R07-U1 · usually age 7 · Little Inventors

Levers and Gears

How do mechanisms change movement?

Pilot unit plan · 4 sessions · not yet classroom-validated

Build: Mechanical grabber

How mechanisms change movement: a lever that lifts a load with fewer beanbags when its fulcrum moves nearer the load, gears that turn each other the other way and faster or slower, and a mechanical grabber in two designs. Children predict, compare fairly by changing one thing, and lift light, soft objects with both grabbers.

Who it is for

Age is a starting point, never a limit. A learner who can show what this unit starts from can begin here at any age.

How they learn: By making, moving and playing: ramps, wheels, levers, a classmate acting as a robot. Pictures and arrows instead of words; no code text.
The adult's role: An adult leads every session and prepares anything powered. Children never handle loose batteries, sharp tools or hot parts.
Session: 45–60 minutes
Hardware: No controller needed: cardboard, wheels, gears; optional enclosed low-voltage modules. The adult prepares or checks any wiring. No loose batteries, coin cells, small magnets, sharp tools or hot parts.

Starts from

Kinds of movement
Show and name ways things move: push, pull, roll and spin.
Built in R06-U1 Machines Around Us
Fair comparison
Compare two designs fairly: change one thing at a time.
Built in R06-U2 Roll, Slide and Balance

Builds, and what it is the input for

Levers and gears
Use a lever or gears to lift or turn something more easily.
Input for R07-U4 Rescue Vehicle Workshop, R15-U1 Mechanisms and CAD

In the studio today

No studio lab or activity for this unit yet.

