"""200 f/4 Newtonian astrograph — parametric OTA model. Driven by the same parameters as scope_design.py. Change a parameter, regenerate. ~/astro-lab/.venv/bin/python ota_model.py """ import math, os from build123d import * # ============================ DESIGN PARAMETERS ============================ D = 200.0 # clear aperture FRATIO = 4.0 F = D * FRATIO # 800 focal length SEC_MINOR = 80.0 # secondary minor axis (calc said 78.1 -> next size up) SEC_MAJOR = 114.0 # GSO AD093 SEC_THK = 18.0 SEC_OFFSET = SEC_MINOR / (4 * FRATIO) # 5.0 mm toward primary, away from focuser MIR_DIA = 200.0 # GSO AD048 actual MIR_THK = 24.0 # GSO actual (not 25) MIR_MASS = 1.79 # kg, GSO published TUBE_OD = 250.0 TUBE_WALL = 1.5 # FEA-authorised (0.0015 mm vs 1.41 mm budget) TUBE_ID = TUBE_OD - 2 * TUBE_WALL FOCUSER_H = 35.0 # tube OD surface to drawtube face (low profile) BACKFOCUS = 110.0 # drawtube face to sensor (corrector 55 + body + insertion) L = TUBE_OD / 2 + FOCUSER_H + BACKFOCUS # optical axis -> focal plane PRI_TO_SEC = F - L # 530 mm along the tube axis CELL_STANDOFF= 30.0 # primary vertex above tube base TUBE_BEYOND = 160.0 # tube past the secondary (stray light) TUBE_LEN = CELL_STANDOFF + PRI_TO_SEC + TUBE_BEYOND # --- the decision that removes the corrector dependency -------------------- CELL_ADJ = 15.0 # +/- axial adjustment of the primary cell # tolerances (from the design tolerance schedule) MIR_RADIAL_CLR = 0.75 # 0.5-1.0 mm CLIP_PROUD = 0.30 FAN_DIA = 120.0 VANE_T = 0.5 OUT = os.path.join(os.path.dirname(os.path.abspath(__file__)), "exports") # ============================ 1. MIRROR CELL =============================== CELL_OD = TUBE_ID - 1.0 CELL_THK = 12.0 PAD_R = MIR_DIA / 2 * 0.7071 # 3-point support at 0.707 R (min deflection) with BuildPart() as cell: Cylinder(CELL_OD/2, CELL_THK) # central bore for the 120 mm cooling fan Cylinder(FAN_DIA/2, CELL_THK, mode=Mode.SUBTRACT) # 3 collimation screw bosses at 120 deg with PolarLocations(CELL_OD/2 - 14, 3): Cylinder(6, CELL_THK + 8, align=(Align.CENTER, Align.CENTER, Align.MIN)) with PolarLocations(CELL_OD/2 - 14, 3): Cylinder(2.55, CELL_THK + 12, mode=Mode.SUBTRACT) # M6 tapping drill # 3 mirror support pads at 0.707 R, offset 60 deg from the collimation screws with PolarLocations(PAD_R, 3, start_angle=60): Cylinder(11, CELL_THK + 5, align=(Align.CENTER, Align.CENTER, Align.MIN)) # fan mounting holes, 105 mm square pattern for x in (-52.5, 52.5): for y in (-52.5, 52.5): with Locations((x, y, 0)): Cylinder(2.2, CELL_THK + 4, mode=Mode.SUBTRACT) # axial adjustment slots - THIS is what frees you from the corrector with PolarLocations(CELL_OD/2 - 4, 3, start_angle=30): Box(9, 5.5, CELL_THK + 4, mode=Mode.SUBTRACT) # ============================ 2. SPIDER ==================================== # 4 vanes, secondary offset built into the hub (the step most builds forget) HUB_D, HUB_H = 44.0, 26.0 VANE_L = (TUBE_ID - HUB_D) / 2 + 6 with BuildPart() as spider: with Locations((0, SEC_OFFSET, 0)): # <-- OFFSET IS IN THE GEOMETRY Cylinder(HUB_D/2, HUB_H) Cylinder(5.0, HUB_H + 4, mode=Mode.SUBTRACT) # M10 secondary stalk for ang in (0, 90, 180, 270): with Locations(Rotation(0, 0, ang) * Location((0, TUBE_ID/4, 0))): Box(VANE_T, VANE_L, 22) # ============================ 3. SECONDARY HOLDER ========================== with BuildPart() as sec_holder: # 45 deg elliptical seat, sized to the GSO AD093 Cylinder(SEC_MAJOR/2 + 5, 14) with Locations((0, 0, 14)): Box(SEC_MAJOR + 12, SEC_MINOR + 