BUILD GUIDE

The two motors hang under the base on small printed pads. The pads put the wheels at exactly the right height, so there is nothing to measure. The little board on the back of each motor tucks up into a window in the base.

1. a

   Plug a cable into the back of each motor first.

   The plug goes into the little board on the back of the motor. Once the motor is on the base, the plug is inside the window and hard to reach.

2. b

   Slide each motor into a bracket, with the plug facing the same way as the flat side of the bracket where the screws go.

   The gold gearbox goes into the bracket, the shaft sticks out the far side. The plug has to face the base.

3. c

   Turn the base upside down. Find the two rectangular pads near the middle, and the square window just inside each pad.

   Each pad has two small holes with a funnel around them. Those are pilot holes for the screws. The window is where the little board and plug go.

4. d

   Feed the cable through the window, then hold the bracket on the pad with the shaft pointing outward and the plug pointing down into the window. Drive in two M2 × 8 screws.

   The board and plug sit inside the window, so the motor sits flat on its pad. The funnel steers the screw in. Turn until snug, then stop: plastic threads strip if you keep going.

   

5. e

   Do the other side the same way. Both shafts point out.
6. f

   Pull each cable gently through its window so the wires come out on the top side of the base.

   The wires leave the plug toward the middle of the robot and bend up along the inside edge of the window. Nothing hangs under the motors to drag on the table or catch crumbs. Do not pinch a wire under a bracket.

7. g

   Push a wheel onto each shaft, flat side lined up with flat side.

   Press straight on, thumb against the table. No glue.

   

The third foot. The printed posts are already exactly the right height.

1. a

   Keep the base upside down. Find the two round posts near the back.

   They are exactly as tall as the caster needs, and each has a funnel hole.

2. b

   Hold the caster on the posts and drive in two M2 × 8 screws.

   Snug, then stop.

   

3. c

   Turn Dusty right side up and set it on the table.

The power bank rides in its own sleeve at the back, and the moto:bit and micro:bit sit on the deck above it. Keep the in-line switch OFF for this whole step.

1. a

   Check that both motor cables already come up through the windows in the base.

   The front of the sleeve sits over the back of each window. Once it is screwed down, you cannot feed a cable through anymore.

2. b

   Set the battery sleeve on the back of the base, open end on the left, the two screw tabs toward the front.

   The tabs and the back wall line up with four holes in the base. Keep the motor wires in front of the sleeve, not under it. The sleeve should sit flat without touching the little motor boards.

   

3. c

   Turn the base over and drive four M2 × 8 screws up through the base into the sleeve.

   Two into the front tabs, two into the back wall. The tray has to be out for this.

4. d

   Stick a strip of foam tape along the rib in the middle of the sleeve floor.

   Sticky side on the sleeve, never on the power bank.

5. e

   Slide the charged power bank into the sleeve, ports facing out the left side, all the way to the closed end. Then push the keeper bar in through the slot in the back wall until its head sits flat.

   The keeper crosses under the USB ports so the bank cannot slide out. Pull it out by the head when you need the bank out.

   

6. f

   Push the two deck posts, peg end down, into the holes near the front of the base.

   They go in snug by hand. The funnel end is the top.

7. g

   Stick a second strip of foam tape under the deck, right over the bank.

   It squeezes the bank gently so it cannot rattle.

8. h

   Set the deck on the posts and the sleeve, and drive four M2 × 8 screws down.

   Two into the posts, two into the back wall of the sleeve. The screw heads sit down in the pockets.

   

9. i

   Set the moto:bit on the four round risers on the deck, connector edge toward the front, so the four holes in the board sit on top of the four risers.

   Two risers are at the back corners and two at the narrow neck behind the connector. The board sits 5 mm up, so the solder bumps and pins underneath never touch the deck. The round power socket is on the left (change orders MOC-006 and MOC-007).

   

10. j

    Drive an M2 × 8 screw down through each hole into its riser. Start all four, then tighten them a little at a time.

    The risers have funnel pilot holes like the rest of Dusty. Snug, then stop: the board must not bend. No zip ties needed anymore.

11. k

    Slide the micro:bit into the connector on the front of the moto:bit, LEDs and buttons facing up.

    It lies flat and sticks out over the brush like a little roof. The gold stripes go in. If it will not go, flip it over rather than pushing harder.

    

12. l

    A grown-up connects the power: the 90° adapter into the bank’s USB-A port, turned so the cable runs toward the front. Then the USB to round-plug cable, the in-line switch, and the Y splitter, with one end into the moto:bit.

    Stick the switch to the edge of the deck with mounting tape where you can reach it. The second splitter end is for the brush motor in Step 9.

