R11-U1 · usually age 11 · Robot Explorers

Build the Rover

What turns a chassis into a robot?

Pilot unit plan · 5 sessions · not yet classroom-validated

Build: Two-wheel rover chassis

A chassis becomes a robot when motors, a driver, a battery and a program are fixed to it, firmly and in balance. Learners assemble a two-wheel rover, check each wheel's direction on a stand, practise its stops, then drive it on the floor (never above 40 of 100, every drive ending by itself within 3 seconds) until it drives straight, turns and stops safely.

Act
Power and safety

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 arranging instruction cards or blocks, predicting what happens, and testing on a kit. Short sentences, with words and pictures together.
The adult's role: An adult oversees circuits, batteries and motors.
Session: 60–75 minutes
Hardware: micro:bit with MakeCode, or a similar child-friendly board. Start in the board's own simulator. A micro:bit is 3.3 V: never connect a 5 V signal straight to it.

Starts from

Motor speed
Make a motor spin and change its speed safely.
Built in R10-U1 Power a Moving Machine
Steering
Make a vehicle go straight and turn on purpose.
Built in R07-U2 Wheels and Steering
Power vs signal
Tell the power path from the signal path, and keep motors off signal pins.
Built in R10-U1 Power a Moving Machine

Builds, and what it is the input for

Motor drivers
Use a motor driver with its own supply, and a stop switch that cuts motor power.
Input for R13-U1 Mobile Robot Hardware, R13-U4 Rescue Rover Mission, R17-U3 Safe Autonomy
Driving a rover
Drive a two-wheel rover forward, back, turning and stopped.
Input for R11-U2 Follow the Path, R13-U1 Mobile Robot Hardware
Mechanical assembly
Assemble a square, firmly fastened chassis with wiring that can't be pulled loose.
Input for R13-U1 Mobile Robot Hardware, R15-U1 Mechanisms and CAD

In the studio today

No studio lab or activity for this unit yet.

