imsolidstate

Acrylic polishing and scratch removal

I recently acquired a 46 gallon ZeroEdge aquarium that was in pretty rough shape. There were a lot of scratches as well as marks from calcareous algae. Here is what I did to repair it.  › Continue reading

Continuous vs. batch water changes

I have been wondering lately about the effectiveness of building a continuous or automatic daily water change system for my reef aquarium. I really hate batch water changes, but they seem like they would be more effective. I decided to do the math and find out if that was true. A continuous water change can be modeled as a differential equation:

 
where is the amount of some dissolved substance at time , is the flow rate in and out of the system, and is the volume of the tank. We can simplify the model by making some assumptions: a continuous water change will consist of a small volume over a long period of time, thus the flow rate will be low enough to assume complete mixing in the high water flows of a reef aquarium. Flow rates should be chosen to provide an equivalent reduction of dissolved material as a weekly batch water change, however the rate is not of interest here since we are purely interested in comparing the amount of dissolved material reduction with a batch water change, not how long it will take. It will be easiest to calculate volume with a flow rate of 1 liter per hour. We can also assume an input concentration of 0, since the water coming in should be from an RO/DI system. This gives:

 
noting that my aquarium is 75 gallons, or 284 liters. We will also set this up as an initial value problem, with being an initial concentration of 50 mg/L of nitrate. The goal is reduction to 45 mg/L which we will compare to a batch water change later. For my 284L aquarium, the total concentration of nitrate would be . This gives:

 
The particular solution for this IVP is:

  › Continue reading

Fix your Keurig

The Keurig is a cool machine, but it has a bit of a flaw. There are two needles that pierce the K-cup, one at the top and one at the bottom. Since the needle at the bottom is piercing plastic and the needle at the top is piercing foil, the needle at the top will pierce first. This wouldn’t be a big deal but the top needle is hollow in the middle and connected to the water supply. When you press down to puncture the K-cup you pressurize the cup so that when it does pierce the foil coffee from the cup is pushed up into the needle. Over time the coffee builds up in the tube behind the needle until one day all those coffee bits conspire together to clog the needle and it won’t brew. Mine only took a little over a month to do this.

It’s not too hard to fix. You have to get some of the plastic covers off of your Keurig though. You will need a philips screwdriver and a T15 Torx driver. All of the Keurigs are a bit different on the outside, but they all appear to have the same mechanism for handling the K-cup. So your covers might be different but the internals are probably the same. Take the covers off so you can get to the internal plumbing.  › Continue reading

Textile needle loom

Probably the most complicated piece of equipment I’ve designed and built to date would have to be a textile needle loom for Goodrich. This machine is fully instrumented with position sensors, accelerometers, load cells, etc. for characterization of a textile needling process. Every parameter from speed and feed to force and distance is adjustable real time. This was definitely the most challenging mechanical design I have completed. I modeled the entire project in Solidworks to verify the design, and had over one hundred custom parts machined.