Sessions

Session 1 · 50 min
How can a lever help me lift?
A lever is a stiff bar that turns on a fulcrum. Moving the fulcrum nearer the load makes the load easier to lift: fewer beanbags on the other end lift it. A fair test changes only the fulcrum: the same soft toy, the same beanbags, the same lever.
The adult says first: “A lever helps us lift. Where the fulcrum sits changes how many beanbags.”
Picture cards for the children (symbols and drawings; they read nothing)
1. ▲ — picture: a triangle fulcrum under a ruler
2. ⬇ ⬆ — picture: one end pushed down, the other end lifting
3. 1 2 3 4 — picture: four beanbags lifting a soft toy
4. ▲ ⬅ — picture: the fulcrum moved near the soft toy
5. ✋ ⛔ — picture: fingers kept out from under the ends
Key words (said aloud, pointing to the card): lever · fulcrum · load
Timing (0 of 50 min at the screen)
1. 10 minAway from the screen: The adult shows the lever, the fulcrum, the soft toy and the beanbags.
2. 15 minAway from the screen: Fulcrum in the middle: place beanbags one at a time until the toy lifts; count.
3. 15 minAway from the screen: Guess with a card; the adult empties the lids and moves the fulcrum; count again.
4. 10 minAway from the screen: Compare the two counts; the adult photographs the lever, no children in the frame.
In the studio
No studio lab: this session is off-screen.
Hands-on
Nothing is powered. Before the session the adult tapes a fulcrum (a triangular card prism) to the table, lays a 50 cm wooden ruler across it with a box lid taped to each end, and does a trial run: the adult picks a soft toy that needs at least 4 beanbags to lift with the fulcrum in the middle. The soft toy goes in one lid. One child at a time places soft beanbags, all the same, into the other lid, one by one and never dropped, until the soft toy lifts, and the group counts them. Nobody presses either end. Then the adult empties both lids, moves the fulcrum to the mark near the soft toy and puts the toy back, and the children count again with the same toy and the same beanbags. Fingers stay out from under the lids.
Evidence to collect
The adult's note of the two counts (fulcrum in the middle, fulcrum near the soft toy) and what each child said about them, and a photo of the lever with its beanbags (no child in the frame).
Predict
Before the second count, each child holds up a card: more beanbags, fewer beanbags or the same number?
Debug
If the two counts are the same, check the fulcrum is really on the mark near the soft toy and the toy has not moved in its lid, then count again.
Reflect
Where have you seen a lever help someone lift something?
⚠ Adult checks: Levers: the weights are soft beanbags at least 6 cm across, placed, never dropped. Nobody presses either end, fingers stay out from under the ends, and the adult empties the lids before moving the fulcrum. Loads are light and soft, at least 6 cm across: a soft ball, a clean sponge, a scrunched-paper ball or a soft toy with no buttons or beads. The beanbags are too big for the small-parts cylinder, and the adult checks their seams.
Works towards: Levers and gears
Session 2 · 50 min
How do gears turn each other?
Gears are wheels with teeth. When one turns, the gear its teeth touch turns the other way. A big gear turning a small one makes the small one go round more times.
The adult says first: “Turn one gear slowly. Watch the other one. Fingers off the teeth.”
Picture cards for the children (symbols and drawings; they read nothing)
1. ⚙⚙ — picture: a big gear and a small gear touching
2. ↻ ↺ — picture: the two gears turning opposite ways
3. 1 2 — picture: the small gear going round twice
4. ✋ ⛔ — picture: fingers kept away from the meeting teeth
Key words (said aloud, pointing to the card): gear · teeth · turn
Timing (0 of 50 min at the screen)
1. 10 minAway from the screen: The adult shows two gears and the pinch point where the teeth meet.
2. 20 minAway from the screen: Turn the big gear once; watch which way and how many times the small one turns.
3. 15 minAway from the screen: Pairs add a third gear: guess its turn with a card, then try.
4. 5 minAway from the screen: The adult photographs a gear chain (gears only) and notes what each child said.
In the studio
No studio lab: this session is off-screen.
Hands-on
Nothing is powered. A classroom gear set on a pegboard, labelled for ages 3 and up with no small-parts warning, and checked by the adult: every gear and peg too big for the small-parts cylinder. The adult puts a big gear and a small gear side by side so their teeth meet (the big one has twice as many teeth) and sticks a paper arrow on each. One child at a time turns the big gear slowly by its handle while the others watch the small gear: which way does it turn, and how many times while the big gear goes round once? Fingers stay off the teeth where the gears meet. Then pairs add a third gear and guess which way it will turn before trying it.
Evidence to collect
The adult's note of each child's guesses and what happened, and a photo of a three-gear chain with its paper arrows (gears only).
Predict
Before each turn, the children hold up the ↻ card or the ↺ card: which way will the other gear turn?
Debug
If a gear does not turn, check its teeth really meet the next gear's and its peg is pushed fully into the board, then turn slowly again.
Reflect
Why does the touching gear turn the other way?
⚠ Adult checks: Gears: from a set labelled for ages 3 and up, with no small-parts warning; every gear at least 6 cm across, and every gear and peg too big for the small-parts cylinder (checked by the adult). Pinch points: fingers stay off the teeth where two gears meet. Turn a gear slowly by its handle, and stop if a finger goes near the teeth.
Works towards: Levers and gears
Session 3 · 55 min
Can a grabber pick it up?
A grabber is two levers working together. The tongs have their hinge at one end; the scissor grabber has a pivot in the middle, where the two strips cross. Squeezing the handles closes the jaws.
The adult says first: “Squeeze the handles. The jaws close. Lift it into the box.”
Picture cards for the children (symbols and drawings; they read nothing)
1. ⋀ — picture: the tongs, hinge at the top