Sessions

Session 1 · 60 min
What turns a chassis into a robot?
A robot needs a frame (the chassis), something that moves it (two motors and wheels), something that powers the motors (the battery, through the board's motor drivers), something that decides (the micro:bit's program) and a way to stop. Balance matters too: a third point, the caster, holds the front up, and the heavy battery sits near the wheels. The parts are looked at and laid out, not connected.
The adult says first: “A robot has a frame, movers, power, a decider and a stop. Let's find each one.”
Learner card
1. Lay the parts on the chassis.
2. Sort each card. Guess first.
3. Where should the battery sit?
4. Roll it down the ramp.
5. Draw your layout.
Key words (show each with a picture): chassis · caster · balance
Timing (10 of 60 min at the screen)
1. 15 minAway from the screen: Lay the parts on the chassis; sort the picture cards with a guess and a reason.
2. 15 minAway from the screen: Balance test: the holder near the front, then near the wheels, down a card ramp.
3. 10 minAt the screen: MakeCode: the adult's blocks in the simulator. Nothing moves there.
4. 10 minAway from the screen: Draw the layout from above, with the power path in arrows.
5. 10 minAway from the screen: Fill in the table; say what each part adds.
In the studio
No studio lab or activity.
Outside the studio: MakeCode editor and its micro:bit simulator (makecode.microbit.org)
Hands-on
Nothing is powered: this session uses unconnected parts, picture cards and the simulator only. First, away from the screen, each pair lays the parts on the chassis board without fixing anything: two motors with wheels at the back, the caster at the front, the battery holder, the robotics board and its micro:bit slot. They sort picture cards into frame, movers, power, decider and stop, with a guess and a reason for each. Then the balance test: with the holder taped first near the front and then near the wheels, each pair rolls the unpowered chassis gently down a short card ramp and watches whether it tips, drags its caster or runs straight. In MakeCode next, the adult shows the adult's blocks: “on start” holding “turn off all outputs”, “set armed to …” 0 and “show icon” set to Heart; “on button A pressed” holding “set armed to …” 1, “pause (ms)” 3000 and an “if then else” whose condition is “0 < 0” with 0 on the left and armed on the right: then “Motor 1 on direction … speed …” and “Motor 2 on direction … speed …” both Forward at 30, “pause (ms)” 2000 and “turn off all outputs”; and “on button B pressed” holding “set armed to …” 0 and “turn off all outputs”. MakeCode's simulator has no robotics board: the board's motor and servo blocks run there but move nothing, so the simulator checks only what the display shows. The learner says what the real rover will do when A is pressed, and why B during the wait stops it from starting. Last, the pair draws its layout from above, with arrows for the power path.
Starting blocks: Built from scratch: the adult builds “on start” holding “turn off all outputs” and a Heart; “on button A pressed” holding a 3000 ms wait, a check that B was not pressed during it, both motors Forward at 30, “pause (ms)” 2000 and “turn off all outputs”; and “on button B pressed” holding “turn off all outputs”. The learner changes only the numbers and the directions in this unit.
Evidence to collect
A prediction for each card, a short test table (Part | My guess | Why) for six parts, filled in by the learner, and the learner's spoken explanation of what each part adds to a chassis, and where the battery balances best.
Test table columns: Part | My guess | Why
Predict
Before the balance test, the learner guesses where the battery should sit, and what the rover will do when A is pressed.
Debug
If the chassis tips or drags on the ramp, move the heaviest part and roll it again: change one thing at a time.
Reflect
Which part turns a moving chassis into a robot, and why?
Works towards: Mechanical assembly, Motor drivers
Session 2 · 75 min
How do we build it so nothing comes loose?
Assembly: the chassis square and level, every part bolted or tied down, and every wire held so a tug cannot pull it out. The motors go on Motor 1 (left wheel) and Motor 2 (right wheel). On its stand, with the wheels in the air, each wheel is checked: does Forward roll the rover forward?
The adult says first: “Build it so nothing comes loose. Then test each wheel on the stand.”
Learner card
1. Build with everything switched off.
2. Tie down each lead.
3. Give each lead a gentle tug.
4. Guess which way each wheel turns.
5. Press A when the adult says. Step back.
Key words (show each with a picture): assemble · lead · stand
Timing (10 of 75 min at the screen)
1. 25 minAway from the screen: With everything switched off: assemble the chassis, motors, caster (deck level), holder and board.
2. 10 minAway from the screen: Tie down each lead; the tug test.
3. 10 minAt the screen: The adult's blocks in the simulator, then download.
4. 20 minAway from the screen: Turns at the stand, one pair at a time (about 5 minutes each): the Heart; A; each wheel; the adult presses B.
5. 10 minAway from the screen: Fill in the table; say how nothing comes loose.
In the studio
No studio lab or activity.
Outside the studio: MakeCode editor and its micro:bit simulator (makecode.microbit.org)
Hands-on
With everything switched off, the pair assembles the rover with the adult: the motors bolted under the back of the chassis, the wheels screwed onto their shafts, the caster bolted at the front with spacers until the deck is level (the wheels are 67.5 mm across; a marble laid on the deck stays put), the battery holder tied down near the wheels, the board bolted on top. The adult puts the left motor's leads into the Motor 1 terminals and the right motor's into Motor 2 while everything is switched off. The learner ties each lead to the chassis with a cable tie and gives it a gentle tug. In the simulator next, the learner checks the adult's blocks, then downloads them (the board switched off, the micro:bit out of the board, USB in; USB out once the light on the back stops flashing, the micro:bit back in). At each pair's turn, the stop drill; with the rover on its stand the adult switches on and checks the sign (a Heart: the drive program). At the adult's word the learner presses A and steps back: after the wait the wheels turn in the air, then stop by themselves. Does each wheel turn the way that rolls the rover forward? Then A again, and the adult presses B while the wheels turn. If one wheel turns backwards, the adult switches off and swaps that motor's two leads, so Forward means forward on both; from now on the direction changes only in the blocks.
Starting blocks: Built from scratch: the adult's blocks from session 1 (“on start” holding “turn off all outputs” and a Heart; “on button A pressed” with both motors Forward at 30 for 2000 ms after the 3000 ms wait).
Evidence to collect
A prediction for each wheel, a short test table (Setting | My guess | What it did) for the tug test, the level deck and each wheel on the stand, and the learner's spoken explanation of how the rover is built so nothing comes loose, and which way each wheel turns.
Test table columns: Setting | My guess | What it did
Predict
Before A is pressed, the learner points to the way each wheel will turn, and says whether the tug test will pull a lead out.
Debug
If a wheel turns the wrong way, switch off and swap that motor's leads; if a wheel does not turn, switch off and check its leads in the terminal.
Reflect
Why is the rover tested on its stand before it ever touches the floor?
