# Bag of Wonder: The Excavator > Dig, scoop and pour! Meet the driver, fill the dump truck, then pull the digger apart. A free interactive 3D exhibit for children aged 2 to 6, from Curiosity's Child in Troy, Michigan. - Interactive exhibit: https://bagofwonder.com/look-inside/excavator/ - Ages: 2 to 6. The story is pitched at the youngest; the tap cards give older children more to chew on. - Cost: free, with no sign-in, no ads and no tracking. - Works on: phones, tablets and computers, in a web browser. Sound on for the narration. ## What it is Interactive 3D excavator (a digger) on a real building site. A time slider follows its day: it rolls in on its tracks, the driver in a hard hat climbs up into the cab, the arm (the boom and the stick) stretches out, the bucket's teeth dig a scoop of soil, the hydraulic rams push the arm like muscles (oil pushes them, like squeezing a syringe), the cab swings round on its turntable, the soil pours into a dump truck, the bucket smooths the ground flat, and at home time it rests its bucket and sleeps on the site. A second slider pulls the digger apart (tracks and wheels, turntable, cab, engine, counterweight, boom, stick, bucket and teeth, hydraulic rams), with labels; tapping a part shows a child-friendly fact. How to play: press play to hear the story (read aloud in Kelly's voice, with the words on screen). Slide the time slider back and forth to see any part again. Slide "Pull apart" to see what is hidden inside. Tap any glowing button for a fact. ## The story 1. Good morning, poppets! This is a building site. Here comes a big yellow digger, rolling along on its tracks. Rumble, rumble! 2. The driver, in a hard hat and a bright jacket, climbs up the steps into the cab. The cab is the driver's seat, with windows all round. 3. Stretch! The long arm reaches out. The first part of the arm is called the boom, and the second part is the stick. 4. Down goes the bucket, into the soil. Its strong teeth dig in, and it scoops up a big bucketful. Scoop! 5. What makes the arm so strong? These shiny rams, like muscles! Oil pushes inside them, just like when you squeeze a syringe. 6. Now the top of the digger swings round on its turntable, while the tracks stay still. Round it goes! 7. Over the dump truck, the bucket opens, and the soil pours out. Whoosh! The truck will carry it away. 8. Next, the digger smooths the ground, nice and flat, ready for building. 9. Home time! The bucket rests on the ground, the driver climbs down, and the digger sleeps on the site. Night night, digger! ## The parts, and what we tell children These are the tap cards, word for word. - **Tracks and wheels**: Instead of tyres, a digger has two long tracks, like giant metal belts. Wheels inside them turn the tracks, so the digger can roll over bumpy, muddy ground without sinking in. - **Turntable**: The turntable is a big, strong ring. It lets the whole top of the digger spin right round, while the tracks stay still on the ground. - **Cab**: The cab is the driver's seat, with windows all round so the driver can see everything. Two joysticks, one by each hand, move the arm and the bucket. - **Engine**: Under this cover is the engine. It works a pump, and the pump pushes oil through pipes to every ram, to make each part move. - **Counterweight**: This big, heavy block at the back balances the long arm and the full bucket, so the digger doesn't tip forwards. It works like a seesaw! - **Boom**: The boom is the first, biggest part of the arm. It lifts up and down, like your arm does from your shoulder. - **Stick**: The stick is the second part of the arm, like your arm from your elbow to your hand. It reaches out, and pulls back in. - **Bucket and teeth**: The bucket scoops up the soil. Strong metal teeth along its edge bite into hard ground, a bit like the prongs of a fork. - **Hydraulic rams**: These shiny rams are the digger's muscles. Oil is pushed in behind the shiny rod, and the rod slides out, like the plunger when you squeeze a syringe. That pushes the arm. - **The driver**: Only a grown-up who has learned how can drive a digger. On a building site everybody wears a hard hat and a bright jacket, to stay safe and easy to see. - **Dump truck**: The dump truck carries the soil away. Its big back can tip right up, so the soil slides out somewhere new. ## Getting the science right What we checked, and the myths we steer around: - The digger is a crawler (tracked) hydraulic excavator, a generic one with no brand on it. Its top half (the house: cab, engine, counterweight) sits on a turntable (the