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Special Content: Repraps for Education

This is part of a series of posts about starting and facilitating a project-based 3D printer club at a local elementary school, with the ultimate goal of replicating the program at schools everywhere. We'll be posting as many details as possible, including lesson plans and supporting materials. For more information about the entire project, including a listing of posts related to it, please visit the 3D Printer Club for Schools project page. 

3D printers are an exciting new technology just starting to gain a foothold in schools. Once built, a printer facilitates many creative endeavors and links to math, science, art, and more. Building a 3D printer is a great project for a school club or a project-based classroom because students have to integrate STEM skills and work as a team. Students who build a printer from scratch (as opposed to just buying a kit or a completed machine) will have a detailed understand how it works and will be able to properly maintain and operate it.

Here we are developing and making available a 3D printer club curriculum that any school can use. We’re developing these lesson plans as they are tested in an elementary school club, with members in grades 2-5. This page will be updates with the latest lesson plans and resources as they are developed.

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To install the heated print bed for my reprap, I placed the PCB on top of the plywood top print plate (which is slightly larger than the PCB), clamped it in place, and then used the holes in the PCB to drill out mating holes in the top plate. I put a washer on a 16mm M3 screw, and inserted it up through the print plate, added another washer, and a M3 nut to hold it securely in place. (I actually used SAE washers, as you can probably see from the photos, and that’s okay, too.)

Next I took my PCB heatbed to Lowes and had them cut a piece of glass to the exact same size. (While I was at Lowes, I picked up some Frost King 2″ insulated pipe wrap.) The glass is about 2.2mm thick, and it was only a few dollars. I cleaned up the edges of the cut glass with some fine grit sandpaper to make it a bit safer, then I put a small piece of Kapton tape (polyimide) on each corner of the glass to provide a little protection from the screws. Using the same tape, I secured the glass to the top of the PCB.

I covered the bottom of the PCB with the Frost King insulated pipe wrap to help keep the heat going up. I had to cut out notches to make room for the screws that would hold it in place (at the corners) as well as the tops of the screws that fastened the print top plate to the print bottom plate. I added a couple bits of extra pipe wrap to the center to help support the PCB and keep it from sagging.

The PCB/glass assembly rests solidly atop the four screws — there is no “play” at all. Here are a couple of pictures. (Click for larger view.)

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OpenSCAD apparently doesn’t have an easy way to make an arc or wedge, or any way to do a partial rotate_extrude. This presented a problem when I started to design my Parametric Encoder Wheel, because in order for it to look nice, it would need to have lots of extruded arcs or partial rotate extrudes in order to make the holes.

Encoder Wheel, OpenSCAD Arc

Creating an Arc with OpenSCAD

Here’s how I solved the problem. Currently this will render slots up to 180 degrees around, but extending it should be pretty easy. If you’re doing a lot of these in your model, be sure to use render(), or badness will occur.


/* 
 * Excerpt from... 
 * 
 * Parametric Encoder Wheel 
 *
 * by Alex Franke (codecreations), March 2012
 * http://www.theFrankes.com
 * 
 * Licenced under Creative Commons Attribution - Non-Commercial - Share Alike 3.0 
*/

module arc( height, depth, radius, degrees ) {
	// This dies a horible death if it's not rendered here 
	// -- sucks up all memory and spins out of control 
	render() {
		difference() {
			// Outer ring
			rotate_extrude($fn = 100)
				translate([radius - height, 0, 0])
					square([height,depth]);
		
			// Cut half off
			translate([0,-(radius+1),-.5]) 
				cube ([radius+1,(radius+1)*2,depth+1]);
		
			// Cover the other half as necessary
			rotate([0,0,180-degrees])
			translate([0,-(radius+1),-.5]) 
				cube ([radius+1,(radius+1)*2,depth+1]);
		
		}
	}
}

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

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Well, I discovered that Popsicle is a brand name, so I’m officially renaming this little guy “StickBot” so the Popsicle police don’t come after me. To be clear, this little bot has nothing to do with Popsicle brand ice pops, and never did. My appologies Popsicle; I hope you still let me eat your ice pops because life just would not be the same without them.

Now that I’ve come clean, here’s a video that show how to assemble StickBot’s right eye. It’s an analog 555 timer-based 1Hz oscillator that controls the right/left PWM servo signals generated by the left eye.

This is the latest version, powered directly by four 1.5V LR61 batteries (similar to AAAA batteries, and often found inside 9V batteries). As a result, it does away with the voltage regulator.