⚠ Adult checks before power-on: Nothing metal touches the micro:bit, its gold pins or the board, and nothing metal lies under it. Before the adult switches on: the micro:bit is firmly in the board, display facing the Link header, its own battery pack and USB unplugged; both switches were off while anything was plugged in or moved. The board's battery is the motor battery: it reaches the motors only through the holder's switch, the board's on/off switch (the power-off switch) and its Motor 1 and Motor 2 terminals. The power-off switch is the board's on/off switch: it cuts the battery to the board, the micro:bit and every motor and servo. Anyone may switch it off at any time; only the adult switches it on. The battery holder rides on the rover, tied down: only the adult opens it, fits cells or works its switch. Safe start: the motors never run just because the board was switched on. “on start” turns them off; only A starts them, after a 3-second wait, and B stops them: a B during the wait clears armed, which A checks after the wait, so the drive never starts. Lift first: the board is switched on only with the rover on its stand, wheels in the air, because a mistake in the blocks could start a wheel at once. On the stand, the board's switch faces the adult, who stands at it; learners stay outside a zone taped 30 cm round the stand. Buttons on a switched-on rover: a learner presses only A, only at the adult's word and only while every wheel is still, with one hand on the micro:bit, nowhere near a wheel, and is back outside the taped edge before the 3-second wait ends. B, the switch, and lifting, carrying or placing a switched-on rover are the adult's: on the floor only the adult presses B. Every program shows its own sign at start, and the adult checks it on the stand before the rover leaves it: the drive program (R11-U1) a Heart, the reading program a sensor number, the line program the No icon. A rover showing the wrong sign does not go on the floor. Fingers, hair, sleeves and cords stay away from the wheels while the board is on; long hair is tied back. The rover is lifted only by its chassis. Floor speed limit: the rover's speed numbers are never above 40 (of 100), a planning choice. Practise the stop before every switch-on: the adult is the stopper. On “Stop!”, the adult switches the board off (on the floor, lifting the rover by its chassis first); learners call “Stop!” from outside the taped zone and never reach for the rover. Rewire only when unpowered: the board and the holder are switched off before any wire, motor, servo or sensor is plugged in, moved or taken out. Never leave a lead loose while the board is on: switch off first; a lead taken out is capped and taped away from the board.
Works towards: Mechanical assembly
Session 3 · 75 min
How does the driver stop the rover?
The board's two motor drivers sit between the battery and the motors: the micro:bit's blocks tell them which way and how fast, and the battery's power flows through them. The stops: the blocks end every drive by themselves (within 3 seconds), B cancels a start or stops the wheels, the board's on/off switch cuts the power to both drivers, and the holder's switch cuts everything. Then the first floor runs: a ramp of speeds that finds the lowest speed that starts both wheels, forward for two pairs and back for two.
The adult says first: “The driver passes the battery's power to the motors. Let's test every stop.”
Learner card
1. The blocks stop it by themselves.
2. Watch the adult press B.
3. The switch stops it at once.
4. Which speed starts both wheels?
5. Never above 40.
Key words (show each with a picture): driver · stop · switch
Timing (10 of 75 min at the screen)
1. 10 minAway from the screen: Guess: which stop always works? Which step of the ramp starts both wheels?
2. 10 minAt the screen: The ramp blocks in the simulator, Forward or Reverse; download.
3. 30 minAway from the screen: Turns, one pair at a time (about 7 minutes each, one run): the stops on the stand; the ramp on the floor, measured.
4. 15 minAway from the screen: The group's results: the lowest start speed, forward and back.
5. 10 minAway from the screen: Fill in the table; say which stop always works.
In the studio
No studio lab or activity.
Outside the studio: MakeCode editor and its micro:bit simulator (makecode.microbit.org)
Hands-on
In the simulator first, the learner checks the adult's blocks with A's drive changed to a ramp: both motors at 10 for 1000 ms, then at 20 for 1000 ms, then at 30 for 1000 ms, then “turn off all outputs”, with both directions Forward (two pairs) or Reverse (two pairs, to drive back); then the learner downloads it (the board switched off, the micro:bit out of the board, USB in; USB out once the light on the back stops flashing, the micro:bit back in). At each pair's turn, the stop drill; with the rover on its stand the adult switches on and checks the sign (a Heart: the drive program). At the adult's word the learner presses A and steps back: after the wait the wheels turn in the air, then stop by themselves. The learner predicts and tests the stops on the stand: A, and the wheels stop by themselves; A, then the adult presses B during the 3-second wait, and the wheels never start; A, then the adult presses B while the wheels turn. With the program waiting for A, the adult carries the rover by its chassis from the stand to the start box and sets it down. At the adult's word the learner presses A and steps back outside the tape; only the adult presses B. The learner watches which step of the ramp (10, 20 or 30) starts both wheels. When the rover has stopped, the adult switches the board off where it stands, and the learner measures with a tape measure how far it went, forward or back, and how far it ended from a straight line. Back on the stand, after the stop drill, the adult switches on: A, then “Stop!”, and the adult's switch stops the wheels at once; last, the adult switches the holder off and the board on, and nothing lights. The group copies every pair's results. Never above 40.
Starting blocks: The learner's session 2 blocks (the adult's), with A's drive changed to the ramp (10, 20 and 30, 1000 ms each), Forward or Reverse.
Evidence to collect
A prediction for each stop and the floor run, a short test table (Check | My guess | What happened | Safe?) for the stops and the ramp, and the learner's spoken explanation of what the driver does, which stop always works, and the lowest speed that starts both wheels, forward and back.
Test table columns: Check | My guess | What happened | Safe?
Predict
Before each stop, the learner says whether the wheels will stop; before the floor run, which step will start both wheels.
Debug
If it does not stop by itself, the adult lifts it and switches off: is “turn off all outputs” last under A? If both wheels start only at 30, tell the adult: the build is checked (a rubbing wheel, a tight caster).
Reflect
Which stop would you trust most if the blocks had a mistake, and why?
⚠ Adult checks before power-on: Nothing metal touches the micro:bit, its gold pins or the board, and nothing metal lies under it. Before the adult switches on: the micro:bit is firmly in the board, display facing the Link header, its own battery pack and USB unplugged; both switches were off while anything was plugged in or moved. The board's battery is the motor battery: it reaches the motors only through the holder's switch, the board's on/off switch (the power-off switch) and its Motor 1 and Motor 2 terminals. The power-off switch is the board's on/off switch: it cuts the battery to the board, the micro:bit and every motor and servo. Anyone may switch it off at any time; only the adult switches it on. The battery holder rides on the rover, tied down: only the adult opens it, fits cells or works its switch. Safe start: the motors never run just because the board was switched on. “on start” turns them off; only A starts them, after a 3-second wait, and B stops them: a B during the wait clears armed, which A checks after the wait, so the drive never starts. Lift first: the board is switched on only with the rover on its stand, wheels in the air, because a mistake in the blocks could start a wheel at once. On the stand, the board's switch faces the adult, who stands at it; learners stay outside a zone taped 30 cm round the stand. Buttons on a switched-on rover: a learner presses only A, only at the adult's word and only while every wheel is still, with one hand on the micro:bit, nowhere near a wheel, and is back outside the taped edge before the 3-second wait ends. B, the switch, and lifting, carrying or placing a switched-on rover are the adult's: on the floor only the adult presses B. Every program shows its own sign at start, and the adult checks it on the stand before the rover leaves it: the drive program (R11-U1) a Heart, the reading program a sensor number, the line program the No icon. A rover showing the wrong sign does not go on the floor. Fingers, hair, sleeves and cords stay away from the