that dispense the shandy.

What’s next

We think the Mix Master 2000’s pretty cool as-is, but there’s always room for improvement. One issue we’d like to address is foaming. The balloon we added on top of the beer vessel helped, but pouring a lot of shandies in succession caused major foam build up. Increasing the amount of back pressure in the vessel could improve this situation, so we’re experimenting with adjustable pressure-relief valves. Coupled with the relief valve, a low-pressure aquarium pump could help to push out the foam more quickly, avoiding a buildup.

While we’re using the Mix Master 2000 for shandies at the moment, it really could be used for any number of two-part drinks: Black & Tans, mixed drinks, or custom non-alcoholic concoctions are all ideas we’re toying around with. As beer geeks, we’re particularly keen to brew two similar beers, one with a bland base and another that has a lot of hops so we can all dial up the perfect hoppy pour.

Parts List

• Main housing — ?” ABS
• Ball valves — McMaster # 4757K52
• Valve gears — FDM
• Valve housing — FDM
• Crank — McMaster #6020K35
• Stepper motors — Lulzbot #817752011303
• Stepper drivers — Sparkfun #ROB-11699
• Arduino Mega
• Display — 4D systems 128x128 Sparkfun #LCD-11377
• Power supply — 12V 5A, 5V 12A
• Meter — salvaged autometer 16v range
• Glass vessels — found in shop
• Glass holders — FDM
• Meter housing — Laser cut acrylic
• Start switch — Sparkfun #COM-11310

We couldn’t have made the Mix Master 2000 without the help of Joe Graceffa’s graphic design skills, Aaron Ferber’s awesome lemonade-making abilities, and Momo Miyazaki's amazing video. This post was co-written with John Grimley.

The creators of the Mix Master 2000, Chris Gold and John Grimley.