Alien Clock: Extending the Clock Hands

Despite the modifications I made to the Facehugger (adding a cutout for embedding the clock mechanism), the shaft of the mechanism doesn’t quite reach all of the way through.

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To remedy this, I attempted to design two nested tubes to extend the minute and hour shafts, which were 3.5mm and 5mm respectively, through the 8mm hole in the Facehugger. On top of these tubes I added keys so that the hands that came with the clock could still be used. Unfortunately, printing nested tubes accurate to 0.05mm while only 3mm thick, all with a 0.4mm nozzle is almost impossible.

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Above is a picture of the outer tube that extended the hour shaft. It doesn’t look too awful, but some intense boogering is visible on the right side. This part is the key that would go in the original hour hand. The minute hand didn’t turn out so well and was essentially one long 3D print blob. I briefly looked into buying a precision 0.2mm nozzle for my Printrbot, but with the ceramic tips currently out of stock I had to think up another way.

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So keeping the trouble I had in mind, I reprinted the Facehugger with a 20mm diameter hole for the clock shaft instead of the original 8mm.

Then, taking advantage of the larger diameter, I designed wider extender shafts (19mm for the hour hand and 14mm for the minute hand). I was also able to make the walls of the shaft thicker, giving the printer more space to accurately print the piece. I also decided that, rather than reusing the hands provided with the clock mechanism and having to design an adapter from the extender shaft to the keyed holes in the hands, I’d design my own that were more in line with the aesthetic of the clock.

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Using the grown Xenomorph tail as inspiration, I designed both clock hands.

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As visible above, the Xenomorph tails look fairly accurate and fit perfectly! Because the 3D printed clock hands were roughly twice as heavy as the thin metal ones that came with the clock, I was a little worried that the clock wouldn’t have enough torque to lift the hands. However, after some brief testing, the clock doesn’t seem to have any trouble with the heavier hands.

Alien Clock: Working Cuckoo Mechanism

The cuckoo mechanism is done, and it works! Below is a description of each of the printed pieces and a video of the mechanism in action.

 

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The main pieces are the four racks and the motor carriage. The racks provide a linear channel for the pinions to crawl along. The motors are mounted into the carriage with the four pinions on the two motor shafts.

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The four racks are mounted together with the backstops facing outwards. This serves to contain the pinions so they’re incapable of derailing.

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The carriage with the two motors mounted.

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The 3D printed parts and motors assembled.

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The entire assembly. I used a wooden dowel that I had on hand to hold the Chestburster and fit into the carriage.

Above is a demo video of the Chestburster actuating. I’m controlling it with an L9110s motor controller to get the required bidirectional motion. Mounted limit switches are visible on top of the assembly glued on the top racks. These currently aren’t wired to anything but would serve as a way for the Arduino to detect that the end of travel has been reached so it knows to stop sending current to the motors. Right now, however, I’m just using delays to run the motor approximately long enough to hit the end stops.

I’m considering keeping the setup like this and not using the limit switches at all. The travel distance is so short, and the time it will be running is so infrequent, that I think the simplicity of not having to use the limit switches would be worth the slight increase in the wear-and-tear on the motors due to stalling out. Another reason I’m considering this is because the limit switches may not match up perfectly with end of travel. Something I didn’t address in my mechanism was the mechanical linkage of the two motors. Because they’re not directly coupled, it’s possible for one motor to operate slower than the other, thereby causing the carriage to misalign and one motor be closer than the limit to the other. Applying current when one motor is at the end of travel limit would cause the faster motor to stall, but would give the slower motor a chance to catch up and resynchronize.

Alien Clock: Cuckoo Mechanisms

A cuckoo clock wouldn’t be very interesting if something didn’t pop out at the top of the hour. The obvious choice here is for the Chestburster to act as the cuckoo. This requires some form of linear motion to attain. I briefly entertained the idea of buying a linear actuator but couldn’t find anything that was the right speed and price.