wheels while the board is on; long hair is tied back. The rover is lifted only by its chassis. Floor speed limit: the rover's speed numbers are never above 40 (of 100), a planning choice. Practise the stop before every switch-on: the adult is the stopper. On “Stop!”, the adult switches the board off (on the floor, lifting the rover by its chassis first); learners call “Stop!” from outside the taped zone and never reach for the rover. Rewire only when unpowered: the board and the holder are switched off before any wire, motor, servo or sensor is plugged in, moved or taken out. Never leave a lead loose while the board is on: switch off first; a lead taken out is capped and taped away from the board. Every drive ends with “turn off all outputs”: no run in this unit drives for more than 3000 ms (a planning choice) before it stops by itself. B stops the motors too, and a B during the 3-second wait cancels the drive. A switched-on rover that is not showing the No icon is live: it may be driving or about to drive. Hands off; the adult stays beside its switch. Stall or runaway: if a wheel is blocked, the rover pushes against anything, a motor hums without turning or the rover leaves the mat, call “Stop!” at once. Floor runs happen only in a cleared area with adults present: at least 1 m clear round the mat, learners outside its taped edge, one rover at a time per adult, who walks beside it.
Works towards: Motor drivers, Driving a rover
Session 4 · 75 min
How do we make it drive straight, and turn?
Driving: two motors at the same number may not roll at exactly the same speed, so the rover drifts. A small change to one motor's number straightens it: the trim. Turning: one wheel at speed 0 and the other forward pivots the rover round the still wheel; one forward and one Reverse spins it on the spot. The pause sets how far it turns.
The adult says first: “Two motors steer the rover. Make it go straight. Then make it turn.”
Learner card
1. Measure the drift.
2. Add 2 to the slower side.
3. Speed 0 holds one wheel still.
4. One back, one forward spins.
5. Never above 40.
Key words (show each with a picture): drift · pivot · spin
Timing (10 of 75 min at the screen)
1. 5 minAway from the screen: Guess: will it drive straight at 30 on both motors?
2. 5 minAt the screen: Both motors at 30: the simulator, then download.
3. 25 minAway from the screen: First turns, one pair at a time (about 6 minutes each, two runs): the stand, then the tape; measure the drift.
4. 5 minAt the screen: The trim and the turn numbers; the simulator, then download.
5. 25 minAway from the screen: Second turns, one pair at a time (about 6 minutes each, two runs): the pivot or the spin; measure the turn.
6. 10 minAway from the screen: Fill in the table; the group shares the pivots and the spins.
In the studio
No studio lab or activity.
Outside the studio: MakeCode editor and its micro:bit simulator (makecode.microbit.org)
Hands-on
In the simulator first, the learner checks the adult's blocks at 30 on both motors, Forward; then the learner downloads them (the board switched off, the micro:bit out of the board, USB in; USB out once the light on the back stops flashing, the micro:bit back in). At each pair's turn, the stop drill; with the rover on its stand the adult switches on and checks the sign (a Heart: the drive program). At the adult's word the learner presses A and steps back: after the wait the wheels turn in the air, then stop by themselves. With the program waiting for A, the adult carries the rover by its chassis from the stand to the start box and sets it down. On the floor the start box is at one end of a 1 m strip of masking tape. At the adult's word the learner presses A and steps back outside the tape; only the adult presses B; after 2 seconds the rover stops by itself, the adult switches the board off where it stands, and the learner measures how far it ends from the tape: the drift. Two runs, each from the stand. If it drifts left, the left wheel is slower: the learner adds 2 to Motor 1's number (or takes 2 from Motor 2's) and keeps it, the trim, never above 40. Then the turns, each guessed first and each a change of numbers only, tried in the simulator and downloaded the same way: two pairs try a pivot (Motor 1 Forward at 30 and Motor 2 at speed 0 for 1000 ms: the right wheel stays still) and two pairs a spin (Motor 1 Forward with Motor 2 Reverse, both at 30, for 1000 ms). At each pair's second turn, the stand again, then two runs on the floor; when the rover has stopped, the adult switches it off and lays a strip of tape along its side, and the learner measures the turn with a paper protractor. The group copies every result.
Starting blocks: The learner's session 2 blocks (the adult's), with the two speed numbers, the directions and the pause changed (speed 0 holds a wheel still).
Evidence to collect
A prediction for each run, a short test table (Speeds (L, R) | My guess (cm) | Drift (cm)) for the straight runs and the turns, and the learner's spoken or written explanation of how the trim makes the rover drive straight, and how a pivot differs from a spin.
Test table columns: Speeds (L, R) | My guess (cm) | Drift (cm)
Predict
Before each run, the learner guesses the drift in cm, or how far the rover will turn.
Debug
If the drift changes from run to run, check the start: the rover square on the tape, the caster straight, the same floor.
Reflect
Why does one number per motor let a rover go straight, turn or spin?
⚠ Adult checks before power-on: Nothing metal touches the micro:bit, its gold pins or the board, and nothing metal lies under it. Before the adult switches on: the micro:bit is firmly in the board, display facing the Link header, its own battery pack and USB unplugged; both switches were off while anything was plugged in or moved. The board's battery is the motor battery: it reaches the motors only through the holder's switch, the board's on/off switch (the power-off switch) and its Motor 1 and Motor 2 terminals. The power-off switch is the board's on/off switch: it cuts the battery to the board, the micro:bit and every motor and servo. Anyone may switch it off at any time; only the adult switches it on. The battery holder rides on the rover, tied down: only the adult opens it, fits cells or works its switch. Safe start: the motors never run just because the board was switched on. “on start” turns them off; only A starts them, after a 3-second wait, and B stops them: a B during the wait clears armed, which A checks after the wait, so the drive never starts. Lift first: the board is switched on only with the rover on its stand, wheels in the air, because a mistake in the blocks could start a wheel at once. On the stand, the board's switch faces the adult, who stands at it; learners stay outside a zone taped 30 cm round the stand. Buttons on a switched-on rover: a learner presses only A, only at the adult's word and only while every wheel is still, with one hand on the micro:bit, nowhere near a wheel, and is back outside the taped edge before the 3-second wait ends. B, the switch, and lifting, carrying or placing a switched-on rover are the adult's: on the floor only the adult presses B. Every program shows its own sign at start, and the adult checks it on the stand before the rover leaves it: the drive program (R11-U1) a Heart, the reading program a sensor number, the line program the No icon. A rover showing the wrong sign does not go on the floor. Fingers, hair, sleeves and cords stay away from the wheels while the board is on; long hair is tied back. The rover is lifted only by its chassis. Floor speed limit: the rover's speed numbers are never above 40 (of 100), a planning choice. Practise the stop before every switch-on: the adult is the stopper. On “Stop!”, the adult switches the board off (on the floor, lifting the rover by its chassis first); learners call “Stop!” from outside the taped zone and never reach for the rover. Rewire only when unpowered: the board and the holder are switched off before any wire, motor, servo or sensor is plugged in, moved or taken out. Never leave a lead loose while the board is on: switch off first; a lead taken out is capped and taped away from the board. Every drive ends with “turn off all outputs”: no run in this unit drives for more than 3000 ms (a planning choice) before it stops by itself. B stops the motors too, and a B during the 3-second wait cancels the drive. A switched-on rover that is not showing the No icon is live: it may be driving or about to drive. Hands off; the adult stays beside its switch. Stall or runaway: if a wheel is blocked, the rover pushes against anything, a motor hums without turning or the rover leaves the mat, call “Stop!” at once. Floor runs happen only in a cleared area with adults present: at least 1 m clear round the mat, learners outside its taped edge, one rover at a time per adult, who walks beside it.
