Kid's Basics: Kids in the Castle

Cardboard castle with motorised drawbridge

Daniel Koch

Issue 25, August 2019

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Put on your armour, Arthur, King of the Britons! Take up your sword and shield! Or maybe an Elven bow and Mithril is more your thing? Either way, fight off the armies of darkness, or your siblings, in your own castle with motorised drawbridge!


In this issue of Kid’s Basics, we’re changing this up a bit. Our cardboard castle is designed with no breadboard, and will introduce you to some hardware skills such as screw terminals and motor mounting, in a way we have only touched on previously. As the project is designed to make use of available, rather than specialised, materials, some steps will require you to adapt to your own situation. However, that said, there are still a couple of unique parts. We will still step you through item by item, and give you tips to think about if you need to adapt.

Something else is different this time around, too. We are going to present three sections of instruction, rather than two. First, we’ll build a frame to mount the electronics and motor for the drawbridge. Then, we’ll cover the wiring and connections, before getting into the actual castle construction. Of course, the motors to raise and lower the drawbridge in castles of old were actually prisoners, slaves, or poorly-paid peasants winding winches, but let’s not let that get in the way of our fun. Small details, right?

Spools for Winch
6mm × 1.2m Threaded Rod
8Gx30mm Wood Screws
8Gx20mm Wood Screws
Base Coat Paint in Grey
Poster Paints / Markers for Decorating
Cardboard Boxes
Pine Fence Palings
Packaging Tape
Masking Tape, 50mm
Philips Screwdrivers
Builder's Square (recommended but not critical)
Paint Rollers
Wire Strippers
Hot Melt Glue Gun and Glue


ELECTRONIC PARTS REQUIRED:JaycarAltronicsCore Electronics
2 × Cradle RelaysSY4065S4310-
2 × Relay BasesSY4064S4318A-
1 × 12V Geared MotorYG2734--
2 × Pushbutton SwitchesSP0710S1060BCE05249
1 × Shaft CouplerYG2602-ROB-12325
1 × Small EnclosureHB6065H0208-
2 × Reed SwitchesLA5070S5153-
2 × MagnetsLM1618T1465-
1 × 12-Way Screw Terminal BlockHM3194P2130ACE05306
6m × Speaker WireWB1702W2100-
2 × M3x12mm ScrewsHP0140H3120AFIT0270
1 × 3AG Fuse HolderSZ2015S6001-
2 × 3 Amp Slow Blow 3AG Fuse (one spare)SF2230S5681-


The Frame:

The first task is to build a frame and mounting area for all the drawbridge electrics, winch, and the drawbridge itself. Ours is made from pine fence palings, but yours can use whatever timber is available. You could use old fence palings, wood from a pallet, scraps from a family member’s workshop, anything of a size that suits your castle. The gateway of your castle can be any size, but if your castle has tall walls on all four sides, consider making the gateway big enough that an adult can get in easily in an emergency. Ours was 1200mm high, and 900mm wide.

Step 1:

Measure two lengths of timber the width of your gateway, and mark using a pencil and builder’s square. If you don’t have access to one of these, do your best with a ruler. Measure two lengths of timber the height of your gateway, and mark them. Measure and mark a length of timber around 200mm long, to be used to mount the electrics.

Step 2:

With an adult’s help, cut along the marks you have made using a hand saw. Consider clamping your work down as well. The correct procedure is to use saw horses to support your work, but if you don’t have them, any stable surface with an edge you can overhang is ok, as long as you hold your work securely and be careful of where the saw is underneath.

Step 3:

Pine as soft as fence palings should not need pre-drilling, but if you have denser or harder wood, mark a line half the width of the timber across both ends of the long pieces, using the assembly diagram as a guide.

Step 4:

Have an adult help you hold the long lengths up against the short lengths, and drill as shown with a drill size smaller than the thread of the screws. Ours was a 3mm drill bit. A clamp makes this easier, but not many people will have access to the right sort and size unless one of your adults is a builder or carpenter, so don’t worry too much.

Step 5:

Screw the pieces together, using the assembly diagram as a guide. You should now have a door frame and a piece left over, around 200mm long, which will be used later.

The Electronics:

The electrics are mounted on the piece of timber cut earlier, and centre on two screw-terminal relay bases mounted using wood screws. The fritzing diagram works as a guide for the connections and mounting layout. The only exception are the reed switches, which are mounted later on the drawbridge and connect now with lengths of speaker wire.

