Tag Archives: success

Hack-O-Lantern

Halloween fast approaches, and I still haven’t managed to make that electroluminsencent Riddler costume I’ve been dreaming about for the last two years. But this year I did manage to come up with a nifty Hack-O-Lantern that uses an Arduino and a pair of diffusers that I printed on my MakerBot Replicator. Here’s what the animation looks like, including my new favorite function, derp().

My apologies for the soul-deadening ambient light in the video. The Hack-O-Lantern looks a lot cooler in person, although if I had more time I’d try to boost the voltage to the LED’s and brighten them up a bit. Right now they’re running off straight off the Arduino, and I didn’t want to burn out any pins by driving too much juice. Maybe next year.

You don’t need to use an Arduino to use these diffusers: if you’d rather just stick a couple of LED’s in there with a watch battery taped to the leads, that will work just fine. The LED’s in the top photo are running in series off 4X 1.2V NIMH 2500 mAh rechargable C cells, and they look great.

The diffuser has a slight lip on the back that you can use to score your pumpkin’s flesh before cutting.

Nightmare fuel, anyone? Here’s all 14 LEDs soldered to hookup wire, fed through the pumpkin’s eye holes.

Once I connected the LEDs to pins 0-13 on an old Arduino Duemilanove I had kicking around (SCORE for finding a set of headers I’d forgotten I ordered six months ago), I put the whole contraption in a plastic bag so the pumpkin guts couldn’t short the hardware.

Working inside that cavity gives you a lot more respect for brain surgeons.

If you’ve carved a pumpkin recently, you’ve probably got some seeds kicking around. Here’s what I’ve been doing with them lately:

Zheng3 Szechuan Pumpkin Seeds

approximately 1.5 cups of pumpkin seeds, washed.
1 tablespoon doubianjiang
1 teaspoon light soy sauce
1 teaspoon hot chili oil
2 tablespoons peanut oil
1 tablespoon Szechuan peppercorns

Mix everything except the peppercorns in a bowl and toss to coat. Set aside for an hour to marinate.

Toast the peppercorns in a wok over medium heat until fragrant. Crush with a mortar and pestle.

Spread the pumpkin seeds and marinade evenly on a flat baking tray. Bake at 350° for about 20 minutes. Sprinkle with the crushed peppercorns and serve.

If you can’t find doubianjiang and you’re not willing to wait for a shipment from Amazon you can probably substitute some garlic powder mixed with Sriacha rooster sauce.

Approximating the flavor and mouthfeel of Szechuan peppercorns is more difficult. Try this:

Dip a jalapeño pepper in powdered laundry detergent and suck on it for 30 seconds. Then put your lips across the terminals of a 9V battery.

It tastes better than it sounds, believe me.

You can download the STL’s and Arduino code here.

The Perfect is the Enemy of the Good

This happens to me all the time. I start looking for information on some technical subject and I end up wading through ancient forum posts and forgotten wikis in a fruitless search for clues. A lot of this stuff seems to be written by and for people smarter than I am. It can be very frustrating.

I usually just want to do X, where X is something straightforward like “pause the print, move the Replicator’s extruder head out of the way, wait for user input, and then resume the print.”

After a few hours of of data forensics and a fair amount of trial and error I have a gCode solution for X. Keep reading.

This is the beginning of a Seej Tournament Bloxen print.

I found the need for this script when I started printing with PLA a week or so ago. I haven’t got the temperatures quite down yet, so my rafts curl up a bit at the edges and sooner or later end up taking the whole print for a joyride around the build platform.

I’m still looking for that perfect raftless print, but along the way I’ve got to actually produce some printed models. So I’ve taken to printing a raft, pausing, and then using painters’ tape to bind the raft down to the build platform.

I’m a huge fan of having a bag of popsicle sticks around any hobby project. They’re cheap, disposable, and can be quickly modified into a variety of simple tools (gaffs, hooks, spreaders, etc) with a pocketknife. They’re also great for evenly applying painters’ tape to rafts.

It’s kludgey, but it works. The only problem I’ve had so far is getting around the print heads to get the tape down on the raft, but with this new script the Replicator moves the nozzles out of the way before pausing the print.

Fair warning: this worked on my Replicator, but there are no guarantees it will work on yours. If this code crashes your extruder head, slags your controller board, or burns your house down and torches all you hold dear and dry-humps the ashes, it’s not my fault.

That said, it’s pretty vanilla gCode and I don’t expect you’ll have many problems with it, assuming your gCode is using millimeters and absolute positioning, which I think is the default output from ReplicatorG.

The first lines you’ll need to look for are:

(<raftLayerEnd> </raftLayerEnd>)
M73 P6 (display progress)

This indicates the end of your raft’s print. The next significant line you’ll see is one that begins with G1:

It should look something like G1 X-4.8 Y-4.68 Z12.6 F3300.0

This is telling your Replicator to start extruding the first layer of your model. In between these two significant lines, you’ll have to add this code:

G91 (*set to relative positioning*)
G1 X-60 (*move the print heads -60mm in X, assuming the print is using mm*)
M71 P60 (Press button to resume print)
G1 X60 (*move the print heads back 60mm in X*)
G90 (*return to absolute positioning*)
M73 P6 (display progress)

Be careful with your X move values. I don’t see anything keeping you from accidentally ramming your extruder heads into the side of your Replicator with too large a value.