Works towards: Driving a rover
Session 5 · 75 min
Can our rover drive straight, turn and stop safely?
The prototype, a two-wheel rover chassis, tested on a short course: one press of A drives the straight from a start box to a mark, then turns to face a stop box, and stops by itself, the two drives within 3 seconds; then it stops on B and on the adult's switch. Before the runs, the safety checks: built firmly, level, the stand first, the stop drill, the speed at most 40.
The adult says first: “Show us your rover. Straight, turn, stop. Then tell us why it is safe.”
Learner card
1. Write your numbers on paper.
2. Both pauses: 3000 ms at most.
3. Check each safety rule first.
4. Press A when the adult says.
5. Watch the adult press B.
Key words (show each with a picture): straight · turn · safe stop
Timing (10 of 75 min at the screen)
1. 15 minAway from the screen: Read the course; write the straight and the turn numbers on paper.
2. 10 minAt the screen: The course blocks with your numbers; the simulator, then download.
3. 10 minAway from the screen: The safety checks, one at a time, each guessed first.
4. 30 minAway from the screen: Turns, one pair at a time (about 7 minutes each, three runs): the course; then B and the adult's switch.
5. 10 minAway from the screen: Explain the rover, its numbers and its stops to the adult.
In the studio
No studio lab or activity.
Outside the studio: MakeCode editor and its micro:bit simulator (makecode.microbit.org)
Hands-on
First, away from the screen, the learner reads the course taped on the floor (a start box, a mark 40 cm ahead, a stop box to one side) and writes the numbers on paper from session 4's table and the group's: the straight (both motors, with the trim, and a pause) and the turn (a pivot or a spin and a pause), the two pauses together no more than 3000 ms. In the simulator next, the learner sets the numbers in the adult's blocks with a second step under A before “turn off all outputs”: both motor blocks again and a second “pause (ms)”, so one press of A drives the straight, then the turn, the two pauses together no more than 3000 ms, checks them, then downloads them (the board switched off, the micro:bit out of the board, USB in; USB out once the light on the back stops flashing, the micro:bit back in). The safety checks, each guessed first: the tug test, the level deck, the stand test, the stop drill, the speed numbers at most 40. At each pair's turn, the stop drill; with the rover on its stand the adult switches on and checks the sign (a Heart: the drive program). At the adult's word the learner presses A and steps back: after the wait the wheels turn in the air, then stop by themselves. With the program waiting for A, the adult carries the rover by its chassis from the stand to the start box and sets it down. At the adult's word the learner presses A and steps back outside the tape; only the adult presses B: does it reach the mark, turn to face the box and stop by itself? The adult switches the board off where it stopped before anyone measures. Then, from the stand again after the stop drill, two runs for the stops: A, and the adult presses B while it drives; A, and on “Stop!” the adult lifts it by its chassis and switches off. Each part is recorded; if one misses, the learner writes the one number they would change, and why. Last, the learner explains the rover to the adult.
Starting blocks: The learner's course blocks (the adult's session 2 blocks with a second step under A), with the learner's straight numbers, then their turn numbers.
Evidence to collect
The unit's evidence: the rover drives straight, turns and stops safely: a prediction for each part and check, a short test table (Step | My guess | What it did | Safe?) for the safety checks, the course and the stops, and the learner's spoken or written explanation of how their numbers, their build and the stops make it safe.
Test table columns: Step | My guess | What it did | Safe?
Predict
Before each check and each part, the learner says whether it will pass, and why it matters.
Debug
If the rover misses the mark or the box, change one number at a time (a pause, or one motor's speed) and run the course again.
Reflect
What would you teach a younger child first about driving a robot safely?
⚠ Adult checks before power-on: Nothing metal touches the micro:bit, its gold pins or the board, and nothing metal lies under it. Before the adult switches on: the micro:bit is firmly in the board, display facing the Link header, its own battery pack and USB unplugged; both switches were off while anything was plugged in or moved. The board's battery is the motor battery: it reaches the motors only through the holder's switch, the board's on/off switch (the power-off switch) and its Motor 1 and Motor 2 terminals. The power-off switch is the board's on/off switch: it cuts the battery to the board, the micro:bit and every motor and servo. Anyone may switch it off at any time; only the adult switches it on. The battery holder rides on the rover, tied down: only the adult opens it, fits cells or works its switch. Safe start: the motors never run just because the board was switched on. “on start” turns them off; only A starts them, after a 3-second wait, and B stops them: a B during the wait clears armed, which A checks after the wait, so the drive never starts. Lift first: the board is switched on only with the rover on its stand, wheels in the air, because a mistake in the blocks could start a wheel at once. On the stand, the board's switch faces the adult, who stands at it; learners stay outside a zone taped 30 cm round the stand. Buttons on a switched-on rover: a learner presses only A, only at the adult's word and only while every wheel is still, with one hand on the micro:bit, nowhere near a wheel, and is back outside the taped edge before the 3-second wait ends. B, the switch, and lifting, carrying or placing a switched-on rover are the adult's: on the floor only the adult presses B. Every program shows its own sign at start, and the adult checks it on the stand before the rover leaves it: the drive program (R11-U1) a Heart, the reading program a sensor number, the line program the No icon. A rover showing the wrong sign does not go on the floor. Fingers, hair, sleeves and cords stay away from the wheels while the board is on; long hair is tied back. The rover is lifted only by its chassis. Floor speed limit: the rover's speed numbers are never above 40 (of 100), a planning choice. Practise the stop before every switch-on: the adult is the stopper. On “Stop!”, the adult switches the board off (on the floor, lifting the rover by its chassis first); learners call “Stop!” from outside the taped zone and never reach for the rover. Rewire only when unpowered: the board and the holder are switched off before any wire, motor, servo or sensor is plugged in, moved or taken out. Never leave a lead loose while the board is on: switch off first; a lead taken out is capped and taped away from the board. Every drive ends with “turn off all outputs”: no run in this unit drives for more than 3000 ms (a planning choice) before it stops by itself. B stops the motors too, and a B during the 3-second wait cancels the drive. A switched-on rover that is not showing the No icon is live: it may be driving or about to drive. Hands off; the adult stays beside its switch. Stall or runaway: if a wheel is blocked, the rover pushes against anything, a motor hums without turning or the rover leaves the mat, call “Stop!” at once. Floor runs happen only in a cleared area with adults present: at least 1 m clear round the mat, learners outside its taped edge, one rover at a time per adult, who walks beside it.
Works towards: Driving a rover, Motor drivers, Mechanical assembly

