Gina

Now I need to drive the motors. I might lash up an Arduino for testing - but not tonight It would be useful to provides two modes - all turned together for focussing and separately for differential focus at 120 degrees. It seems quite possible that once set up the focus may not change. If this were so I would not need to faff about with driver code. For testing on the guttering I could run a USB cable to an Arduino at the ASC (if I can find a long enough one). I might reduce the supply voltage for testing so that I can run the Arduino directly off the main supply (Arduino max is 12v and I normally run at 13.8v) though if I use USB that can provide the Arduino power. For a simple setup I could use the ULN2003 drivers and run the motor power off the 5.1v supply for the RPi using unmodified 5v stepper motors.

Well, it's assembled - rather tricky to get the screws in while compressing the springs.

Just printed the six gears I think the design seems alright now. Should have the mechanicals done soon. Then I need to decide on which stepper drivers to use but it will probably be A4988. After that I have the software code to sort out. Nicest would be to program the RPi to drive the stepper motors but I have used simpler arrangements for focussing in the past just using an Arduino and a single control wire. But no wires at all beats one wire

The motor plate didn't work out so I've redesigned it and now printing it. The motor mounting stopped the gear rotating!

A couple of photos - the offset adjuster plate attached to the camera and then the motor plate sat on top of that, in the second.

Gears.

I think I've done it I think I've designed suitable parts to hold the motors and the lens onto the camera Oh - got the gears to do

And this is the intermediate plate that set the offset. This shows the way up for printing - it will actually go the other way up. With the threaded bosses downwards. These take the adjusting screws and will be tapped. The larger holes allow movement for offset adjustment. This fastens onto the existing camera tube.

And this is the resulting adjustment plate. The motors are space 6mm from the plate.

This is the complete triple control.

I think I may have a workable design. The small circle on the back of the motor shows the line-up of the shaft and a hole can be arranged in the plate to clear the end of the shaft.

A little tricky to mount the motors. Here is a screenshot of cross-section diagrams showing the gear on screw and then the stepper motor roughly placed. It may have to be at a different angle in the horizontal plane to allow for the fixings to clear the gear on the screw. Of course, once one motor position is determined the others are simple 120° around the lens.

I can think of two ways to drive the screws - a pair of spur gears, one on the screw and one on the motor shaft or a shaft from the screw downwards with the motors mounted below the camera. I think I favour the first option. As long as the top part doesn't touch the bolts holding the plate to the camera sleeve, it should be possible to mount motors gears and screws on the lens holder - yellow part shown above.

Here a screenshot of SketchUp showing what I have in mind. The green part is the camera sleeve on top of which is a plate (orange) with oblong holes and screws to clamp it to the camera sleeve. Then the lens holder with its spokes is attached to the plate with screws and springs. Somehow the screws would be driven by the stepper motors.

Idea - plate on top of camera sleeve that can be moved for offset. Then the mechanism for focussing etc. could go on top (possibly). The first photo attached shows the current manual screw and spring adjuster arrangement whilst the second shows that there would be room for stepper motors on the top of a sliding plate (for offset). But how to arrange a screw drive from the motor is another matter I'll have a play with SketchUp...

I've got enough 28BYJ-48 stepper motors and A4988 driver modules for remote focussing - that isn't the problem! It's the mounting hardware and control software that is more of a problem and, of course, the coupling from motor to adjuster screws. Doubt I shall be doing anything hardware wise but may give it thought and maybe try some design work in between clearing up (no.1 priority ATM).

Hmmm... Impossible!! I'm wasting my time trying to get focus and orthogonality on the lens manually - I've tried enough now and it just isn't practical. So it has to be remote (or give up!). I may think about it but doubt I shall do anything for a while - I'm fed up with it so time for a break, can't do with the hassle. Time to stop!

The springs have arrived and there is a size that will do nicely With a fine and clear night forecast I may try that later.

I have springs coming tomorrow so I'll see what I can do with manual 3 point focussing and a spring on each screw. Assuming the pack contains some springs of suitable size.

Probably the easiest way to do remote controlled focussing is with three instances of the Astroberry Focuser driver or maybe one driver modified for three focusers. This would then use three A4988 stepper drivers and three 28BYJ-48 5v motors modified for bipolar connections. Shafts from the stepper motors would then go up to the screw driven focussing. Another possibility might be to use the Arduino Nano if I don't run out of pins. Haven't worked out the control arrangements though.

More paper and paint for my watercolour painting and another bird feeder for peanuts I don't expect to buy any more astro gear for the foreseeable future. Maybe nuts and bolts etc. but nothing expensive.

I've tried the adjuster plate flat on the camera tubs and tried adjusting the focus by loosening the grub crew that holds the lens slightly, moving the lens very carefully into focus and then tightening up again. Went out of focus!! Tried pulling and pushing the lens against the flexibility of the ABS spokes and I could move it in and out of focus. So the focus adjustment needs to be extremely fine. I think decent focus would only be obtained with considerable luck by manual adjustment. This is all pointing to the need for remote control

I think I'll go for very small compression springs on each screw and replace the sealing/spring ring with soft plastic foam just for thermal insulation and sealing.

Here's a photo of the lens adjustment system. Even if I got this correctly set, it won't stay that way due to the plastic moving under pressure - it's already bending. Having the spring in the middle and adjuster screws further out on arms is not going to be satisfactory. I had set the lens upright by arranging the room lights at the edge of the field in each of the three directions. Then I adjusted focus by giving the screws the same number of turns. But by the time I had the rig outside on the guttering the focus had changed.

Conclusion from above :- The offset adjustment seems alright now but the lens adjustments are far from it. One possibility would be to remote control the three lens adjustments. This would be possible but quite a lot of work. It should be possible to get the lens perpendicular to the front of the camera but there is still the focussing. The problem is how to retain perpendicularity whilst changing focus ie. moving the lens up and down.