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3D Printing

The drop mechanism needs one custom mechanical part: a housing that turns the bare 9 g servo into a payload bay — holding the servo, guiding the payload and bolting onto the frame platform. This page documents the printing workflow available to the team and the design requirements for that part.

Status: housing not yet designed

The workflow below is in place and the requirements are fixed, but the actual housing model does not exist yet — no CAD file, no test print. What follows is the requirements list a design must meet, not a report on a finished part. General frame printing (platform, mounts) is covered in Frame Extension.

The workflow

Step Tool Notes
CAD Tinkercad browser-based, no install, good enough for boxy brackets; export as STL
Slicing UltiMaker Cura free; profile for the university's printers
Printing university 3D printers FDM; plan for queue time — iterate in CAD before printing, not by reprinting

The loop is deliberately simple: model in Tinkercad, export STL, slice in Cura, print, test-fit, adjust. For a part this small a print is fast — the bottleneck is printer access, so measure twice (calipers on the real servo and payload) and print once.

Material and print settings

  • PLA is fine. The drone flies indoors; there is no UV or heat exposure, and PLA prints dimensionally accurately — which matters more for a press-fit servo pocket than impact resistance does. PETG is an option if a part ever turns out too brittle, at the cost of stringier prints.
  • Walls over infill. For a small bracket, strength comes from perimeters: 3 wall lines (≈1.2 mm with a 0.4 mm nozzle) and modest infill (20–40 %) beat thick infill with thin walls.
  • Orient for the load. FDM parts are weakest between layers — orient the print so the payload's weight and the servo's torque load the part along the layers, not across them. Avoid supports inside the servo pocket; a support-scarred pocket will not fit.
  • Mass matters. Every gram of housing is a gram off the payload budget of a 3.5-inch CineWhoop. Aim for the lightest part that survives handling — cut away material that carries no load.

Designing around the 9 g servo

The standard 9 g micro servo has a 23 × 12.5 mm body with two mounting tabs on the long axis. Practical dimensions for the pocket:

  • Cut the pocket 23 × 12.5 mm plus ~0.2–0.4 mm clearance per side and test-fit — FDM holes and pockets come out slightly undersized, and exact shrinkage depends on the printer, so calibrate on a small test piece first.
  • Support the servo by its mounting tabs (screwed or zip-tied), not by friction on the body alone; servo torque will work a friction fit loose.
  • Leave room above the body for the cable exit and for the arm's full swing between the 1100 µs and 1900 µs positions (see Servo Mechanism).

M3 mounting

The frame platform provides M3 standoffs and screws, so the housing mounts with M3 hardware:

  • Screw bosses: ≥ 3 mm of plastic wall around each hole; don't put a hole at the edge of a thin wall.
  • Hole diameters: 3.2–3.4 mm for a clearance hole (screw into a standoff or nut), ~2.8 mm for M3 self-tapping directly into PLA. Self-tapping into PLA survives only a few insertion cycles — for a part that gets removed often, use clearance holes and the standoffs' threads.
  • Match the hole pattern to the platform described in Frame Extension — design the two parts against the same drawing, not from memory.

Requirements for the housing (design checklist)

  • Holds the payload captive with the servo at 1100 µs (closed) and releases it cleanly at 1900 µs (open) — gravity drop, no pushing.
  • Servo pocket per the dimensions above; servo fixed by its tabs.
  • Pin/arm path designed so vibration cannot creep the release open (over-centre geometry or a positive stop, not friction).
  • Mounts to the platform's M3 standoffs; payload hangs below the centre of gravity, clear of the prop ducts.
  • Payload can be reloaded on the ground in seconds, by hand, without tools.
  • Cable routing to the Pi (signal) and the BEC (power) without pinching.
  • As light as possible — target the housing plus servo well under the mass of the payload it carries.

Once a model exists, its STL and print settings belong in Frame Extension → CAD models alongside the other printed parts.