windjammer

I had a look at your guide log with PHD2 Log Viewer - a handy tool to look at log data if you don't have it (its a free download). It shows two guiding periods of 25mins and 19mins at time points 19:51 and 20:16 with sub arcsecond RMS errors. That is a vey good starting point. Nothing wrong with with the mount on this data. For the other periods the log shows dithering and mount settling starting and failing - the mount is bouncing around. What are you trying to accomplish with dithering ? Turn it off ! Every time the mount settles you kick it with a dither ! There are a lot of experts on PHD's user forum who might be able to help you with these more sophisticated PHD settings like dither. My understanding of dither is that it is an effort to reduce the effect of camera defects like fixed pattern noise. Are you sure need it ? I agree with Vlaiv 's recommendation on PHD guiding assistant - very helpful. Also run the PHD star cross test - this will point up RA and DEC backlash issues, if indeed you have them. A high end mount like EQ8, well tuned as you say, should be OK in that regard. Let us know how you get on Simon

Hi I use PHD2 so not familiar with ASIair. But, those aggression values look high compared to what I am used to. My mount is a diy gem, so it is a not precision bit of kit at all. I guide at 10-20ms exposures and 100ms interval, so a 5sec gap between exposures seems v high - you might try changing that. All that stuff about guiding to the seeing is not right IMHO - what you have to avoid is resonance between guide impulse and how fast the mount moves, so the delay between guide exposures is the important thing. The mount has to settle before the next guide exposure and impulse. Your EQ8 is meant to be a precision bit of kit, 5 seconds accurate tracking should be business as usual, so a lot of what vlaiv says is quite right! But before you get the spanners out and take it to bits try some more guiding experiments. Simon

Hi everyone A quick look process of the Witch's Broom, Western Veil supernova remnant. Ha, 42x 300s from 16-17 June. SW Startravel 150 F5, Atik 460EX etc. Weather has gone off so stuffed for S2 and O3 for a while. Simon

Hi everyone A quick look process of NGC 6820/6823 in Ha (14x 300s) from 9 June. Perhaps catch SII and OIII later on this week, thunderstorms permitting... Simon

Hi Here is Galaxy Messier 106 and other galaxies. Pic is Ha, G, B composite - I found mapping Ha directly onto the R channel gave more interesting results than using the R exposures and futzing the Ha data afterwards. The black hole driven Ha emission out of plane is quite visible. First pic is is a close up crop of M106, the second is the full field of view (about half a degree, 30 arc minutes, on a side). Third pic is a close up star chart view of the companion and line of sight galaxies. Barred Spiral Galaxy M106, NGC 4258. (Distance: 23.7 million lyrs, Diameter: 135,000 lyrs, Angle subtended: 18.6x7.2 arcmin, Magnitude: 9.1, Constellation: Canes Venatici, The Hunting Dogs) Other galaxies are also present - some of the brightest below, but there are others in the frame (very dim, better in the R frame): 1. right, bottom of centre is galaxy NGC 4248 (distance 17.1 million lyrs, diameter 6,000 lyrs, 1.3x0.5 arcmin, Mg 12.5) 2. far right, bottom of centre are the galaxy pair NGC4232 (top, 333 Mlyrs,1.2x0.5 arcmin, Mg 13.2) and NGC 4231(bottom, 340 Mlyrs, 0.8x0.6 arcmin, Mg 13.6) 3. Top, far right (uncropped pic) is galaxy NGC 4226 (334 Mlyrs, 1.1x0.5 arcmin, Mg 13.5) 4. Centre, just above M106, is dwarf galaxy galaxy UGC 7356 (PGC 39615) visible as a faint blur (22 Mlyrs, 0.9x0.8 arcmin, Mg 15.1) Details: Photograph taken in Ha, R, G, B astronomik filters. Total exposure time 11.8 hrs (8.3 w/out R). R 1x1 bin - 42x300s = 3.5hrs, 28 May 2023, scope East side, prime focus G 1x1 bin - 53x180s = 2.7hrs, 03 June 2023, scope East side, prime focus B 1x1 bin - 73x180s = 3.7 hrs, 04 June 2023, scope East side, prime focus Ha 1x1 bin - 23x300s = 1.9hrs, 05 June 2023, scope East side, prime focus Rig: Imaging scope: SW Startravel 150mm F5 Refractor, Baader Diamond Track, 2.5x Celestron Luminos 2inch imaging barlow, Atik 460EX mono Guide scope: SW Evostar 90mm F10, with guiding XY stage, ZWO 120MM camera Guiding: 2 stage PHD: high frequency guide scope (mount tracking) and low frequency OAG image train guiding (guidescope flex) Mount: Home made German Equatorial pillow block mount, permanently rooftop mounted. Spring loaded DEC axis gearing. Other gadgets: ST4 based anti vibration shutter, ST4 based PEC Processing: PixInsight: Lights, Darks, Flats, Biases, Align Calibration, Linear fit, BXT, Channel Combination, SCNR(G). StarNet2 star removal/star layer GradXpert: Gradient removal Topaz DeNoise AI: Noise removal Affinity Photo: 32 bit image processing (curves, high pass masking, selective colour)

