Grade 7 technology project: how to build a cell phone tower model

The cell phone tower is a Grade 7 Technology project about structures. The crane project is about a circuit; this one is about why a shape holds itself up. It is a good project to pick if you would rather explain a frame than wire anything.

Watch the whole build first

Eighty seconds, the whole tower going up in order. Worth watching once before you start, because a lattice is much easier to assemble when you already know the finished shape.

What it is made of

The Slotbok cell phone tower kit is cut by laser from 3 mm MDF or plywood. The parts are flat, labelled, and slot together — tabs and slots meet closely enough that there is no glue and no sanding in this one.

The build order

The model goes together from the ground up, in eight steps, and it is worth doing them in order — a lattice is only stiff once it is closed, so a half-built tower feels much floppier than the finished one.

1. The square base. The footprint that everything else stands on, and the widest part of the model.
2. The four legs, cross-braced. Four uprights that lean in towards each other, with cross-bracing between them. This is the part that does the structural work.
3. The round platform. The deck near the top that the antennas mount to.
4. The four antenna masts. The short uprights that stand on the platform.
5. Ten dishes and two panels. The equipment that goes on the masts, and the last thing to fit.

Leave the dishes and panels until the end. They are the smallest parts and the easiest to knock off while you are still handling the frame.

Why the tower is that shape

Three things about the shape are worth being able to explain, because they are what the project is actually assessing.

It is a lattice, not a solid tower. A solid column of that height would use an enormous amount of material and weigh a great deal, and most of that material would be doing nothing. A lattice keeps material only where the forces run, so it gets nearly the same stiffness for a fraction of the weight.

It is braced with triangles. A square frame can be pushed over into a diamond without any of its sides changing length. A triangle cannot change shape at all unless one of its sides stretches or breaks. That is why the cross-bracing is there: every time you add a diagonal, you turn a square that can fold into two triangles that cannot.

It is wide at the bottom and narrow at the top. Wind pushing on the top of a tall tower tries to tip it over, and the wider the base, the harder that is — the same reason a stepladder splays at the feet. The taper also puts the most material where the bending force is greatest, at the bottom.

What the parts on top do

The equipment on a real mast is not all the same, and the model shows two kinds.

The flat panels are the antennas that talk to phones. They face outwards in different directions so that between them they cover the area around the tower, and each one handles the phones in its own slice of that area.

The round dishes point at other towers. They carry the tower's traffic back into the network over a narrow microwave beam, which is why a dish has to be aimed precisely at one distant point while a panel spreads its signal over a wide area.

And the reason all of it sits on a tall structure at all: radio at these frequencies travels best in a straight line. Height is what gives the antenna a clear line to the phones and to the next tower, over the buildings and trees in between.

What to write down while you build

Most of the marks are for the write-up, not the model. Worth noting as you go:

• Push the tower gently sideways after the legs go on but before the cross-bracing, and again afterwards. Describe the difference — that one sentence is the whole structures lesson.
• Count the triangles you can find in the finished frame.
• Which direction each panel faces, and why they are not all pointed the same way.
• Where the model is weakest, and what you would change if you built it again.
• A photo at the end of each stage, so the report has pictures without you having to stop and write.

Afrikaans terme

If you are doing this project in Afrikaans: Graad 7 Tegnologie (Grade 7 Technology) · skoolprojek (school project) · selfoontoring (cell phone tower) · raamwerkstruktuur (frame structure) · driehoek (triangle).

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.

• Cell Phone Tower School Project Kit — Grade 7
• All Grade 7 Technology projects

Other build guides: electromagnetic crane 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.