The board for the factory turned out harder than I thought. It replaces the RoboClaw, the buck converters, the servo driver and a pile of wires: an STM32, two motor drivers, the Raspberry Pi right on the board, an electronic fuse with current readback on every load, the xArm, 6 ToF sensors, 3 lidars.
The fun part was the routing. We started with Freerouting: on this board it spent 37 minutes just fanning the pads out to vias. Then we found fastroute, a Rust port of Freerouting: the same stage in 25 seconds. After that we ran experiments and watched how many links stayed unrouted:
- 6 layers, power pours handed to the router as obstacles: 350 unrouted after 4 hours
- 8 layers and pours after routing: 91
- a split power plane, and the 10-15 A nets only on the 2 oz outer copper: 76
- threw out 92 of 763 parts, updated fastroute from 0.1.7 to 0.1.13: same plateau, 1.5-2x faster
- widened the board up to the wheels and lengthened the tail, +30% area, tuned the router rules: 56
- Fable redid the part placement from scratch: the microcontroller block moved to the tail, a 2 mm ring around the fine-pitch QFNs, an empty band between each motor driver and its connector for copper: 27
Funny that the new placement gave more than the extra layers and area combined. And Fable separately caught that a 1.2 mm track at 10 A would burn, even though DRC happily passes it. The last 27 links we finish by hand.
We'll make it at JLCPCB in one order, with almost nothing done by hand: a script exports the factory files and checks each of the 166 BOM lines against their stock through the API, and the factory solders everything on both sides. In the same box come 10 sensor boards that an agent designed in an evening (it turned out the VL53L8CX can't run on 3.3 V alone, it needs its own 1.8 V regulator and a level shifter) and nylon brackets printed there too. Roughly ~$1.5-1.8k.