I’m sure there’s a more elegant way to write this code, but I’m never one to let perfection be the enemy of the good. It’s done, it works, and I can improve upon it later.

This code also seems to disable the Pause button once the user has pressed it, which is irritating but I can’t bring myself to spend the energy tracking that particular bugaboo down. I’d also like to find a way to get the nozzle’s current position, move the heads, and then return to that position. I’ve found tantalizing hints on just how to do that, but that’s a hack for a different day.

Socket to me.

I can’t think of many designs that aren’t improved by making them glow. LED’s are the tinker’s equivalent of Photoshop Layer Effects.

The LED socket is my attempt to play industrial designer; I wanted to make an object that was intuitive, elegant, and easy to use. So I started small.

It’s designed to hold a 5mm LED and battery without trimming the leads.

The recessed cradle for the LED is straight on one side so the user is guaranteed to get the orientation of the cathode correct. The grooves on the sides should just fit 5mm LED leads if they’re bent with two 90° angles around the bottom of the socket.

The bottom of the socket is also grooved so that the socket can stand on its base like a candle.

Instructions: Feed the leads through the holes at the top of the socket. Insert the battery through the hole at the bottom of the socket. If the bulb doesn’t light, flip the battery around.

Once the bulb is lit, bend the LED leads around the bottom of the socket and press them into the side grooves to keep them out of the way.

This uses a DL1025 or equivalent battery.

Zheng3 Penny Ballista

This nefarious device can easily launch a U.S. penny across a room when printed at 1:1 scale. It’s one of the primary engines used in a game of Seej.

This is another design inspired by The Art of the Catapult.

The nock on this model is the very tip of the throwing arm from the Zheng3 Penny Catapult, turned on its side and modified a bit so that it fits smoothly into the firing groove.

I repurposed the winding keys from the Zheng3 Penny Catapult to hold the ballista’s rubber bands in place.

To assemble:

Construction is really simple! Needlenose pliers are recommended, but not strictly necessary.

You’ll need two elastic bands to complete this ballista. Tie a single band through the bore on one of the two D-shaped locking keys. Repeat the process with the other locking key.

Feed the end of one band through the rectangular bore on the ballista’s left post. Insert the tenons of the locking key into the square mortises on the post to lock the band in place. You’ll be tempted to repeat the process with the other side, but don’t give in. It will save you precious minutes of frustration.

Unlike the Zheng3 Penny Catapult, these locking keys should be a snug fit. If some settling of the plastic during printing has made the mortises too small, trim the tenons a bit with your blade of choice.

Center the nock on the knot that connects the two rubber bands. Make sure that the penny’s cradle is facing forward.

Feed the end of the band that’s been locked down through the rectangular bore on the nock. Tie the free end of the band to the second band. Now feed the free end of the second band through the outside of the rectangular bore on the right post and loop it through the second locking key.

The nock has a wee nub on its underside. Slide this nub into the ballista’s firing groove; it will improve accuracy.

Load a penny into the nock, pull it back, and fire away. Be safe! Don’t hit the cat.

Flagrant stagecraft alert: There’s a piece of hookup wire holding the nock in firing position for dramatic flair.

You can download this model for free here. You might also be interested in the Seej Starter Set.

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The Penny Catapult

Download the STL here!


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Here’s a basic torsion catapult. It uses one or more elastic bands to launch a U.S. penny if you print it at 1:1 scale. You probably won’t get enough torque to be impressive with less than 3 bands.

Construction is snap-together, but it wouldn’t hurt to put a drop of super glue on the joints for durability.

Feed an elastic band through each of the bores on the side braces. Tie it through the bore on each winding key. Slip the end of the throwing arm through the rubber bands. Repeat with as many rubber bands as will fit through the holes.

Twist each key 10 times and then lock it in place by inserting the locking tenons into the square holes on the side braces. The more twists, the more launching power you’ll have. Careful, pennies can sting, especially if you take an Abe to the forehead.

You can change the payload’s arc by raising the front of the catapult.

Inspiration for this catapult came from The Art of the Catapult. You won’t find a better introduction to medieval siegecraft than this book. It’s got plans to build all kinds of stuff from catapults to trebuchets. Very kid-friendly.

If you read The Art of the Catapult you’ll learn that “catapult” is more of a catch-all term for this breed of siege engine. This model would more properly be called a mangonel.

If you’re looking to build stuff with a PG rating, Whoosh Boom Splat: The Garage Warrior’s Guide to Building Projectile Shooters is a better bet.

Flagrant stagecraft alert: the clever-eyed among you will note the use of black electrical tape to keep the throwing arm cocked for the photo.

ReplicatorG Settings:

HBP: 120° C
1.8mm Black ABS
Using Raft
Layer Height: .25
Number of shells: 1
Feedrate: 25 mm/sec
Travel Feedrate: 55