For this week’s project, I really wanted to cast a hammer. I had two competing ideas for the sensors: to use a pressure sensor to light up different LEDs depending on the striking force, or to use a magnetic sensor to light up a single LED every time it touches a magnet. I liked both designs due to their potential to teach kids how to use tools.
Once in the lab, I made two important discoveries: There were no pressure sensors, and standard-sized hammers are just too big for the vacuum forming bed. While I had to give up on my first idea, I was determined to make the second one work. After writing the Go-Go program for my sensor, I used modeling clay and the handle of a pin vise to create a mini mallet. The first mold turned out lopsided since the handle was set too loose in the clay. Adding a thin strip of cardboard underneath kept the handle stable during the second try.
I cast the mallet with Vytaflex-40 urethane rubber, and learned a couple of things about casting. Setting the sensor inside the rubber is really hard. When I was programming the Go-Go board, I noticed the sensor had to lay flat across the magnet in order to register. That meant I continuously needed to adjust the sensor so that it stayed flush with the head of the mallet. One thing that helped was casting the rubber in its natural color. I could always see where the tip of the sensor was relative to the tip of the hammer. Despite my best efforts though, the sensor still broke the surface in one spot.
I also learned to always use mold release if the hardness is over 20. Two days after I poured, my creation was still a little bit tacky (there might have been something wrong with the urethane). It was also really stuck in the mold. I had to use scissors and a lot of force to get it out. Unfortunately, I lost a lot of fidelity trying to separate the rubber from the plastic, and the end result is unpretty. But the overall system still functions as I intended it to, which is a plus.
To complete my design, I used the laser cutter to create a base for the magnet and the LED. This way, a child can see the LED and the magnet at the same time. I soldered wires to the LED so that I could connect it to the Go-Go board.
This is a video of the final result. The LED lights up when the mallet contacts the magnet.
THE GO-GO CODE
Here is the code I used:
forever[ifelse sensor1 < 500