Note also that we have used two colours of single-core wire here, with speaker wire for the reed switches. This is for instructional clarity, and you can happily use speaker wire split down the middle for the same wiring, to save yourself buying different wire. While on the subject of speaker wire, you will notice that there is a line down one wire. This is called a ‘trace’, and is used to keep track of which wire is which.

Depending on the plastic colour of your wire, the trace colour varies. Sometimes it is light, at other times, dark. There is much debate, even among tradespeople and engineers, as to the conventions. Some say trace means positive, others say trace is negative, while still more change depending on the colour being light or dark. Make up your own mind, but stay consistent, and write it down somewhere on or near your work.

One more thing to note: it may be handy to photocopy or print the wiring schematic diagram, and highlight each connection as you make it. There are a lot of wires around for this project, and they aren’t as easy to keep track of as on a breadboard!

We’ll pick up the instructions at step 8, following from part 1. In each case, if there is a wire involved, you’ll need to cut to length and strip the ends. We haven’t shown this in each step as it is repeated every time. If you don’t have access to wire strippers, pliers work with care. Apply enough pressure to partly cut the insulation, and pull.

Note: The wiring diagram shown here is a step up from the Fritzing diagrams that show you how to wire your circuit on a breadboard. Be very careful to wire your circuit as we show you here. Make sure you trace all of the lines carefully. It is very easy to get mixed up where masses of red lines cross each other. One incorrect connection could cause the circuit not to work, so double-check the wiring before applying power. It is also good practice to twist the wires together before securing into the screw terminal or risk one or more coming out.

Step 8:

Mount the relay bases with 8Gx20mm wood screws, and the terminal block as shown. The bases mount with the yellow tabs facing away from you. Label the left-hand base ‘Up’ and the right-hand base ‘Down’. Mark the screw terminals for +12V and GND, as shown.

Step 9:

Take the reed switches, and label one ‘Top’ and one ‘Bottom’.

Note: You may find the reed switches are difficult to read. We recommend using a permanent marker to highlight the embossed labels.

Step 10:

Measure the enclosure, and mark a line down the centre. Measure the length of the enclosure and mark a line one third from each end. Where the lines meet, drill holes for the pushbutton switches. Ours were 7mm holes but yours may be different.

Step 11:

Cut two lengths of speaker wire around 300mm long, and strip one end of each. Feed the bare copper of one pair of wires through the eyelets on the bottom of one switch. Repeat for the second switch.

Step 12:

Mount one switch into the enclosure, fasten its retaining nut, and label it ‘Up’. Label the end of the pair of wires as well. Mount the other switch and label it and its wires ‘Down’.

Step 13:

Clip or screw the lid on the enclosure. Ours has holes for cables, but you may need to drill some. Screw the enclosure to the board below the relay bases.

Step 14:

Cut a length of speaker wire long enough to go from the end of your drawbridge, down to the floor, and up to the electrics. Ours was 2.5m long. Cut another length of speaker wire long enough to go from about a quarter of the way up your drawbridge and up to the electrics. This made ours about 1.5m.

Step 15:

Take the longer length, and strip the wires of one end. Twist the strands so that they stay together. Wrap the wire without the trace around the screw for the COM terminal on the ‘Top’ reed switch. Tighten the screw into place. Wrap the wire with trace around the screw for the ‘N.C.’ terminal on the ‘Top’ reed switch. Label the end of the wire ‘Top’.

Step 16:

Using the short length of speaker wire and the ‘Bottom’ reed switch, repeat step 15.

Step 17:

Cut a length of speaker wire around 500mm long. Label one end ‘Motor’ and split and strip the wires on the other end. Choose whether your trace is negative or positive. Ours was black so we’re going negative. Feed the wires through the eyelets on the motor terminals, taking care of positive and negative. Twist them firmly.

Note: Even though a motor can run both directions when power is applied, wiring the positive and negative leads as we describe will ensure the motor travels in our intended direction.

Step 18:

Connect a length of wire from terminal 8 on the ‘Up’ relay base to the GND terminal block. Don’t connect the terminal block end yet, just feed it in and leave the screw loose. Do the same for terminal 8 on the ‘Down’ relay base to the GND terminal block.

Step 19:

Connect terminal 4 of each base to the +12V terminal block, and terminal 2 of each base to the GND terminal block.

Step 20:

Connect terminal 5 of each base to terminal 7 on the same base. Connect both of the wires with traces from the reed switches to the +12V terminal block.

