Corrective maintenance

Summary¶

Corrective maintenance repairs known damage or component failure. Unlike scheduled maintenance (interval-based), corrective maintenance is triggered by a finding from the post-flight check or post-crash inspection. The most common corrective tasks are arm shaft replacement (5 minutes), propeller replacement (2 minutes), and motor mount O-ring replacement (15 minutes). The arm shaft is designed to fracture on impact — finding a fractured shaft is a success of the failure hierarchy, not a build defect.

Concept¶

The failure hierarchy as maintenance guidance¶

libdrone's failure hierarchy deliberately routes crash energy toward the arm shaft first, protecting the electronics and PCCF layers. When a crash occurs, the arm shaft is expected to fracture. This is the design working correctly. Corrective maintenance after a crash therefore focuses on the arm shaft and motor before inspecting anything deeper.

The hierarchy: bumpers (absorb first impact) → arm shaft (fracture fuse) → motor (bend or strip threads before transmitting force to PCCF) → PCCF layer (last resort — structural damage here grounds the drone for full inspection).

A crash where only the arm shaft fractured is a best-case outcome. A crash where the PCCF layer cracked requires more thorough inspection and is a more serious airworthiness event.

Reference¶

Common corrective tasks and time estimates¶

Arm shaft replacement procedure¶

1. Remove battery. Disarm. Remove props on the affected arm.
2. Disconnect MR30 motor connector.
3. Remove 2× M2 screws at the arm tab (accessible from the arm root).
4. Slide the arm shaft out of the T-slot along the arm axis.
5. Inspect the T-slot walls for cracking. Run a finger along the inside of each wall. Any crack felt or visible → do not reuse this T-slot. Ground the drone and consult the repair procedure for PCCF layer replacement.
6. Print a replacement arm shaft (PETG, standard profiles, ~20 minutes).
7. Slide new shaft into T-slot. Verify tab seats fully with no rocking.
8. Install 2× M2 screws finger-tight + 1/4 turn.
9. Reconnect MR30. Install new props on this arm.
10. Acoustic ping: tap the CF rods — all should ring. A rod that thuds has loosened — tighten the pinch bolt.

Motor mount O-ring replacement¶

→ See scheduled-maintenance for the complete O-ring replacement procedure. Corrective replacement after a crash follows the same procedure.

After corrective O-ring replacement, always re-torque the motor mount screws (0.4–0.5 N·m cross-pattern) and verify the passive cover does not contact the arm head except at the O-ring contact zones.

Prop replacement¶

1. Remove the prop nut (CCW prop = CW nut thread; CW prop = CCW nut thread).
2. Pull the prop straight off the motor shaft.
3. Inspect the motor shaft for bending: roll it on a flat surface. Any wobble = bent shaft = motor replacement required.
4. Fit new prop. Torque nut to 0.8–1.0 N·m. Verify prop seated fully.
5. Run balance check on magnetic balancer before first post-replacement flight.

Procedure¶

Post-crash triage sequence¶

Run in this order — stop at the first hard finding:

1. Props — visual inspect all 4. Replace any damaged prop before anything else.
2. Arm shafts — press each arm laterally. Any play = fractured shaft. Replace before continuing.
3. Motor mount O-rings — inspect for tearing or displacement on the affected arm. If torn: replace before continuing.
4. CF rods — acoustic ping all 4. Dull sound = loosened rod. Tighten pinch bolt.
5. T-slot walls — run finger inside the T-slot of any arm that experienced the crash impact. Any crack = ground the drone.
6. Electronics — visual inspect all connectors, capacitor, and solder joints on the FC and ESC. Any loose joint or dislodged component — address before powering on.
7. Conformal coating — if any chip or crack in the coating over the FC or ESC, repair before next flight in humid conditions.

Rationale¶

Why arm shaft replacement does not require special tools¶

The T-lock system was designed for field-replaceable arms with no tools beyond a 1.5mm hex key (for the M2 screws). A repair kit for field deployment is: two pre-printed spare arm shafts, an M2 hex key, four spare props, and four M5 prop nuts. Total mass: ~80g. A drone grounded by a fractured arm at a deployment site can be airborne again in under 10 minutes.

Connections¶

requires: - failure-hierarchy - arm-shaft - floating-motor-mounts related: - scheduled-maintenance - post-flight-check - coupon-validation leads_to: - scheduled-maintenance