Design calculations

These are design calculations for a prototype, not measured performance. None of them is acceptance evidence.

Stored firing energy

The two parallel 470 µF capacitors give 940 µF. At the nominal 12 V charger setpoint:

E = ½ C V² = 0.5 × 940e-6 × 12² = 67.7 mJ

For a 1.3–1.9 Ω match, the ideal initial current is 6.3–9.2 A, limited by ESR, MOSFET resistance, wiring, terminal resistance and PCB copper. The pulse is a capacitor discharge, not a rectangular constant-current pulse.

Energy margin must therefore be demonstrated using production-lot matches at temperature. The calculation alone is not acceptance evidence.

Bleeder

With 2.2 kΩ across 940 µF:

τ = RC ≈ 2.07 s

The theoretical voltage is below 1% after roughly 9.5 s. Component failure, an inserted ARM jumper or firmware state can invalidate that expectation: always measure the bank before handling.

Magnetometer criterion

Firmware evaluates |Bx| / |B|, where X is the board and rocket longitudinal axis. The default threshold is 0.22 for 120 ms, after qualification and a 3 s post-arm inhibit.

The criterion is deliberately configurable in source, because airframe magnetic bias, launch latitude, rail angle and rotation materially affect it. The defaults are starting values, not validated flight settings.

PCB current path

The high-current capacitor, match and MOSFET loop has dedicated rear-copper reinforcement. Charger and sense branches remain narrow. Rev A requires a scoped inert-load discharge test and thermal inspection before any match test.