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.

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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.

Settings

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.

 

HAL 9000: Replica Design

For my design of the HAL 9000 enclosure, I mainly used Adafruit’s HAL 9000 replica guide as a baseline.  However, I decided to 3D print most of the pieces since I don’t have access to a laser cutter or any power tools.

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The only piece that I ended up buying was the button, so I followed that section of the tutorial closely, but mainly used the linked references for the design of the case.

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Because of the 250x150mm limitation of the print bed, I broke up the case into parts.  The two outside sets of pieces are the vertical walls of HAL, the two pieces with center holes are horizontal walls that will have wiring run through them.  The top piece on the center-left side is the top of HAL.  The piece with a grid of holes is the speaker grill.  Lastly are the two black pieces, which form the main plate with a hole for the red “eye.”  Also notice the black rectangle at the top; this will be the space to put the HAL 9000 label.  I left this to save myself time measuring when applying the label.

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The next step was gluing all of the pieces together, and HAL starts to take shape!

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Because the plate is black, even if I don’t cut the label to the exact size, it won’t be noticeable.

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The last step is popping in the painted button, and HAL 9000 is complete!

One additional step I’d like to use in the future is applying the same coating, sanding, and painting steps I used for the sword on HAL, to make the replica look more metallic and accurate.  This would not only help cover up the seams between parts but would also help me replicate the brushed aluminum look on the original HAL’s black face plate.

 

3D Printed Sword: Design

After OpenADR was not selected as a finalist in the Hackaday Prize Automation Challenge, I decided to take a brief break from working on the vacuum after working in full-fledged competition mode for the previous few months.  I spent a few weeks trying to think up simple projects that would keep me occupied but wouldn’t take up too much of my time.  I also wanted to use this time in between big projects to develop new skills and get outside of my comfort zone a little bit with a project that I wouldn’t normally pursue.  At last, inspired by the wide array of medieval props I saw at the Pittsburgh Renaissance Festival, I decided to 3D print a medieval longsword and attempt to make it as realistic as possible.

Challenges

While 3D printed parts certainly aren’t new territory for me, designing a realistic weapon really pushed me to think through challenges that I had not encountered before. Creating large and unwieldy objects using FDM introduces new constraints in terms of printability and strength.  When creating my own parts from scratch, I have a lot of flexibility and can design pieces while keeping in mind the limitations of 3D printing . For this project though, I had to rethink the design process to make printing possible because I was trying to replicate something that (1) exists in the real world and thus should look a certain way and (2) wasn’t designed to be easily 3D printed.  Strength is also a concern as 3D prints are notoriously weaker than regular, injection-molded plastic parts and can delaminate when too much stress is applied across the Z-axis. I wanted the sword to be as realistic as possible (i.e., long and pointy), so keeping the sword sturdy without too much bending was also a big priority.

In addition to the 3D printing structural challenges, appearance was also a big concern – this too is where I wanted to push myself.  It isn’t easy to pass off a plastic part as metal given the differences in texture and shine.  Furthermore, given the size of the sword, I had to print the blade in segments, and so finding a way to smooth out the joints was a significant problem in addition to the normal visibility of  layer lines. Just designing, printing, and assembling the blade (a.k.a. all the things I already knew how to do!) was the easy part – the bulk of the work was in the finishing stages of making the sword look realistic.

Design

I started this project by researching the general properties of longswords.  I spent a lot of time looking at modern replica swords, movie swords, and historic swords from the middle ages so I could get a good idea of what I wanted my own sword to look like.  Two great references that I found were the Wikipedia page for longsword and the website My Armoury, which has more history, mechanics, and specifications of medieval weaponry than you could ever possibly need.

From those resources, I determined that I wanted a sword, roughly 1.1-1.2m in length, with a blade about 90cm long, 5cm wide, and 5mm thick.  In additional to the dimensions I also wanted accurate blade geometry.  This required me to read up on blade cross sections, profile tapering, and distal tapering.  I also decided to print out the sword in PLA due to its stiffness and ease of printing.