Materials

Per pair: a BBC micro:bit and its USB cable (USB micro-B at the micro:bit end)
A computer with a web browser for MakeCode (makecode.microbit.org); no installs needed
Per pair: a Kitronik Compact All-In-One Robotics Board for BBC micro:bit (stock code 5693), its Link header fitted with a 2.54 mm pin header by the adult (soldering is adult-only)
Kept by the adult: 4 × AA alkaline cells (1.5 V each, 6 V nominal) in a holder with a screwed-shut cover and its own on/off switch, wired by the adult to the board's power terminal block; no rechargeable cells, Li-ion, LiPo, RC or coin-cell packs
Pencils and paper for the test tables
Per rover: two right-angle geared TT motors with yellow wheels (Kitronik stock code 25100), leads soldered on by the adult
Per rover: a flat chassis about 20 cm by 12 cm (stiff corrugated plastic or thick card), a smooth plastic ball caster with spacers to level the deck, cable ties, M3 nuts and bolts, and a stand (a box that holds the wheels in the air)
Masking tape, a tape measure, a short card ramp, a marble, a paper protractor and picture cards: chassis, wheels, caster, battery, board, micro:bit

⚠ Safety before any session

Batteries: only AA alkaline cells in the board's closed holder, and USB from a computer for downloads; no rechargeable cells, power banks, Li-ion, LiPo, RC packs or coin cells.
Cells: the adult fits four new alkaline cells of one type, the right way round, never mixes new and used cells, takes spent cells out and screws the cover shut.
The power-off switch is the board's on/off switch: it cuts the battery to the board, the micro:bit and every motor and servo. Anyone may switch it off at any time; only the adult switches it on.
The board's battery is the motor battery: it reaches the motors only through the holder's switch, the board's on/off switch (the power-off switch) and its Motor 1 and Motor 2 terminals.
A motor never runs from a micro:bit pin: it runs only from the board's motor terminals, powered by the board's battery.
Lift first: the board is switched on only with the rover on its stand, wheels in the air, because a mistake in the blocks could start a wheel at once.
Fingers, hair, sleeves and cords stay away from the wheels while the board is on; long hair is tied back. The rover is lifted only by its chassis.
Floor speed limit: the rover's speed numbers are never above 40 (of 100), a planning choice.
Floor runs happen only in a cleared area with adults present: at least 1 m clear round the mat, learners outside its taped edge, one rover at a time per adult, who walks beside it.
Stall or runaway: if a wheel is blocked, the rover pushes against anything, a motor hums without turning or the rover leaves the mat, call “Stop!” at once.
Rewire only when unpowered: the board and the holder are switched off before any wire, motor, servo or sensor is plugged in, moved or taken out.
Never leave a lead loose while the board is on: switch off first; a lead taken out is capped and taped away from the board.
The battery holder rides on the rover, tied down: only the adult opens it, fits cells or works its switch.
Learners press only A, at the adult's word, with every wheel still and one hand on the micro:bit only. B, the switch and moving a switched-on rover are the adult's.
Only the parts the plan names connect to the micro:bit, through the board's Link header. Never connect a 5 V signal or supply to a micro:bit's pins or battery socket: it runs at 3.6 V at most.
If the board, a motor, the holder or a wire gets warm: switch the board off, don't touch it, tell the adult.

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

Read each step aloud first: your words come before the learner's card. The card uses short sentences; show each key word with a picture.
These plans assume one adult for up to four pairs. Learners plug the USB cable into their own computer, gripping the plug, while the adult watches; only the adult handles cells and battery packs. With more pairs, add an adult or bring fewer pairs to the real board at once.
Each session's timing keeps screen time to short bursts (15 minutes at most), with building, acting or testing away from the screen between them.
Before the first session on the real board, set up each computer and test a download: either pair each micro:bit once with WebUSB (then MakeCode's Download button sends the program straight to it), or download the .hex file and drag it onto the MICROBIT drive. The light on the back flashes while the program copies: unplug only after it stops.
To download, the board is switched off and the adult takes the micro:bit out of it (or the learner does, with the adult watching), holding it by its edges and pulling it straight out; the learner plugs in USB, downloads and unplugs USB once the light on the back stops flashing; the micro:bit goes back in the same way, straight and firmly, display facing the Link header, before the adult switches on. Every swap wears the edge connector a little: swap only to download or at a pair's turn, and never rock the micro:bit out.
Powered work rotates: one rover at a time per adult, each pair (or team) taking its turn while the others work away from the screen. Planning figures: a turn takes about 3 minutes to set up (the stand, the sign, the stop drill, the stand check) and about a minute a run, so each session's timing gives every turn its minutes.
The pack is 6 V nominal (4 × 1.5 V), at the edge of all three ranges: the bottom of Kitronik's recommended 6.0–10.8 V for the board, and the top of the TT motor's 3–6 V and the servo's 4.8–6 V. Expect it to vary: new cells can read above 1.5 V each with nothing running (Energizer's handbook works an example with an open circuit voltage of 1.6 V), and the pack sags under load, because each fresh cell has 150 to 300 milliohms of internal resistance (Energizer E91). Kitronik's board page lists under Requires a Power Supply that links to its 3 × AA holder; these plans use 4 × AA instead, because 3 × AA is 4.5 V nominal, below the board's recommended 6.0 V and the servo's 4.8 V.
Kitronik labels the board Age 11+ and tags it Designed for_Engineers. These plans are adult-led for that reason: the adult builds, wires, powers and switches every rig and keeps the battery holder; the learner changes numbers in blocks, presses the micro:bit's buttons when the adult says, and watches from outside the safe zone or the gate's path.
Before the first session, add the extensions on each computer: in MakeCode's Extensions, search for Kitronik and pick the Kitronik robotics Board; for the line sensor, search for Kitronik clip detector.
The MakeCode simulator prepares the work. Only the real board, seen working by the adult, counts as evidence: a simulator run is never physical success.
Hand out each session's test table with its columns ready: the learner fills it in, and the adult writes only for a learner who needs it. Making their own tables is taught in R09-U3.
The studio's Arduino labs are written for ages 12 and up and are not used in this unit, not even its motor or steering labs: they wire a 5 V Uno, never a micro:bit.
Carried over from age 10: the same board, battery and power-off switch; the same motor blocks with a speed from 0 to 100; the power path from R10-U1 (battery, board, motor, back), now through two motor drivers; and the safe stop rule from R10-U3 (when unsure, the safe choice), now: stop when the line is lost. The servo socket stays empty at age 11.
Motor 1 drives the left wheel and Motor 2 the right; the left line sensor is on P0, the middle one on P1 and the right one on P2.
Every drive ends with “turn off all outputs”: no run in this unit drives for more than 3000 ms (a planning choice) before it stops by itself. B stops the motors too, and a B during the 3-second wait cancels the drive.
An engineering note, not a maker's quote: the board's driver chip keeps the last speeds it was sent. If the program halts (it crashes, or the micro:bit is pulled out), a wheel that was turning can keep turning; after a reset, “on start” turns the motors off only once the program runs again. Only the switch is sure to stop the motors.
If both wheels stall, the pack's voltage can sag far enough to reset the micro:bit. The safe start then keeps the motors off until A, so the rover sits still showing its sign: treat it as live and switch off.
Planning choices, not sourced figures: the speeds 30 and 25, the floor limit of 40 of 100, the 3000 ms drive limit, the 3-second wait after A, the lost-line stop's 20 passes of 100 ms, the run time-out of 300 passes, the detector's starting height of 10 mm, the 1 m clearance and the 30 cm zone.
This unit builds on steering from R07-U2 (two motors at different speeds or directions turn a robot): here the same idea drives a real rover, forward, back, round a still wheel and on the spot.
This unit assumes motor speed, steering and the power path, not block programming: the adult builds the blocks, including “on button A pressed”, the armed check and the Heart, and the learner presses A and changes only the numbers and the directions.
In R10-U1 the direction changed only in the blocks. On a rover, Forward must mean forward on both wheels, so the adult fixes a backwards motor once, switched off, by swapping its leads; after that the direction changes only in the blocks.
B turns the motors off once they run, and a press of B during the 3-second wait after A cancels the drive: B sets armed to 0, and A drives only if armed is still 1 after the wait.
The lowest speed that starts both wheels (session 3) must stay below the line-following speeds of R11-U2 and R11-U3 (30, and 25 after tuning): if both wheels start only at 30, check the build before R11-U2.
Before session 2, the adult solders leads onto both motors (soldering is adult-only), finds a stand that holds the wheels in the air, and packs the caster with spacers so the deck sits level on the 67.5 mm wheels.
Readiness decides, not age: a learner who already builds a rover that stays together, drives it straight, turns it and stops it safely can move on to R11-U2.