2. ✕ — picture: the scissor grabber, pivot in the middle
3. ✋ ➡⬅ — picture: a hand squeezing the handles together
4. ● ⬆ ▢ — picture: a soft ball lifted into a box
Key words (said aloud, pointing to the card): grabber · hinge · pivot
Timing (0 of 55 min at the screen)
1. 10 minAway from the screen: The adult shows the tongs and the scissor grabber, and fits the split pins.
2. 10 minAway from the screen: Decorate the handles with crayons.
3. 25 minAway from the screen: Try both grabbers on every load, from the mat into the box.
4. 10 minAway from the screen: Each child says which grabber suited which load; the adult photographs the grabbers (the build only).
In the studio
No studio lab: this session is off-screen.
Hands-on
Nothing is powered. Before the session the adult cuts long strips of thick card, two per grabber, and makes each scissor grabber's pivot hole by the hole rule. At the adult's side-table station the adult tapes two strips together at one end to make the tongs, and pushes a split pin through each scissor grabber's pivot, flattens its legs and tapes over them. Children decorate the handles with crayons, then try both grabbers on the loads (a soft ball, a clean sponge, a scrunched-paper ball and a soft toy with no buttons or beads), lifting each from a mat into a box. The grabbers stay on a tray the adult keeps between sessions.
Evidence to collect
The adult's note of which loads each child lifted with each grabber, and a photo of the two grabbers beside the loads (no child in the frame).
Predict
Before each lift, the child points to the grabber they think will hold that load.
Debug
If a load slips out, look at where the jaws touch it: grip it lower, or nearer the hinge or pivot, then lift again.
Reflect
Which grabber was easier to squeeze shut, and why?
⚠ Adult checks: Holes: only the adult makes them, at a side table, with a single-hole punch (near an edge) or a sharp pencil pushed through the card into a blob of modelling clay (further in). The punch and the pencil stay at the adult's side table, out of the children's reach. Split pins are small and pointed: the adult keeps the box, flattens each pin's legs and tapes over the ends, and counts the pins out and back in. Fitted pins stay under the adult's check: before each session, and before a build leaves the table, the adult checks every pin is flat, taped and tight. Moving parts: fingers stay out of joints and gaps while a linkage moves; move it slowly by its handle. Loads are light and soft, at least 6 cm across: a soft ball, a clean sponge, a scrunched-paper ball or a soft toy with no buttons or beads.
Works towards: Levers and gears
Session 4 · 55 min
Which grabber lifts better?
A fair comparison of the two grabbers: the same four loads, the same mat and box, one try each, and half the children starting with each grabber. Count how many loads each grabber lifts into the box. A tie is a result too.
The adult says first: “Same loads, same box, one try each. Which grabber lifts more?”
Picture cards for the children (symbols and drawings; they read nothing)
1. ⋀ ✕ — picture: the tongs and the scissor grabber side by side
2. ✓ ✗ — picture: a tick card and a cross card
3. 1 2 3 4 — picture: four loads on a mat
4. ☝ — picture: a finger pointing to the better grabber
Key words (said aloud, pointing to the card): compare · fair
Timing (0 of 55 min at the screen)
1. 10 minAway from the screen: The adult checks every split pin; the children practise one lift each.
2. 30 minAway from the screen: Each child lifts the four loads with both grabbers; a partner lays the cards.
3. 10 minAway from the screen: Show and tell: which grabber lifted more, and why.
4. 5 minAway from the screen: The adult photographs the card rows, no children in the frame.
In the studio
No studio lab: this session is off-screen.
Hands-on
Nothing is powered. Before the session the adult tries both grabbers on the four loads, to check that at least one load is lifted by one grabber and not the other (if none is, the adult swaps a load for one that is), and picks one harder load for ties, by the load rule. The adult checks every split pin is flat, taped and tight. At the adult's station each child lifts the same four loads from the mat into the box with both grabbers, one try each: half the children start with the tongs and half with the scissor grabber. A partner puts a ✓ or ✗ card beside the mat for each try. Each child shows the adult their two rows of cards and says which grabber lifted more, and why. A tie is a result too: the child then tries the harder load the adult chose in the trial, with both grabbers. After the session the grabbers stay in the setting: the adult takes them apart and counts every split pin back in.
Evidence to collect
The unit's evidence: each child lifts light objects with two mechanism designs (the tongs and the scissor grabber), the same four loads with each, shown and told to the adult; kept as the adult's note and a photo of the two rows of ✓ and ✗ cards, never of the child.
Predict
Before the trials, each child points to the grabber they think will lift more of the four loads.
Debug
If a try looks unfair (a load moved first, or two hands used), say so and try that load again from the same place on the mat.
Reflect
If you made a third grabber, what one thing would you change?
⚠ Adult checks: Split pins are small and pointed: the adult keeps the box, flattens each pin's legs and tapes over the ends, and counts the pins out and back in. Fitted pins stay under the adult's check: before each session, and before a build leaves the table, the adult checks every pin is flat, taped and tight. Builds with split pins stay in the setting: after the last session the adult takes them apart and counts every split pin back in. Loads are light and soft, at least 6 cm across: a soft ball, a clean sponge, a scrunched-paper ball or a soft toy with no buttons or beads. Photos are of the build only, taken by the adult on the setting's device, following its photo policy: no child in the frame, no names visible, the build on the table or floor, not in a hand. Nothing is uploaded to this studio and no name goes into it; the adult's notes follow the setting's records policy.
Works towards: Levers and gears