Blade

Mechanics

My primary concern, at first, was the thickness of the blade.  While PLA is stiffer than ABS, it is still pretty bendy when it comes to a meter long part that’s only 5mm thick.  PLA is also brittle so it wouldn’t take much bending to snap the blade.  To alleviate these concerns, I decided that the blade should have steel rods at its core.  I still had plenty of 2mm x 300mm steel rods that I used as axles for OpenADR, and decided to use these.

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The next concern was print geometry.  A meter-long blade obviously wasn’t going to fit on my Printrbot, so I needed to determine how to split it up into multiple pieces.  The two obvious options were splitting it down the middle lengthwise and printing it in multiple left and right half chunks (left image).  Extending this idea, I could have also had the left and right chunks mismatched (middle image) so that it’d be harder for the blade to break along the blue, horizontal lines.  The last option would be printing out vertical chunks of blade (right image) without any bisecting along the long axis.  For all of the options, I planned on using cut sections of 2mm steel rod to hold the parts together.

I ended up going with the last option for several reasons.  My concern with the first two options was warping.  A big benefit of bisecting along the long axis was that it would allow me to print out large chunks on the long, 225mm X axis of my Printrbot.  However, 225mm is a big 3D print and tends to cause warping, even using PLA.  Without the strength advantage of large, sturdy sections there wasn’t much point to the left/right bisection option.  I was also concerned about space for the metal spine and connectors in the first two options.  While a single 2mm rod fits fine in a 5mm blade, the blade thickness quickly decreases due to the distal taper.  It quickly reaches a point where both vertical and horizontal steel rod connectors won’t fit in the blade cross section.  With the last option, all I needed to add was a single vertical rod to hold the segments together.

Aesthetics

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With the mechanical design handled, the next step was the aesthetics.  The first thing I tackled was the blade cross section.  It seemed like historically, the most common types of blade cross section were lenticular and diamond, with the former being popular in the early middle ages and the latter becoming more popular in the late middle ages.  Considering this, I opted for the diamond cross section, thinking that its flat features would be easier to sand later on.

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Despite going with the diamond cross section, I still designed both main options. One of my secondary goals for this project was to make everything available in OpenSCAD so others could design and print their own swords, and so I wanted to design the different options as modules in case someone in the future has more patience for sanding than I do.  I also included the option for fullers.  While I ultimately didn’t include fullers in the blade I made,  mainly due to concerns about thickness and strength, they certainly add aesthetic appeal when included.

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The next step was designing the actual blade.  To help simplify the implemention in code, I mostly based the profile taper of my blade designs on mathematical equations, with one custom option as well.  From left to right, the blades shown above were designed as follows:

  • A custom blade that has an array of widths passed in.  To demonstrate this I went with a sawtooth-like design, but it’s currently extendable out to any design as long as it’s symmetrical across the z-axis.  There was no historical precedent for this blade type, but it seemed like a cool option to have.
  • An elongated elliptical blade with the ellipse length and width passed in.  Historically, this kind of blade provided a good compromise between a cutting and thrusting, allowing a wide blade without sacrificing the sharp point.
  • An exponential blade with the width of the blade decreasing exponentially.  Again, this didn’t really have any historical precedent, but it was easy to add and has an interesting aesthetic.  Without a point, this blade would be no good for thrusting but would provide a good cutting edge.
  • A linear blade with the blade tapering to a fine point.  Historically this type of blade was used predominantly for thrusting.

For the aesthetics I was looking for, I went with the elliptical blade because I thought it looked like a traditional middle ages longsword.  With the width of the blade only tapering off at the very point, it also provided a good amount of structural integrity.

Printability

With the entirety of the blade designed, the next step was making it printable.  I quickly refactored the design of the blade so that the 90cm blade is broken up into 18 50mm segments.  The blade segments were then separated and spread out so as to be printable.  I also added ~2mm holes in each segment to allow space for the metal spine.  The width and thickness at the bottom of the blade had enough space for three metal spines, which allowed for an increase in stiffness and strength.

