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Stub Mandrel

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Everything posted by Stub Mandrel

  1. I managed a test last night, this is an edit of my post in the 'what are you doing tonight' thread after sleeping on it. Main conclusion- too much stiction on the dob part, I need to make it smoother! Not really an issue with the platform, I think I need to dose it with silicon polish at the very least. It moves in jumps and the minimum AZ move is often nearly a full FOV at ~30mm and getting a target centred at 5mm took forever! Alt is much better but not perfect, although if unbalanced it can move on its own. As for the platform, PA was easy, at least to the suggested approach of getting Polaris in the finder and adjusting until it stayed still during a slew. The polar angle must be pretty accurate as I just set everything level and the task was setting it due north. Errors were rapidly apparent so a button to stop the slew early will be welcome. My finder's cross hairs come out at 45 degrees but that didn't make the process difficult. Better PA could be achieved with a polarscope in the finder holder and getting Polaris to travel around the circle. Getting the track rate was hard. A first everything drifted off top left regardless of speed. This made me think it was running too slow. I reduced the delay down to about 15ms until the stars definitely went off the right side pretty sharpish. I then increased the delay, and eventually settled on about 64 milliseconds delay by the time clouds came in, which isn't bad given the estimate was ~68 and expected to need to speed up to allow for compression of the roller. I think the earlier problem was using Lyra which was very high and I suspect a combination of PA error and an unbalanced scope slowly moving in ALT when near vertical. It was easiest to judge movement using small stars near the edge of the FOV rather than bright ones at the centre. Next time I will use a 25mm plossl with cross hairs. Incidentally I used a Szentmartoni EP made according to a recipe on SGL that uses three small binocular objectives for about 33mm. As promised it was sharp to the edge and comfortable to use! I changed to a Skywatcher UWA 5mm to 'fine tune' the tracking rate. the sky wasn't very dark, but I went back and (just) split the double double at 300X - seeing wasn't brilliant, but it seemed to be keeping in place even at that magnification, certainly long enough for planetary imaging. Changes needed: I will wire the disabled reset button on the shield across the end limit switch. This will provide a way of interrupting a polar alignment slew, as initial drift is obvious in a couple of seconds, you don't need to wait for a full slew. I will round the default track speeds 0.1ms and keep the adjustment step of 0.1ms. The 0.1ms seems fine enough and it's annoying that all the readouts are not round numbers - and no point reading the delay to finer resolution than the adjustment. I may change the step to 0.05ms, at the expense of slowing down the tuning process a little. Although up to speed up tracking and down to slow it seemed logical, as up increases the delay and vice versa. It's confusing to press up and see a number decrease. The debounce period for the buttons is too long, as are some of the 'confirmation delays' of 1s. I will reduce both. The 'nudge RA' increment was WAY too aggressive, the briefest of presses and the view changes completely. A remote handset might be a useful addition, perhaps with a reduced set of controls. Mechanically, everything worked fine with the platform. Balance is great and I didn't even bother with a nut on the pivot bolt for the dob, so worth considering a plain pin instead. There is some wobble when moving the scope, but it isn't excessive and I didn't notice any when hands-off. Main beef is with the dob itself, I must find a way of reducing 'stiction' and counter-intuitively locking the alt movement. But my brain is already thinking of ways to add steppers and belt drive to ALT and AZ - perhaps for 2021!
  2. All cloudy here now, Goodnight all!
  3. Tested out the platform! Main conclusion- too much stiction on the dob part, I need to make it smoother! As for the platform, PA was easy, at least to the suggested approach of getting Polaris in the finder and adjusting until it stayed still during a slew. Errors were rapidly apparent so a button to stop the slew early will be welcome. Getting the track rate was hard. A first everything seemed too slow, but eventually I got to about 64 milliseconds delay, which isn't bad given the estimate was ~68 and expected to need to speed up to allow for compression of the roller. Started on Lyra, but found Altair more comfortable once it was above roof level. Once sorted went back and split the double double at 300X, seemed to be keeping in place even at that magnification, certainly long enough for planetary imaging. Some small software tweaks needed but the mechanics are fine. Just need to make the teflon pads on the dob part slippier!