Hi I don't have a mesu but a couple of points: your setup to my eye looks wrong - the scope is outsize for the mount. You seem to have 4x 10kg weights, two of them a twice as far from the centre of gravity of the OTA. The load of weights and OTA at 80kg+ are hanging off tiny bearing surfaces. The pics of scopes others have posted here are tiddlers in comparison ! When the wind catches the end of the very long OTA the torques on the drive mechanics must be very large - as I understand it the mesu is a direct pressure drive with a small diameter drive shaft pressing against the edge of a larger disk on which the scope sits. So it is only the tiny pinion that can resist wind-driven turning moments of the disk. Everything flexes, so the important thing is how fast do the vibrations die away. If the mount settles in 2 or 3 seconds after an impulse that would generally be considered a reasonable performance. If the wind kicks at a higher rate then even a good mount would not function adequately. Looking at your clever tests with the test dial indicator, the settling time does seem a bit long. Can you improve the damping so the mount settles faster - sometimes loosening up nuts and bolts can help detune the system. Some foam packing of the OTA to the mount might absorb some vibration. Vibration pads at the tripod feet might also help to drain away the energy. Lots of small improvements to the damping are probably more likely that one big fix, unfortunately. Your OTA is a huge windsail - if performance is good as you say with no wind, then perhaps raise the observatory walls to shelter the OTA (even a removable canvas wind break might do). The usual remedy for wind is a dome with observing slit, perhaps that is the way to go. Simon

PL - I think if you painted out the kangaroo, jello and extra disciples then Vlaiv would be happy. He knows what he likes!

That looks the business. Elegant and neat but meaty and robust. Just right. Envious!

I think it is probably wind, but maybe something else as well as olly suggests. I would just park the data, and retry on a still night - remove one variable from the equation. You have the bare bones of some great pics in the works IMHO - I would be pretty encouraged with what you have: the bright moon and wind blew me off completely this month, so stick with it! Simon

Yes, wow

The forces at the motor end of the string are small - they feed into a 6000:1 gear train which does the heavy lifting. You could stop the motion at the motor with your finger, at the other end it would have your arm off! These gears are actually quite tough - a bit of aluminium U channel and you can make a tight little gear box for pennies. The Mod0.5 compound gears come in 50:10 and 48:12 - if you need something with more grunt you can mix with metal gears. The plastic Mod1 worm gears are also worth a look:

Yes, moon was a real bummer. First clear-ish nights in an age and the moon is seriously up. I was aiming for Leo but the moon parked its butt right there. Loads of detail in M51. You did well to get the surrounding luminosity on M51 - plus a few galactic interlopers! Stars look a good shape right across frame. Only issue is star colour ? Simon

>>How long to put it together? I bought the plumb blocks April '15, finished (ha!) mechanics March '16, and fabricated motor drives for first light September '16. But it never stops accreting stuff - really needs a 'planned maintenance' period now to strip down, and do a clean rebuild. But astronomy gets in the way! A few oily gearbox pics here to show you what are missing with a belt gearbox...