Step 21:

Connect the wire with trace from the ‘Top’ reed switch to terminal 3 on the ‘Up’ relay base. Connect the wire with trace from the ‘Bottom’ reed switch to terminal 3 on the ‘Down’ relay base.

Step 22:

Connect the wires with traces from both of the pushbutton switches to the +12V terminal block. Connect the wire with trace from the ‘Up’ pushbutton to terminal 7 of the ‘Up’ relay base. Connect the wire with trace from the ‘Down’ pushbutton to terminal 7 of the ‘Down’ relay base.

Step 23:

Connect the positive wire for the motor to terminal 6 on the ‘Up’ relay base. Double check which convention you used for the trace. Our trace was negative so the wire with trace is our positive. Connect the negative wire of the motor to terminal 6 on the ‘Down’ relay base.

That’s it! You’re all wired up! Well, nearly. You can plug the relays into their bases now, they only go in one way. Our project is designed to be powered by 12 volts DC, as this is what most of the geared motors in the size range required, run on. You can power it with a plug pack, 8AA batteries in a holder, or an old 12V car battery. Most car batteries used in the last five years or more are sealed, maintenance-free types, and so are safe. Do not use one which is unsealed or has inspection caps. A 7 amp-hour alarm or NBN sealed lead acid battery is ok too, but be sure to insulate the power terminals for safety and avoid kids playing with them.

Whatever power supply you use, use a fuse and fuse holder as close as possible to the battery, in case you accidentally short-circuit it. You can still twist the connections as you have so far, just cover them in tape.

Now you can power up your creation by attaching wires from the battery to the +12V and GND terminal blocks. But to test it, we’ll have to wait until the rest of the castle is built.

How Do The Relays Work In This Circuit?

We used a reed switch in last month's Kid's Basics, but relays are something new to Kid's Basics. Relays come in big and small sizes, and these ones are bigger than they need to be, but the screw bases made for them decided their use here. We’ll cover relays themselves in the future.

1. When the circuit is first powered up, there is no current path through the two relays. However, if the drawbridge is in the ‘down’ position, then the ‘normally closed’ (NC) contact is connected to the ‘common’ (Com) contact on the ‘Top’ reed switch, because there is no magnet to actuate it. There is a current path as far as terminal 3, the 'normally open' (NO) contact of one side of the relay.

2. If the pushbutton switch ‘Up’ is pushed, current flows through the coil of relay 1 ‘Up’ to GND. The contacts change over, so the NO terminal 3 of the ‘Up’ relay is now connected to the COM terminal 5. Current can now flow through the reed switch, into the NO terminal 3, out of the COM terminal 5, and into terminal 7, the relay coil. This means that when the pushbutton is released, the current path remains through the relay contacts, which have the effect of ‘self-latching’ the relay. Here we see the the circuit while the ‘up’ button, SW1, is pressed.

On the other set of contacts on Relay 1, the ‘Up’ relay, current flows from +12V, through terminal 4, which is NO but has been closed by the energised relay, across through the COM terminal 6 and out to the motor. The motor’s other terminal is connected to the COM terminal of relay 2, the ‘Down’ relay, which is not energised and is in its ‘normal’ state. Therefore, the motor current flows through COM terminal 6 and NC terminal 2 of the ‘Down’ relay, to GND, completing the circuit.

3. This state remains with the motor running until the drawbridge reaches the top. At that point, the magnet activates the top reed switch SW3, the ‘Top’ reed switch, causing its contact to change from the NC to the NO position. This cuts the current path to the coil of Relay 1, which causes the contacts to change to their ‘normal’ state and break the current path through NO terminal 4 to the motor.

4. The whole operation is the same for the ‘Down’ relay and pushbutton, with the ‘Bottom’ reed switch in play this time. This shows the circuit moments after the ‘down’ button has been pressed and released again.

Construction: The Castle

A whole castle built in a day? Tell ‘im ‘e’s dreamin’!! In the middle ages, stone castles took decades to build. Yours can be ready in as little as a couple of hours. The cardboard boxes to make it are easy enough to come by. We asked at a few shops and came away with enough. Maybe a friendly manager may help you out - Jaycar even have signs in their stores offering the boxes for free for people moving house.

You have two choices: You can build a whole castle from boxes, or you can build the gateway and corners, then use other material for the sides. Old Real Estate signs, sheets or blankets, cardboard flattened from large boxes like whitegoods; all of them will do fine.