  4. Good, but could have been 20-30 minutes shorter!
  5. Oh Oh... Wimbledon. They'll probably repeat 2019 and cut Horizon off halfway through...
  6. Could also be collimation/alignment as well as not enough spacing for the corrector. Download the trial of CCD inspector and see what it says. Of course the risk is you will want to buy it...
  7. I agonised for over a year. I don't regret going for the ASI1600MM.
  8. Their website is promising a new batch of ASI1600MM - in May 2021!
  9. People don't normally use a diagonal with a Newt, it's function is to make the viewing position more convenient. A Newt's view is rotated 180 degrees, not flipped, so just turn your star atlas upside down.
  10. Hopefully coming to Cura soon! Chris - is there no holding you back?
  11. I noticed it applies to hammers a couple of months back. Reminded me to post a puzzler I wrote about it in another forum.
  12. A middle way is to buy a mirror set and then build a scope around it, that way you can have exactly the scope you want without the years of angst finishing a huge mirror!
  13. A play with curves could brighten that up and keep the sky background dark and make it look even nicer.
  14. Not looking great here, and set to be 100% at 10Pm...
  15. Yes - I mean Arduino Sketch rather than sketch drawing
  16. I will be putting all the STLs and the sketch on my website soon, I'll drop a link here when I have, but I want to do a proper test before I do in case any adjustments are needed. I also need to draw the finished dimensions of the two wooden panels as accurate locations are important.
  17. That unshielded bearing is annoying me...
  18. 52° 78', but I made the platform for 52 degrees as I am likely to be using it further south. It has a few degrees of adjustment built in.
  19. I don't want to put it on wet grass... to photograph it. Perhaps tomorrow evening?
  20. I'm cautious of making a definitive statement but everyone who has seen the stacked images seems to agree that the images in different colours are coming out at slightly different scales giving radial colour fringes, which suggests chromatic aberration. Olly (I think) pointed astigmatism making stars in the corners seem squished and Vlaiv noticed the star shapes varied between R G and B. It's hard to believe with so many independent voices saying that the fault is with the optics, not the stacking. Also, I think I've never had misaligned stars more than once or twice and have always been able to improve them by getting rid of bad subs or changing stacking settings. I know you can get rid of artefacts like this through processing, but they will rob the image of small high-contrast details. More importantly, when you pay the premium on a multi-element apochromatic scope isn't getting rid of these effects exactly what you are paying for?
  21. It's finished! All I need now is a clear evening to test it. Photos to follow.
  22. D'oh! Tilting the platform from side to side is pretty pointless... it needs to be slewed not tilted for azimuth adustment. Never mind, a single adjustable foot at the pivot end would be tricky to implement anyway as the pivot is in the way. Slewing will have to be physically moving the platform, which should be fine in practice.
  23. And now done a test with the scope (passed) and made two adjustable two feet for the north end and paddle for the limit switches, now printing a first try at a switch housing. I'm going to have a fixed foot at the south end (with a curved foot) so (to a first approximation) if the two feet are turned by the same amount it will adjust the polar alignment in AZ only, turning them the same amount in opposite directions will adjust it in azimuth only. I feel child-like anticipation!
  24. I've just done a test, using a leisure battery instead of the telescope. Not as heavy, but placed right at the front to put all the weight on the rollers and way below the CofG so much less balanced. All went well, except near one extreme (probably beyond the range I actually need) it stalled but the motor current was limited at only about 200mA, I upped it to 400mA and it worked perfectly. The stepper is a 900mA one so I've got plenty of headroom if needed. Left to sort: Adjustable feet (printing one now) limit switch arrangement. Properly wiring up
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