13. m

    Flip the switch ON, then tap the button on the power bank once. The micro:bit should light up.

    Nothing? Check every plug. Then check the bank is charged: pull the keeper bar, slide the bank out and press its button to see the lights.

14. n

    Switch off and run test T1 below. It proves the laptop can find Dusty and put code on it.

    Do the Code Lab setup first if you have not. Flash with the cable, unplug the cable, then switch Dusty on.

First code of the project, written with Claude and tested one wheel at a time. No sensors yet.

1. a

   Switch the power off.
2. b

   Find the red and white wires on each motor cable. Those two run the motor.

   Blue and black power the turn counter. Yellow and green carry its signals. Fold those four back and tape them. Dusty does not use them yet.

3. c

   Connect the left motor’s red and white wires to the moto:bit LEFT MOTOR terminal, and the right motor’s to RIGHT MOTOR.

   Red goes where the board says red. White goes where the board says black. A grown-up checks before you switch on.

4. d

   Slide the moto:bit switch to RUN MOTORS.

   STOP MOTORS keeps the wheels still while you work, even with power on.

5. e

   Run test T2 below with Dusty held in the air.

   In the air, not on the table. It does not know about edges yet.

6. f

   Fix any backward wheel in the spec, then run test T3 on the floor and measure your real speed.

   Your measured speed goes in the spec. The cliff math and the experiment both use it.

The two pink arms carry the cliff sensors out in front of the wheels. That head start is what lets Dusty stop in time.

1. a

   Find the header pins in the sensor bag and snap off two pieces of 3.

   They are gold pins held in a black plastic strip. If it is a strip of 6, bend it at the middle notch with pliers and it snaps into two 3s. Use the straight pins, not the bent ones.

2. b

   Push the short ends of one 3-pin piece through the three holes marked OUT, VIN and GND, from the back of the sensor.

   The back is the side without the two tiny bumps. The black plastic sits flat against the back, and the short ends poke through on the bump side. The long pins point up when the sensor faces the table.

   

3. c

   Hold it so it cannot tip while you solder.

   Tape the plastic strip down, or push the long pins into a scrap of foam with the bump side facing up.

4. d

   A grown-up solders the middle pin first.

   Iron at about 330 to 350°C. Touch the tip to the pin and the gold pad together for about a second, feed a little solder into the joint (not onto the iron), take the solder away, then the iron. 2 to 3 seconds per joint: longer can cook the tiny sensor.

5. e

   Check the pins stand straight up, then solder the two outside pins.

   Tilted? Reheat the middle joint and nudge the strip straight while the solder is melted.

6. f

   Check every joint.

   Good is a small shiny cone around the pin. A round ball sitting on top needs reheating. Solder joining two pins is a bridge: drag the hot tip between them to split it. Nothing may stick out lower than the two bumps, or the sensor cannot sit at 3 mm. Snip a long pin end with flush cutters.

7. g

   Do the second sensor the same way.
8. h

   Put a sensor face down in the foot of each arm, and hold it with an M2 × 6 screw and nut.

   The two tiny bumps must look down through the window.

   

9. i

   Hold the right arm against the outside of the right ear at the front of the base. The left arm, with the extra pad, goes on the left.

   

10. j

    Push an M2 × 8 screw through the slot and the ear, and add a nut on the inside.

    Snug, not tight yet.

11. k

    Set Dusty on the table. Slide each arm until the sensor is 3 mm above the table, then tighten.

    Two US pennies stacked are almost exactly 3 mm. Slide them under the sensor, push the arm down onto them, tighten, pull the pennies out.

12. l

    Pick off anything stuck on the moto:bit SENSOR pins.

    The board ships with its pins pushed into black foam, and bits can stay behind. Foam stops the plugs from going on, and it leaks a little electricity between pins, which throws off the sensor numbers.

13. m

    Peel six jumpers off the ribbon: yellow, red and black for the left sensor; green, red and black for the right.

    Red is always 3V3 and black is always GND. Each sensor gets its own signal color, so you can tell left from right at a glance.

    

14. n

    Push one end of each left sensor jumper onto its pins: yellow on OUT, red on VIN, black on GND.

    Push straight down until the black plastic sleeve stops. About 5 mm of pin disappears inside. A sleeve sitting crooked is only half on.

15. o

    Switch the power off. Push the other ends onto the P0 column of the moto:bit: yellow on top, red in the middle, black on the bottom.

    P0 is the left column of the first SENSOR block. Top is the row closest to the micro:bit slot.

    

16. p

    Right sensor the same way on the P1 column: green on OUT and the top pin, red on VIN and the middle, black on GND and the bottom.

    P1 is the right column of that same block. Leave the SERVO block alone: its middle row is full battery power, not 3V3.

