Assembly Manual

Section 01

Safety first

Section 02

Meet PROBE LX-3

PROBE LX-3 is a small differential-drive robot: a 245 mm dome on a 209 mm base, two N20 motors at the rear and a ball caster up front. Inside is a Raspberry Pi 5 on a Geekworm X1200 UPS, an Adafruit motor bonnet, a USB camera and a VL53L1X distance sensor. The dome twist-locks onto the base, so the electronics are one quarter-turn away.

Spec	Value
Size	Ø245 mm × about 186 mm tall, without the lidar
Drive	Differential, two N20 gear motors (plain or encoder) and a front ball caster
Compute	Raspberry Pi 5. 2 GB is enough
Power	Two 18650 cells on a Geekworm X1200 UPS for the Pi. Four AA cells for the motors
Sensors	Arducam B0385 USB camera and a CQRobot VL53L1X time-of-flight sensor
Motor driver	Adafruit 4280 DC + Stepper Motor Bonnet, I2C address 0x60
Printed parts	Seven core parts plus one optional, all printed with no supports
Add-ons, no reprint	RPLIDAR A1M8 on top. WM8960 audio HAT and two speakers inside

Directions used in this manual

Front is the camera side. Rear is the battery-cradle side. Left and right are as the robot sees them.

Hardware only

No software ships with PROBE LX-3. You get a robot with a camera, a range sensor, two drive motors and a Pi 5, and you write the software you need. The wiring section lists every bus and address.

Section 03

Parts and tools

Nothing ships with PROBE LX-3, so this is your shopping list. Brand names are the exact parts the design was modelled and fit-checked around. Swap in equivalents at your own risk, and check dimensions before you print.

Section 04

Printing the parts

Every part is sized for a 256 mm bed, has 3 mm design walls, and prints with no supports. The dome needs at least a 245 mm circle. Everything else fits a 220 mm bed.

Part	Size (mm)	Orientation on the bed	Notes
Dome	Ø244.8 × 120	Rim down	Leaves 5.6 mm per side on a 256 mm bed. The inside of the top bridges about 45 mm; a little sag there is hidden.
Base	Ø209.4 × 41.5	Floor down	Plain shell with 49° walls.
Electronics tray	Ø123 × 26	Underside down	Carries the Pi 5 posts and the AA cradle. For electronics changes, reprint this part, not the base.
Drive plate	161 × 124 × 7.5	Top face down	Nut pockets face the bed and the caster pad faces up.
Camera bracket	67 × 61 × 35.6	Flat back face down	Holds the camera and distance sensor, and clicks into the dome's rail.
Wheel hub × 2	Ø31.8 × 19	Flat on its side, axis vertical	PLA or PETG. The D-bore presses onto the N20 shaft.
Wheel tyre × 2	Ø43 × 19	Flat on its side, axis vertical	TPU. Stretches over the hub.
Lidar adapter (optional)	64 × 78 × 21.7	Flat face down	Only for the RPLIDAR add-on.

Setting	Value
Material	PLA or PETG. Tyres in TPU.
Layer height	0.2 mm (0.16 mm on the camera bracket for a crisper latch)
Wall loops	Enough to fill the 3 mm design walls, about 4 to 5 at 0.4 mm line width
Infill	15 to 20 %, gyroid or grid
Supports	Off. No part needs them.
Brim	Optional on the dome and base if your bed adhesion is marginal

After printing:

• Clear every hole: the insert holes, pilot holes, and screw holes through the plate and base.
• Push a zip tie through each speaker loop inside the dome to clear it, even if you are not fitting audio yet.
• Check the dome's ledge, the three bayonet notches and the rail block's groove for stringing.
• Test-fit the dome on the base. That is step 1.

Section 05

Shells and prep

The robot goes together bottom-up. Have everything from the parts list and all printed parts cleaned up before you start.

1. 1

   Test-fit the shells

   1. 1.Check that the dome's ledge, the three notches and the rail block's groove are clean and free of stringing.
   2. 2.Set the dome on the base with the camera about 30° counter-clockwise of the front, seen from above. The notches drop over the base lugs.
   3. 3.Twist clockwise until it stops. It should turn freely through about 30° and stop hard at each end.

   Lift the dome off again. It goes back on in step 13.

2. 2

   Heat-set inserts in the electronics tray

   You need: 4 × M3×4×5 heat-set inserts, soldering iron with an insert tip.

   1. 1.Turn the tray upside down on a towel.
   2. 2.Press an M3×4×5 insert into each of the 4 holes on the underside, straight and flush.
   3. 3.Let them cool for a minute before loading them.
3. 3

   Nuts into the drive plate

   You need: 4 × M2 nuts, masking tape.

   1. 1.Lay the plate top face up. That is the flat face, without the pad.
   2. 2.Press an M2 nut into each of the 4 hex pockets on the arms. These hold the motor brackets.
   3. 3.Tape over all 4 pockets, then flip the plate so the raised caster pad faces up.

Section 06

Drive plate

1. 1

   Build the wheels and mount the motors

   You need: 2 × N20 motors, 2 × printed wheel hubs, 2 × printed TPU tyres, 2 × brackets, 4 × M2 screws.

   1. 1.Stretch a tyre over each hub until it sits evenly all the way round.
   2. 2.Press a wheel onto each motor's D-shaft. Line the flat in the hub bore up with the flat on the shaft, and push the wheel fully home.
   3. 3.Lay a motor on each rear arm, with the wheel pointing outward and the solder tabs (or encoder board) toward the centre.
   4. 4.Line the gearbox's front face up with the arm tip. The wheel should sit about 1 mm clear of the tip.
   5. 5.Encoder motors only: the encoder board drops into the shallow pocket beside the wire slot.
   6. 6.Set a bracket over the gearbox with its two ears over the arm's two holes.
   7. 7.Drive 2 M2 screws through each bracket into the nuts. Snug them only. Overtightening crushes the gearbox.
   8. 8.Spin each wheel by hand. It must turn freely and not touch the plate.
2. 2

   Mount the caster

   You need: 1 × ball caster, isopropyl alcohol.