So the alternative was using regular rotary motors and designing a rotary-to-linear motion converter. Luckily I have a whole drawer full of cheap DC motors from my work on OpenADR. Next, linear motion is a well-documented subject so designing a converter couldn’t be that hard, right?

As it turns out, it can. I am by no means a mechanical engineer. My degree and job are in computer/software engineering, so I had a great deal of trouble designing a linear mechanism I was satisfied with. I also wanted to avoid complex control electronics, so I wanted a design that produced reciprocating motion. This would let me to use a basic MOSFET to control the motor in a single direction along with a limit switch to detect a full stroke from the cuckoo.

Naturally, I chose to use a piston mechanism, most commonly used in cars to convert linear motion to rotary motion. The motor turns a linkage arm which then forces the piston (in my case the Chestburster) up and down a guide channel. The direction the motor is spinning doesn’t matter and a limit switch at the bottom of the guide would detect when the piston is fully retracted.

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I got as far as designing the whole mechanism for 3D printing before deciding to scrap the it. The large number of linkages added unnecessary complexity and I was worried about the arms bending or snapping. Additionally, with the length of the guide added to the lengths of the arms, the whole mechanism was too long to fit in the depth of a human sternum and therefore the mannequin.

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My next thought was to use a Scotch yoke mechanism. It’s much simpler, shorter, and wouldn’t require multiple axles to be added for assembly. The red part at the bottom of the design is a telescoping tube assembly to help reduce the depth of the design. I got as far as printing and assembling the mechanism (minus the telescoping tubes). Unfortunately, the design broke pretty much right out of the gate. The slot in the yoke requires low friction to work properly and the friction of the PLA on PLA proved too much. The axle going in the slot snapped off far too easily.

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So with my previous two attempts failing, I decided to eschew reciprocating motion for something simpler. I have a few spare L9110s motor controllers and can afford to use one if it makes the mechanical design easier. So I opted for a rack and pinion system. This is essentially just a linear gear being driven by a rotary gear. By mounting the motors on the carriage within four racks, simple and constrained linear motion is achieved. This also allows for the depth of the mechanism to be equal to the height of the Chestburster. There are also plenty of rack and pinions available on Thingiverse and so I found one to use for my system.

Alien Clock: 3D printed parts are done!

I’ve finally finished the 3D printed Facehugger and Chestburster!

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The Chestburster was a simple print that used a file sourced from Thingiverse. I’m pretty happy with the way it turned out. I printed it with PLA at a 0.2mm layer height to get a good balance between speed and resolution. One issue I did notice was a striping along the Z axis. After some investigation, I attributed this to a slight bend in the Z-axis screw on my Printrbot. The striping is pretty faint, however, so I’m hoping that a layer of paint will cover it up. Additionally, there’s already a hole in the base of the Chestburster design which will make mounting it to the cuckoo mechanism trivial.

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The Facehugger was a little more difficult. I also sourced this from Thingiverse. This is an amazing piece of work by user Agisis that’s perfectly split up for 3D printing. It’s also divided into opposable pieces which will make attaching it to the victim’s face much easier.

However, because the Facehugger will be making up the clock face, I wanted to modify the body so the clock mechanism can be easily inserted. I also wanted to provide a hole in the front for the main shaft to protrude through. Unfortunately, after importing the STLs into OpenSCAD to modify, I found out the file had a bunch of errors and OpenSCAD couldn’t render it properly. After running the complex body through several STL-cleanup programs (e.g. MeshLab, Netfabb, etc.) I still couldn’t get OpenSCAD to render. About to give up and resort to drilling a hole through the completed body, I decided to read through the 150+ comments to see if someone else had encountered the same problem (Side Note: If you read through the comments, you’ll see that Agisis is one of the most helpful authors on Thingiverse. He provides a bunch of assistance to people having issues with printing, and provides a lot of advice for painting the finished product.). Lo and behold, user rodrifra had already fixed the STL files. With the repaired STL files, modifying the body was simple and all that was left was printing!