17. q

    Twist each sensor’s three wires loosely together, fold the extra length, and tape it to the side of the deck.

    The jumpers are 30 cm long and Dusty needs about 10. Keep the loops away from the wheels and the brush.

The big one. By the end of this step Dusty stops itself at the edge of a real table, and you have the numbers written down to prove it.

1. a

   Check the sensor wires: left sensor on P0, right sensor on P1.
2. b

   Run test T4 and write down the numbers.

   On the table and held over the edge, for each sensor. Try white paper, bare wood and a black placemat. Table and edge should be far apart: maybe 200 on the table and 900 over the edge.

3. c

   Put your numbers in the spec, then run test T5, the loop timer.

   It tells you how often Dusty checks for the edge. The cliff math needs that number.

4. d

   Ask Claude for test T6, the edge program. The logic below is what it has to do.

   The rules are already in your spec. Your prompt only has to say which ones this program uses.

5. e

   Before you flash it, switch MakeCode to Blocks and find each line of the logic below.

   Find the thresholds, the check inside forever, and every pause. If you cannot explain a block, ask Claude about it before you run it.

6. f

   Test on a low table. Twenty approaches: ten straight on, five at an angle, five into a corner.
7. g

   Write down every single run in a notebook.

   Twenty out of twenty, or keep fixing. Tell Claude exactly what happened on the runs that failed.

8. h

   Then spring the trap in T5b.

   It shows how code that looks fine can make Dusty notice the edge too late.

A second way to notice the edge that works in a completely different way, so the two cannot fail for the same reason.

1. a

   Cut the blue and the black jumper about 10 cm from one plug.

   Keep the pieces that still have a plug on the end. The plug is what pushes onto the moto:bit pin.

2. b

   Strip about 3 mm of plastic off each cut end and twist the thin wires inside together.

   A grown-up tins them: a little solder on the bare wire so the strands stay together.

3. c

   Slide a short piece of heat shrink onto each wire before soldering.

   Once the wire is soldered on, the tube cannot go on from the other end. Tape works if there is no heat shrink.

4. d

   A grown-up solders blue to the NO tab and black to the C tab. NC stays empty.

   The letters are molded into the plastic next to each tab. Hook the bare wire through the hole in the tab, then solder. Do this before the switch is screwed on, so the heat cannot soften the arm. C is common, NO is normally open.

5. e

   Slide the heat shrink over each joint and shrink it.

   A hair dryer or the side of the iron works. It stops the two tabs from touching.

6. f

   Screw the switch to the pad on the left sensor arm with two M2 × 10 screws and nuts.

   Arm pointing down, little wheel toward the front.

   

7. g

   Set Dusty on the table. The wheel should rest on the table and push the arm in with a click.

   No click? Loosen the arm slot and lower it a little.

8. h

   Switch off. Plug the wires onto the P2 column: blue (NO) on top, black (C) on the bottom. The middle pin stays empty.

   P2 is the left column of the second SENSOR block, just right of P0 and P1. Same picture as Step 6.

   

9. i

   Run test T7 to check the switch, then ask Claude to add the whisker to your edge program.

   T7 needs no motors. The whisker rule is already in your spec: 1 on P2 means stop.

10. j

    Test it with both infrared sensors covered by tape.

    Only the whisker is working now. Does Dusty still stop?

Now Dusty earns its name. The brush motor spins far too fast for a brush, so three printed gears slow it down before it reaches the roller.

1. a

   Cut pipe cleaners into pieces about 30 mm long and push one through each hole in the roller.

   Center each piece so the same length sticks out both sides.

   

2. b

   Check the motor has no gear on its shaft yet.

   The gear will not fit through the hole in the right-hand wall of the mount, so it goes on after the motor is in. If the gear from the Batch 1 test is still on, wiggle it straight off. If it cracks, a grown-up prints a new one (dusty-pinion-revA5.stl, a few minutes).

3. c

   Snap the rocker switch into the square hole in the back wall of the motor mount.

   Easier now, before anything else is in the way.

4. d

   Thread the zip tie before the motor goes in. Push its tail down through one slot in the floor of the mount, along underneath the floor, and up through the slot on the other side of the curved motor cradles. Leave a big loose loop over the top.

   The two slots are on either side of the motor cradles, about halfway along. The flat band runs under the floor and the square head stays on top, beside the motor, never underneath.

5. e

   Put the motor into the mount, through the loop, shaft pointing to the right side. Tip the shaft end in first so the shaft and the round collar around it go into the hole in the right-hand wall, then press the back end down until it clicks into the two curved cradles.

   The flat sides of the motor face up and down. The collar sits in the hole, and the back of the motor rests in the rear cradle.

