OnStep electronics enclosure — SKR PRO, WiFi, GPS, RTC, weather

What it is

An enclosure for the electronics of an OnStep telescope mount, made of flat panels bolted to four corner posts. It holds the controller board, the WiFi, GPS and clock modules, four aviation connectors, a switch, two LEDs, a fan and a weather sensor — and it clamps to a tripod leg where nothing that rotates can reach it.

Prototype status — testing in progress: this model is still being validated through printing, assembly, electrical testing and real-world use. Dimensions, settings and minor details may change after test results. Inspect wiring, cooling and every mechanical attachment before field use.

Outside 257 × 210 × 87 mm, clear space inside 247 × 200 × 79 mm.

What goes in it

Air: the fan pulls out, it does not push in

Heat that the drivers put into the air has to leave the box, and for that the air carrying it has to leave. A fan pushing into a closed case moves nothing. It sits on the lid, the highest point, and takes the hot air away where hot air already goes; cold air comes back in through the louvres low down on the sides.

Intake area is 3180 mm² against the 2463 mm² of the fan throat: the inlet is not the restriction. One short panel is nothing but a 20 × 2 louvre grille, and each long panel carries a row of 5.

Nothing sits over a pin header

A module you cannot plug a Dupont lead into is a module you may as well not fit. The pin rows of every module were measured from the component geometry — the Ø1.00 through-holes for the ESP32, the Ø1.50 ones for the DS3231, the header solid for the GPS — and the space above each row, 15 mm tall, is a volume that no printed part is allowed to enter. It is a check that fails the build, not a note in a document. It caught three parts.

The modules are held by small retainers screwed onto bosses that stand outside the board footprint and overlap only its edge. None of the four has usable mounting holes, and each for a different measured reason: the ESP32 has none at all (the four Ø2.60 circles are pad faces — the hole underneath is Ø1.00), the DS3231 has its battery holder under both of them, the GPS has a solid slab in its model, and the BME280 has no model of the real board.

How it hangs on the tripod

Two clamps on the upper tube of one leg, 35 mm apart, 25 mm long each, for a Ø31.75 mm tube. The place is not a preference: it is the only one left. Everything that rotates — both axis modules, the counterweight bar, the tube — was swept and its envelope measured, and above Z = −150 it reaches everywhere. The roof of this box clears that envelope by 17.6 mm.

What you print

23 printed parts, approximately 1188 cm³ of solid material. No supports are intended.

Print every panel with its outer face up. The labels are raised, not engraved: face up they are three extra layers, face down they would be pressed into the bed.

What you buy

• 4 × M3 × 8 cylindrical head

• 5 × M3 × 10 cylindrical head

• 26 × M3 × 12 cylindrical head

• 4 × M4 × 35 cylindrical head

• 4 × M5 × 16 cylindrical head

• 4 × M5 × 35 cylindrical head

• 35 × M3 brass heat-set inserts

• 4 × M4 brass heat-set inserts

• 8 × M5 brass heat-set inserts

Electronics and panel hardware:

• 1 × BIGTREETECH SKR PRO V1.2 controller board

• 1 × ESP32 D1 Mini, 1 × NEO-6M GPS, 1 × DS3231 + AT24C32 RTC

• 1 × 27 × 20 mm Waveshare-format BME280; verify the exact board dimensions before assembly

• 1 × Sunon 60 × 60 × 25 mm, 24 V fan

• 3 × GX16 4-pole panel connectors for AR, DEC and FOC

• 1 × GX16 2-pole panel connector for 24 V input

• 1 × SPST ON–OFF panel toggle with M12 × 0.75 neck, rated at least 10 A at 24 V DC

• 2 × 5 mm indicator LEDs with resistors sized for the actual circuit

• 1 × external GPS antenna with SMA plug, plus the required wiring, fuse and 24 V supply

The enclosure does not define a universal OnStep wiring diagram. Driver modules, pinout, fuse rating, wire gauges, LED resistors and firmware must follow the actual controller and OnStep configuration used.

Parametric CAD verification

Every dimension comes from a parametric chain with 43 verifications, and the solid model goes through a gate that fails on: a part that is not one closed solid, two printed parts sharing space, a bought component intruding into a printed one, a connector that does not actually cross its panel, anything above a pin header, a retainer that does not touch its module, a seat count that drifted, an insert in two parts at once, a screw touching PETG, and a seat left without wall around it or floor under it.

PETG, 0.4 mm nozzle, 0.3 mm layer. Use 4 walls on panels and 5–6 on posts, brackets, jaws and knobs. A 35–40% gyroid infill is a conservative start for the enclosure and 45–55% for the tripod hardware. Bed 300 × 300 mm.

English and Italian illustrated assembly manuals are included, with a complete printed-parts catalogue, insert and screw locations, electronics list, print orientation, cooling, weather-pod assembly and tripod installation.

PETG, 0.4 mm nozzle, 0.3 mm layer. Bed 300 × 300 mm.