We got two axis working and nearly calibrating (rotation and x), a gear bearing replaced, and software humming along and communicating with iMac. We finally were able to build upward from our plastic foundation. The extruder and all z axis stuff will be suspended from a framework of 1/16″ aluminum angle stock – and it’s 3/4″ off the floor so the bottom electronics aren’t dragging anymore.
In order to make mathematical forms – or any forms, the two axis must numerically correlate together. So the number of motor steps to make one full table revolution will be related to the number of steps needed to move the table linearly from “min” to “max” (about 7″). We use opto-endstops to sense the limits. The best tab to block the opto endstop (and signal a min,max, or full table rotation) was a foil strip from a teabag packet. Great tea too.
Today we experimented with crayons. We gradually heated a hot melt glue gun (that we adapted for crayons) starting at 109 degrees, we notched up the temperature with a rheostat until the crayons melted enough to extrude a bead. At about 113 degrees it worked. We notched the temp up to 127 degrees to try different viscosities of melted wax and feed rates. We discovered that crayons need to be preheated – so a heat tube on an extruder should be the length of the crayon.
We also discovered the pitfalls with melted crayons. The hardened beads are very brittle and, even though it seemed great that they harden in seconds after being extruded, they do not self adhere well. Whatever we create with crayons will probably be very delicate.
So, even though the experiments were encouraging, and they clarified some design questions, we are migrating to a more consistant and robust medium for now. latex caulk (mostly because of time and deadline considerations).
The two steppers that control the tables rotation and x-axis are installed and working beautifully. I do need a new belt for the rotatory table. The cannibalized carousel-CD player design is a good one for a single extruder – but I will need to revise it when I want 4 (yes four, and I’ll post the sketch tomorrow). Next post should have video too.
The extruder assembly is taking shape and we did our first set of experiments with the extruder and crayons with good success. The current heating element responds predictably to linear increases in voltage up to 119 degrees. then it jumps. I think we will need to pulse-control it and prolly make a separate controller with sensor (thermistor).
According to the folks at crayola, different colored crayons will have slightly different melting points because of the varying clay content in each color. I intend to eventually test 4 color families to for melting point variations – red, yellow, blues and earth tones/blacks.
Today we discovered that we can obtain two motorized axis in one ready made assembly. We cannibalized a carousel 5-disc CD player from the late 90’s and found an amazing $5 solution. Since the motors are standard DC, I’ll have to incorporate some type of position sensing – but that my be a great way to avert the impending shortage of i/o pins on the arduino board.
Also, we are going full bore on fund-finding effort. Next application to submit – blackrock foundation – deadline 3/13.
We also talked about a beach robot that makes sand castles by spitting sand and water as it rolls on one axis.