On the subject of whole castles, decide first whether you are building a whole castle, or just a fortified wall like Helm’s Deep in J.R.R. Tolkien’s Lord of the Rings. We went with a wall, plus some corners to show you how to keep going.

Before we go on, something needs to be decided. Winch drums are needed to wind the cable used to raise and lower the drawbridge. We 3D printed these to get our idea worked out, but we later made some using sections of cardboard tube from a roll of cling wrap, and end caps made from the plastic lids of drinking chocolate containers. You can use fishing line reels, small empty wire reels, or anything similar. It needs to have a drum diameter of between 40 and 100mm (this will affect your raise/lower speed and the load on your motor), and end caps between 5 and 10 millimeters bigger to stop the cable winding off the sides. The inner diameter is not critical, but will need to be packed out with masking tape to meet your threaded rod size. If using the cardboard roll and end-cap idea, just make the hole to suit. Hot melt glue works well for both assembling and attaching these to the shaft.

Step 24:

Find a piece of plastic or thin plywood to use to mount the motor and winch. This should be around 50mm wide, 100mm long, or greater, and no more than 5mm thick, although if it is thicker, you can work around it with some thought. On a piece of paper, make a hole for the shaft of the motor to pass through. Put the paper over the motor shaft. Use a pencil to mark the location of the mounting screw holes on the motor.

Step 25:

Use this paper as a template to mark and drill the plastic or plywood support as shown. The screw holes are likely to be 4mm clearance, and the shaft 6mm. On the opposite support piece, mark a hole in line with the motor shaft to take the end of the threaded rod.

Step 26:

Now screw the board with the electrics on it to the top of the frame as shown. On the same side, mount the plywood or plastic bracket with the motor mounting holes. Mount the rod support bracket at the same height on the other side of the gateway frame.

Note: You could cover the wiring with a take-away box or discarded Tupperware lunch box to avoid the kids playing with the wiring.

Step 27:

Mount the motor using screws to suit, probably M3x10mm but maybe a different thread and length, depending on your motor and support material.

Step 28:

Slide the shaft coupler onto the motor shaft and tighten its grub screw. You may, depending on the coupler and shaft, need to drill out the coupler. Ours was 4mm and needed to be 5mm. Get your adult to help with this, as it can be dangerous. The coupler needs to be held securely, and the sharp metal shavings avoided.

Step 29:

Now it is time to mount the winch drums. Regardless of what you have chosen, either reused reels or tube and end-caps, slide both onto the threaded rod, then slide the end of the rod through the bracket opposite the motor, at an angle, until enough is through to clear the shaft coupler when you lift the rod into line with the motor shaft.

Step 30:

Slide the rod toward the motor until it seats all the way into the coupler, and tighten the grub screw firmly. Slide the winch drums to the ends, leaving about 10mm or so between them and the frame of the gateway. Glue in place with liberal use of hot-melt glue. Our prototype used hubs, but these are not as easy to get. Later we tested glued-on home-made drums, which work just as well.

Step 31:

Cut a piece of cardboard or corflute plastic big enough for your drawbridge, and use masking tape to attach one end to the bottom of the gateway frame like a hinge. You may need to staple the masking tape to the frame if the timber is rough-sawn.

Step 32:

Cut a piece of light duty hook-up wire, string, or strong fishing line long enough to go from the top of your drawbridge while it is flat on the ground, to the winch drum, plus around five turns of the drum. Make a hole in the drawbridge at the top and tie the string, wire, or fishing line through it.

Step 33:

Tape the other end firmly to the winch drum. Repeat for the other side.

Step 34:

Use the adhesive tape on the reed switch labelled ‘Top’, and mount it at the top of the drawbridge as pictured, on the same side as the electrics. Tape the speaker wire into place. Repeat for the reed switch labelled ‘Bottom’, in the position shown.

Step 35:

Set up boxes to line up with your gate as shown, before taping them together. This is a great teamwork exercise if working with friends or siblings, but if not, ask an available adult to help you. Use 50mm masking tape, as it will have to be painted over later.

Step 36:

Stack boxes so they nest together to build your wall. Play with the arrangement until you get it right, and don’t worry if there are small gaps. Choose a box at the end that can form your corner foundation. It should be one of your bigger ones. If building a castle with four walls, keep going for your whole first layer. Tape your first layer of boxes, then arrange the next layer. Again, small gaps are ok.