slewing ring) and can turn all the way round while the tracks stay still. - The arm is the boom (from the turntable) and the stick (also called the dipper arm), with the bucket on the end. Each is pushed by hydraulic rams (cylinders): the boom by two, the stick and the bucket by one each. - Hydraulics: the diesel engine drives a pump; the pump pushes oil to the rams; oil pushed in behind the piston slides the shiny rod out. The syringe comparison is about liquid pushing a plunger, which is fair for young children. - The counterweight at the back balances the arm and a loaded bucket so the machine does not tip forward (the seesaw comparison). - Tracks spread the machine's weight so it does not sink into soft ground; a toothed wheel (the sprocket) drives each track and rollers carry it. - The cab has two joysticks for the arm, bucket and swing; pedals or levers drive the tracks. Only a trained adult operates one; on site everybody wears a hard hat and high-visibility clothing. - The page simplifies: the soil goes from the hole into a dump truck in one scoop; real loads take many. The arm's movement is computed from the real pin positions on the model, and the rams always point barrel-to-rod as on a real machine. - Gentle wording: no danger, no accidents; the digger works slowly, and at home time rests its bucket on the ground, which is what operators really do when they park. - The driver climbs up by the handrail onto the track and in through the cab door, and climbs down facing the machine, as operators are taught (three points of contact). The page swings the left control console aside while he gets in; on real machines it tips up when the safety lever is raised, which this model's cab is too small to show. ## How to use it with children Watch the whole story with the sound on. At the rams, pause and ask, "Where are the digger's muscles?" Then pull the digger apart and find the boom, the stick, the bucket and the counterweight. Ask more than you tell, and let the child drive. Then step away from the screen: fill a syringe (no needle) with water and connect it with a tube to a second syringe: push one and watch the other's plunger slide out. That is how the rams work. In the sandpit, use a toy digger or a spoon to scoop, swing round, and tip into a toy truck. On a walk, spot real diggers from a safe distance and count their parts. A few minutes together is plenty. The exhibit is a doorway to the real thing, not a replacement for it. ## Credits and licenses The real scans, maps and photographs belong to their makers, under the licenses below. The words, story and code are Curiosity's Child's. - The digger: [a crawler excavator by sloumod](https://sketchfab.com/3d-models/ef66e8b2650a44b6bc91edd2c0327a34) (CC BY), a generic yellow digger with no brand on it, cut into its working parts for this page - The building site is a watercolour painting Kelly made for this page with Grok - The driver: made for this page with [MakeHuman](http://www.makehumancommunity.org) (CC0), dressed like a picture Kelly made with Grok - [the dump truck by ElectroNick](https://sketchfab.com/3d-models/781c616da8f44982a59cb3fc3fa67f98) (CC BY) - [the pile of soil, a real photo-scan by Air Digital](https://sketchfab.com/3d-models/5161c064eea048f6888a107d6d1ca7f2) (CC BY) - The light and the soil's surface: [Poly Haven](https://polyhaven.com) (CC0) - The falling soil and the bumpy ground are made in code - Real sounds from Freesound ([CC0](https://creativecommons.org/publicdomain/zero/1.0/), thank you!): [a building site](https://freesound.org/s/193351/) (sengjinn), [a real excavator at work](https://freesound.org/s/187563/) (qubodup, from a US Government film), [a dump truck tipping dirt](https://freesound.org/s/872390/) (MillennialGhost), [evening birds](https://freesound.org/s/256784/) (radwoc) - Music-box tune made for this page - Narrated by Kelly, in her own voice ## More on the Things That Go shelf - [The Car](https://bagofwonder.com/look-inside/car/index.md): A family car’s whole day: buckle up, drive the lanes, swish through the rain. Then pull it apart! ## About Bag of Wonder A free library of interactive 3D "look inside" science exhibits, made at Curiosity's Child, a licensed home daycare in Troy, Michigan. Secular and science-based; welcoming to all. - All exhibits and how we make them: https://bagofwonder.com/llms.txt - For grown-ups and AI assistants: https://bagofwonder.com/look-inside/about/ - To cite: "The Excavator", Bag of Wonder, Curiosity's Child (Troy, Michigan). https://bagofwonder.com/look-inside/excavator/