Build Guides 26 September 2026
Grade 7 technology project: how to build an electromagnetic crane, step by step
The electromagnetic crane is one of the classic Grade 7 Technology projects: a working model that has to lift and move a load, driven by a circuit that has to switch on and off. This guide walks through the whole build in the order the parts come out of the box — ten steps, then the test.
Watch the whole build first
Under three minutes, every part going on in order. Worth watching once before you open the box.
What you need
Everything below is in the Slotbok electromagnetic crane kit — eighty pieces, packed flat:
- Three 3 mm MDF sheets, with every part labelled
- Eleven bamboo sticks, for the pivots, the axles and the crank handle
- White twine, a small glue bottle and a sheet of sandpaper
- An iron nail, copper wire, speaker wire and two 2 mm cable ties
- Four AA batteries, a battery holder and an ON/OFF switch
- A two-page assembly guide
Two things are not in the box: paper clips for the magnet to pick up — any office paper clip works — and a second pair of hands, which helps on the glued joints.
The ten steps
1. Press out the parts
Push every piece gently out of the three MDF sheets. Work along the little tabs rather than forcing a part out of the middle. Sort the pieces into groups as you go, and lightly sand any rough edges with the sandpaper. This step takes longer than it sounds, and doing it properly is why nothing binds later.
2. Find the boom parts
Pick out the parts for the two booms: the tall lower boom that carries the weight, and the short top boom, which is called the jib. Laying them out in two piles before you glue anything saves picking through the pile later.
3. Build the two booms
Run a thin line of glue along the joints and slide a square collar onto each end. Build the jib the same way, with the short panels and the small collars. Thin is the word that matters here — glue that squeezes out of a slot has to be wiped before it dries.
4. Find the chassis parts
Pick out the base plate, the tray walls, the brackets and the wheel discs. The chassis is the part that carries the battery, so it is the heaviest piece of the model.
5. Build the chassis
Turn the base plate over and push the four axle brackets into their slots. Glue two discs together for each wheel and push them onto the axles — doubling the discs is what makes a wheel thick enough to stay straight. Then slot tray walls A and B into the base; those two walls are what hold the battery box.
6. Mount the booms
Put the lower boom between the rear brackets and push a bamboo stick through as the pivot. Fit the jib on top of the boom and pin it with another bamboo stick. At this point the crane can flop about — that is normal, and the next step fixes it.
7. Fit the support links
Hold the boom upright with two long links, one on each side. Brace the jib with the other two links, with the spacer washers between the jib and the links. Pin them and add the washers. The frame is now strong and stable, and the whole model stops wobbling.
8. Winch and twine
Push a short bamboo stick into the crank to make the handle. Tie the twine to the drum, then thread it up through the collar rings, over the jib and down from the tip. Wind a couple of turns onto the drum so the line does not slip when you first crank it.
9. Make the electromagnet
Lay the iron nail in the groove between the two holder plates. Wind the copper wire tightly around it — the more turns you get on, the stronger the magnet. Keep the turns neat and side by side rather than crossing over themselves. Then tie the twine to the top hole of the magnet, so it hangs from the winch line.
10. Connect the battery
Close the lid on the battery holder and set it in the battery tray. Run the speaker wire up the boom to the magnet, sand the ends of the copper wire so the bare metal shows, and twist them onto the speaker wire. Sanding matters: copper wire is sold with a thin coat of enamel on it, and current will not pass through the coating.
Try it out
- Put some paper clips under the magnet and switch ON.
- Turn the crank to lower the magnet onto them.
- Wind the crank back to lift them.
- Switch OFF. The magnet lets go, and the clips drop.
Leave the switch off between tries. The coil draws current the whole time it is on, so the batteries last a lot longer if it only runs while you are actually testing.
If nothing sticks, the usual causes are the enamel on the copper wire ends not sanded off, a loose twist in the joint, or too few turns on the nail.
Why it works
A current flowing through a wire makes a magnetic field around it. Wind that wire into a coil and the fields of all the turns line up and add together, so a coil is much stronger than a straight wire. Put an iron nail down the middle and it gets stronger again, because iron carries a magnetic field far better than air does.
That is the whole trick, and it is also why the switch matters. A permanent magnet is always a magnet. This one is only a magnet while the circuit is closed — open the switch, the current stops, the field collapses, and whatever it was holding falls. A real scrapyard crane works on exactly this principle, at a much larger scale.
Two things change how strong it is: the number of turns of wire, and how much current flows. More turns, stronger magnet.
What to write down while you build
Most of the marks for a Technology project are not for the model itself — they are for showing what you did and what you found out. Worth noting as you go:
- How many turns of copper wire you got onto the nail.
- How many paper clips it lifted, and whether that changed when you added more turns.
- What the twine does over the jib, and why the line runs over the tip rather than straight down.
- Where the crane was least stable before the support links went on, and what the links changed.
- Anything that went wrong and what you did about it. This is usually the easiest part of a report to write and the one most learners leave out.
A photograph at the end of each step is the simplest way to have material for the write-up without stopping to take notes.
Afrikaans terme
If you are doing this project in Afrikaans: Graad 7 Tegnologie (Grade 7 Technology) · skoolprojek (school project) · hyskraan (crane) · elektromagneet (electromagnet) · stroombaan (circuit).
Get the kit
The kit is cut in our own workshop in Gauteng, and every design is built once by hand before it is packed, so the slots and tabs are known to fit.
Other build guides: cell phone tower kit, Grade 7 · mine headgear kit, Grade 8 · hydraulic arm kit, Grade 9.
Questions about a kit, a class set or delivery to your town: message us on WhatsApp.
- 01 Drawn
- 02 Cut
- 03 Test-fitted
- 04 Filmed
- 05 Packed
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