Polar Printer

Project PolarPrinter
The project is to build a model of a highly portable, easily scalable 3D printer based on polar printer technology.

Conceive


When we were handed this project, we had a rough understanding of small electronics and stepper motors. We knew nothing about printing parts on the Makerbot and even less about programming arduinos. Thanks to the last team working on the project we had a rough understanding of the math that would be involved and they pointed us in the right direction to figure out how to program the arduino and run our motors. Our first brainstorming session was a good one, we came up with a few realistic goals that we thought we could get close to completing in a four week period. we wanted to have one of three poles built and running (even if it wasn't running smoothly). We each decided to work on a different task so we could get more accomplished.

Design


There was allot that needed to be done before we were able to come up with what we thought was a suitable design. We were all starting from scratch in almost every aspect of this project. The appropriate software needed to be downloaded, we had to do allot of research, and read and watch many tutorials to help us understand the tools that we were working with. We inevitably hit software snags dealing with incompatibility and format issues.

We played around with the Arduino paired with an Adafruit motor shield and we were able to get our steppers to run. Motor 2 however, was skipping steps which caused the motors to be out of sequence which would spell disaster for our printer. After some light troubleshooting, we were able to rule out a voltage issue, faulty motor, faulty motor shield and Arduino, and any faulty wiring. We finally figured out that the RPM was set too high in the Arduino code, this is apparently a common problem and is easily fixed with a few keystrokes. We tweaked the Adafruit multistepper code and ended up with this https://commons.wikimedia.org/wiki/File:Arduino_code_1.pdf

We had to come up with a way to allow for the printer head to move out from the motor assemble and back in without changing the plane that the printer head was moving on. In order to do this we had to maintain a right angle between the motor and the printer head. We used Pythagorean Theorem to solve for the speed the step motors would run at. We know that the height of A is always 12 inches because that was the distance that the two U-bolts were mounted at. That just meant that we had to find the ratio of ∆C: ∆B. This ratio would allow us to keep the printer head level while the printer head was moved from the initial point to the next point that was required. We are looking to find the change in B and the change in the C. First we chose two B and then using the Pythagorean Theorem we found the C.
 * A2+B2=C2
 * 1) 122+62=C2
 * 2) 122+92=C2

For finding ∆C
 * C2-C1 =∆C
 * 15-13.42 =∆C
 * 1.58=∆C

For finding ∆B
 * B2-B1 =∆B
 * 9-6=∆B
 * 3=∆B

We now know the ratio to be 1.58:3. This means that for every 3 units the base moves (either towards the motor or away from it) hypotenuse has to move 1.58 units. The step motors can now be programmed with this ratio and the printer head should stay on a level plane.

We had a hazy idea of what we wanted our finished product to look like but we needed to clear up some things and come up with a solid plan for actually creating it. These are some early sketches that we came up with for a realistic and build-able design given the materials at hand and our knowledge. We settled on what is represented in sketch 2 for the motor assembly, but this still left the issue of how we would be controlling our Z axis. we thought about using a pulley system or a cog belt and a set of gears. After presenting this problem to our class we got some great feedback. It was suggested that we use a piece of all thread and a bracket to control vertical motion. A motor will drive the all thread and the motor assembly will move up and down as the threads pass through the bracket. Pictured is a not-to-scale model of the motor bracket and the motor mount that we printed on the makerbot.

Implement
After a point we needed to put all of this talk into effect. The first thing that we decided to build was the motor assembly, we rigged a piece of plexi glass with our stepper motors and a set of U-bolts. We then fitted the motors with small spools and then wount the spools with thread that would temperarily serve as our cable (our finished product will use braided fishing line). We fed the thread through the U-bolts and tied a nut to the end to simulate the wieght of the print head. Here is a picture of our finished motor assembly and a short video of it in action.

The next big task as far as the building is concerned was to build the motor mount, the stand which will support the motor assembly and be responsible for moving the assembly on the Z axis. For the base of the mount we decided to use wood because it is cheap, sturdy and easy to work with. for the top and center support we used plexi glass and the whole thing is bolted together using a light gauge all thread. In the middle is a piece of 3/8" all thread which will be driven by a motor to control the vertical movement of the motor assembly. We tapped the all thread at either end to make way for guide pins that are inserted in holes in the plexi glass to hold everything in its place.

We took some measurements and found that the size of the bracket should be 2 inches high X 1 inch wide X 3.5 inches long and are 1/4 inch thick. We also measured the all-thread and the nut to find the size that the hole for the all-thread to pass threw and the indent that would be needed for the nut to sit in. It was decided that 1/4 inch holes for the bracket to attach to the motor assemble would be a good size. Once the two pieces were built we rotated one side 90 degrees and attached it to the other piece.

At first we thought we would print 3 brackets to allow for optimal stabilization of the motor assembly. However, when we had presented to the class about our trouble shooting of the step motors skipping we also talked about how we planned to attach the motor assembly to the all-thread. It was brought to our attention that the more nuts that are attached to the all-thread the more likely it was going to bind from the nuts not being lined up precisely. It was decided that only one bracket would hold a nut and the others would be there to stablize the assembley.

In order to print this bracket on the 3D printer it needed to be in a .x3g file format. First we downloaded and installed an extension that would allow us to export the file as a .stl file. Once the file was exported as a .stl which allowed me to import it into Makerware. When we imported the bracket file into Makerware it wanted to convert the inches in millimeters, we were unsure if this will create an issue but there did not seem to be another way. From Makerware we were going to export it to a memory card as a .x3g file but Makerware was having some problems. We are planning on trying again to get this printed next week.