Learning Goals 3 min
By the end of this lesson you will be able to:
- Build the Gear Shooter with its Medium Motor in port A.
- Use [A v] run [clockwise v] for (3) [rotations v] to spin an exact amount and launch the gear.
- Explain the difference between unregulated start and regulated run-for-rotations control.
Meet the Model — the Gear Shooter 6 min
What is a gear?
A gear is a wheel with teeth around its rim. When two gears mesh, the teeth lock together. Turning one gear then turns the other.
The science behind it
Meshing gears pass on turning force, called torque. A small gear driving a big one trades speed for force — the big gear turns slower but harder. Counting how many times a gear turns, its rotations, gives precise, repeatable moves.
Where you meet it
Gears live in bicycles, clocks, can openers and car gearboxes. A basikal climbs a hill more easily in a low gear, thanks to this trade.
What we'll build
We'll build a Gear Shooter. A Medium Motor on port A spins a gear an exact number of rotations. The sudden stop flicks the gear off and launches it.
Warm-Up 4 min
Last lesson, [A v] start motor [clockwise v] ran the fan until you stopped it. Today the motor stops itself.
Quick-fire puzzle
Priya runs this on the Gear Shooter. How many times does the motor turn?
when program starts :: events hat [A v] run [clockwise v] for (2) [rotations v] :: motors
Reveal the answer
The motor turns exactly 2 full rotations, then stops by itself. There is no stop block — and there does not need to be. The block has its own finish line. This is regulated control.
New Concept — run for rotations 10 min
Think of the difference like a tap and a measuring jug. [A v] start motor [clockwise v] is a tap left running. [A v] run [clockwise v] for (3) [rotations v] is a jug that fills to an exact line and stops.
Blocks reference
| Block | Category | What it does |
|---|---|---|
[A v] run [clockwise v] for (3) [rotations v] :: motors | Motors | Spins the motor an exact number of full turns, then stops itself. Regulated. |
[A v] run [clockwise v] for (360) [degrees v] :: motors | Motors | Same idea, measured in degrees. 360 degrees = 1 rotation. |
[A v] start motor [clockwise v] :: motors | Motors | From last lesson: runs until stopped. Unregulated. |
Unregulated vs regulated — the big idea of Level 1
| Block | When does it stop? | Good for |
|---|---|---|
[A v] start motor [clockwise v] :: motors | Only when a stop block ends it. | Fans, spinners, anything that should run "until told". |
[A v] run [clockwise v] for (3) [rotations v] :: motors | By itself, after the exact amount. | Launchers, arms, precise moves. |
Why it matters
The Gear Shooter must spin the tyre up to speed, then stop sharply to flick the gear off. The exact stop is what launches it. Spin direction matters — the wrong way will not launch.
Build & Program — the Gear Shooter 17 min
Part A — Build
Build the Gear Shooter. A Medium Motor spins a rubber tyre. A gear sits on top of the tyre and is flicked away when the motor stops.
Components & ports: EV3 Brick · Medium Motor → port A.
- Attach the Medium Motor to the frame; plug it into port A.
- Fit a gear on the motor axle and mesh it with the axle holding the rubber tyre.
- Mount the tyre so its top edge is exposed and free to spin.
- Rest a gear (on a short axle) on top of the tyre, ready to be launched.
Part B — Program
Spin the tyre fast for a few rotations, then let the block stop it sharply.
- Drag in the hat that starts the program:
when program starts :: events hat
- Spin the tyre an exact amount, then stop sharply:
[A v] run [clockwise v] for (5) [rotations v] :: motors
- Run it. Watch the gear fly off as the motor stops.
when program starts :: events hat [A v] run [clockwise v] for (5) [rotations v] :: motors
Expected behaviour: the tyre spins up, and when the five rotations finish the motor stops dead — flicking the gear forward. No stop block needed.
What changed: last lesson you needed [A v] stop motor to end the spin. This block stops itself.
Try It Yourself — three small builds 11 min
Goal: Spin up for longer — 10 rotations — for a stronger, faster launch.
when program starts :: events hat [A v] run [clockwise v] for (10) [rotations v] :: motors
Goal: Measure in degrees instead. Half a rotation is 180 degrees — try a tiny spin, then a big one.
when program starts :: events hat [A v] run [clockwise v] for (180) [degrees v] :: motors wait (1) seconds [A v] run [clockwise v] for (720) [degrees v] :: motors
Goal: Arjun loads two gears in a row. Fire the first, pause one second to reload, then fire again — both from one button press.
when program starts :: events hat [A v] run [clockwise v] for (6) [rotations v] :: motors wait (1) seconds [A v] run [clockwise v] for (6) [rotations v] :: motors
Mini-Challenge — start vs run, side by side 6 min
Combine both motor blocks in one program so you can feel the difference. First run an unregulated [A v] start motor [clockwise v] for two seconds, then a regulated [A v] run [clockwise v] for (3) [rotations v].
It works if:
- The first spin needs a [A v] stop motor to end it.
- The second spin stops itself with no stop block.
Recap 2 min
You met regulated control. [A v] run [clockwise v] for (3) [rotations v] spins an exact amount, then stops itself — perfect for a launcher. Compare that with last lesson's [A v] start motor [clockwise v], which runs until told to stop.
- run motor for rotations (block)
- Spins a motor an exact number of full turns, then stops by itself. Regulated.
- Regulated
- A motor command with a built-in finish line — it stops after a set amount.
- Rotation
- One full turn of the motor axle. 1 rotation = 360 degrees.
Homework 1 min
Find the best launch. Try 3, 5 and 8 rotations. Note which one shoots the gear furthest.
Bring back next class: a one-line note of your best rotation number and how far the gear flew.
Heads up for next class: EV3-L1-03 builds the Dual Gyro launcher and adds motor speed control.