Planned studio features

Not built yet. The unit runs without them.

A micro:bit rover simulator in the studio, with the board's power path and both motor drivers drawn and every control labelled as a code setting or a simulated input.
Printable picture cards for each session's key words and the parts cards, and printable learner cards.
A printable safety checklist for the rover, and a floor course to print or tape.

Sources

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

Microsoft MakeCode for micro:bit: Simulator
“The JavaScript simulator allows you to test and execute most BBC micro:bit programs in the browser. It allows you to emulate sensor data or user interactions.”
Microsoft MakeCode for micro:bit: Transferring programs (USB)
“Most of the time you'll be writing and testing your programs in the simulator. … Click Download to download the .hex file.”
Microsoft MakeCode for micro:bit: WebUSB (pairing for one-click downloads)
“The first time you pair your micro:bit with your computer you’ll need to go through a few easy steps to get setup. … Once your micro:bit is paired, MakeCode will use WebUSB to transfer the code directly and you won’t have to drag and drop .hex files from a folder.”
Microsoft MakeCode for micro:bit: Transferring with Chrome on Windows (the .hex file)
“In File Explorer, drag and drop the .hex file from the download folder onto the MICROBIT drive. … The LED on the back of your micro:bit flashes during the transfer (which should only take a few seconds). … To rerun your program, press the reset button on the back of your micro:bit.”
Microsoft MakeCode for micro:bit reference: On Start
“The on start is a special event that runs when the program starts, before any other event.”
Microsoft MakeCode for micro:bit reference: On Button Pressed
“Start an event handler (part of the program that will run when something happens, like when a button is pressed). … For button A or B: This handler works when the button is pushed down and released within 1 second.”
Microsoft MakeCode for micro:bit tutorial: Smiley Buttons
“Click on the Basic category in the Toolbox. Drag a show icon block into the on button A pressed block.”
Microsoft MakeCode for micro:bit reference: Pause
“Pause the program for a duration of the number milliseconds you say. … To convert from seconds: 100 milliseconds = 1/10 second and 1000 milliseconds = 1 second.”
Microsoft MakeCode for micro:bit reference: If
“Run code depending on whether a boolean condition is true or false. … If you want some other code to run when the opposite condition is true, you put it in an additional block area called else. … If the light level is < 100, this code sets the brightness to 255 when the button A is pressed:”
Microsoft MakeCode for micro:bit tutorial: Digital Watch (the if then else block)
“Below the pause, put a if then else block. Change the condition in the if to use a 0 < 0.”
Microsoft MakeCode for micro:bit reference: Show Icon
“This program shows a happy face and then a sad face with the show icon function, with a one second pause in between. … interval (optional), the time to display in milliseconds. default is 600.”
Microsoft MakeCode for micro:bit source code: libs/core/icons.ts (icon and block names)
“block="heart" … block="no" … block="stick figure" … block="show icon %i"”
Microsoft MakeCode for micro:bit source code: libs/core/basic.cpp (block names)
“block="show leds" … block="clear screen" … block="forever" … block="pause (ms) %pause"”
Microsoft MakeCode for micro:bit source code: libs/core/input.cpp (block names)
“block="on button|%NAME|pressed" … block="button|%NAME|is pressed" … block="acceleration (mg)|%NAME" … block="light level" … block="temperature (°C)"”
Microsoft MakeCode for micro:bit: Assignment Operator (the set block)
“In blocks, a variable assignment happens with the set block when you set a value to a variable. … In the Variables category of the Toolbox you can create or choose a variable to assign:”
Kitronik Compact All-In-One Robotics Board for BBC micro:bit (the maker's product notes)
“With the Kitronik Compact Robotics Board, the BBC micro:bit can be used to drive 4 motors (or 2 stepper motors) and 8 servos. … Power is provided via either a terminal block or servo-style connector. The supply is then controlled by an on/off power switch to the board. … The board then produces a regulated 3.3V supply, which is fed into the 3V and GND connections to power the connected BBC micro:bit. This removes the need to power the BBC micro:bit separately. The 3V and GND pins are also broken out on the Link header, which means external devices can also be powered. … To add them to the editor, select the cog icon in the top right of the editor. Then, select Extensions from the drop-down menu and in the search bar type and enter Kitronik. Pick the Kitronik robotics Board from the list and the new blocks will be added to the menu in the editor. … Supply Voltage | 3V - 10.8V … Servo / Motor Voltage | Same as Supply voltage (3-10.8V)”
Kitronik Compact Robotics Board for BBC micro:bit datasheet
“The Link header breaks out all the usable pins from the BBC micro:bit, and is designed to allow 2.54mm pitch pin header to be easily soldered into place. … GND V SIG … Operating Voltage (Supply via Terminal Blocks or Servo Power Connector) | +3.0V - 10.8V (Recommended: 6.0V - 10.8V) … Servo Output Connections | 8 (Provide supply voltage to servos) … External Connections (Link Header) | All BBC micro:bit Pins (IO Pins 5mA max sink/source current) … Power Supply via Link Header to External Devices | 3.3V, 90mA max current draw … Motor 3 on direction Forward speed 10 … set Servo 1 to 180 degrees … turn off Motor 3”
Kitronik Compact Robotics Board for BBC micro:bit datasheet (its motor drivers, its I2C pins and its motor outputs)
“The Robotics Board features 2 Dual H-Bridge Motor Driver ICs (capable of driving 2 standard motors or 1 stepper motor each) and 8 servo outputs (capable of driving standard and continuous rotation servos), all controlled from the BBC micro:bit using the I2C protocol via a 16-channel driver IC. … The 17 available I/O pins allow other input devices, for example, sensors, or output devices, such as ZIP LEDs, to be added to the board. The I2C communication lines are also broken out (Pins 19 & 20) … Motor Output Connections | 4 [2 stepper motors] (1.5A max current draw per motor)”
