REV B Desk robot · one sheet of board · two rubber bands
Small parts, big personality.
An ESP32-C3 for a brain, a 0.96″ OLED for a face, two micro servos on rubber-band tracks, all in a box folded from one sheet of grey board. Everything is on the mat. Scroll and it puts itself together.
Scroll to assemble01 Bill of materials
Everything on the mat.
Pick a line, or tap a tag on the mat, to read its sheet. Then keep scrolling: the parts leave the mat in build order.
02 Servo block
Two servos, one block.
The die-cut sheet slides to the middle of the mat, printed side up. The servos lose their mounting tabs and lie on their sides, back to back, with a strip of board between them. One goes in upside down, so both shafts share one axle at the front.
Before the glue
Check by hand that each servo spins freely: the same body is sold as 180° and 360°. Find its stop point with a 1.5 ms pulse (turn the trim if there is one, otherwise note the pulse for the firmware). Then saw the tabs off flush and file them, without cracking the case. Hot glue, servo, spacer O, servo: one block, leads to the back, tacked onto its printed outline.
M1 → GPIO6 · M2 → GPIO7 · block 49.9 mm wide
03 Fold it up
One sheet, one box.
Front and back fold up first and their flaps turn in; then the sloping sides rise, their notches sliding around the servo turrets, which end up 2.5 mm proud. Once the sides are glued, the block is held captive.
V-folds in board
On the printed side, two 45° cuts along each blue line meet just short of the far face: lift the strip out, fold towards the V and glue it with PVA. Leave about 0.3 mm of skin, and try one on an offcut first. Glue the slot patches R behind the axle slots before folding. Cut the windows first, the outline last.
V · 69.1 × 53.5 mm · 41 / 23 mm inside · board 1.5 mm
04 Tracks
Rubber bands for tracks.
The drive wheels press onto the servo horns, a bamboo skewer runs through the slots for the idlers, and a band goes round each pair. The box now stands on its own, 7.7 mm off the desk.
Tension and line-up
Push the axle back in its slot until the band no longer slips while you hold the drive wheel, then fix the axle with a drop of hot glue on the skewer. Drive wheel and idler must sit in one plane or the band climbs the flange: washers D set the gap. Push the robot by hand: the bands should run without leaving the grooves.
Ø 30 × 6 mm wheels · wheelbase 39 mm · track ≈ 70 mm
05 Under the shelf
The basement.
Under the shelf there are only 12 mm. The accelerometer is glued flat, the servo header lies on its side with the plugs pushed on sideways, the switch pokes out of the back and the buzzer faces its four holes. Wires bound for the boards go up through the slot.
Power nodes, no perfboard
The header’s V+ pins are the power node: switch, both servos, the diode to the 5V pin and the battery divider all land there. Its GND pins are the ground node, fed from the charger’s OUT−, never from B−. At most three wires per pin, heat-shrink on every joint, and the 470 µF stripe towards ground.
U4 INT1 → GPIO5 · J1 470 µF · SW1 · BZ1 → GPIO1
06 Power and brain
One shelf, three tenants.
The shelf rests on the servo block, its legs glued inside the sides. The battery lies across the front; the charger and the SuperMini sit side by side at the back, USB ports in their windows. The antenna faces the battery’s edge from 8 mm away, never across it.
Wire it safely
The battery is soldered straight to B+ and B−, no plug and nothing else on those pads. OUT+ goes through the switch to the header’s V+, OUT− to its GND. From V+ a 1N5819 Schottky feeds the board’s 5V pin, so USB and battery can share it; until it is fitted and checked, plug the SuperMini’s USB in only with the switch off. Charging works from the other port, switch on or off.
BT1 3.7 V 1000 mAh · U2 4.2 V · U1 ESP32-C3
07 The face
Two eyes and a sensor.
The OLED goes behind its window, glass against the board, with the distance sensor above it looking straight ahead. Four wires chain the I²C bus from the SuperMini to the face, on to the sensor and down to the accelerometer. Then the face wakes up.
Mark the window first
The lit area is not centred on the glass: switch the display on with a full pattern, hold it against the front, mark the lit edges and cut the window there. Read each module’s silkscreen, VCC and GND swap between boards. Colours used here: white 3V3, black GND, yellow SCL, blue SDA.
DS1 0x3C · U3 0x29 · U4 0x18 · SDA GPIO8 · SCL GPIO9
08 Close the lid
Shut, not glued.
The lid hinges on cloth tape at the back and drops onto its two stops; its own weight keeps it shut. It is the way back to the battery, so it never gets glued. The button on top reaches GPIO3 through a two-pin plug.
Before the first power-up
Multimeter first: no short between OUT+ and OUT−, or from the 5V and 3V3 pins to ground; continuity on every ground; the diode conducting one way only. Then USB alone, then the battery with the switch off, then on. Touch the charger, the regulator and the servos: warm at most.
C · 71.4 × 53.5 mm · SW2 → GPIO3
09 Assembled
Say hello.
One sheet of board, two rubber bands, a handful of boards and some thirty wires: a small robot looking back at you. Turn it around, look underneath, tap a part to read its sheet again.
Original design and code · cardboard chassis v1, drawn from the project’s templates and not built yet · component data from the datasheets linked in the parts list · GPL-3.0