Materials

Per group of up to six: a big cardboard box of prepared parts (pre-cut by the adult), masking tape, glue sticks, crayons and large sheets of paper for drawings
Small scissors with rounded, blunt ends for every child, with left-handed pairs
The adult's picture cards for the session, drawn large (drawn by hand today; printable cards are planned)
A lever: a 50 cm wooden ruler, a triangular card prism as the fulcrum (taped to the table, a second mark near one end), two box lids, a soft toy and soft beanbags, all the same, each at least 6 cm across, their seams checked by the adult
A classroom gear set on a pegboard, labelled for ages 3 and up with no small-parts warning: large plastic gears, each at least 6 cm across, a big one with twice as many teeth as a small one, every gear and peg checked against the cylinder
Long strips of thick card cut by the adult (two per grabber), and a box of split pins (paper fasteners), kept by the adult
A single-hole punch, or a sharp pencil and a blob of modelling clay, kept at the adult's side table
The loads, each at least 6 cm across: a soft ball, a clean sponge, a scrunched-paper ball and a soft toy with no buttons or beads; one harder load for ties, chosen in the adult's trial (a heavier soft toy with no buttons or beads); a mat and a box to lift them into

⚠ Safety before any session

Nothing in these units is powered: no batteries, no plugs, no controller. Every machine is pushed, pulled or turned by hand.
Levers: the weights are soft beanbags at least 6 cm across, placed, never dropped. Nobody presses either end, fingers stay out from under the ends, and the adult empties the lids before moving the fulcrum.
Gears: from a set labelled for ages 3 and up, with no small-parts warning; every gear at least 6 cm across, and every gear and peg too big for the small-parts cylinder (checked by the adult).
Pinch points: fingers stay off the teeth where two gears meet. Turn a gear slowly by its handle, and stop if a finger goes near the teeth.
Loads are light and soft, at least 6 cm across: a soft ball, a clean sponge, a scrunched-paper ball or a soft toy with no buttons or beads.
Balls: soft and at least 6 cm across, well over the 44.4 mm small-ball size. No marbles.
Small parts: nothing loose, or that could come off, that fits inside the small-parts cylinder (31.70 mm wide, 57.10 mm long). No beads, marbles, buttons, small magnets or coin cells. If in doubt, leave it out.
The one exception is split pins, which stay under the adult's check.
No craft knives, box cutters or pointed scissors near the children: the adult cuts thick card before the session, away from them, and only the adult makes holes (see the hole rule).
Scissors: only small scissors with rounded, blunt ends, used sitting down, with left-handed scissors for left-handed children. Children cut paper and thin card only.
Holes: only the adult makes them, at a side table, with a single-hole punch (near an edge) or a sharp pencil pushed through the card into a blob of modelling clay (further in).
The punch and the pencil stay at the adult's side table, out of the children's reach.
Split pins are small and pointed: the adult keeps the box, flattens each pin's legs and tapes over the ends, and counts the pins out and back in.
Fitted pins stay under the adult's check: before each session, and before a build leaves the table, the adult checks every pin is flat, taped and tight.
Builds with split pins stay in the setting: after the last session the adult takes them apart and counts every split pin back in.
Moving parts: fingers stay out of joints and gaps while a linkage moves; move it slowly by its handle.
Photos are of the build only, taken by the adult on the setting's device, following its photo policy: no child in the frame, no names visible, the build on the table or floor, not in a hand.
Nothing is uploaded to this studio and no name goes into it; the adult's notes follow the setting's records policy.

Safety for every band

Low voltage only: battery packs or USB. Never mains electricity.
Never connect a motor straight to a controller pin: use a driver and a separate supply.
Every moving robot has a power-off switch within reach that cuts the motor battery (or all power). A software stop button is extra, never a replacement.
No coin or button cells and no loose small magnets; battery compartments screwed shut.
Guard wheels and moving parts against pinched fingers; keep robots slow and indoors.
No exposed lithium cells, improvised chargers or lasers.
No Li-ion, LiPo or RC packs: AA alkaline or NiMH cells in a closed holder with a switch, or USB.
Check polarity and voltage before power-on; a 3.3 V board must not receive 5 V signals.