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I discovered a problem when adding in the spine, however.  Originally, I kept the distal taper of the blade the same as the profile taper, so the blade was the top half of an ellipse when viewed across both the X and Y axes.  However, while the blade was thick enough to allow for a 2mm hole at the base, this quickly became impossible toward the top of the blade.distaltaper

To alleviate this, I tripled the width of the ellipse (in terms of blade thickness), but capped the maximum value at 5mm.  An exaggerated example of this is shown in the picture above.  The blade is constant 5mm thick for the bottom half, but still tapers off at the top.  Due to how thin the blade is, this modification is barely noticeable.

One thing to note when looking at my OpenSCAD code is that I only made this printability modification for the elliptical blade.  It took some tweaking to get everything configured correctly, and I didn’t want to spend too much time tweaking for blades I had no intention of printing.  I might go back in the future to fix this, but for now the printability and segmentation code will have to be ported to the other blade types to print one of the other blades.

Hilt

With the blade complete, the next step was designing the hilt.  The three parts on a traditional, medieval sword are the crossguard, grip, and pommel.  I was going to design something elaborate and decorative, but decided I’m no artist, and OpenSCAD doesn’t lend itself well to organic and artistic designs.  Instead I opted for more spartan, geometric designs.

Crossguard

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The two options in the back were the customizeable options with an elliptical shape in the back and rectangular one in the front.  Two arrays are passed into the modules that determine the width and height of the shape from left to right.  I liked the custom rectangle shape so much that I went with that design for my final crossguard.  The front two options are a flat hilt and curved hilt with pointed edges.

Grip

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The grip is just a simple octagonal shape that I made by creating an OpenSCAD cylinder with eight sides.  I designed it to be printed in two pieces because the entire 200mm piece wouldn’t fit on my printer.  I also included a little octagonal segment in the middle, that’s printed separately, in case I wanted a visible separator for the two-handed grip.

Pommel

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The last piece is the pommel.  On a normal sword this acts as both a counterweight for the blade and a means of preventing hands from slipping off the grip.  Since everything is made out of plastic, and because I don’t intend on using this as an actual sword, this piece is purely decorative.

I was originally going to make this part a little extravagant with a gemstone and went as far as designing it, but decided to go with a simpler approach to keep with my minimalist design.  The left design is the gemstone pommel.  The four holes in the base cylinder are meant to have paperclips inserted that can then be bent to hold in the stone.  For gemstones I was intending to use some fake pirate gems I found on Amazon, but a gemstone mock-up was provided in the OpenSCAD design as a visual reference.

The design I ended up using is on the right.  It’s a simple low-poly shape and went well with the rest of the hilt.  It’s an octagonal shape made in the same fashion as the custom blade and crossguards with a customizeable array that determines the radius of the octagon.

With the design work all finished, the next steps are printing, assembling, finishing, and then finally painting the whole thing! So next post – Keith gets crafty!

OpenADR: Pump Test

While I’m putting the design for the OpenADR mop module together, I decided to do a quick test of the 3D printed pump I’ll be using to move the water/cleaning solution from the internal reservoir to the floor.  The pump I am planning to use is a 3D printed peristaltic pump from Thingiverse.

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For my test setup, I used the another of the cheap, yellow motors that I powered the wheels on the main chassis and the brushes on the vacuum module to drive the pump.  I threaded some surgical tubing from a full glass of water, through the pump, and into an empty glass.  I then ran the motor off of 5V.

Overall the pump ran great, albeit a little slower than I anticipated.  The next step is integrating it into the mop!

OpenADR: Mop Design Decisions

In my last post, I described the beginnings of the first module for OpenADR, the vacuum.  With the Automation round of the Hackaday Prize contest ending this weekend, though, I decided to start working on a second module, a mop, before perfecting the vacuum module.  The market for robotic vacuum cleaners is looking pretty crowded these days, and most of the design kinks have been worked out by the major manufacturers.  Robotic mops, on the other hand, are far less common with the only major ones being the Scooba  and Braava series by iRobot.  Both of these robots seem to have little market penetration at this point, so the jury’s still out on what consumers want in a robotic mop.

