Material selection philosophy

Summary¶

libdrone uses three materials — PETG, PCCF, and ASA — each assigned to the function it performs best. No single material is best at everything. The design rule is: match the material to the mechanical demand of the zone, not to convenience or cost. Using the wrong material in the wrong zone produces a drone that fails unpredictably rather than at the designed weak point.

Concept¶

Right material, right zone¶

Every material has a characteristic combination of stiffness, toughness, thermal resistance, printability, and cost. These properties trade off against each other — a stiffer material is typically more brittle, a tougher material typically deflects more under load. The goal is not to find the best material overall but to assign materials so each zone gets the property it needs most.

Stiffness resists deformation under load. High stiffness is needed where dimensional precision must be maintained — the structural core of the X body, where rod channels and T-slot positions are fixed geometry.

Toughness absorbs energy without fracturing. High toughness is needed at crash contact zones — arm shafts, tabs, the bottom X body layer — where impact energy must be absorbed and dissipated rather than transmitted into the structural core.

UV and thermal stability matter for externally exposed surfaces that see weather and sunlight continuously. UV degradation causes surface cracking and embrittlement over time; thermal creep under sustained load causes dimensional change.

The weakest link is a design tool¶

The arm shaft is deliberately the weakest structural element. This is not a deficiency — it is a controlled failure point. A drone that breaks predictably at the cheapest, fastest-to-reprint part is more maintainable than one that breaks unpredictably at an expensive or difficult-to-replace component.

The material assignment reinforces this: PETG arm shafts sacrifice before PCCF X body layers, which sacrifice before the electronics. The failure sequence is designed in, not left to chance.

Reference¶

Procedure¶

Rationale¶

Why not use one material throughout¶

A single-material frame forces a compromise — either everything is stiff and brittle (PCCF throughout: expensive, crash-catastrophic, hard to repair) or everything is tough and compliant (PETG throughout: structurally inadequate for the rod channel dimensional requirements).

The three-material approach assigns the optimal material to each function at the cost of managing three filament types and three print profiles. The maintenance burden is justified by the performance and repairability gains.

Why PCCF for the structural core specifically¶

The X body rod channels and T-slot pockets are precision geometry. Rod channel diameter is 2.2 mm for the PCCF layers — any dimensional creep changes the rod preload and the assembly alignment. PCCF's low thermal expansion coefficient and high stiffness maintain these dimensions across operating temperatures. PETG would creep under the sustained compressive load of the pre-tensioned rods.

Why not use carbon fibre composite (CFC) plate¶

CFC plate is stiffer and lighter than printed PCCF but cannot be produced in a 3D printing facility, requires cutting tools, and cannot carry the complex 3D geometry (rod channels, T-slot pockets, counterbores) that the X body layers require. PCCF printed parametrically gives 90% of CFC's stiffness at full geometric freedom and zero external fabrication dependency.

Connections¶

requires: [] related: - petg - pccf - asa - cf-rod-architecture - failure-hierarchy leads_to: - petg - pccf - asa