Hardware — Wiring
The Anatomy
Every wire on the mower, from the 24 V drive pack to the donor Greenworks 60 V blade system it never electrically touches. The Pixel 6 does the thinking, a powered hub feeds it and its two serial devices, the ESP32 bridge turns orders into PWM for the Cytron MD30Cs and their wheelchair motors, and the blade answers only to an opto-isolated relay on the Greenworks switch circuit. Click any component for its dossier — wiring, hookup steps, and the ways it can hurt you — and the full bill of materials waits at the bottom.
The Watchdog Chain
Three watchdogs stand between a dropped link and a spinning blade: the dashboard pings every 250 ms; if the brain hears nothing for 600 ms it zeroes the motors and drops the blade; if the ESP32 hears nothing for 300 ms it stops the motors and opens the blade relay itself. A yanked USB cable, a crashed app, or a dead wifi link all end the same way — everything stops, blade first.
Click any block for wiring, hookup steps, and warnings. Dashed ⏚ stubs = the 24V-side common ground (ESP32, Cytrons, relay coil side, DC-DC, battery). The Greenworks 60V domain (red, dashed border) never bonds to it — the only crossing is the relay’s dry contacts in the low-current switch loop. The physical e-stop (SR-002) is the battery cutoff switch in the 24V bus itself — opening it kills the Cytrons and the DC-DC rail, which drops the blade relay coil, so drive and blade both stop without any firmware involvement. Parts removed from the design (30 kg servo, LM2596HVS bucks) are listed under the Ledger.
Select a component above to open its dossier
Appendix — Bill of Materials
The Ledger
01 — Purchased
| # | Component | Source | Qty | Unit | Notes |
|---|---|---|---|---|---|
| 1 | Electric Wheelchair Motor 24V 250W | Amazon | 2 | $72.00 | Rear drive, one per wheel |
| 3 | HAUL-MASTER 8 in. Pneumatic Swivel Caster | Harbor Freight | 2 | $17.00 | Front, undriven, 360° |
| 6 | Cytron 30A Motor Driver MD30C | Amazon | 2 | $38.50 | PWM + DIR, one per wheel |
| 7 | 24V 20Ah Battery | Amazon | 1 | $130.00 | Drive + electronics pack |
| 8 | Isolated DC-DC Converter 24V→5V 3A | Amazon | 1 | $7.99 | EMI isolation for 5V LV rail |
| 10 | LDROBOT D500 Lidar | Amazon | 1 | $79.00 | 360° scanning, CP210x USB |
| 13 | USB-C Powered OTG Hub (UGREEN) | Amazon | 1 | $12.59 | Pixel ↔ ESP32 + lidar |
| 14 | USB-C PD Trigger Board | Amazon | 1 | $9.99 | Pixel charging from 12V rail |
| 15 | 60A ANL Fuse and Holder | Amazon | 1 | $13.00 | Main fuse at the 24V battery |
| 16 | 8 AWG Wire, 10 ft, with Lugs | Amazon | 1 | $26.99 | Main power bus |
| 17 | 16 AWG Hookup Wire Assortment | Amazon | 1 | $14.49 | Logic + signal wiring |
| 19 | PC817 Optocoupler (4-pack) | Amazon | 1 | $9.99 | Blade-engagement isolation |
| 22 | XT60/XT90 Connector Pack | Amazon | 1 | $22.99 | Battery + bus connectors |
| 24 | Fasteners M3/M4/M5 Assortment | Amazon | 1 | $19.99 | |
| 25 | Heat Shrink / Zip Ties / Wire Loom | Amazon | 1 | $12.99 | |
| ≈ $615 total purchased | |||||
02 — Inventory Checkout
| Item | Notes |
|---|---|
| Wheel hub adapters ×2 | Machined 6061, motor shaft → 10" tire |
| 6061 aluminum stock | Brackets and mounts |
| HAUL-MASTER 10 in. pneumatic tires ×2 | Rear drive wheels |
| MPU6050 IMU | SLAM heading aid on the ESP32 (planned) |
| ESP32-WROOM-32D dev board | Motor bridge |
| Battery disconnect switch (Joinfworld, 12–48V) | SR-002 — master cutoff in the 24V positive bus; hardware stop for drive + blade |
| 5V relay module | Blade switch-circuit engagement |
| BTS7960 43A motor driver | Purpose TBD |
| 16A 2×12 terminal block distribution module | 24V power distribution |
| Donor Greenworks 60V mower | Deck, blade motor, and 60V pack — kept isolated |
03 — Dropped from design
| Item | Why it was removed |
|---|---|
| 30 kg servo | Was to actuate the Greenworks lever; superseded by relay-only blade control |
| 2× LM2596HVS 60V→9V buck | Likely the servo's isolated-side supply; orphaned once the servo was dropped |