I printed one leg at a time in PLA at a 0.1mm layer height, for maximum resolution. At an hour and a half a leg, it took a while! Next was the tail, which I printed in three parts with the same settings for a total time of five hours. Last were the body files. I printed both pieces at a 0.2mm layer height to speed things along, and am happy with the results! The bottom took a total of an hour and a half to print and the top took two and a half.

Next up for these parts is gluing everything together and then painting!

Alien Clock: Description

Note: This is a mirror of my "Alien Cuckoo Clock project" submitted to the 2017 Hackaday SciFi contest. For more information, visit the project link.

The Alien Cuckoo Clock consists of several discrete pieces that will be combined to form the clock. The different pieces are:

  • Facehugger
  • Chestburster
  • Clock mechanism
  • Cuckoo mechanism
  • Mannequin
  • Electronics

Thingiverse is a great repository for premade 3D printed files and many of the designers there are far more skilled in 3D modelling than I will ever be, so I’ll be reusing open source designs from there for the Facehugger and Chestburster. I will, however, be painting them myself.

Rather than reinventing the wheel (errr… clock) I decided to buy a clock mechanism to use as the clock internals and hands. The upside of this is not having to handle clock controls or complicated gearing, but the downside is that the cuckoo mechanism will have to be synced with the clock somehow so it can be properly triggered at the top of the hour.

I’ll be designing the cuckoo mechanism myself, probably using gears or other basic components from Thingiverse. I have quite a few spare, generic, yellow motors from OpenADR, so I anticipate designing a mechanism to convert that rotary motion into the linear motion required by the Chestburster cuckoo.

The mannequin will serve as the body of the Facehugger/Chestburster victim (chestburstee?). I anticipate finding a spare full-body mannequin, if possible, and cutting off the lower portion and arms. However, if I can’t find one I can create the torso using duct tape casting and find a lifelike mannequin head on Amazon.

I’m hoping to keep the electronics for this project as simple as possible. I have plenty of Arduino’s laying around so I’ll be using one for the controller in addition to a few end-stop switches for the cuckoo mechanism and maybe a hall effect sensor to detect the top of the hour.

3D Printed Sword: Build

Printing

Material

The filament I decided to use was silver Hatchbox PLA.  After printing the coloring of the plastic turned out more of a shiny gray than a silver.  While I knew I was going to paint the sword anyway, I wanted a grayish base color so that the color of the filament wouldn’t show through.  Plus, if the sword ever gets scratched, the dull gray scratch color will look more realistic.

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My biggest concern for the printed parts used for the sword was the strength, specifically the strength between print layers.  This was most critical on the blade of the sword, due to its length and weight providing a lever arm that could cause the prints to snap.  Additionally, due to the way I decided to print out the blade, speed became an issue.  I oriented the sword segments so that the blade was divided along the X-Y plane.  This meant that the longest axis was in the Z direction.  The Z-axis is also commonly the slowest on a 3D printer, mainly because a leadscrew is usually used.  To compensate for all of these design concerns, I tried to find an optimal balance between weight, strength (particularly layer adhesion), and print time.

After reading numerous studies and suggestions, I decided on a layer height of 0.3mm and width of 0.4mm.  I also ran the hotend a little on  the hotter side at 210C.  Because I planned on sanding and finishing, allowing for a little stringing (a common result of too-high hotend temperature) was well worth the added strength and layer adhesion it provided.  I also kept the infill a little low at 10% so the blade wouldn’t be too heavy.

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The 18 50mm segments of the blade are shown above.  They turned out pretty good with minimal stringing.  One noticeable feature on the outside of the blade segments are the vertical lines.  These are caused by interaction between the internal hole perimeters and outside perimeters.  There’s isn’t enough space for both sets of perimeters and so some external artifacts are present on the outside.  Luckily these can be easily hidden by the finishing process.

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The two halves of the pommel didn’t turn out as well as I’d hoped.  Because I printed with the center of the pommel on the bed, there wasn’t enough support for the circular arch that would hold the grip.  This can hopefully be fixed with some sanding and finishing.  Also shown above is the hole that the blade will be glued into.

