Projects

# Honeycomb Puzzle

Daniel Koch

Issue 51, October 2021

An open-ended, adaptable puzzle with a range of complexities and options.

## BUILD TIME: A WEEKEND DIFFICULTY RATING: Intermediate

This puzzle started life as a maths exercise in a year 4 classroom, then evolved into a high school art installation, before suddenly morphing into the puzzle presented. The journey was convoluted but the premise has remained the same: constructing a pattern through a tessellated group of hexagons.

Hexagons seem to captivate children and adults alike. A lot of people find them a visually engaging shape when massed together, even though they’re not terribly common in nature, unless you count the abstract, irregular examples. One of the best examples of regular hexagons en masse is honeycomb, and this serves as the visual inspiration for our puzzle.

It is designed to be very open-ended, meaning there is no fixed way to use it. The basic premise is a frame which contains space for a number of hexagons. Some of these light up, while others do not. All have electrical contacts and magnets on them. There are LEDs in the light-up hexagons, which are wired in parallel so that when one illuminated hexagon is attached to the previous, its LED lights, building a chain. Because all units are externally identical, you have to try a hexagon before figuring out if it is illuminated or not.

When we say open-ended, we mean it. There are multiple ways you can assemble the hexagons electrically, and magnetically. The result is multiple operating modes for the puzzle that you can completely customise.

You may choose to wire all sides of the hexagon to the LED, which means all that needs to be done is to connect the right number of LED hexagons to each other in the right order to complete a path. However, if you choose to wire only two incoming and two outgoing contacts, the puzzle suddenly becomes harder. You have no way of knowing by looking at the piece which of its two sides have active contacts.

The basic premise of using the puzzle is to create a path of light across the otherwise unilluminated array of hexagons. Before delving into how to use the puzzle any more deeply, we will first show you how to build it. It is easier to understand how the puzzle works by seeing it built, so we will show you all the build options and describe how each works. The basic frame and non-electrical components are the same between versions, however, so we’ll examine those first.

# THINGS TO THINK ABOUT BEFORE YOU BUILD

Reading the entire article before you make building decisions will serve you well. The main things to consider are whether you will make the hexagons with the magnet poles facing alternately, or half and half. In other words, three sides of the hexagon with north poles outward, next to each other, and three with south poles outward next to each other; or each hexagon has three north poles facing outward and three south poles outward, in between each other.

The effect of this is that the half-and-half version will only go into the array one way, which makes the puzzle simpler by reducing the rotation options for each piece. Only the location of the piece determines whether it lights up.

Having alternate magnet poles facing outward means the pieces will go into the array in three rotations, meaning that even if a piece is in the right location, it will not light up unless it is correctly rotated if you have chosen the single-path wiring, making the puzzle much harder to solve.

On the subject of the frame, we designed this project to be built with 3mm or 6mm plywood or MDF as a backing, and 42mm x 11mm primed pine as a frame. These are available from major and most independent hardware stores. However, this project’s final construction stage was conducted during Greater Sydney’s lockdown. Because demand for DIYODE tends to increase during these times, and has a readership across the country and beyond, rather than just the local area, we fit the criteria to continue working.

We also fit the criteria to be able to buy supplies during this time. However, lockdowns, whatever we think of them, only work when everyone minimises their time out in the community.

Accordingly, we decided to make the backing and frame from things we already had here in the workshop, and that ended up being foam-cored cardboard. This isn’t as strong or durable for the purpose as the pine/ply option. However, it is easier to work with using basic hand tools, and requires even less skill. In a way, the lockdown made the project more accessible than it was before. You can choose to make a frame from ply and pine, or foam core, or something else, depending on what skills and materials you have access to.

# MATERIALS AND SOURCING

Sadly, magnets of the sort we’re after here are not commonly a retail item. We did find some online sellers who had thicker magnets than we were after, but no one had the right item in stock for the right price. We used 10mm x 2mm neodymium magnets from one of the usual online marketplaces, but if you find a local supplier that we didn’t, please consider them. We prefer to buy from real retailers, even online-only ones, rather than those two other options.

The other major point is the countersunk screws used. These are not commonly a retail item in M3 thread, particularly not in the quantities required. Twelve are needed per hexagon. We sourced these from Element14. This company used to trade as Farnell, but the business has evolved significantly. Once upon a time, you needed an ABN to buy anything.

Now, anyone can order from the website. They are, however, still a trade supplier, so they don’t have the level of question-and-answer time that retailers have. So, while the non-trade maker can’t ask dozens of questions about what they should buy, anything that can be found on the Element14 website can be bought by anyone with a credit card.

