[Bassnut (Fred)]

A bit of a techy update.
The structure is finished and in the rain, no detection of leaks so far.
3D printed rack and pinions fitted and tested with motors.

I used 4 motor/gearbox/gears around the dome rack in parallel to spread the load because they were cheap and I had them. Very strong.

Spring loaded door hinges from bunnings worked a treat to mount the motors, covers dodgy alignments to keep gear/pinions nicely meshing.

The 2 motor drives (Pololu MAX14870 $28) are remarkably small but easily handle the small load allowing smooth accel/decel and current limiting.

The plan to use an ultrasonic proximity detector (Sensortechnik UPR-A 1500 CP TVPA 24 C $80 on ebay, more elsewhere) instead of fancy software to calculate dome rotation, on test works better than expected. Its a proper industrial sensor with a built in teach function and tracks the dome slot very well.

The dome top has no electrical connection at all with the base (no nasty slip ring). It will communicate with the base via a wireless link and the slot cover will be powered by a battery, charged by a small solar panel on the top.

Ive decided to build/program the dome control electronics myself using Picaxe 28X2, RF transceivers and custom PCBs instead of a PC or PLC, more fun, way cheaper.