Control. Hmm.

The first thing is to detect where the sectorplate is. I messed about a bit and decided to try optical detectors. I tried the idea of having one as a a reference and then driving a lead screw a given number of turns. Sounds elegant, but you are not driving a sectorplate in a line, you are driving it in an arc. Either the lead screw has to pivot, or the connection from the lead screw to the sectorplate has to accommodate lateral movement. Messy, and draggy if you try to reduce backlash. I was also concerned that any method of a reference point and driving a given number of steps takes no account of a steel lead screw in a wooden frame with possible differential expansion issues.

I therefore decided to fit four slotted optical detectors triggered by a 5mm wide brass down stand on the sectorplate itself. The optical detectors are basic ones, widely available direct from China for about 50 p each.

So how to move it? I did mention that even heavily laden very little force was needed to move it. Anyway I have been tidying up the flat and I came across a fishing reel loaded with fly line backing. A braided cord, very strong and made not to fray. A reel? Got me thinking.

So I lashed up a dead cheap stepper motor to test it, I was surprised how well it moved. A bit of lathework and soldering  and I had a capstan. Note also the rather neat control panel.

That gave me a method of moving from position 4 to 1, but how to pull it back.  I searched through my assortment of springs but nothing really met the requirement of a long but linear pull. Back to angling again, four strands of live bait elastic line formed a long spring with a fairly linear pull. I think it is the same as shirring elastic sold for tailoring.

Arduino Nanos are now as cheap as chips direct from China. Actually at less than £ 1.50 a go they are actually half the price of a bag of chips from the chippy. We live in strange economic times, so I bought some. Long time since I had a play with C++, so time to brush up my knowledge. The control nano is on the right, the one on the left just acts as a dedicated stepper driver.  A LM 339 forms a track circuit detector which provides an occupied output. Power is from a LM 2956 module, input supply is 12 to 24 V. A surprisingly light load, 80 mA quiescent, 350 mA when moving. The only external connection is on the right, control panel, power supply and signal interlock.

Alignment is decent. Time will whether it wanders. I will add all the rails once it is part of a board.

I enjoyed that as a project and I think it meets my objectives. Light, self contained with all the control within its own footprint. Easy to remove and put on the bench if it needs maintenance. In the ethos of the 1/50 project not expensive to make.