Botbench

Plan LEGO 51515 and EV3 31313 robot builds, rehearse them in a 2D simulator and export Pybricks code, up to behaviours picked by Jev

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Overview

Botbench is a workbench for the two LEGO robot kits most people still have in a cupboard: Robot Inventor (51515) and EV3 Home Edition (31313). Tick the boxes you own, plug parts into a hub's ports, and it tells you what that build can do, rehearses it in a top-down simulator, writes the Pybricks MicroPython to run it, and then connects to the real Inventor Hub over Web Bluetooth so you can watch it sense, drive it by hand and switch its behaviour from the page. The top of the ladder adds a decision layer: a laptop bridge asks TypeSafe's Jev which behaviour fits a goal written in plain words, while the motors stay under the hub's own control loops.

Live: botbench.neorgon.com

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Features

• Port planner -- every port is checked against the connector family (LPF2 and EV3 do not mix), the port type (EV3 motor ports A-D, sensor ports 1-4) and the parts actually in your boxes
• Combination matrix -- eight chassis types against each hub you own, with what is missing and how many distinct port layouts exist
• Simulator -- differential drive with the build's real wheel size and axle track, a colour sensor reading a painted floor, a ray-cast distance sensor, a bumper, three arenas
• Rule table brain -- if-sensor-then-motors rules with hold timers and a proportional line follower; edit values while it runs
• Modes and decider -- follow line, explore, avoid, stop, picked twice a second from plain-language facts by a local stand-in, gated by confidence, with the exact Jev request shown beside the arena
• Export -- Pybricks programs for either hub, plus bridge.py (bleak over Bluetooth LE, HTTPS to Jev, key kept on the laptop)
• Link to the hub -- Web Bluetooth to an Inventor Hub running Pybricks: live facts, a teleop pad (keys or buttons, one byte each), mode buttons, the stand-in decider as a browser-side bridge, and the hub's raw output; a virtual hub runs the same protocol against the simulator so the whole tab works with no hardware
• Project ladder -- 18 projects in five levels, each marked against your kits, the simulatable ones loading straight into the arena
• Models and ideas -- published builds with instructions for either kit, and ideas past the box, each marked against the kits you own and split into what the arena can rehearse and what only the real robot can tell you
• Paths and hardware -- firmware options per hub and what to buy for each path: microSD, Wi-Fi dongle, Raspberry Pi Build HAT, an API key

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How the AI layer is split

Layer	Runs on	Rate	Does
Control loops	the hub	~100 Hz	line following, avoiding, stopping
Facts	the hub	2 Hz	turns readings into categories: front=blocked;floor=line edge;mode=explore
Link tab	this page, Chromium	2 Hz	the same facts over Web Bluetooth; teleop and mode bytes back; the stand-in decider, never Jev
Bridge	laptop or Raspberry Pi	2 Hz	reads facts over BLE, holds the API key
Jev	TypeSafe API	per call	one Choice question picks the mode, one Noul asks if the goal is met
Gate	the bridge	per call	switches only above a confidence threshold, sends one byte back

Two things the simulator taught the design, both now in the exported hub code: numbers are turned into categories on the hub because comparing numbers is on Jev's documented weak-spot list, and a crossed line is latched between reports because a 22 mm line passes under the sensor in a tenth of a second.

The browser never calls Jev: there is no CORS story and a key must not ship in a static page. The simulator's decider is a hand-weighted local stand-in that imitates the answer's shape, labelled as such.

The hub link

The Link tab speaks the Pybricks BLE profile directly (service c5f50001-…, the command/event characteristic, WRITE_STDIN 0x06 out, WRITE_STDOUT 0x01 in, START_USER_PROGRAM 0x01), which is the same channel Pybricks' own "hub to PC" tutorial uses. The program still gets onto the hub through Pybricks Code, because compiling MicroPython in the browser is a build this site does not carry; an experimental button pastes the source into the hub's REPL instead, paced on the echo, and is marked as untried on hardware. Web Bluetooth exists in Chrome and Edge only, over https or localhost.

The virtual hub is the simulator attached to the same link: it prints the same facts line and takes the same bytes, so the tab, the decider and the teleop pad can be tried before a hub is in the room.

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Running locally

ES modules require an HTTP server (not file://):

make serve

Tests over the pure modules (build, brain, export, the link protocol):

node --test test/*.test.mjs

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Architecture

botbench-site/
├── index.html          # Shell, CSP, header and footer kit contracts, the five panels
├── css/style.css       # Template base plus the workbench layer
├── js/
│   ├── app.js          # Entry point
│   ├── catalog.js      # Hubs, devices, kits, chassis types, firmware, extra hardware
│   ├── build.js        # Port validation, capabilities, combination matrix
│   ├── brain.js        # Rule runner, modes, facts, the Jev request, the local stand-in
│   ├── sim.js          # Arenas, kinematics, sensor models (no drawing)
│   ├── simview.js      # Canvas, clock, brain-in-the-loop
│   ├── export.js       # Pybricks programs (rules, modes with teleop) and the Jev bridge
│   ├── link.js         # Pybricks BLE profile, facts line, link over a transport; BLE and virtual transports
│   ├── linkpanel.js    # The Link tab
│   ├── projects.js     # The project ladder
│   ├── models.js       # Published models and bigger ideas, with sources
│   ├── models-panel.js # The Models and ideas tab
│   ├── state.js        # Workbench state, validated persistence
│   ├── render.js       # Build, projects, paths, export panels
│   ├── simpanel.js     # Simulator controls, readout, rule editor
│   ├── events.js       # All listeners
│   └── neorgon-*.js    # Vendored kits (header, footer, beacon, dom, persist)
├── test/               # node --test over the pure modules
└── docs/architecture.mmd

LEGO, MINDSTORMS and Robot Inventor are trademarks of the LEGO Group, which does not sponsor or endorse this project.

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