Quad BLDC Drone ESC Design
Thought
I’ll quickly check the schematic/layout readiness state for the ESC and power-management sections, then tell you whether they’re ready for PCB modeling or what must be fixed first.
Thought
Not yet. The PCB viewer can show a rough layout now, but the ESC PCB and power-management PCB are not ready for meaningful PCB modeling/layout release.
Main blockers:
- Current board outline is 160 mm × 100 mm, not your required ≤60 mm × 200 mm.
- ESC schematic is incomplete: MOSFET power stages, gate-drive support, current sense, bulk capacitance, MCU↔DRV8308 control wiring, reset/boot/debug, and decoupling still need completion.
- ERC still has many unfinished MCU/DRV8308 floating-pin warnings.
- PM board is closer, but still has one known ERC issue: U7 NC tied to SW, which is datasheet-guided but tool-flagged.
- Placement is congested around motor connectors/drivers and needs a deliberate split/placement plan.
Recommended next steps:
- Decide board partition: separate ESC PCB + PM PCB, or one combined board within 60 × 200 mm.
- Finish the ESC schematic power stages and support passives.
- Set the board outline(s) to the 60 × 200 mm limit.
- Then run structured PCB placement for PM high-current corridor, four motor stages, MCUs, connectors, and thermal sensors.
Choose separate boards
Finish ESC schematic
Set board outlines
Fix PM ERC
Plan component placement
Refine this doc
Ask about this doc
Power Management Board Notes
Scope
Initial schematic block for the separate 6S LiPo power-management board that powers:
- ESC board
- Flight controller
- E/O camera
Telemetry requirement: temperature only, accessed through the flight-controller interface. No onboard datalink transmitter/receiver.
Input and Current Basis
- Battery: 6S LiPo, 22.2 V nominal, 25.2 V fully charged
- ESC high-current basis: 80 A continuous board current, 144 A max, 208 A simultaneous spike case
- Motor basis: 20 A continuous, 36 A max, 52 A spike per motor
Selected Motor
- Motor: Skystars Koko 2207.5 / 2275 1950KV
- Product URL: https://www.rotorama.com/product/skystars-koko-2207-5-1950kv
- Intended setup: 6S LiPo with 5-inch propeller
- KV: 1950 KV
- Stator size: 2207.5, 22 mm × 7.5 mm
- Configuration: 12N14P
- Shaft: 5 mm hollow titanium alloy
- Mounting: 16 mm × 16 mm, M3
- Weight: 32 g
- Leads: 20 AWG, 150 mm
- Internal resistance: 78.5 mΩ, from secondary listing
- Idle current: <1.1 A at 10 V, from secondary listing
- Max current: 36 A for 180 s, from secondary listing
- Max continuous power: 1000 W for 180 s, from secondary listing
Design impact:
- The existing 36 A max-per-motor sizing assumption matches the published motor max current.
- The existing 20 A continuous-per-motor board sizing remains a conservative design assumption until propeller/thrust test data is selected.
- The existing 52 A spike-per-motor assumption remains a transient design margin above the published 36 A/180 s value.
- Four motors imply 144 A published max aggregate and 208 A assumed simultaneous spike aggregate.
First-Pass Schematic Architecture
- J10: 6S LiPo input connector
- J11: protected 6S output to ESC board
- PM_6S_PROTECTED: high-current protected battery bus
- U7: LMR33630-Q1, 6S-to-5 V synchronous buck, initial 3 A auxiliary rail
- U8: LGS5145, 6S-to-3.3 V buck, initial 1 A logic/analog rail
- PM_5V_AUX: regulated 5 V output for flight controller / E/O camera auxiliary power
- 3V3_A: regulated 3.3 V rail for STM32 logic/analog NTC pull-ups
- D1/D2: 33 V-class TVS clamps on 6S bus/output
- D3/D4: 5 V TVS clamps on regulated output rails
Regulator Design Values Used
LMR33630-Q1 5 V rail:
- Feedback top: 100 kΩ
- Feedback bottom: 24.9 kΩ
- Inductor: 8 µH initial, per datasheet 5 V / 3 A / 400 kHz typical example
- Bootstrap capacitor: 100 nF
- VCC bypass: 1 µF
LGS5145 3.3 V rail:
- Feedback top RF: 13 kΩ
- Feedback bottom RG: 4.3 kΩ
- Feedback reference: 0.812 V typical
- Inductor: 10 µH initial placeholder pending detailed ripple/current calculation
- Bootstrap capacitor: 100 nF
- External Schottky catch diode included per datasheet topology
Open Sizing Items
- Flight-controller voltage/current requirement
- E/O camera voltage/current requirement
- Selected ESC high-current output strategy: external QS8-S anti-spark harness connector, bolt-down 100 A class MIDI/MEGA fuse holder, and PCB busbar/lug interface instead of a normal PCB connector
- Existing XT60/XT90 Flux-library PCB connector options are not acceptable for the full 80 A continuous / 208 A spike basis; J11 is marked as a temporary excluded schematic placeholder only
- TVS surge-energy rating must be checked against wiring inductance and expected load-dump/motor transient conditions
- Final regulator inductor saturation currents, capacitor ripple ratings, and thermal layout must be calculated from actual load currents
Selected 80 A ESC Output Connector and Protection Strategy
Use an external high-current harness and bolted protection path rather than putting the full ESC current through an undersized PCB connector.
