Electronics installation
Summary¶
Electronics installation populates an assembled airframe with the FC/ESC stack, power components, sensors, and video system. This is written for a bought (not printed) frame — there is no Platform layer, no GX12 payload interface, no three-zone printed wire channel geometry. The EMC discipline that made those channels matter still applies; you now enforce it by wiring choice and cable management rather than by printed geometry. The sequence is fixed: capacitors first, then route every cable to its final position, then bolt the stack down, then solder power, then signal. Conformal coating is strongly recommended before first power-on. Firmware-agnostic — applies to ArduPilot (Cinematic) and Betaflight (Agile) builds alike.
Concept¶
Why capacitors install first¶
The bulk electrolytic capacitor (1000 µF class, low-ESR) must be soldered directly to the ESC VBAT/GND pads before any motor or power wiring is connected. The first time full battery voltage is applied through any path, inrush current will spike — the capacitor needs to be in place to absorb that spike before it reaches the MOSFETs. Installing it last means the first power test is the first unprotected high-current event. A smaller ceramic capacitor (100 µF class) on the FC's 5 V rail handles the faster spikes the electrolytic cannot respond to quickly enough. Both are mandatory regardless of frame.
Route before you bolt¶
Every cable must be routed to its final position before the FC/ESC stack is bolted down. Attempting to route cables with the stack in place means working around standoffs and connectors in a tight space — the probability of disturbing a previously soldered joint increases. Route, verify, then bolt.
EMC discipline without printed channels¶
A printed Platform enforced power/signal separation physically, with walls. On a bought frame, you enforce the same separation by cable routing discipline: keep motor phase wires, battery leads, and any other high-current run physically apart from GPS, receiver, and UART signal wires — zip-tie them into separate bundles along different sides of the frame rather than letting them cross freely. The principle (star grounding, twisted pairs on high-current runs, capacitors at the source not on a pigtail) is unchanged; only the enforcement mechanism changed from geometry to discipline.
Reference¶
Installation sequence¶
| Step | Action | Gate check |
|---|---|---|
| 1 | Solder bulk capacitor directly to ESC VBAT+/GND pads. Leads ≤ 5 mm. Solder smaller ceramic cap to FC 5V pads. | Cap body flat on ESC surface, no pigtail wire |
| 2 | Route ALL cables to final position. Do not bolt the stack down yet. | All cables reach destinations without tension |
| 3 | Solder ESC-to-motor connections. Twist all 3 phase wires per motor immediately after soldering. | — |
| 4 | Battery leads: twist + and −, keep short. Route away from GPS/compass. | No sharp bends, minimal loop area |
| 5 | Bind receiver (ELRS) before installing. Route receiver signal wire on the opposite side of the frame from power wiring. | Link confirmed before final mount |
| 6 | GPS/compass (if fitted): route cable away from power wiring. GPS GND via FC, not a separate wire to ESC. | Never adjacent to phase wires |
| 7 | VTX: power from a regulated BEC output, never straight off the main pack unless the VTX is explicitly rated for that voltage. | Confirm VTX voltage rating against actual supply before connecting |
| 8 | Bolt down FC/ESC stack. Solder joint inspection under magnification. | All joints shiny, concave fillet — no matte or balled joints |
| 9 | Conformal coating (recommended): mask connectors and USB, two thin coats, full cure before first power-on. | UV inspect if using a UV-reactive coating |
| 10 | Wire management: zip-ties at regular intervals, minimum separation between antennas and power wires. | No wire contacts rotating parts |
Star ground topology (mandatory, any frame)¶
ESC GND pad ← master ground point
├── Battery GND lead (direct)
├── FC GND (short direct wire)
├── Bulk cap GND (on pad)
└── VTX/BEC GND
GPS GND → via FC → NOT a separate wire to ESC
Receiver GND → via FC signal GND
Never create a second GND path from any subsystem back to the battery.
Procedure¶
Solder joint inspection criteria¶
Inspect every joint under a loupe or USB microscope:
- Accept: shiny surface, concave fillet flowing onto wire and pad, wire fully tinned, no cracks
- Reject and resolder: matte or grainy surface (cold joint), balled solder not wetting the pad, visible crack at wire-to-solder interface, solder bridges between adjacent pads
High-current joints: after visual pass, a voltage-drop check under load is worth doing if you have the bench gear — a joint with unexpectedly high resistance at current indicates a poor connection even if it looks fine.
First power-on sequence¶
- Transmitter on first.
- If possible, power the FC alone first via a current-limited bench supply or USB, bypassing the ESC — verify the FC boots and connects to its ground station software.
- Connect the battery via a current-limiting device if you have one (a "smart" charge protector or similar) for the very first connection.
- Motor test with props off — verify all motors respond and spin the expected direction.
- Verify battery voltage reads correctly against a handheld multimeter.
Rationale¶
Why conformal coating precedes first power-on¶
Solder flux residue left on PCB surfaces is mildly conductive and hygroscopic. In humid conditions it can create resistive leakage paths between adjacent pads. Coating applied over clean, inspected joints seals this permanently; coating applied after the first power cycle may seal in moisture already absorbed. Clean, inspect, coat, cure, then power on.
Why this atom no longer assumes a printed Platform¶
The previous version of this atom (now archived) assumed a specific printed electronics-carrier geometry with defined chimneys and routing channels. That geometry doesn't exist on a bought frame. The EMC principles it was built to enforce are unchanged and are restated here without assuming any particular printed part exists to enforce them physically.
Connections¶
requires: - star-grounding - twisted-pairs - capacitor-placement-emc related: - ferrite-beads - voltage-regulation - conformal-coating leads_to: - acceptance-validation