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Lastly are the grip and pommel.  The grip was printed in two halves and held together by a metal spine.  Three 2mm holes were extended through the length of the grip so the pommel and blade could both be securely attached.

Assembly

The majority of the build time was spent assembling the blade, because it’s the most complex part.  I used cyanoacrylate glue (super glue) due to it’s good adhesion to PLA.  The brand I used was also labeled as “gap filling.”  I figured this would be useful if the tops and bottoms of the blade segments were slightly warped or didn’t match up properly.

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I also used a metal spine to prevent stress on the glue joints and provide additional strength to the blade.  Due to the metal pieces only being 300mm long, I trimmed the rods so that, when transitioning from one rod to another, the joint is in the center of a blade segment.

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I was able to fit three metal spines at the wider base of the blade.

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I cut the metal rods so that a decent portion would protrude from the bottom.  These extra length could then be used to mount the blade to the grip.

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With the pieces all glued together, the next step was coating it!

Finishing

The process of finishing the blade was divided into three main parts, coating, sanding, and painting, with an additional step of leather wrapping the grip.  These steps weren’t terribly difficult, but nevertheless the finishing took a long time, with each step requiring patience.

Epoxy Coating

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The first step in finishing the sword involved coating the plastic in epoxy.  The brand I used was XTC-3D.  It works like most epoxy, involving mixing the two parts together to get a rapidly curing mixture.  I then had about five minutes before the epoxy hardened to brush it on to the plastic.  After this was a four hour wait for the epoxy to finish curing.  Once completely hardened, the epoxy left a hard, clear coat over the plastic.  This had the added benefit of adding more strength to the plastic by holding together the print layers and separate parts.  Because I planned on sanding the pieces anyway, I used an excessive amount of epoxy when coating, as is evident by the visible epoxy drips.

Because I had to apply the coating two each side of the blade separately, I had to wait four hours between each half.  I also wanted to apply three coats to the blade.  What resulted from this was the week long process of coating the blade because I only effectively had time for one half of a coat once I had gotten home from work.

Sanding

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The next step was sanding down the epoxy coating to a smooth, metal-like surface.  This was by far the most tedious process.  I initially bought plain sandpaper and started the process of sanding everything down by hand.  As I soon realized, this was a profoundly terrible idea and would have taken forever.  I shortly gave up and bought a random orbit sander.  The benefit of the “random orbit” was that no directional sanding lines would show up on the finished piece, and so the sword would look uniformly smooth, just like actual steel.

New toy in tow, I forged (pun intended) on with the process of smoothing out the pieces of the sword.  I started out by using 80 grit sandpaper to sand the flat surfaces of the blade entirely flat, and then slowly worked my way through 150, 220, 320, 400, and 600 grit sandpapers.  These left me with an incredibly smooth surface that was ready for painting.

One downside of the sanding that I noticed was that the vibrations caused some of the superglued joints to come undone.  Both the pommel and a piece of the blade had to be reglued.  The blade one actually happened after painting and was difficult to repair.

Painting

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The last step was painting everything.  This was the simplest step, but was still time consuming due to having to wait for each coat to dry before flipping over the sword to paint the other side.  I spray painted each of the pieces separately with silver spray paint, with several coats for each piece.

Leather Wrapping

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As a bonus step, I decided to wrap the hilt in leather to add a nice touch to the finished product.  I cut the leather roughly to size stretched it out a bit, then superglued one edge to the grip.  I specifically left the grip unpainted so that the glue would have a stronger hold on the plastic part.  I then tightly wrapped the leather around the octagonal grip, applying glue on each face.

Failings

While I’m fairly happy with how the finished product turned out, there are two things that didn’t turn out as I’d hoped.  Mainly the stiffness of the blade was lacking and joints between blade segments couldn’t handle the stress of the finishing process.

Stiffness

While the PLA is stiff enough to prevent significant bending, the metal rods have a certain flexibility that allow some give at the inter-blade joints.  As a result, the blade is more flexible than I’d like.  I had to handle the sword very carefully for fear of the joint bending causing the blade to crack or break.  If I attempt a repeat of this project, or something like it, I’ll have to consider a fix for this.

