One of the many kinds of machines that we have never made before is a cocktail robot. But recently, after being invited to participate in Barbot 2010, we put together this little drink mixer.

Cocktail robots are a funny breed. No two seem to work the same way and many (like ours) have few enough moving parts to barely count as robots at all. The granddaddy cocktail robotics event is Roboexotica (for which you can read about last years robots here), but we’re showing off our machine tonight and tomorrow night, much closer to home at the DNA lounge in San Francisco.

Our machine is named “Drink Making Unit.” (Descriptive, isn’t it?) It has three fluid paths, and can produce cocktails with up to three components. It has an integrated 8×8 RGB LED matrix that it uses for data display, and an ice bucket to chill drinks as they go through the system.

How *do* you build a drink-mixing robot? We spent a remarkably long period of time looking for true food-safe valves and pumps to use for this project. The “standard” way to do this is to use solenoid-controlled valves, or sometimes compressed-air powered valves, but the solenoid valves are notoriously unreliable and we aren’t planning to keep compressed air (or CO2) around. The other obviously safe way to transport liquid in a known food-safe environment is to use a peristaltic pump. These are great, but we felt a little silly either making our own from scratch or paying about $100 each for commercial units that barely move milliliters per minute. We also looked at various diaphragm pumps, aquarium pumps, and so on, but mostly came up with products that were either expensive or of questionable construction for use with food, or gave completely uncontrolled throughput volume.

Finally, after making some progress on a design consisting in part of ketchup bottles and servo motors, we came across an unexpected solution while browsing eBay for other pump types: breast pumps.

If there’s one consumer group that I can expect to be more picky than me when it comes to food safety it’s new mothers, so these pumps– designed to move food grade fluids without contamination– aren’t actually a crazy thing to consider. They are cleanable, don’t use much power, and are inexpensive. Amazon sells a pair of these “Evenflo Comfort Select Performance” units for $45. (Try as I might, I could not find a three-pack anywhere.)

These pumps are designed to run off of 4.5 V from three AAA cells, up to about 350 mA each. There’s a mechanical on-off switch and a suction control on each. Here’s what they look like inside:

The suction control engages or releases a small pressure relief valve. The device is basically mechanical, running from that single motor. Of course, this means that it’s easy enough to add our own power control, and 5 V (switched through a PNP transistor) is perfectly adequate to run the pump. The fluid handling is done external to this unit, and relies on gravity and relatively low fluid volume to avoid drawing liquid into the diaphragm pump mechanism– liquids stay in the clear plastic “cup” of the unit until expelled through a flexible silicone valve.



For input into the pump, we measured the cup size and determined that size 5.5 stoppers were the right ones. Stoppers are available pre-drilled, and we cut some carefully-sized stainless steel tubing to adapt to them. From there, Tygon “food and beverage” tubing goes down to carafes filled with our fluids.

These pumps are not designed to lift liquids over a large vertical distance, so we constructed a platform on which to support the carafes at a more comfortable height.

The silicone rubber valves at the bottoms of the pumps normally are fitted into baby bottles. We didn’t need the bottles, but rather funnels. We constructed some appropriately shaped funnels by cutting the stems of disposable plastic champagne glasses.

The three funnels below the pumps direct their fluids into this translucent trough, which is our ice bucket. At the lower right hand of the ice bucket, there is a hole drilled, where the contents can drip into a fourth cut-off champagne glass funnel, into a larger piece of Tygon tubing that becomes the spout where you put your glass.

Finally, the controller is based on a modified Meggy Jr RGB. In place of a speaker and the two right buttons, it now has three PNP transistors that control the three pumps. The 8×8 RGB display scrolls out “DRINK MAKING UNIT,” or other messages as needed.

For its maiden voyage (resisting the urge to use the word virgin, here), we configured the Drink-Making Unit to construct white russians.

Here is how it looks ready for action, with the fluids loaded into their carafes and ice loaded into the bucket:

After we push the button, the pump pulls the cream up the the tube from the carafe and squirts it out the valve below. (It’s nice and creepy looking.)

The cream lands on the ice, and then runs through the hole in the ice bucket to the champagne glass funnel below.

From the funnel, to the tube, to the glass:

And repeat for the Kahlua and vodka.

Again, we’ll be showing off our little Rube Goldberg drink mixer at Barbot 2010 and we invite you to stop by and try it out for yourself– hope to see you there.

You may also want to check out this youtube videothat we made while trying out the Drink Making Unit, so that you too can experience the process of having your drink made by a silly and inefficient cocktail robot. :)