3xD 2.7-rc3 release notes

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11 November 2026 · Release candidate · Pending owner approval

Compared with the previous complete 2.0-rc2 release, 2.7-rc3 brings 2.7 mm M3 direct-plastic pilots, round lower spring cups, flat upper faces on the front arms, a three-finger A1 retainer and larger chassis countersinks. The pod sides and motor flange now specify SUNLU PA6-CF. Both chassis setups have complete kits and unsliced single-car Bambu Studio projects.

Downloads

Each complete kit contains 43 distinct STL selections, per-car quantities, hardware lists, cutting DXFs, manifests, checksums and validation. There are 46 required physical pieces per car. The printed project includes its 4 mm chassis and 3 mm pod plate. For GRP, cut the 3 mm chassis and 3 mm pod plate separately using the included cutting files. Combined and individual plate projects are supplied. Optional arm and shim choices remain separate; default arms are 4-1.

All changes since 2.0-rc2

  • Direct-plastic M3 holes: 2.7 mm. The former 2.5 mm pilots are enlarged on the rails, servo mounts, body fittings, front root brace, pod sides, motor flange, rear guide body and A1 retainer. This includes both underside and battery-top rail pilots. The former 2.5 × 2.7 mm oval pod-base pilots become round 2.7 mm holes. Screw centres, blind depths and hardware lengths stay the same. M3 clearance holes, M2 holes, bearings and kingpin interfaces are unchanged.
  • Round lower side-spring cups. Both rail shoulders now have round cups with 0.5 mm rolled rims and longer tapered transitions. The existing wide 10.7 mm floor, 11.8 mm mouth, 2.35 mm depth, spring axes and seating height are retained, along with the 120.8 mm maximum outside span and battery interfaces.
  • Flat upper arm faces. All eight front-arm variants have flat boss/web upper faces for face-down printing. Mounting ends, kingpin axes, K1 and double-D seating floors, rearward shift and dot markings remain. The default 4-1 pair is included in the car projects.
  • Three-finger A1 retainer. The front ball-gripping finger is removed from the unreinforced A1 M3×8 version. The remaining snap surfaces, bridge and two screw towers are retained. Its pilots are now 2.7 mm, with the existing 5.52 mm blind depth. Continue using two M3×8 countersunk screws through the 3 mm pod plate; check retention and articulation physically.
  • Larger chassis countersinks. Mouth diameter increases from 6.2 to 6.6 mm at 90°, giving 1.65 mm nominal depth around the existing 3.3 mm clearances. This applies to 24 round seats and the two swept servo slots on both chassis versions. Through holes, chassis outline and cutouts remain unchanged; the pod plate is unchanged.
  • SUNLU PA6-CF pod parts. Both pod sides and the motor flange move from the previous PETG recommendation to the owner-selected SUNLU PA6-CF, on their own plate. The servo-saver spacers remain PETG and the bumper remains TPU. The PA6-CF profile is provisional and requires calibration.

What to replace and reuse

For each chassis setup, 22 STL selections change and 21 are unchanged. The changed selections are the chassis, both rails, both servo mounts, all eight optional/default arm variants, both pod sides, front body post, rear body mount, rear body peg, front root brace, A1 retainer, rear guide body and motor flange. Replace the applicable parts to adopt the complete revision; only one selected arm pair is fitted per car.

Reuse the unchanged 12.80 mm reversible bearing carriers, +1 mm front hubs, selected P2 cups, spring brace, rear crossbrace, battery parts, upper kingpin braces, bumper, pod plate and production spring-lip rear-guide cap. Preserve each chassis setup's own bearing geometry and axle-height datums. Per-car quantities and hardware lengths are unchanged from 2.0-rc2.

The unselected rear-guide cap trials and M3 hole coupon are excluded. No reinforced A1, B1/B2, historical M3×6 retainer or obsolete rear-guide body is substituted. Use the complete current manifest when selecting parts; earlier mixed plates and G-code retain superseded geometry.

Print projects and material settings

Projects target a Bambu P1S with a 0.4 mm hardened nozzle. Materials are separated into PLA structure, PLA body/battery fittings, PLA precision parts, SUNLU PA6-CF pod parts, TPU bumper and PETG servo-saver spacers. The printed-chassis project adds a PLA chassis/pod plate.

Precision arms and A1 use 0.08 mm layers; structures generally use 0.16 mm, the motor flange 0.12 mm, PETG spacers 0.10 mm, and TPU/printed sheet parts 0.20 mm. Structural parts have four to six walls and 100% infill; the TPU bumper uses 30% infill. Supports are selected locally for servo mounts, carriers and rear body parts. Flat-top arms and A1 have supports off; inspect their bridges when slicing.

The combined projects use a common 0.08 mm first layer. Individual plate projects use their intended first-layer settings; use the supplied PETG spacer-only project for 0.10 mm including the first layer.

SUNLU PA6-CF is provisional and uncalibrated: the included profile uses a Generic PA-CF baseline with 280°C nozzle and 60°C textured-bed settings. Calibrate flow and fit, follow the spool preparation guidance, and use hardened nozzle and extruder gears. Material selection does not establish thermal endurance or printed strength.

Validation and release history

Frozen archive hashes, all selected meshes, quantities and embedded 3MF meshes were verified. XML references, materials, grounding, spacing and bed exclusions pass the recorded checks. Exported 2.7 mm pilots measure 2.6999967–2.7000046 mm. The final printed-chassis project opened in Bambu Studio.

This complete release collects the chassis change from 2.1-rc1, retainer change from 2.3-rc1, arms from 2.5-rc1, pilot changes from 2.6-rc1 and rail cups from 2.7-rc1. The superseded complete 2.7-rc2 had a Bambu import error. Rc3 corrects 3MF relationship serialization and declares the production extension; its STL geometry and quantities are identical to rc2. Use rc3 projects. Previous frozen files remain preserved.

Projects remain unsliced; release approval and physical validation are pending. Checks still needed include screw grip and thread life, three-finger retention, arm bridges, spring/body clearance, carrier clips and flanges, material calibration, full vehicle motion and endurance. Website publication does not approve the design.

View the full release history