Details for the previous version can be found here: StickBot V2.0 - Untethered!. The original tethered version can be found here: StickBot: A Simple 6-Legged Walker. I’ll try to get updated schematics and more assembly videos up soon.

I’ve had a few people ask me if I have a kit for this little critter. I’m working on one geared toward kids — it’s a fun project to do with kids, and it seems like they really learn a lot from it.

The parts for this eye include:

  • 555 Timer IC
  • 1k ohm resistor
  • 330k ohm resistor
  • 2.2uF capacitor
  • About 9 inches of Cat 5 network cable, phone cord, or other similar wire
  • Some electrical tape, solder, and soldering iron
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Here’s a video of my very hackable 12-channel logic level shifter/translator with a voltage regulator. This video demonstrates how it works. There’s more detail here at the DIY 12-Channel Bidirectional Logic Level Shifter post.

In this example, it’s translating from 7.5V to 3.3V. In another example at the link above, I’ve demonstrated the hackability by wiring it up to drive a 3.3V Nokia 5110 LCD, using five of the 12 channels as logic level translators. Channel two is wired directly to 3.3V for power, channel three is wired directly to ground, and the transistor on channel nine is turned so that the 5V signal controls the gate, which allows PWM control of the LED with full power from the regulator.

Music: “Art Now” by AlexBeroza (CC BY 3.0)

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40-pin female headers are inexpensive and easy to trim down to size, and with a dot of CA glue (super glue), you can even easily make other configurations, like 2×4. Sometimes they’re even described as “break-away” headers, although admittedly they don’t break away as easily as the male pin headers. Just keep in mind that if you don’t score it, it could shatter.

Someone was looking at one of my PCBs and commented that it’s “impossible to break them apart without destroying at least 2-3 pins each time.” Using this technique, I’ve never “destroyed” any more than one, and with a little care, the edges turn out quite nicely.

Music: “The New Music” by AlexBeroza (CC BY 3.0)

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The goal was to crawl on the cheap, and what’s cheaper than popsicle sticks craft sticks and fishing line? Next we’ll wire up a 555 circuit so it can roam untethered, but until then, here’s how to make one of your own. But first the video! :) (UPDATE: Details about the untethered “version 2″ with the 555 timer circuits can be found at StickBot V2.0 - Untethered!.)

Supplies

  • 4 Popsicle craft sticks (like Popsicle brand ice pop sticks)
  • 3 small eye screws
  • A few feet of mono-filament (fishing line). We used 10 lb test.
  • 3 pipe cleaners (one is just decorative)
  • 1 small cable tie
  • A bit of masking tape
  • 1 mini micro hobby servo

How to Make It

  1. Body: Stack four popsicle craft sticks, and drill three pilot holes through all of them — one in the center and one at each end. Three of the sticks will be the legs, and one will be the body.
  2. Joints: Arrange the legs on top of the body, and fasten them together with three small eye screws. On most eye screws, the threads will not go all the way to the top, so the legs should be free to move back and forth.
  3. Muscle: With a small cable tie (and possibly a dab of glue), fasten a 3.7g mini micro hobby servo to the body stick, centered between the middle and hind legs, with the motor shaft at the rear. Attach a servo arm so that it points out like the legs when the motor is in its center position. (You can get these motors on ebay for a couple bucks.)
  4. Tendons:Cut six lengths of monofilament, each about 9 inches long. For each line, tie a knot into one end, and thread it from the bottom through the hole at the end of the leg. The knot should be big enough that it won’t slip through the hole. Thread the mono-filament from the legs as follows (in this order):
    • Front left: Left to right, though the center eye, and through the right end of the servo horn.
    • Front right: Right to left, though the center eye, and through the left end of the servo horn.
    • Back left: Left to right, though the center eye, and through the left end of the servo horn.
    • Back right: Right to left, though the center eye, and through the right end of the servo horn.
    • Middle left: Left to right, though the front eye, and through the right end of the servo horn.
    • Middle right: Right to left, though the front eye, and through the left end of the servo horn.
  5. Adjustment: Carefully pull each line snug so that the legs are all perpendicular to the body, and tape them down to the servo horn. Trim off the ends, leaving an inch or so for later adjustment or tightening.
  6. Legs: Cut some pipe cleaners into six 3-inch lengths and wrap each one around the end of a leg. Bend the legs so that they all touch the surface, and are angled toward the back of the crawler. It can take a little time to get it just right, and you’ll probably want to adjust it when you get the motor hooked up.
  7. Antennae: Add some antennae if you wish by wrapping a couple 5-inch lengths of pipe cleaner to the front legs.
  8. Brain: Power the servo with an Arduino, Basic Stamp, or other micro controller, and program it to turn left and right continuously. There’s a sample sketch below.