Selected connector direction:
- QS8-S anti-spark connector pair, 8 mm bullet style
- Common published ratings found: about 110 A continuous, 180 A burst/max, and higher short peak ratings depending on supplier
- Use genuine parts only; derate aggressively for enclosure temperature, solder quality, and vibration
- Mechanically strain-relieve the harness so connector and solder joints do not load the PCB
Selected protection direction:
- 100 A class bolt-down MIDI or MEGA fuse in an external holder rated at least 58 VDC, preferably 70 VDC
- Use the fuse as serviceable catastrophic short protection, not as motor phase-current limiting
- Keep TVS clamps on the PCB close to the PM board input/output busbar interface
- Add copper/busbar geometry for PM_6S_PROTECTED; do not route this path as standard PCB traces
Schematic Busbar / Lug Pad Implementation
Added Würth Elektronik REDCUBE 7461147 M5 high-current PCB terminals as the PCB busbar/lug interface. Each terminal has 16 PCB pins tied together to spread current into copper pours/busbar geometry.
Terminal assignments:
- J14: QS8-S battery positive lug pad, PM_6S_RAW before external fuse
- J15: QS8-S battery negative / return lug pad, GND
- J16: external MIDI/MEGA fuse holder input lug pad, PM_6S_RAW
- J17: external MIDI/MEGA fuse holder output lug pad and protected ESC positive, PM_6S_PROTECTED
- J18: protected ESC negative / return lug pad, GND
Retired placeholders:
- J10 and J11 XT60 placeholders are disconnected and marked Exclude from BOM / Exclude from PCB.
- Do not use XT60 for this high-current path.
Fuse-path interpretation:
- The external fuse holder connects physically between J16 and J17.
- PM_6S_RAW and PM_6S_PROTECTED must remain separate nets in the schematic and PCB.
- Regulators and ESC feed from PM_6S_PROTECTED only, after the external fuse.
Exact External Fuse / Holder Selection
Primary selected fuse path uses Littelfuse 58 V MIDI/BF1 parts, suitable for the 6S LiPo pack voltage and the 80 A continuous ESC output basis.
Primary fuse:
- Manufacturer: Littelfuse
- MPN: 142.5631.6102
- Series: BF1 58V MIDI / SLO-BLO bolt-down fuse
- Rating: 100 A, 58 VDC
- Interrupting rating: manufacturer page lists 1000 A at 58 VDC; datasheet family data indicates 40–150 A versions up to 2000 A at 58 VDC
- Mounting: M5 bolt-down
- Mounting torque: 4.5 Nm ± 1 Nm
- Typical cold resistance: 0.44 mΩ
- Typical voltage drop: 70 mV
- Typical I²t: 42,500 A²s
- Housing color: blue for 100 A
Primary holder:
- Manufacturer: Littelfuse
- MPN: 04981038HXF or covered variant 04981038HXFC
- Series: MIDI-Flex bolt-down single fuse holder
- Rating: 58 VDC, up to 200 A MIDI fuse
- Fuse type: MIDI/BF1 style bolt-down fuse
- Mounting: bolt-down holder, M4 mounting hole, accepts high-current MIDI fuse hardware
Higher-voltage MEGA alternative:
- Fuse MPN: Littelfuse 0898100.U-1M6
- Series: MEGA 70V SF56
- Rating: 100 A, 70 V, M6 single-hole bolt-down
- Use only with a holder explicitly rated for the selected MEGA 70 V fuse family; do not assume every MegaVAL/MEGA holder is 70 V rated.
Do not use:
- MTA MidiVAL 32 V fuse/holder parts for this design, because they do not provide the preferred ≥58 VDC rating.
- Low-current PCB blade fuse holders; they are below the 80 A continuous requirement.
Rationale:
- 80 A continuous and 208 A spike exceed the safe range of the XT60 and the available Flux XT90 PCB connector results
- Bolt-down fusing handles heat and vibration better than small PCB blade fuse holders at this current level
- A connector-plus-fuse harness keeps high-current service parts off the sensitive logic section while preserving the low-cost PM board regulator design
Layout Notes
- All PCB boards must fit within an approximate maximum footprint of 60 mm width × 200 mm length.
- Keep PM_6S_PROTECTED as copper-pour/busbar geometry, not a normal trace
- Route aggregate 6S current lengthwise so the required 40–50 mm equivalent copper/busbar width fits inside the 60 mm board width.
- Place D1/D2 close to input/output connectors with short return to power ground
- Place buck input capacitors tight to VIN/PGND pins
- Keep SW nodes small and away from NTC/ADC/SPI signals
- Use star/controlled return strategy so ESC switching currents do not flow through flight-controller/camera ground references
- If the fuse/REDCUBE/QS8 interface plus regulator/logic areas cannot fit while preserving the high-current corridor, keep the PM board separate instead of merging it into the flight controller.
Scope
Input and Current Basis
Selected Motor
First-Pass Schematic Architecture
Regulator Design Values Used
Open Sizing Items
Selected 80 A ESC Output Connector and Protection Strategy
Schematic Busbar / Lug Pad Implementation
Exact External Fuse / Holder Selection
Layout Notes
