Closed Loop Drop-BOB … The Cold Drip Coffee maker that could!


So its been longer than I’d have hoped for this post, but I was so torn in my design ideas that I decided to wait a little. I let the ideas settle in my mind and eventually, the inspiration came!

I had a few design criteria to make this Cold Drip coffee maker:

  • Simple & Elegant
  • Easy to manufacture with many “off the shelf” components
  • Hack-able
  • Not offensive to Jenn’s Eye (The wife) … so It can be kept in the kitchen
  • Has a certain “Bobby Style
  • Not too expensive (I’ll probably optimize this later) 
The worst part is that I did not want to settle on any of these criteria … none more important than the other, but all required.
Cold Drip Coffee Maker – “Closed Loop Drop-BOB V1.0” (**Name is a work in progress)
Let me remind you of the progression of the designs prior to V1.0:
V0.1 – the proof of concept
V0.2 – functional prototype
V0.5 – New and improved looks

And now, just recently out of the Alpha stage and graduating to the Beta testing stage: The V1.0 – “Closed loop Drop-BOB” (Name is a work in progress) … The model is not fully manufactured yet (still a few parts on order & to order at the moment). But here is what I’ve got so far:
It all started with the simple wooden bracket shown above. Even though this is not what I want for the final V1.0 product, It helped me visualize what I actually want.

Once I made the bracket, I quickly drilled and taped the brass plug and attached it. Oh, I skipped the part where I cut glass … I’ll come back to that.
This is the part that actually gave me a kick in the ass to make this thing. Since I took apart my original prototype, I’ve been drinking peasant coffee (you know from an espresso maker, like the rest of the world)… After tasting this liquid nectar from the slow drip process, I was all hyped up and wanted to finish this new and improved version.

 It was so good to see this familiar coffee colour (Canadian spelling eh). And since I started making smaller batches, I was able to minimize waste. It takes the same amount of grounds to make 2 shots of extra delicious cold drip, as it does to make 2 shots from an espresso maker … This is for those who think Cold Drip costs more on grounds … not necessarily.

 So back to the glass cutting part. This is the part of the design that forced me to re-think my ways … At first I wanted to make my own water reservoir because I couldn’t find anything on the market that would work with a drip valve (open at the bottom & the top). I also wanted to potentially control the temperature with a peltier plate … but that will be for a later version.

I eventually came to the conclusion that I should modify a container to suit my purpose. Diamond tip glass cutting bits are a little expensive (but who am I kidding … I love buy new tools).

I did the entire cut on my drill press, with the glass inside another glass filled with water. Make sure you have no air bubbles.

The hole came out nice. Only a few little chips were missing, but nothing I can’t deal with by using some washers and O-rings.

This part was the most tricky … and the reason I spent over a hour standing in front of the brass fittings part of the local hope depot store.

Turns out that compression fittings are not easy to combine with other types of fitting .. like MIP, and Pipe treads, etc … I needed some distance between my valve and the glass ,so I can add my little beauty of a “Close Loop” servo control box (more on this later) … You see, the next great idea I had was not to connect anything other than a single hole to the bottom of a glass (or, steel, or wood, or coconut, etc). This allows me to use virtually any container that I can make a 3/8″ hole at the bottom.

Seems to work nice. Got the distance I was looking for by connecting the 1/8″ compression thread valve to a flared copper pipe, to a female MIP, to a 3/8″ OD short brass pipe and connected all that with some O-rings to prevent leakage … I feel like I can optimize this later for cost and simplicity, but good enough for V1.0.
Here’s where all the magic happens. This little box is less than 2 square inches … And packs the servo, the valve, and the photo-interrupter all in a tiny little robust package. (The wireless controller ESP8266 will also be fit into here shortly … if it ever arrives)
Once this think is fully built, I should be able to control and monitor the drip rate from my smart phone … from anywhere in the world!

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