Details on floating caliper brake 1. component parts. A clamp is in two halves that go around the shaft. The clamp is free to rotate with the shaft until it meets a sprung stop on one side, and an adjustable fixed stop on the other. The hinged side of the clamp carries two long studs that screw down to the base plate and serve as fixed stops to limit the travel in that direction. The other side of the clamp has a foot that bears down on a sprung plate, with adjustable stops to limit the travel in the other direction. The clamp is lined with oil soaked leather for a smooth motion. The clamping tension bolt is adjusted for (1) just hold any imbalance in the axis and (2) just start to slip before the springs bottom out, and (3) not provide so much force as to strip the gearbox. The bolt can be tightened down to lock the shaft completely if required. The clamp only constrains the shaft rotation and applies no other lateral or vertical forces on the bearings. The purpose of the spring is to take up backlash from the straight cut gears - important for DEC guiding. Approach the target in the direction that compresses the spring, and DEC guide adjustments into the backlash void will be powered by the spring relaxing. So you get a nice star cross pattern, that works over a field of view or more. Not so important for RA which always guides in one direction, and in this setup the stops either side are adjusted for no gap. The springs do not help backlash when slewing outside of the spring range, but a fast slew rate makes this less of an issue. 2. RA close up. Fixed stop and sprung stop. 3. RA from the other side - spring stop 4. DEC brake Food for your design - will your hubs take a splined shaft ? If necessary you could have a short single ended shaft coming out to take extra stuff like brakes. Simon

Having metal in the hand concentrates the mind! I need to think some more about the details in your post (more diagrams would help!) but moving up to 925:1 sounds sensible from a torque point of view, but as you say, reconciling the slew rate is a sod. If I understand right, you propose 50cm between axis and centre of the gearbox - that sounds quite wide, so wedge would be wide also as belts are transverse across the wedge ? If so, collision issues near meridian ? Re weight - the DEC axis has to be counterbalanced, so that doubles (conservative) the load. The bearings sound utterly solid! - and the frames, wedge and pier are going to be just as important to carry through the whole design. You asked >>better view of how you geared/aligned motor, gearbox and shaft 1. shelf to bring gears and motor to centre height 2. motor shelf 3. 1296:1 gearbox, key chuck to disengage, 4:1 final drive coupling 4. stepper, slew DC motor, transfer gearbox, servo actuator 5. later developments 6. upgraded transfer gearbox (DEC). RA is more beefy - cogging on the DC motor affects stepper 7. DEC (RA similar) as was ca 6 months ago. Pickup gear opposite the motor drive for angle sensor. Updated brake central between plumb blocks. I'll post on the brake details next email. Simon

Here are some pics for the RA assembly and connection to DEC. I will post on other questions tomorrow! I hope this is useful. 1. internals of the RA shaft - M16 rod, lock nuts at LHS, and travelling nut at RHS. Two rawl nuts placed face to face in between. Travelling nut has a screw in it that engages with the internal slot in the shaft shown in 2. As you turn the M16 stud, the travelling nut moves down the stud and forces the leaves of the rawl nuts to open and bite into the inside of the shaft, fixing the M16 stud to the shaft, Centreing disks at each end keep the stud centred in the shaft. 2. Interior view of shaft showing internal packing and slot to engage travelling nut. 3. RA final drive gear, packing pieces and DEC plate. Packing pieces locate between gear and DEC plate to accommodate RA Jesus nut. 4. Machined final gear and packing pieces. Test stud in the gear shows where the RA shaft stud will come out. 5&6. Holes in the final gear to take a locating key for the RA shaft. 7. Bolting the RA gear to the shaft stud - 200 grunts. 8. Close up of attached gear and locating key. 9. Bolting DEC plate onto RA packing plate. 10. DEC bearings and test shaft attached. Pics 9 and 10 give a view of the RA brake mark1 - similar to your idea. A curved clamp, fixed at one side and a tensioning bolt the other side. Tighten the bolt and the clamp bears down on the shaft. The bearings did not like this at all - so made it floating (will describe later). Simon

I will hunt out pics and post. Check out this wonderful project posted here a few years ago - similar geometry to you I think https://stargazerslounge.com/topic/347485-a-very-large-goto-gem-built-with-diy-techniques/