# The Build:

Parts Required:JaycarAltronicsOther
1180 x M3x6mm Countersunk Screws *-H3129A
1180 x M3 Nuts *HP0426H3178
1180 x M3 Flat Washers *HP0431H3183
412 x M3 Solder Eyelets *HP1350H1504
49 x Amber LEDs of Choice *  LED Sales: SF_FLAT_AMB
49 x Resistors to Match Chosen LEDs---
6 m Tinned Copper Wire *WW4032WR0420
4 m Red Light Duty Hookup Wire *WH3010W2250
4 m Black Light Duty Hookup Wire *WH3011W2251
590 x 10x2mm Rare Earth Magnets *--Online Marketplace
Materials
Framing Material of Choice, See Text
Glue of Choice, See Text
Rubber Bands
3D Printed Puzzle and Side Pieces

## Materials

* Quantity required, may only be sold in packs.

Quantities based on a build of 64 inactive pieces, 25 illuminated pieces, plus side infill.

Because the electrical aspects of this puzzle are just LEDs wired in parallel, there is no schematic or Fritzing. The different ways to wire the pieces are physically different but would look the same on a schematic and the Fritzing will not add anything to what the photos show. Diagrams are used where relevant.

The puzzle is designed to be contained within a frame made from 42 x 11mm project pine, and 6mm plywood for a backboard, but as discussed, that’s not what you see in the images. The puzzle pieces are 3D printed in two parts. The lid of each is printed in translucent PLA so that it cannot be clearly seen through but will transmit the light from an LED very well. The lower part, the main body, has been printed in eSun Dark Yellow Silk. This is closer to a gold colour than a honey colour but it still has a nice effect and was more accessible and affordable than some of the filaments we looked at which may or may not have looked more like honey.

There are pieces for the edge of the puzzle, which will be fixed to the frame and be non-removable. These are parts of a hexagon: Divided at the edges in one version to form a trapezium, and in the middle of the sides in the other to form an irregular pentagon. As we printed these on a separate printer, they will be obvious in the photos for being printed in eSun PLA+ Gold, a non-silky filament with less vibrancy than the main pieces.

# THE PUZZLE PIECES

The first thing to do is decide how big you want your puzzle to be. The frame is built to hold an array of pieces, and the size of the array is entirely up to you. We chose an 8 x 8 configuration. Print the number of puzzle piece bodies that you need. It is necessary to print the parts and install the hardware before making the frame, because not only do many printers and slicers have a slight tolerance and may print up to a millimetre or so bigger or smaller than the digital model, the hardware will add tiny offsets here and there, too. The results will add together to be a small but significant difference.

For each puzzle piece, install twelve sets of contact hardware. These are a 6mm M3 countersunk screw, flat washer, eyelet terminal, and nut. The head of the screw should protrude ever so slightly from the surface of the outside of the piece, by a matter of 0.2mm or less. It’s just enough to make contact over the face of the plastic. You may need to vary the amount depending on the quality of the print. In the inside, the washer, terminal, and nut go on in that order. There are six screw holes along the top of the piece and six along the bottom. Note that on pieces which will not illuminate, you may omit the eyelets and even the washers.

Next, it’s time to get the glue out. You can use any glue of preference but we chose hot melt glue. While it’s annoyingly stringy, it sticks well to PLA and the surface of the magnets, and is a good compromise between strong and removable. Glue six magnets into the recesses, ensuring they are just below the surface of the print, again by around at least the 0.1mm to 0.2mm mark. The ability of the magnets to tolerate a greater distance between them will depend on what you source. Ours could easily bond with a total 1.5mm gap, 0.5mm depth each side plus the space between the pieces.

Finally, you will need a number of the trapezoidal or pentagonal pieces used to fill in at the sides of the array, in the gap where whole hexagons meet the frame and hold the intermediate one out from the frame. These are used later as electrical connection points, so they need the same complement of magnets and screws as the full pieces. We’ll refer to these from here onwards as the fixed pieces.

# THE FRAME

If building with timber, clamp a piece of 42 x 11mm pine along one long side and another along one short side of your backboard. Now lay out the array starting from the corner, and using the trapezoidal and pentagonal pieces against the sides. Measure the total length and width, then mark the limits of the array. This will likely be several millimetres more than would have been the case based on the theoretical size of the digital model. We glued our foam-core sides on from the start, to push the pieces against. The foam core can be cut with a knife while assembled, but it will not withstand clamping.

You can choose to butt joint or mitre the corners. We would have mtired them, so that influences the overall measurements of the timber, but with foam core, it’s not so viable. Cut your long and short sides, and then cut down the size of the backboard. Use glue and small nails to assemble the frame as pictured. In our case, we just sliced the foam core and glued the two new sides on.