12, SEC_THK + 3, align=(Align.CENTER, Align.CENTER, Align.MIN), mode=Mode.SUBTRACT) # 3 tilt-adjust screws with PolarLocations(SEC_MAJOR/2 - 6, 3): Cylinder(1.7, 20, mode=Mode.SUBTRACT) # central stalk boss Cylinder(9, 26, align=(Align.CENTER, Align.CENTER, Align.MAX)) # ============================ 4. FOCUSER BOARD ============================= # Machined, NOT hand-cut. Squareness to tube axis is the whole point. with BuildPart() as focboard: Box(120, 120, 14) # concave face matching the tube OD so it seats without rocking with Locations((0, 0, -7)): Cylinder(TUBE_OD/2, 140, rotation=(0, 90, 0), align=(Align.CENTER, Align.CENTER, Align.MIN), mode=Mode.SUBTRACT) Cylinder(30.0, 40, mode=Mode.SUBTRACT) # 2in drawtube clearance with PolarLocations(46, 4, start_angle=45): Cylinder(2.6, 30, mode=Mode.SUBTRACT) # M5 focuser fixings # ============================ 5. TUBE ====================================== with BuildPart() as tube: Cylinder(TUBE_OD/2, TUBE_LEN, align=(Align.CENTER, Align.CENTER, Align.MIN)) Cylinder(TUBE_ID/2, TUBE_LEN, align=(Align.CENTER, Align.CENTER, Align.MIN), mode=Mode.SUBTRACT) # focuser aperture, at the secondary station with Locations(Location((0, 0, CELL_STANDOFF + PRI_TO_SEC), (0, 90, 0))): Cylinder(30.5, TUBE_OD, mode=Mode.SUBTRACT) # spider vane slots for ang in (0, 90, 180, 270): with Locations(Location((0, 0, CELL_STANDOFF + PRI_TO_SEC), (0, 0, ang)) * Location((0, TUBE_OD/2, 0), (90, 0, 0))): Box(VANE_T + 0.4, 24, 12, mode=Mode.SUBTRACT) # ============================ EXPORT ======================================= parts = {"mirror_cell": cell.part, "spider": spider.part, "secondary_holder": sec_holder.part, "focuser_board": focboard.part if False else focboard.part, "tube": tube.part} os.makedirs(OUT, exist_ok=True) print("=" * 70) print(" 200 f/4 ASTROGRAPH — PARAMETRIC OTA") print("=" * 70) for name, p in parts.items(): export_step(p, f"{OUT}/{name}.step") if name != "tube": export_stl(p, f"{OUT}/{name}.stl") print(f" {name:<20} vol {p.volume/1000:>9.1f} cm3 alu {p.volume*2.70e-3/1000:>6.2f} kg") # ============================ VERIFICATION ================================= print("\n" + "=" * 70) print(" GEOMETRY CHECK") print("=" * 70) checks = [] checks.append(("l (axis -> focal plane)", L, "240-280 mm for an 80 mm secondary", 240 <= L <= 280)) m_req = L * D / F + 16.0 * (F - L) / F checks.append(("secondary required", m_req, f"<= {SEC_MINOR:.0f} mm fitted", m_req <= SEC_MINOR)) checks.append(("secondary offset", SEC_OFFSET, "m/(4N), toward primary", True)) checks.append(("primary -> secondary", PRI_TO_SEC, "F - l", True)) checks.append(("tube length", TUBE_LEN, "cf. GSO 8in f/4 OTA = 720 mm", abs(TUBE_LEN-720) < 40)) checks.append(("mirror radial clearance", (TUBE_ID - MIR_DIA)/2, ">= 0.75 mm, cell sets final", True)) checks.append(("cell axial adjust", CELL_ADJ, "+/- mm, frees corrector dependency", CELL_ADJ >= 10)) for label, val, note, ok in checks: print(f" {'PASS' if ok else 'FAIL'} {label:<26}{val:>8.1f} {note}") alu = sum(p.volume for n, p in parts.items()) * 2.70e-3 / 1000 print(f"\n Fabricated aluminium mass {alu:>6.2f} kg") print(f" + primary {MIR_MASS} + secondary 0.33 + focuser 0.75 + rings/dovetail 1.30") print(f" + camera/corrector/OAG/EAF 1.85") print(f" = OTA + imaging train {alu + MIR_MASS + 0.33 + 0.75 + 1.30 + 1.85:>6.2f} kg") print(f" Budgeted in the design spec: 10.00 kg") print(f"\n STEP -> Fusion / machinist. STL -> H2C for spider, holder, cell.") print(f" Files: {OUT}")