I mentioned I was getting a 3D printer soon, but didn’t say much else about it. Well, I’m happy to announce that it arrived and I assembled it in a few work days. It is now churning out high-quality prints, mostly of upgrades for the printer itself. Check it out, here is a picture of the printer with an upgraded fan duct on the print head!
I spent a lot of time printing things like this elephant. Just fun little tests of my ability to turn a digital file into a physical object, and a great gift. I knew before getting the printer that it wasn’t going to be a “plug and play” device, but I had no idea how much really goes into getting good prints! At this point, I am moderately confident in some of the nuances, but I don’t have a good enough intuition to be introspective about it. I’ll leave my lessons learned for a later post.
The reason I built this 3D printer in the first place was to enable lab experiments that would otherwise be too costly or too time consuming. I was heavily influenced by a few tweets/blog posts from Russell Neches. In particular, he posted a picture of what happened to a print after autoclaving. The ability to create custom made sterilizable tools in a microbiology lab for a few cents within hours is clearly going to change the way we do lab work. As a computer scientist in a wet lab, I figured I could use some of my interdisciplinary skills to help the community of makers/hackers/DIYers/whateverers advance how we actually do day-to-day science.
I’ve only had my printer up and running a few days, but I think I have a nice example of how they can enable better (at least cheaper) science in the wet lab. While I mentioned how amazing it is to print autoclavable parts, sometimes you just want to avoid letting your media or cultures touch anything contaminated at all. For example, if you wanted to move sterile media from a reservoir into a continuous culture of bacteria (e.g., a chemostat), you would not want to contaminate the media by allowing it to flow through some filthy pump. Instead, labs typically employ peristaltic pumps, which move liquid through sterile silicone tubing without ever touching the contents of the tube. Unfortunately, these pumps are usually very expensive, and the more accurate you want them to be, the more expensive they get.
So, how do we build a cheap and open-source peristaltic pump? Turns out, someone has already posted the 3D models needed to print a very nice pump. Another plus, these are relatively simple objects to print.
After just a bit of assembly, we have a working peristaltic mechanism.
The next step is to figure out how to drive the pump. A geared motor would probably have enough torque, but wouldn’t have much accuracy. I happened to have this little stepper motor around. It isn’t that powerful, but I figured it was worth a shot. To attach the shaft of the pump (a M3 screw) to the stepper motor, I needed a coupler. Those aren’t too easy to find around here, especially in metric sizes. Fortunately, I could print one!
With a pretty simple circuit based on an 8-channel NPN Darlington and an external 12v power supply, I could drive this stepper motor with any Arduino and 4 output pins. This tutorial from the Arduino website helped me get the circuit working, but make sure you check the datasheets for the Darlington and stepper you have — many have different pinouts than the pictured circuit.
With everything hooked up, turning on the Arduino yields a moving peristaltic pump!
I don’t have flexible tubing that fits this pump, so actually pumping water will have to wait. When I find some, I’ll post another video of it working.
I did almost nothing to get this working. I downloaded a few open-source models from thingiverse.com and a tutorial from arduino.cc and put it all together. The community of people putting this sort of data online is amazing, and I really believe it will revolutionize the way we all do science.