Dome drive crank 5.

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Tuesday: The friction wheel drive looks very promising despite the doubts expressed by experienced forum members. Those who failed probably did not have my wide and flat plywood, dome base ring. Nor did they, probably, use enough pressure or the same 4" wheel size and type of tyre. The tyre is so grippy on the plywood underside of the base ring, that it pulls to the side if not absolutely tangential.

The first image shows the BB locked into the 2x4 by an alloy plate. A hidden lock-ring sits behind the plate embedded in the 2x4. The bolts holding the plate ensure a lack of movement.

 The second image shows the necessary offset to achieve tangential drive.

I don't see that I have much choice than to stick to a manual drive given my very limited abilities with electronics and modern software. The crank requires very little effort to turn the dome. So it will hopefully extend my ability to continue observing into ripe old age.

The third image shows the 2x4 lever, the crank and the friction roller in place. I still need to trim back the steering wheel bracket so that I can move the BB nearer to the apex of the octagon angle. At the moment the crank strikes the extended stainless steel [shelf] bracket if it gets too close.

It is an interesting challenge to achieve the correct geometry using familiar items from some of my other pastimes. Total cost should be under £30 equivalent. All constructive time consumed is my own. Just keeping up the insurance premiums on my own, active longevity.

The fourth image shows a clamped roller pressing with a through bolt for the 2x4 pivot. The extra extension of the BB axle had allowed me to bridge the 2x4. This worked fine for a full 360° until the roller moved inwards on the BB axle. There was nothing to restrain it from moving inwards. Only outwards. Easily fixed tomorrow.

I could have chosen a bulkier crank and left a flange but couldn't get the pedal off after years of attachment. The crank came with a recycled bike from a flea market. So the thread was probably never greased before fitting.

I knew the roller needed more work but I didn't want to waste time on that. Just in case the friction roller idea didn't work at all. The 2x4 set-up still looks horribly crude to my eyes but I'll persevere until I get it working faultlessly. Then  I can make it look a bit prettier. A length of square section, scrap aluminium tube? We shall see.

Motor drives, with slaving to the telescope movements, is much favoured by those with the necessary knowledge and skill. Which I mostly lack in that direction. What with affordable, AI domestic robots just around the corner, I think I'll wait for mine to crank the dome around. At whatever rate seems most suitable at the time. I just hope it can manage the stepladder! Or I'll have to make it a chain drive down to the ground floor. Which rather defeats the purpose.

Click on any image for an enlargement.

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