I’ve been thinking through the design of this module for a while now. The design for the vacuum module was simple enough; all it required was a roller to disturb dirt and a fan to suck it in. Comparatively, the mop module will be much more complex.  I don’t plan on having any strict design goals yet for the mop like I did with the vacuum given that the market is still so new.  Instead, I’ll be laying out some basic design ideas for my first implementation.

The basic design I envision is as follows: water/cleaning solution gets pumped from a tank onto the floor, where it mixes with dirt and grime.  This dirty liquid is then scrubbed and mopped up with an absorbent cloth.  I know that probably sounds fairly cryptic now, but I’ll describe my plans for each stage of this process below.

Water Reservoir

Both the Scooba 450 and Braava Jet have tanks (750mL and 150mL, respectively) that they use to store cleaning solution or water for wetting the floor.  The simplest way to add a tank to the mop module would be to just integrate a tank into the module’s 3D printed design that I described in an earlier post.  This is a little risky, however, as 3D printed parts can be difficult to make water tight (as evidenced by my struggles with sustainable sculptures).  Placing the robot’s electronics and batteries near a reservoir of water has to potential to be disastrous.  A much safer bet would be to use a pre-made container or even a cut plastic bottle.

Being an optimist, however, I’d rather take the risk on the 3D printed tank to take advantage of the customizability and integration that it would provide.  In the case of the sculptures, I wanted to keep the walls thin and transparent.  I won’t have such strict constraints in this case and can use a much more effective sealant to waterproof the tank.  And just to be on the safe side, I can include small holes in the bottom of the chassis (i.e., around the tank) near any possible leaks so the water drips out of the robot before it can reach any of the electronics.

 

Dispensing of Water

 

The next design decision is determining how to actually get the water from the tank to the floor.  While I looked for an easily sourceable water pump, I couldn’t find a cheap one that was small enough to fit well in the chassis.  Luckily there are some absolutely amazing, customizeable, 3D printed pumps on Thingiverse that I can use instead!

Disturbing Dirt

The biggest complaint when it comes to robot mops seem to be a lack of effectiveness when it comes to scrubbing dirt, especially with dirt trapped in the grout between tiles.  The Braava uses a vibrating cloth pad to perform its scrubbing while the Scooba seems to use one of the brushed rollers from a Roomba.  Both of these options seem to be lacking based on users’ reviews; the best option would be to use scrubbing brushes designed especially for use with water (rather than the Roomba’s, which are designed to disturb carpet fibers during vacuuming). As with the vacuum module, however, I had a hard time finding bristles or brushes to integrate into my design.  Unfortunately using a roller made of flexible filament (i.e., my solution for the vacuum module) isn’t an option in this case, since it’s not capable of the same kind of scrubbing efficacy as a regular mop.

For my first version, I’m just going to use a microfiber cleaning cloth.  This has the benefit of being washable and reusable, unlike the cleaning pads on the Braava, and yet I can still achieve some scrubbing functionality by mounting the cleaning cloth to a rotary motor.

Water Recovery

A mop that leaves dirty water on the floor isn’t a very effective mop, so some sort of water and dirt recovery is required.  The Scooba uses a vacuum and squeegee to suck the water off of the floor back into a wastewater tank.  The Braava’s cleaning pad, on the other hand, serves double duty and acts as both a scrubber and sponge to soak up the dirty water.  Both of these options seem perfectly valid, but the Braava’s method seems like an easier implementation for a first revision.  It’s also the method that conventional mops use.  The microfiber cloth I decided to use for scrubbing can also serve to absorb the water and dirt from the floor.

It’s important to note, however, that using the absorption method for water recovery limits the robot’s water capacity and the amount of floor it can clean.  The mop could have a 10L water reservoir, but if the cloth can only absorb 100mL of there will still be 9.9L of water left on the floor.  The Braava only has a 150mL tank and 150sqft. of range because its cleaning pad can only hold 150mL of water.  I’ll have to do some testing on the microfiber cloths I use to determine the maximum capacity of the mop module.

Next Steps

Designing and printing out the mop module!