Got it—I’ll prioritize a clean, CNC-routeable single-layer placement over compactness, enlarging the hexagon and spreading the ESP32/driver signal corridor before routing.
The PCB currently has a 110 × 105 mm hexagonal outline with all 18 footprints placed on top, no overlaps, and the single bottom-copper CNC stackup preserved.
Remaining
Enlarge and re-place to eliminate the congested ESP32-to-TB6612FNG corridor.
Recheck single-layer routability and antenna keepout.
Routing has not started; 23 airwires remain.
Execution stopped because no ACUs are currently available.
Each motor is budgeted at 0.75 A typical and 1.5 A brief peak. TB6612FNG approval is conditional: 1.5 A must be brief; sustained current must remain within the Pololu carrier thermal limit (1 A/channel nominal continuous, ambient/cooling dependent).
5 V Budget
Table
Load
Typical
Peak
Motor 1
0.75 A
1.50 A brief
Motor 2
0.75 A
1.50 A brief
ESP32-C3 DevKit
0.15 A
0.50 A
Driver logic/margin
0.05 A
0.10 A
Total
1.70 A
3.60 A
At 3.0 V cell voltage and 85% conversion efficiency: typical input is 3.33 A and peak input is 7.06 A. The cell, protection, holder, switch wiring, terminal interface, and boost input must support this transient.
Selected Boost Implementation
External Pololu U3V70F5 (item 2891), fixed 5 V step-up regulator. Manufacturer documentation: 2.9-5 V input, 80-95% typical efficiency, 10 A instantaneous input, 8 A for several seconds, and 7 A prolonged input. The 7.06 A calculated peak is within its short-duration capability, not its prolonged 7 A limit. Board interface J3 is a Würth 691137710006 six-position 5.00 mm through-hole terminal block rated 16 A; use short heavy wires or the module's large terminal-block holes, never ordinary 2.54 mm headers. Assignment: 1 VIN+, 2 GND, 3 5V_LOGIC, 4 5V_MOTOR, 5 ENABLE unused/default-high, 6 spare.
Selected Master Switch
External panel switch Daier KN3A-101, SPST ON-OFF, documented 20 A at 12 VDC. It connects through SW1, a 15 A/contact 5.08 mm PCB terminal interface, using short heavy conductors. This exceeds the calculated 7.06 A depleted-cell transient.
Motor Protection
F1/F2 remain Bel 0ZRM0125FF1A radial PPTCs. At 23 C: hold current 1.25 A, trip current 2.50 A; maximum trip time is 20 s at 6.25 A. This carries the 0.75 A normal load and does not claim to interrupt a 1.5 A brief peak, but responds to a prolonged high-current stall. Temperature derating and measured motor current remain mandatory.
Remaining Rating Blocker
The mandatory Same Sky SJ1-3524N 3.5 mm jacks are documented at only 1 A. A bounded search found no through-hole 3.5 mm jack with manufacturer-documented rating >=1.5 A. Switchcraft 35RAPC4BV4 was also checked, but its drawing provides no current rating. Therefore the 3.5 mm motor connector is not production-approved for the 1.5 A brief peak. No contact paralleling is claimed. Preserve power-off-before-insertion and STBY hardware disable.
Verification Still Required
Measure free-run, loaded, and locked-rotor current; verify protected cell and holder pulse capability; load-test the assembled boost/wiring; monitor TB6612, PPTCs, switch wiring, terminals, and jacks thermally.