>>you have set your RA shaft 90deg of how i envisioned it. Yes - no choice really, the bearing blocks are so large. It is funny how are there are so many ways of arranging the same bits to make a GEM. Flange bearing blocks are very similar to your wheel mounts but would need a shaft, so I think you are onto something here with single ended assemblies. The wedge could be made quite narrow with small format bearing assemblies - the wedge is the thing that gets caught up in the meridian flip, so the smaller the better. >>Also, I considered these pillowed bearings, how to they fare play-wise? Perfect as far as I can tell. No mount glitches I can trace to the bearings. The wearing-in process is odd - they don't come aligned, so when you first put a shaft though a pair of them the blocks have to be very loose and gradually tightened down. The bearings gradually (and noisily) move in the housings until they line up. After a while of running the shafts glide freely. I had to watch a few youtube videos of burly blokes using huge levers to adjust bearing blocks before I got my head round it. >>Everything is bolted. Yes, a bolt up top to bottom. Actually, more properly a screw up! That thing has more or less every thread known to man tapped into it, M1.4 to M16. So the bolts and screws have spring or lock washers to keep them tight. There isn't much vibration going on a big scale to work things loose. Motor couplings and grub screws get a housekeeping check every so often. The trick to a tight thread in soft metals like Aluminium is to go straight in with the 2nd cut tap and skip first cut and plug taps. On rigidity, the pillar could be better. The 4 pipes are secured top and bottom with barrel nuts and its one of those things you make and find out can't be assembled! I think 3 pipes might be better with cross bracing, or just get a big fat pipe. But it works OK and bigger fish to fry. >>Where did you find these long bolts Do you mean the long nuts ? e-bay is good for all of them. The M8/M10 and M12s are usually used for suspended floors and ceilings, so very cheap. The M16s I think are actually track rod adjusters from the auto world. M6 down to M3 most often spacers in electronic assemblies. The tapped right angle hole in them is the bit you have to do - they are very handy. >>aluminium rather than steel, any particular reason? Corrosion and weight if you don't need the strength of steel. The Al bits are as bright now as the day they went on. The steel parts and gears I brush with a thick gear oil every so often to keep rust at bay. As you know there are huge forces working when the scope is loaded up and everything will flex at some point. Most bracketry is non critical so Al will do. Steel right angle is the strongest stuff I know. Motor and gear mounts are the most critical - if they flex they wind up like springs rather than turning the shafts, until the stored energy lets go and moves the shaft. Not a smooth motion. I picked up the thick wedge plates for 50quid at an engineering show. Humungous pillar bottom plate was £70 from ebay (Droitwich Aluminium I think) - it was a hoot machining that. The large round was an off-cut (!) from an ebay someone. >>Is it an OnStep system too? No, too far off-piste for that - not really compatible with anything. As you probably gathered from earlier posts I wasn't able to reconcile tracking resolution with a fast slew speed - so each axis has two motors: stepper tracking motor and a DC slew motor. There is a servo that moves an idler gear to engage stepper or DC motor into the train as needed. It has separate encoders on the axes but in the process of debugging my arduino project I found the knack of star hopping, even to invisible targets. Surprisingly easy to do and great fun, so the goto stuff and alignment faff is not attractive. The only mount oriented computer stuff are the PHD guide cameras - ZWOs with their ST4 guide interface. ST4 is very simple to interface motor drives to, just 4 active-lo lines for RA/DEC fast/slow and if nothing just default motion (RA) or stop (DEC). With ST4 it has automatic adaptive PEC, an anti-vibration shutter and guidescope flex correction. This is where all the action is in my view - getting 50kg to single and sub arcsecond rms in both axes and being consistent enough for 10, 15 and 20 minute exposures running all night. Still working on the all atmosphere global cloud zapper... I have some ideas on the wedge: For the hinge I have an M16 rod running in M16 long nuts attached to the wedge plates. Doing it again I would look at, say, 2 inch pipe attached with U clamps to the top plate and sitting on V blocks or similar attached to the bottom plate. I would also put side reinforcements on the wedge to stop twisting. For the elevation adjustment there is a very elegant arrangement going around using a pushrod and a dividing plate - don't know any details but looks solid. Looking at commercial mounts their profile is narrow so the meridian flip can be delayed as long as possible up to south and restarted as soon as possible after south. With your wheel bearing assemblies you could get away with a narrower wedge than the plumb blocks, but a narrower wedge and thus a shorter hinge might be less stable. Hope this is useful Simon

>>Still unclear how to set az for PA, I am thinking maybe a second brake disk freespining on top of the one already existing on top of the pier. Yes, with a tangent arm to make adjustments...

