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Case study · By Ewan Wills, product designer · UK · Last updated

Mobile robotics · Team project · Doc EW-CS-05

ASTRO. Line-following waste-collection robot

A buggy that follows lines on the floor to a colour-coded pickup point, grabs a waste container, locks it inside behind two doors and carries it back to base. Six of us built it in 2024 for a Heriot-Watt engineering course that runs the project as a bid: our team was a small company, ASTRO, pitching a prototype to a made-up client, EnviroSecure, who wanted hazardous waste moved without anyone carrying it.

I was managing director and chief mechanical designer. With one other teammate I designed the body, the drive, the gripper, the lift and the doors in CAD, and built the prototypes.

Project facts ↓ How it did
CAD render of the ASTRO waste-collection buggy: a laser-cut MDF body on four yellow wheels, with door pulleys on the roof
Sht 02 — Project facts

What it is, and who did what.

ProductAn autonomous buggy that collects waste containers from colour-coded points and drops them at base. It follows a black line, reads the floor colour to know where it is, and stops with an alarm if something blocks the way.
TeamSix students, Heriot-Watt University, 2024. Coursework run as a mock company bid, not a client job.
My partManaging director (running the team and the plan) and chief mechanical designer: the body, drive, gripper, lift and door mechanisms in CAD, and the prototypes. Teammates led the electronics, firmware, web interface and pitch.
DriveFour wheels from two DC motors, through 1:1 laser-cut gears on bearings. The drive and driven gears are the same part: the wheel gears have the same hole shape as the motor shaft.
GripperOne servo swings two arms through gears and links. The arms are the same radius as the containers, with printed guides that match the container's lip.
LiftA DC motor turns a long M4 bolt; a nut on the gripper rides it up and down between rails. A printed coupler joins motor and bolt, keyed to the motor shaft at one end and the bolt head at the other.
DoorsA servo opens both doors through a pulley. The servo only turns 180 degrees and the doors need 270, so the pulley is 2:1, and one band is crossed so the doors open in opposite directions.
BuildLaser-cut 4 mm MDF and PLA prints. 782 g complete. Parts came to £66.62, plus £1.60 for five printed test containers.
Sht 03 — Mechanics

From gripper to buggy.

First concept render: the gripper and its gears on a base plate with two DC motors
First concept: the gripper, its lift and the drive motors.
Gripper render with arrows showing the two arms swinging closed
One servo swings both arms.
Side render of the drive: two wheels linked by a laser-cut gear
Drive: one motor turns two wheels through a 1:1 gear.
Sht 04 — Results

How it did.

On the bench, the gripper lifted a container loaded from 10 g up to about 100 g of loose bolts, slowing only slightly at the top. We stopped at 100 g, because that was more than the brief needed. On the finished buggy it collected each 50 g container from its pickup point and delivered it to base.

The sensors were tested the same way. The distance sensor read within 1.4% between 10 and 50 cm. The line sensor needs to sit 4 to 8 mm off the floor.

What's missing: there is no charging station, so someone charges the battery by hand. The circuit board hangs off the end of the body with nothing under it. And the web page that sends the buggy out gives no sign that it heard you, so the only confirmation is watching it move.

Sht 05 — Questions

Quick answers.

What does ASTRO do?
It drives to a pickup point you choose on a web page, picks up a waste container, shuts it inside and takes it back to base, following lines and floor colours.
Was this a real contract?
No. EnviroSecure is a fictional client. The course runs the project as a company bidding for its contract, so the pitch, the budget and the roles were all part of the assessment.
What did you design?
The mechanics: body, drive, gripper, lift and doors, with one other teammate. I also ran the six-person team as managing director.

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