Step 37:

Repeat these steps until you have a wall as high and long as you need it. Small gaps can now be filled using cut up cardboard taped over from the outside. Castle walls were built with rough-hewn stone and where never perfectly flush, although some were better than others.

Step 38:

Have a helper hold the drawbridge up, and use the adhesive tape to mount the magnet on the frame of the gateway, in line with the ‘Top’ reed switch. Take note of the little arrows moulded into the cases. You may be mounting it on the boxes and not the timber frame.

Step 39:

Use masking tape to mount the magnet for the ‘Bottom’ reed switch to the ground. If using outside, mount it to a scrap of timber.

Step 40:

Manually opening and closing the drawbridge, listen for the clicks as the reed switches work. They’re not terribly loud but if you’re close, you’ll hear them. If you don’t, adjust the magnets or swap them for stronger ones until you have success.

Now, your castle is structurally complete. Power up the electrics, stand clear, and push the ‘Up’ pushbutton. The drums will wind a few turns of the cable then start pulling the drawbridge up. Be ready to disconnect the power of the reed switches don’t work, but if you adjusted them well in step 40, they will. The drawbridge should stop when it reaches the top. Now press the ‘Down’ button and see if that bit works too. If something is not working, go back over the instructions and make sure all connections are correct, and that everything is adjusted correctly.

All we need to do now is to decorate!

Decorating your Castle:

You may choose to leave your castle unpainted, but if you want to paint it, you have a couple of options. You can paint it plain grey or some other stone colour. Alternatively, you can go for a stone block look. This is achieved by laying down a base colour that represents the mortar between the stone blocks. We used a sample pot of house paint for ours. Over the top of this base coat, which has also served as an undercoat to take the colour from the cardboard and its printing, poster paint is used with a small roller to form blocks. Don’t be too careful or use masking tape: It isn’t a brick wall, but a wall made from uneven stone blocks. Because of this, being a little careless adds to the effect.

Additionally, you can place random blocks sparsely in a light colour, then darken it a few shades at a time and slowly add more and more random blocks, until you have covered all the space with painted blocks of different sizes and shades. You can even add hints of green, blue, red, and yellow to change the shades slightly. This can produce some very realistic results and be a lot of fun too!

Alternatively, grab some markers and go nuts!

Rule the Lands!

What castle is really a castle without a Queen or King, or both? This printable, quick craft can give your castle the leader it needs!

STEP 1: Print out the complete or colour-your-own version.

STEP 2: Cut out both halves as close to the lines as you can.

STEP 3: Use scrap white paper to make strips to join the sides with glue.

Best to get the permission of whoever owns the printer you are using though. You can download either of these designs from our website.

Where to from here?

In a future issue, we are going to build some add-on projects for our cardboard castle. In the mean time, though, why not get adventurous yourself? Many castles had a portcullis, a strong grating made usually of wrought iron slats interwoven and riveted together. It was suspended in the gateway arch behind the drawbridge, and held by pins. In an emergency or surprise attack, these pins were disconnected by levers and the portcullis would suddenly fall and close the gateway. This way, the defenders inside could fight off the attackers, but a physical barrier was still present.

You can make your own out of cardboard. Maybe yours will just be decorative and attach to the top of the arch, or you may make yours functional. If you do, you'll need something for it to slide in, and small cable trunking is great. We won't give you too much help - this section is all about encouraging your creativity and problem solving skills. Another common feature of castles in a certain phase of their history is the moat. This was a ditch that surrounded the castle walls and was either full of water, or dry. The prevented siege engines and rams getting close to the walls, made tunneling under the walls harder, and made it harder for attackers on foot. Scottish legend even holds that some were full of thorny thistles!

Yours can be simple blue crepe paper, but we're sure that your creativity can go further.

Finally, while we didn't make any, your castle walls can be finished in 'castellations' or battlements, the familiar up/down stepped stonework at the top that allows defenders to look out or fire arrows then duck back behind solid stone. Bodiam Castle in England is a great Internet search for both a moated and castellated castle.

A NOTE ABOUT SAFETY: It's worth noting that with young kids around, we need to be cautious of a few things. The cables which raise and lower the drawbridge are a potential entanglement hazard. You should also ensure you use a fused / protected power supply, or fuse it yourself. If your kids are old enough to enjoy this then it's unlikely to be an issue, however take care and provide appropriate supervision.