# WIRING UP

Now it is decision time. There are a variety of ways to use the pieces of this puzzle, and some require different wiring to others. Before we do this, however, a note on soldering. We have used solder-tab eyelets to connect electrically to the screws used as contacts. You will need to be careful soldering these, as the screws are in direct contact with the printed plastic, and the eyelet is in contact with a washer which is squeezed against the plastic on the other side. If your soldering skills are reasonable then this should not be a challenge, you just need to make it fast. If you do, there will be enough heat sinking in the washer, screw, and nut to stop the plastic melting.

# POWER SUPPLY

There are three options regarding power for customising your puzzle. Power is generally delivered to the puzzle via the fixed pieces anchored to the side. You may choose to mount screws into the frame sides so the full hexagons can also be origins, as we have done. You may instead decide that the electrical contact must originate from one of the fixed 3D printed pieces.

You may connect positive and negative power to all of the fixed pieces, and simply designate which start and finish point you want to use to build your puzzle path at any given time. Alternatively, you may power only one fixed piece at a time via a plug and socket that can be moved, as your start point. This means that the path can finish anywhere, and the object of the puzzle when used this way is to create any path that uses a chosen number of light-up hexagons and meets a fixed piece at both ends of the path. Remember, the final fixed piece at the finish will light up once there is a string of hexagons connected to it. We would have used headers for this if we went down this road, but we went with the ‘all fixed pieces powered’ option.

Finally, you can choose to plug in power to two fixed pieces and build a path between them. With two lit up, this helps define where the path must start and finish, as opposed to the ‘fixed start point, any ending you choose’ version above. This one is better for younger puzzlers.

As far as wiring the active pieces, these are the options: You can wire all the sides in parallel, so that any face contacting a live connection will cause the LED to light, and any active hexagon connected to any face of any other active one will light. This is the easiest of the options when it comes to solving puzzles. All that is required is to create a path from one point to another, with active hexagons touching one another.

The second option really increases the complexity of the puzzle. You can choose to wire only two sides, or three, or four, or five, getting easier to solve the more you wire. The sides do not need to be opposite each other. Assuming only two sides are chosen, you can make any two sides the active faces. Then, the next hexagon in line will only light if both pieces have an active face touching each other.

With that decision made, an LED must be installed into each active piece, including the fixed side pieces. You’ll need some extra wire here, as even if you use only two sides, the LED legs won’t be long enough to do the job. We used tinned copper wire for this, as the two poles are not near each other.

# LED CHOICES

The LEDs we chose are from LEDsales. We chose a flat-faced Superflux-style LED in amber, to go with the ‘honey’ look. For this reason, we printed the lids in clear PLA, so the light can shine through. Alternatively, you can use any colour LED or even RGB LEDs of the sort that have a pre-programmed controller IC in them, cycling through patterns and colours. We decided not to use regular 5mm T1 ¾ LEDs because it is hard to get them with a decently wide angle. We did find some, however, and again they’re from LEDsales. These are amber, in a yellow tinted diffused case, with a good viewing angle. Our prototype has some of these fitted from before we decided to use the superflux ones. Really though, the choice is entirely yours. In addition, you could use white LEDs of any flavour, and print clear coloured lids.

# HOW MANY PIECES?

Besides your fixed side pieces, you will need enough unilluminated pieces to fill the array, minus however many are in the shortest route possible between two sides. That forms the maximum number of unilluminated pieces you will ever need. Most of the time, however, some will be left over at the conclusion of the puzzle.

The number of illuminated pieces is up to you and depends a lot on how you choose to construct the puzzle. With the all-sides-wired option, the same pieces can always be used to make any path, so you’ll need as many as the longest path you would care to form.

However, with the some-sides-wired or two-sides-wired options, you’ll need more. You could of course choose to have a fixed start point, end point, and path. If this is the case, you can print this many pieces and every time you do the puzzle, you are aiming to get the same pieces in the same places.

Alternatively, you can print as many more as you want, wired with different patterns so that many paths are possible. This applies whether you choose the ‘one starting point, any end point’ option, the ‘fixed start, fixed end’ option, or the ‘all fixed pieces illuminated’ option.

# GAMEPLAY

There’s a lot of information above, because there are a lot of options. How you use the puzzle is very customisable, and there are options and combinations we haven’t listed. The use of different path options means you can set a path up yourself, put aside unused pieces, then see if someone else can reconstruct the pattern. You can have a set number of pieces as discussed, and see if you can reconstruct the pattern over and over, or you can use different pieces and just see what patterns you end up producing.