ASA — properties and libdrone use
Summary¶
ASA (acrylonitrile styrene acrylate) is used exclusively for the four bumpers on libdrone. It is more expensive and harder to print than PETG, but its UV stability prevents the surface degradation that PETG bumpers would show after sustained outdoor exposure. Parts that stay inside the frame or are replaced after crashes do not need ASA — only the permanently external surfaces that live in sunlight justify its use.
Concept¶
UV degradation in outdoor polymers¶
Ultraviolet radiation breaks polymer chains over time — a process called photo-oxidation. The result is surface chalking, colour fading, and progressive embrittlement. A bumper that has UV-degraded behaves differently in a crash: instead of absorbing energy by deforming, it fractures prematurely because the surface layer is brittle.
PETG has moderate UV resistance but degrades noticeably after 6–12 months of outdoor exposure in direct sunlight. For parts that are replaced regularly after crashes, this is acceptable. For permanently external cosmetic and protective surfaces, UV stability is required.
ASA's acrylate component provides UV resistance comparable to ABS without ABS's tendency to crack over time. It is the standard UV-stable filament for outdoor functional parts.
Reference¶
Material properties¶
| Property | Value | Notes |
|---|---|---|
| Print temperature (nozzle) | 250–260°C | |
| Bed temperature | 90–100°C | PEI sheet or garolite |
| Enclosure | Strongly recommended | Warping without enclosure |
| Cooling | 10–20% | Minimal cooling to reduce warping |
| Nozzle | 0.6 mm hardened steel | Same nozzle as rest of build |
| UV stability | Excellent | Design lifetime outdoors: 3–5 years |
Bumper specification¶
| Parameter | Value |
|---|---|
| Quantity | 4 per drone + 4 spares recommended |
| Print orientation | Flat |
| Mass target | ~3 g each |
| Fit | Slides onto arm shaft service notch — hand-crush compliance test required |
Coupon 4 — bumper fit and compliance¶
Print one bumper at production settings. - Test 1: slides onto arm shaft service notch with light hand pressure - Test 2: hand-crush the bumper — it should flex noticeably without cracking - Fail (cracks under hand crush): increase cooling slightly or lower print temperature by 5°C and reprint
Procedure¶
Rationale¶
Why not use PETG for bumpers¶
PETG bumpers are functionally adequate for indoor or covered-storage drones. For libdrone deployed in civil preparedness roles — outdoor storage, transport in vehicle boots, operation in direct sunlight — PETG surface degradation over a season of use is a maintenance burden. ASA eliminates this at the cost of a more demanding print profile for four small parts.
Why not use ASA for more parts¶
ASA warps more readily than PETG on large flat prints and requires enclosure and higher temperatures. For arm shafts, X body layers, and the platform — large complex parts where print failure is expensive — PETG's easier print reliability outweighs ASA's UV advantage. The bumpers are small enough that the ASA print risk is manageable.
Connections¶
requires: - material-selection-philosophy related: - petg - pccf leads_to: - cf-rod-architecture