One option would be to use a different type of joint.  The current, flat joint that I’m using allows for some space between the segments where the metal rods can bend.  If I had used some type of overlapping joint it’s possible that the flexibility would have been reduced.

Another alternative would be to use a stiffer material for the blade spine.  Something like carbon fiber rods would be much hopefully be much stiffer.  The only concern with this would be the lack of flexibility putting more strain on the glue joints between segments.

Cracking

The biggest issue I had was with the blade segment joints not being strong enough to withstand the finishing process.  Specifically the vibrations from the sander caused the joint adhesion to fail in one particular spot.

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Near the top of the blade, where the cross section of the blade was small and only one spine held the segments together, the glue joint repeatedly failed.

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At first I reapplied both the glue and the epoxy coating and sanded it down again.  However this caused a second failure, at which point I gave up and just used a lot of super glue and some light sanding.  Fortunately the poor finish isn’t too noticeable at a distance.

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Another part of the blade partially cracked towards the bottom.  Some of the epoxy came out between the blade segments leaving a slight crack.  Because spray paint is so thin, it was unable to hide this defect.

I think the only solution to the strength problem would be to  change the way I’m joining the segments since the superglue doesn’t seem to be strong enough.  Two different methods I could use would be heat or friction welding when using PLA, or solvent welding when using ABS.  These methods would hopefully make the whole blade into one cohesive unit.

Another possible option would be to use a different kind of paint.  I used spray paint which is thin by necessity and has trouble hiding defects.  Using a thicker, brush-on paint would have done a better job hiding the cracks that popped up.

Finished Product

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Despite the issues I had I’m mostly happy with the finished product.  Unfortunately not all projects can be resounding successes, but I learned some new techniques and have a nice decoration for my office now!

OpenADR: Mop Module v0.1

For the sake of design simplicity and ease of assembly, the mop module is broken up in to two main parts based on the module base design.  The front of the module (the 150mm^2 square) is devoted almost entirely to the water storage tank and the rear is where all of the electronics and mechanics are.

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The picture above is a failed print of the front part of the mop module.  Rather than just tossing this piece, I ended up using it to test out the waterproofing capability of the XTC-3D print sealant.  It ended up working perfectly.

Despite the failed nature of the above print, it still demonstrates the main sections of the front of the mop module.  The main water tank is bounded by two walls, the left in the picture being the back wall of the water tank and the right wall being the front.  The small gap between two walls on the right side of the picture is the location of some holes in the base of the module that will allow for the water to be evenly dripped onto the floor.

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This bottom view of the part gives  a better view of the holes

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Two holes in the back of the water tank provide an input to the pumps.  Because combining electronics and water is a big no no, I added some holes in the bottom of the module so that any leaks around these holes would drip onto the floor rather than flooding the electronics section.

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This is the back of the mop module where all of the magic happens.  The holes in the bottom provide mounting points for the two motors that will drive the pumps.

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The two pillars in the very back provide a point to mount the base of the pump.

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The two, dual-shaft motors have one output shaft extending out of bottom that will be connected to the scrubber and one extending upwards that will be driving the pump.

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A picture of the downwards facing shafts.

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The above picture shows the back of the module with all of the hardware mounted.  Unfortunately, I didn’t give enough space for bolt heads that hold the motor in place.  The pumps can’t pushed down as far as I intended and so they don’t line up with the holes I left in the mounting pillars.  Luckily the mounts are sturdy enough to mostly hold the pumps in place and so I don’t need to mount them for testing purposes.

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These are the two halves the the scrubber that will hold the microfiber cloth that will be used to scrub the floor and soak up excess water.  The two halves are made to be pressed together with the cloth sandwiched in between them.

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This picture shows the cloth and scrubber assembled.  I underestimated the thickness of the cloth, so two won’t currently fit side by side.  I’ll need to either make the cloth smaller or move the scrubbers farther apart.

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Above is an overall picture with all of the pieces put together.