Notes for the adult

Say each step aloud: your words come first. The children read nothing. Each session's picture cards show symbols and drawings only; say the key word as you point to its card.
These plans assume one adult for up to six children. The adult leads every step, prepares every cut before the session, makes every hole (by the hole rule) and keeps the craft box and the split pins.
With a whole class, run a carousel: one station of up to six children run by the adult, and independent stations within the adult's sight where the others have a defined task with no scissors, split pins or ramps (each plan's “Whole class:” note names them). Groups swap until every child has been at the adult's station.
Whole class: the lever, the gears and the grabbers stay at the adult's station. The independent stations are drawing a lever with its fulcrum and its load, and drawing two gears with arrows showing which way each turns.
Inclusion: every child takes part. Mobility: a child can show a movement their own way (hands, arms or a large soft toy), be the robot on big, clear squares in a wheelchair, lay the cards or give the instructions, or move a large soft toy across a table-top grid. Vision: large, high-contrast or tactile picture cards (raised outlines). Hearing: say each key word and point to its card at the same time, facing the child. Left-handed children get left-handed scissors with rounded ends.
In this unit, a child who finds squeezing hard can use the tongs with two hands, or point to the load while a partner lifts it and lay the ✓ or ✗ card.
Evidence is showing and telling: a demonstration, a photo of the build (never of a child, no names visible) or a drawing that you keep, or your own short note. No names in the studio, no scores, no uploads.
The CPSC's small-parts rule is written for toys for children under 3, and it exempts paper and writing materials such as crayons (16 CFR 1501.3, quoted). These plans apply its cylinder check to the loose objects children handle, and to anything that could come off, a stricter planning choice: groups mix ages and younger visitors come in. Paper and crayons stay in use; the adult collects glue-stick caps and crayon stubs at the end of each session.
No screen in this unit: every session is away from the screen. Robot Instructions has no level for it.
A fair test can only show something if the result can differ: that is why the adult's trial run picks a soft toy that needs at least four beanbags with the fulcrum in the middle, so that the count near the soft toy is clearly smaller, and why the grabber trial checks that at least one load separates the two designs. The gears' result is fixed by their teeth: twice as many teeth, two turns.
Split pins are small parts with pointed ends, so only you handle them: keep their legs flattened and taped, check the tape before each session, and take the grabbers apart yourself at the end (the CPSC's sharp-point rule is quoted in the sources).
This unit relies on two earlier ideas: kinds of movement (R06-U1: a lever turns, a gear spins) and a fair comparison, changing one thing at a time (R06-U2). It does not teach them again.
Readiness decides, not age: a child who already lifts or turns something more easily with a lever or gears has what R07-U4 needs from this unit.

Planned studio features

Not built yet. The unit runs without them.

Printable picture cards: lever, fulcrum, gears and their turns, the two grabbers, ✓ and ✗.
A printable card gear template: large gears, the big one with twice as many teeth, each centre marked for the adult to pre-punch, for settings without a gear set.
A printable grabber template: the strips with the scissor grabber's pivot marked.

Sources

The facts this plan relies on, in each source's own words.

US CPSC: Child Safety: Summary Information for Small Parts, 16 C.F.R. Part 1501
“A small part is any object that fits completely into a specially designed test cylinder 2.25 inches /57.10mm long by 1.25 inches /31.70 mm wide that approximates the size of the fully expanded throat of a child under three years old. … A piece of a toy or article that breaks off during testing that simulates use or abuse by children. … Toys and games that are or contain small parts as manufactured and that are intended for use by children from 3 to 6 years old must be labeled to warn purchasers not to buy them for children under 3 years old because those children could choke on the small parts. Marbles, small balls, and balloons require similar warnings.”
US eCFR, 16 CFR 1501 (a CPSC rule): Method for identifying toys and other articles intended for use by children under 3 years of age which present choking, aspiration, or ingestion hazards because of small parts
“This regulation does not apply to toys or articles which are solely intended for use by children 3 years of age or older. … The following articles are exempt from this regulation … Books and other articles made of paper; … Writing materials such as crayons, chalk, pencils, and pens; … Any components or pieces (excluding paper, fabric, yarn, fuzz, elastic, and string) which have become detached from the article as a result of the use and abuse testing shall be placed into the cylinder, one at a time.”
US eCFR, 16 CFR 1500.19 (a CPSC rule): Misbranded toys and other articles intended for use by children
“Small ball means a ball that, under the influence of its own weight, passes, in any orientation, entirely through a circular hole with a diameter of 1.75 inches (44.4 mm.) in a rigid template 1⁄4 inches (6 mm.) thick. … Marble means a ball made of a hard material, such as glass, agate, marble or plastic, that is used in various children's games, generally as a playing piece or marker. … Any toy or game intended for children who are at least three years old but less than eight years of age that contains a small ball shall bear the following cautionary statement: … Any marble intended for children three years of age or older shall bear the following cautionary statement:”
US eCFR, 16 CFR 1500.48 (a CPSC rule): Technical requirements for determining a sharp point in toys and other articles intended for use by children under 8 years of age
“The sharp point test prescribed by paragraph (d) of this section will be used by the Commission in making a preliminary determination that points on toys and other articles intended for use by children under 8 years of age, and such points exposed in normal use or as a result of reasonably foreseeable damage or abuse of such toys and articles, present a potential risk of injury by puncture or laceration”
NHS (Gateshead Health NHS Foundation Trust): Scissor Skills
“Children may have the skills to use small scissors by three to four years of age, but scissor skills are not fully developed until 6 years of age. … Children will need supervision for sharp scissors. Make sure that scissors have rounded rather than pointy ends for safety. … Always provide left handed scissors for left handed children. … Start with thick solid lines to cut.”