research July 1, 2013

DDR Mat Construction and Stockrooms

Because of all the labs on campus, Caltech has its own supply of construction materials, almost like a mini-Home Depot. For MechE’s and people wanting to build things, the most important places to get building materials on campus are the Central Warehouse, Stockroom, and Carpenter shop. The Central Warehouse has metal and plastic, like sheet metal, acrylic plastic, and various kinds of rods, tubes, and blocks. The Stockroom has screws, bolts, washers, etc. The Carpenter shop has wood (plywood, MDF, 2x4s, etc.). The best part is that everything is right on campus, so it’s extremely convenient. Additionally, the Carpenter shop and Central Warehouse sell material by the square foot (or sometimes even square inch), so you don’t have to buy the entire 4’x8’ piece of plywood if you only want a few square feet.—-These places are especially convenient because the Caltech DDR (Dance Dance Revolution) Club has funding to build two arcade-style DDR pads this summer! Since going to Home Depot requires finding someone with a (large) car, which is difficult, we’ll probably end up buying materials from the stockroom, warehouse, and carpenter shop on campus and ordering the rest of the things we need online. (We might be able to get one trip to Home Depot with some upperclassmen that are planning to build a loft.)

In the last few years, I’ve built two simpler DDR mats, but the sheet metal contacts I used get dirty easily, which makes the arrows lose sensitivity. (This is a problem with many commercial DDR pads too.) One of the typical (and easiest) methods to make DDR arrow sensors is to have two sheets of sheet metal on top of each other, separated by a small gap. When you step on the arrow, the top piece of sheet metal will bend and touch the bottom piece, completing a circuit and registering an arrow press. Unfortunately, it’s easy for dirt and moisture to get in-between the sheet metal plates, which interferes with the arrow presses, meaning we have to clean the sheet metal plates periodically.

Bottom half of an arrow - the folded paper around the edges separates the bottom layer of sheet metal from the top

Simpler DDR mat I built during winter term So this time, we'll be using a different sensor design. Unlike the commercial DDR mats or the DDR mat in the pictures above, we'll either be using DDR floor pressure sensors (the same kind they use in arcade machines) or thin steel mending plates that contact screws when you step on an arrow. The floor pressure sensors would last for a long time, and the steel mending plates and screws would be relatively easy to replace (and/or clean). Since finding someone with a flatbed truck is difficult, we had some trouble figuring out how to transport plywood for the DDR mats from Home Depot. But, I recently learned that the Carpenter shop on campus has plywood, so some friends and I went over there and bought the plywood we needed. It's now sitting in the dorm lounge, and hopefully we'll be able to cut it on a table saw soon.