Fluid Logic

After retrying some tests and observing the results, I became less convinced that this fluidic half adder was working.

One thing mentioned by someone who did experiments with fluidic half adders (thanks for the work) was that making the adder too small did not work well with a larger fluid flow. I'm finding that a small fluidic device has a smaller range of pressure over which it will function, so it is more difficult to get working conditions to exist.

So what to do? Make a bigger device! The next one I made was 25mm, or about one inch in chamber diameter and an overall length including entry and exit tubes of 75mm, or about 3 inches. Once printed, which took 3 hours, this FHA (fluidic half adder) correctly performed the AND function, however the XOR terms were drippy. The conditions of test were a weak gravity feed of water. I noticed also that in the beginning stage of the gravity feed, when the pressure was greater, the device performed better.

When you think of it, we have two streams and to get an XOR result, the stream must pass over the receiving cup, so it must have a certain minimal pressure or the device will not work. So what I will do next is print a larger gravity feed mechanism for my fluidic adder.

I should also note that in the second design I tweaked the size and location of the receiving cup such that the stream would clear if it shot straight out of the entry tube. To do this, it must have sufficient pressure.

Above is an OpenSCAD drawing of a fluidic half adder. It works by fluid interaction within the chamber of streams entering the top two channels.

If either stream is on and not both, then that stream travels around the central cup and exits out the XOR output in the bottom center. If both streams are on then they collide and redirect each other into the cup and exit out the AND output diagonal at the bottom. And of course if both streams are off then neither output is on. The XOR output is the sum of the two input channels and the AND output is the carry out.

I am currently printing this device with a 15mm cross sectional diameter chamber in translucent orange PLA from ColorFabb. We will soon see how well it works.