A Simple Arduino Sketch

#include <Servo.h>

#define SERVO_PIN       9    // what pin is the servo on?
#define LEFT_EXTENT     0    // how far left should the servo go?
#define RIGHT_EXTENT    180  // how far right?
#define PAUSE           500  // how many milliseconds between steps?

Servo myservo;

void setup() {
  myservo.attach(SERVO_PIN);
}

void loop() {
  myservo.write( LEFT_EXTENT );
  delay(PAUSE);
  myservo.write( RIGHT_EXTENT );
  delay(PAUSE);
}

Video Music Credits

The music in the video is by Morusque (CC BY-NC): http://ccmixter.org/files/Nurykabe/32448

Updated Name

I realized that Popsicle was actually a registered brand name and not just a common word, so in order to avoid any confusion or trouble, I changed this little guy’s name to StickBot. This project does not (and never did) have anything to do with Popsicle brand ice pops. In fact, I’m not even sure the craft sticks I uses were actually from Popsicle brand ice pops. So my sincere apologies to the Popsicle people; I hope you continue to let me eat your ice pops because life would simply not be the same without them!

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Here’s a list of common abbreviations for electronic components on circuit boards (PCBs).

AE Aerial (antenna)
B Battery
BR Bridge rectifier
C Capacitor
D, CR Diode
DSP Digital signal processor
F Fuse
FET Field effect transistor
IC integrated circuit
J Jumper wire
JFET Junction field-effect transistor
L Inductor
LDR Light dependent resistor
LED Light emitting diode
LS Speaker
M Motor
Mic Microphone
MOSFET Metal oxide semiconductor field effect transistor
OP Op Amp
Q Transistor
R Resistor
RLA, RY Relay
SCR Silicon controlled rectifier
SW Switch
T Transformer
TFT Thin film transistor
TH Thermistor
TP Test point
Tr Transistor
U Integrated circuit
VC Variable capacitor
VR Variable resistor
X Crystal, ceramic resonator
XMER Transformer
XTAL Crystal
Z Zener diode
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If the hot shoe (flash mounting point) on your Canon Digital Rebel camera is loose, then your flash might not be stable on the camera or operate properly. It may not be immediately obvious how to fix it. This video shows you how to do it with a couple of flat screwdriver tips and a tiny PH000 Phillips head screwdriver. (They often sell these in sets of five or seven.) The trick is to lift up on the clip so that the front lip clears its catch and it can slide back. You may need to lift it over the screws as well if they’re really lose.

(Yes, that’s a Spider Man bandage. I have an excuse; I’m a daddy.)

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Here’s a hot wire foam cutter that I made from scraps, following a general design I saw in Make magazine a couple years ago. I picked up 20 feet of 30-gauge nichrome (nickel chromium) wire on ebay for $2.09, shipping included, and the rest of the stuff I happened to have on hand. Aside from the wire, I used a 12V power supply [see power details below] that I got from Radio Shack decades ago, a bit of peg board, some scraps of pine, a few nails, a foot or so of standard household electrical wire, and a steel rod.

Hot Wire Cutter

Hot Wire Cutter

I used the ground wire to fasten the cable tightly against the rail.

Hot Wire Cutter, Side View

Hot Wire Cutter, Side View

From the bottom, you can see how the ground wire loops around, and how the nichrome wire is attached.

Hot Wire Cutter, Bottom View

Hot Wire Cutter, Bottom View

Here’s a name that I carved out of foam. I tried using carbon paper to transfer a printout to the styrofoam, but that wasn’t very effective. Instead I mostly followed the little dent made by the pencil as I tried to trace.

A Name Cut out of Styrofoam

A Name Cut out of Styrofoam

Power Details

I originally used a 12V power supply because that’s what I had on hand, and it didn’t look like it would pull enough current to melt the wire. At about 2 amps, though, it made the wire glow, and I knew that was more than enough heat for the styrofoam. So I decided to reuse an old camcorder power supply that was rated at 7.5V/1.6A. With this power supply, the contraption ended up drawing 1.1A and the wire was at a more “Goldilocks” temperature — not to hot and not too cold. It slows down the cutting a bit, but I think it also makes it more controllable.

Resources

Here are some great resources I found. I wish I’d found these before I started!

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