6. f

   Pull the zip tie tight over the motor and snip off the tail.

   Snug so the motor cannot lift or slide backward. Cut the tail close to the head so it cannot touch the gears.

7. g

   Press the motor gear onto the shaft where it sticks out of the right-hand wall.

   Hold the back of the motor with your other thumb so it does not slide back. Stop when the shaft tip just peeks through the gear and a paper-thin gap is left between the gear and the wall. If it slips, a grown-up adds a tiny drop of superglue, kept off the teeth.

   

8. h

   Push the two dowels into the two small holes in the top of the base, to the right of center near the front.

   They stick up a little over 1 mm. They are tiny: use the pliers, and do this over the towel.

9. i

   Set the motor mount on the dowels so they go into the two holes under its right edge. The mount sits flat, gear on the right.

   The dowels put the motor gear exactly where the big gear will be. If the mount rocks, a dowel is not in its hole.

   

10. j

    Lay Dusty on its side on the folded towel. Hold the mount down and drive two M2 × 8 screws up from under the base, through the two holes just right of center near the front, into the mount.

    Do this now, before the roller goes in: the roller covers both holes. Turn each screw a little at a time, back and forth, so the mount pulls down evenly. The zip tie band under the mount makes a tiny bump; that is expected. Snug, then stop.

11. k

    Slide the big gear onto the peg on the right side plate, big side first. Add the washer and an M2 × 6 screw into the end of the peg.

    The gear must spin freely. If it drags, back the screw off a quarter turn. Turn it slowly by hand: the motor gear should turn with it all the way round without catching or clicking. If it catches, check the mount sits flat on its dowels.

    

12. l

    Slide the axle in from the left side plate, through the roller, and out the right side plate. Push the roller gear onto the right end and the collar onto the left end.

    The flat side of the axle lines up with the flat inside the roller and the roller gear.

    

13. m

    A grown-up wires the brush: the splitter’s second end to its screw-terminal jack, then through the rocker switch to the motor tabs.

    Power off while wiring.

14. n

    Switch on and check which way the roller spins.

    The bristles at the bottom must move backward, toward the tray. Wrong way? Power off, swap the two wires on the motor tabs.

    

The tray catches what the brush flicks. It snaps in from underneath and pops back out, so you can weigh what Dusty picked up.

1. a

   Check the tray: flat bottom, thin clean front edge.

   Trim any brim off the front edge, because that edge rides on the table.

   

2. b

   Turn Dusty upside down on a towel. Set the tray in place with the ramp toward the brush, and press until the back clicks over the hook and the two side bumps click in.

   To take it out: push the back wall of the tray a little toward the front so it slips off the hook, and lift.

   

3. c

   Set Dusty on the table and look from the side. The bristles should just touch the table.

   Pressed hard, the brush acts like a brake. Too high, it misses crumbs. Trim the pipe cleaners to adjust.

4. d

   Check the tray from the side: the front edge touches the table, with a thin gap under the back.

   If the front edge scrapes hard, sand it a little.

5. e

   Weigh 5 grams of crushed cereal, sprinkle it in a strip, and let Dusty drive through it with the brush on.
6. f

   Pop the tray out and weigh what is inside. Write down the number.

   Do this three times and take the average.

The robot is finished. This weekend turns it into a science project, and this is what the display board is really about.

1. a

   Run test T8: your edge program becomes the main program, random bounce on A and Spot Clean on B.

   Spot Clean sweeps a 1 foot square in front of Dusty in rows, like mowing a lawn. The logic below is what it has to do. The cliff sensors still work the whole time.

2. b

   Tape a 1 foot (30 cm) square on the table. Put Dusty at the bottom left corner, facing into the square, and press B.

   Adjust the row time until Dusty just reaches the far tape, and the turn time until each turn is square.

3. c

   Load test T9 and run the speed experiment at four speeds: 25, 50, 75 and 100. Twenty runs at each.

   Touch the gold logo to change speed. Cushion on the floor anyway.

4. d

   For every run, write down how far the sensor went past the edge before Dusty stopped, in millimeters, and whether it fell.

   A ruler along the edge makes it easy. Slow-motion video makes it exact.

5. e

   Make the first chart: speed along the bottom, stopping distance up the side.
6. f

   Spill race: 5 g of cereal in the square. Press B and time Spot Clean until it stops. Weigh the tray.
7. g

   Same 5 g, same square. Press A and stop random bounce after the same time. Weigh the tray.

   Same time, same crumbs, same spot. Only the pattern changes.

8. h

   Do three tries of each pattern and make the second chart: grams picked up by each pattern.

   If there is time, try white paper, bare wood and a black placemat.