Re the brake - my first brake iteration was as you suggest, massive bolt pushing a pressure pad, but it generated some unappealing creaking noises from the bearing blocks when tightened! So I changed to a floating caliper type brake, much happier. My particular design has straight cut gears axis to motor so an overtight brake can strip the gearboxes (4 chamber epicyclic 1296:1 - as you say even a feeble stepper can generate huge torques through these ratios). After a few annoying accidents I bought a 0.05-5Nm torque wrench to get consistent brake pressures and to stay out of the danger zone. Your belt drive system may avoid this issue, but something to bear in mind! >>I will take precision over speed any time of the day. Hehe - in despair I took the opposite approach. I didn't think I could get more than agricultural precision out of my home workshop, so went ahead hoping that fancy electronics would make up for the shortcomings. Which is more or less where it ended up - my current bottlenecks are elsewhere than the mount. BTW, are these the kind of SUV bearing assemblies you are talking about ? https://www.autodoc.co.uk/ridex/8054987?gshp=1&gclid=EAIaIQobChMIo-nezdqD_gIVPIBQBh38ZAF_EAQYASABEgI-2vD_BwE They look very interesting indeed. Makes one wonder if you need any shafts at all. Just bolt two together at right angles and off you go (I simplify :)). You must supply some sketches! Have you any ideas about getting rid of the meridian flip ? Some GEMs seem to have managed that. A neat trick if you can pull it off with your about to be acquired welding skills. I think it is done by extending the pier along the RA axis toward the pole and fixing the GEM at the end of the extension. I suppose a similar effect would be to extend the RA axis well away from the pier and put the DEC axis at the end of that. Neither of those speak well to stability, but if it could be cracked.... Simon

I can see that 256 ustepping and 0.9degree steppers is a factor of 150x over my example! Technology moves on... The A4988s may be a problem, but I have had losing lock issues with various stepper controller iterations with different chips over the years, and looking at motor specs it did not seem surprising. It would be interesting to see how many turns per second you can get out of your steppers in your little test jig ? I've never managed more than about 4 or 5 turns per second out of any of my stepper collection - mostly motors salvaged from old printers so I can't vouch for the quality. But you have plenty of room at the bottom with 256/0.9 motors. Progress is v rapid! Interesting doing away with a worm - will you have a brake on each axis ? It would be handy if when you took a belt off the scope did not swing round (massive inbalance was one of you design goals!) Good luck with the welding - some pics when you have a chance plse Simon

Hi I have been down this route! A wonder about your choice of motor drive - I found it very difficult to get more than a few hundred full steps per second out of a stepper without stalling, even when whacking it with huge drive voltages. Suppose you microstep, x16 at best case, that gives about say 3kHz your max stepping rate. You want at least one step per arcsecond of RA (1 second of time is 15 seconds of RA, say 20 for the sake of argument). So normal tracking rate is one ustep every 50ms or 20Hz. The maximum slew speed you can achieve is 3kHz, or 150 times tracking. So slew rate would be 24hrs/150 or about 10 minutes for a whole RA revolution = 36 degrees/minute. I think you might find that slew rate a bit slow, and that is if everything works. On the gearing, tracking rate at 20Hz, that means one turn of the stepper every 48steps*16ustep/20 = 38 seconds assuming 7.5 degree steppers. The final RA drive is one turn per 24hrs or 86400 seconds, so gear ratio of the entire RA train is 86400/38 = 2,300:1. DEC axis is basically the same again. You might have a look at the stepstick stepper driver modules - a pack of 5 for less than 10 quid, based on the Allegro A4988 stepper controller (comes in1 and 2 amp versions). This will do all the microstepping current control, 20Khz current limiting, and also enables you to switch your stepper with anything up to 35V external supply, while only needing a 5V supply for the controller. All you need to do is supply direction, pulse, and ustep setting for it to go. This would take a lot of work off your arduino - I actually built my controllers out of discrete logic using 4988s. I hope this is helpful - apologies if you clocked this already! Simon

A way round having to change the weight after the flip is to spring load the axes. The idea is attach a brake around the shaft whose tension you can adjust. The brake encounters a sprung obstruction as the axle rotates, compressing the spring. The brake pressure is adjusted so the axle slips when the spring pressure reaches a certain level (before the spring bottoms out). So the spring acts as a restoring force just like the slightly heavy weight. And the spring pushes in the same direction whatever the flip. Same technique on the DEC axis removes backlash in the gears over a short range (until the spring relaxes), but is enough to give bidirectional DEC guiding over a session - but obviously you have to approach the target from the compressing direction to have the spring loaded up. Simon

Very promising indeed for a single frame. Are the spacings quite right on the MPCC - star shapes etc ? Simon

beautiful!