Kitronik Compact All-in-One Robotics Board getting started guide (the maker's product notes)
“Simply locate the micro:bit edge connector on the board, and push the micro:bit into it, ensuring the LEDs are facing the Link Header. … To start, we can code the motors to be off, so that they are not running straight away. … Motor 1 on direction Forward speed 50 … turn off Motor 1”
Kitronik Robotics Board MakeCode extension source code: robotics.ts (block names)
“block="set%Servo|to%degrees|degrees" … degrees.min=0 degrees.max=180 … block="%motor|on direction %dir|speed %speed" … speed.min=0 speed.max=100 … convert 0-100 to 0-4095 (approx) … block="turn off %motor"”
Kitronik Robotics Board MakeCode extension source code: robotics.ts (the motor names, its I2C writes and the all-off block)
“block="Motor 1" … block="Motor 2" … let outputVal = Math.clamp(0, 100, speed) * 40; … This secret incantation sets up the PCA9865 I2C driver chip … pins.i2cWriteBuffer(chipAddress, buf, false) … block="turn off all outputs"”
Microsoft MakeCode for micro:bit: Extensions
“You can add an extension by going to Toolbox and clicking on the Extensions category. … This will open a window giving you a place to search for extensions.”
micro:bit Foundation technical docs: Power supply (motors need their own supply)
“This means that if you require more than 90mA V1 / 190mA V2 from the edge connector, (e.g. driving lots of NeoPixels or a small motor) these should have power supplied to them externally.”
Kitronik In-Line Geared TT Hobby Motor (the maker's product notes)
“Note: when using a microcontroller, do not drive these motors directly with the microcontroller, always use them in conjunction with a motor driver board. … These hobby motors have an operating voltage of between 3V and 6V, with 4.5V being nominal. … At 4.5V, they have a speed of 90RPM no-load and 72RPM at load. … Stall current | 1.25A (approx).”
Kitronik Yellow Wheels and right-angle geared TT motors, stock code 25100 (the maker's product notes)
“| 25100 | ✓ | ✓ | … They fit directly onto the geared hobby motors TT style shaft and can be screw fixed firmly in place. … The motors operating voltage (3V to 6V) make it suitable for use in battery powered applications. … This is a 90RPM geared hobby motor. … Wheel Diameter (with tire): 67.5mm.”
Microsoft MakeCode for micro:bit source code: sim/state/misc.ts (the simulator's pulse and I2C)
“export function pulseIn(name: number, value: number, maxDuration: number): number { let pin = getPin(name); if (!pin) return 0; return 5000; } … export function i2cWriteBuffer(address: number, buf: RefBuffer, repeat?: boolean): void { // fake - noop }”
Energizer E91 datasheet (AA alkaline cell)
“Classification: Alkaline … Nominal Voltage: 1.5 volts”
Energizer E91 datasheet (AA alkaline cell): its internal resistance
“Nominal Voltage: 1.5 volts Nominal IR: 150 to 300 milliohms (fresh)”
Energizer Alkaline Manganese Dioxide Handbook and Application Manual (the maker's technical note)
“Most devices are designed to operate within a voltage range (for example from 1.6 volts to 0.9 volts per cell) to accommodate this sloping discharge characteristic. … The voltage drop of a battery under load is a function of total effective resistance and current drain rate. … Open circuit voltage = 1.6 Volts”
Kitronik 3x AA Battery Holder with Flying Leads (the maker's product notes; the 5693 page's Power Supply link)
“3x AA Battery Holder with Flying Leads, Pack of 10 … Holds 3 x AA batteries.”
Kitronik Mini 180 Degree Metal Gear Servo MG90S (the maker's product notes; the 5693 page's Servos link)
“Stock code: 2592 … Discontinued - This page is for reference for existing customers of this product. It is not possible to buy this item. … If this servo is being used with a BBC microbit then it will need a separate power supply. You may also need to level shift the PWM voltage to insure it is at the same voltage as the servos supply. … The MG90S metal gear servo is rated to operate between 4.8V and 6V”
Kitronik Compact All-In-One Robotics Board for BBC micro:bit (the maker's product notes: its age label, tags and Requires list)
“Age 11+ … Age recommendation_11+ … Designed for_Engineers … Requires: … Power Supply. … Also requires parts, such as; … Servos”
micro:bit Foundation support: Connecting a power supply to the micro:bit
“Usually, you will need a USB type-A plug at one end, and a USB micro-B plug for the other end, to be plugged into the micro:bit. … In addition to USB powering, the BBC micro:bit can also be powered using a battery pack containing 2 x zinc or alkaline AAA batteries. … To insert the battery connector, grip the base of the connector between your thumb and forefinger and push the connector into the JST socket on the board. To remove the battery connector you may need to wiggle the connector to release. … also has a power saving mode that helps you conserve battery power, meaning that you may not have to disconnect the battery pack between uses. Hold down the power/reset button to enter/exit this mode. … Please do not mix different types of batteries or mix new and used batteries … Please insert the batteries the correct way round (with the correct polarity) … Please remove spent batteries form the battery holder … Do not short-circuit the battery supply terminals, for example by placing a metal object across the terminals … Only use Zinc or Alkaline batteries with your BBC micro:bit … If you find it difficult to remove the battery pack, please do not force it. … Please do not plug your micro:bit directly into the mains or into a portable charger. They supply a voltage stronger than the micro:bit can safely handle.”
micro:bit Foundation technical docs: Power supply
“This table implies an operating voltage range of the micro:bit device as a whole as being 1.7V min and 3.6V max. … It is advised that you do not power the micro:bit from USB battery packs.”
micro:bit Foundation technical docs: Edge connector (nRF52 GPIO table)
“KEY | Description | section | Min | Max … VIO≤3.6 | Tolerable pin voltages for IO pin with VDD ≤3.6 | 9 | -0.3V | VDD+0.3”
Microsoft MakeCode for micro:bit: micro:bit pins (the power pins)
“Watch out! The pins labelled 3V and GND relate to the power supply of the board, and they should NEVER be connected together.”