   1. 1.Wipe the raised round pad clean with isopropyl alcohol if you have it.
   2. 2.Peel the caster's adhesive backing, centre the caster on the pad, and press hard for 30 seconds.
   3. 3.Optional backup: drive 2 short self-tapping screws through the caster's holes into the pad. Go no deeper than 6 mm, or they will reach the base floor.
3. 3

   Route the motor wires

   1. 1.Feed each motor's wires up through the 10 × 5 mm slot just inboard of that motor.
   2. 2.Remove the tape from the nut pockets.

Section 07

Chassis

1. 1

   Join the drive plate, base and tray

   You need: 4 × M3×10 button head, 2.0 mm hex key. One set of 4 screws clamps all three parts together.

   1. 1.Stand the drive plate on its wheels and caster.
   2. 2.Set the base on the plate, lining up its 4 small holes and 2 wire slots with the plate's.
   3. 3.Drop the tray into the base with the posts up and the battery cradle over the motors, at the rear. Feed the motor wires up through the tray's matching slots.
   4. 4.Tip the assembly onto its side.
   5. 5.Drive 4 M3×10 button screws up through the plate and base floor into the tray inserts.

Section 08

Electronics

1. 1

   Pi 5 and X1200 stack

   You need: Pi 5, X1200 with its spacers and 4 × M2.5×20 screws, 2 × 18650 cells.

   1. 1.Fit both 18650 cells into the X1200 first. The holders face down, and you cannot reach them once the stack is in.
   2. 2.Set the Pi 5 on the X1200 with the spacers between them, so the pogo pins meet the pads on the Pi's underside.
   3. 3.Stand the stack on the 4 tray posts, with the 40-pin header toward the rear and the USB and Ethernet end toward the robot's left.
   4. 4.Drive 4 M2.5×20 screws down through the Pi 5, spacers and X1200. The tips cut their own thread into the posts. Stop at snug.
2. 2

   Motor bonnet

   1. 1.Press the motor bonnet straight down onto the Pi's 40-pin header.

   Optional: fit two 8 mm M2.5 standoffs in the Pi's rear holes to support the bonnet.

3. 3

   4AA battery pack

   You need: 4 × AA holder, 2 × zip ties, 250 mm or longer.

   1. 1.Stand the pack on its edge on the rear cradle, between the ribs.
   2. 2.Thread 2 zip ties through the tunnels under the cradle, up both faces of the pack, and over the top.
   3. 3.Put the tie heads on top of the pack, pull tight, and trim.
4. 4

   Base wiring

   You need: small flat screwdriver.

   1. 1.Left motor to bonnet terminal M1. Right motor to M2. If a wheel runs backward in testing, swap that motor's two wires.
   2. 2.4AA pack leads to the bonnet's motor power terminal, red to +. Leave the pack switched off, or leave a cell out.

Section 09

Dome

1. 1

   Camera and distance sensor into the dome

   You need: camera bracket, Arducam B0385, VL53L1X, 4 × M2×8 socket pan, 2 × M2×5 button, 2 × M3×10 button. Load the bracket on the bench first, then slide it into the dome.

   1. 1.Camera: with the lens facing away from the bracket, set the board on the 4 short standoffs. Gently drive 4 M2×8 socket pan screws through the board into the standoffs. Plug the camera cable in through the window in the bracket plate.
   2. 2.Distance sensor: plug its cable in first, with the connector facing down. Set the board on the 2 long standoffs with the chip facing away from the bracket, and fix it with 2 M2×5 button screws.
   3. 3.Set the dome upside down on a towel. Find the rail block on the ledge below the camera opening.
   4. 4.Hold the bracket with the lens toward the opening. Drop the dovetail key into the open end of the groove and push the bracket toward the wall.
   5. 5.The latch rides up over the block and clicks into its notch as the key hits the end stop. The lens now sits in the Ø24 opening, and the sensor chip faces its window.
   6. 6.On the dome's rim face below the camera, find the two recessed holes. Drive 2 M3×10 button screws up through them into the bracket key until snug. The heads sit below the rim face, so the dome still seats on the base.
   7. 7.Route both cables down toward the base with at least 70 mm of slack. They must reach the Pi with the dome unlocked.

   To remove the bracket

   Take out the 2 screws, push the latch arm up (toward the dome top) where it passes the end of the block, and slide the bracket back out.

2. 2

   Connect and close

   1. 1.Camera USB lead to any Pi USB port.
   2. 2.Distance sensor to the Pi's I2C pins: 3.3 V, GND, SDA (GPIO2), SCL (GPIO3). Reach them through the bonnet's pass-through pads or a stacking header. The sensor (0x29) and the bonnet (0x60) use different addresses.
   3. 3.Tuck the cables so nothing crosses the base lugs.
   4. 4.Set the dome on about 30° counter-clockwise, then twist clockwise to the stop. The camera now faces the front, over the caster.

   To open: twist counter-clockwise to the stop and lift.

Section 10

Wiring reference

Every connection in one table, and the I2C addresses to expect. Leave at least 70 mm of slack on every cable that runs from the dome to the base: the dome twists 30° to unlock, and nothing should pull on a plug.

i2cdetect -y 1

Section 11

Checks before first power-on

Run these with the robot on the bench before its first drive.

Section 12

Writing your own software

PROBE LX-3 ships with no software. Use whatever language or framework you like. Here is what each device needs from the Pi.