pipnina

1 minute ago, Thalestris24 said:

I'm thinking a belt tensioner not needed. When I did the heq5 belt mod I recall needing a couple of goes to get the belt tension right. After that I never needed to adjust it again. For a star tracker with no significant load, even less need?

Louise

That's fair. I just know that when belts are assessed on printers it seems to show tighter is better, reduces vibration and ghosting etc. There isn't a huge load there either really, but if high tension proves important it might be a relatively easy fix.

Vlaiv already has a long slot for the motor to be moved around so in theory hand tightening could be done easily enough. Like you say it took me a few goes to get the rowan mod right but I managed it by hand...

I dunno

1 hour ago, vlaiv said:

Belts arrived, and I made first test of printed pulleys and how they work with belts:

 

I'm happy with results so far.

Idea is to have 3 stages. Two stages will be 5:1 reduction (80 teeth to 16 teeth) and last stage will be 10:1 (160:16). That will give total of 250:1 or 0.81"/step.

3 belts are required - 2x200mm and 1x360mm - those are supposed to be standard sizes.

Whole thing sounds like it's playing space invaders - very distinct "8bit" squeal is heard from the motor, but I guess that is from 18 steps per second or step about each 50ms. One can almost hear pitch changing like sine wave as motor is doing micro stepping.

Major hurdle now is to design easy to assemble and rigid box with ability to adjust tension on belts. I won't be using idles idlers unless I absolutely must - as those require additional bearings.

Perhaps the 3d printed belt tensioner for 3d printers could be adapted a bit to fit the motor, allowing people to just twist a little thumb screw and tension/relax the belt?

Or at least, the principle of it anyway. https://www.thingiverse.com/thing:4718212

Re: Belt drive

If you used a reduction from motor shaft to an intermediary shaft with one belt, then put the smaller size pulley on the intermediary shaft above the larger pulley, you can then have a second thicker belt attach between that small pulley and a very large pulley for the RA axis shaft.

I found pretty cheap pulleys that are very thick (2cm thick 45cm length). Thicker pulleys means less stretch effect as well, and if tensioned properly, no appreciable backlash.

For a "poor man's EQ5", maybe doubling up the pulleys would be necessary to reach the 10KG imaging limit without stretching... Printed pulleys probably would let us get a bigger reduction than the pulleys I've seen available commercially too.

For a larger mount especially however... A clutch or brake needs to be considered. Worm mounts naturally cannot move without the motor driving them as the worm gear can drive a gear but cannot be driven by it. This protects our equipment from the consequences of poor balancing and random power or software failures!

For the small tracker belts could still work though, maybe easier as the free-fall problem isn't as much of a concern for small 1-3kg payloads.

I think one thing to consider is that barn door trackers are very limited and, imo, not very good and actually kind of bad value. If this star tracker was even twice as expensive at 100 euros or so, chances are its performance would outstrip the typical barn door by so much, it would still be a worthwhile price. Especially as the cheapest manufactured tracker otherwise costs €300+.

My gen1 star adventurer makes a little clock ticking noise, the stepper in there is probably only using a resolution of something like 2 steps per arcsecond or so, this project is targeting about 4 ticks/second as a homebrew project!

Your eccentric gear looks very promising to me, I think it could be optimised by getting the number of teeth in the inside gear to be as close to the outside gear without locking them together, then making the eccentric movement roughly the same as one tooth pitch. If this is right it becomes a bit like a cheaty strain wave gear in my mind?

1 hour ago, vlaiv said:

Yes, I used herringbone gears before - and I really like them, but here it is a no go (or maybe it could be done but assembly would be very difficult) - because planetary system must slide into outer gear on assembly - something not possible with that configuration.

Regular helical gears would produce additional force in axial direction, so not sure if that would hamper performance.

One thing that worries me about helical gears is sliding action direction. With straight gears all the sliding happens along layer lines of 3d print - which is good sliding direction. As soon as we change the angle - there is additional component of sliding action that happens in "vertical" direction - which is notoriously poor for sliding (layer lines act as teeth on a file and grind against other teeth - so it's as smooth as running two files one against the other and expecting smooth motion ).

Here is couple of things that I think improvement can be found in:

1. using lubrication

2. using 0.2mm diameter nozzle to improve accuracy of small features like gear teeth

3. Checking out what happened here:

This is FreeCad wire frame view of sun gear and planets:

-SNIP-

 

Ah yes, assembly would be a bit tricky. The only way I can think of to make that buildable is to split a herringbone gear into two halves, then using a bolt going top-down to secure them. This way each half of the gear can be twisted into place I think...

Regardless as you say, a bit too complicated.

As for single-helix gears, I think they should still work fine as any axial force is going to be very small compared to the rotational forces we desire. Consider that the HEQ5 only produces a torque of around 2.4 newton meters at the driven end... I can far exceed that with a torque screwdriver and my wrist, and this is a big mount for up to 10kg payloads + counterweight and ideally operating at arcsecond accuracy or better.

As for the vertical sweeping motion, maybe i am missing something but I think actually the gear does not shift vertically during a gear mesh, the horizontal plane doesn't move and it just creates a barber shop pole illusion. The layer lines should be safe I think.

For the freecad screenshots, I think you are in perspective view, if you switch it to orthographic I think it will be easier to see the tolerance between gears!

17 minutes ago, vlaiv said:

Few pics of internals that I promised:

 

base ring attached to stepper with 6002 bearing and sun gear (sun has 15 teeth, base annulus has 81 - both are module 1).

Next comes planet system: planet gears with carrier - they have 608 bearings inside and are supported by 6002 at top and bottom. Top and bottom gear in each planet have 33 teeth, and bottom is module 1 while top is 0.94... something something (can't remember it like that as fraction it is 48/51):

 

Planetary set installed:

 

Then comes output annulus with attached output shaft. It has 84 teeth at module 48/51:

 

It is supported by two 6002 on each side - one resting against top planetary carrier and other against gearbox housing.

Here it is installed:

 

There is gap between top and bottom annulus - which is where "split ring" in the name of the system comes from.

In the end - there is gearbox housing - which is nothing special, just a seating supporting the last bearing (giving rigidity and center to whole assembly) and means to bolt it to base of housing.

 

You can now see where the bulk of assembly comes from:

1. 81 teeth x 1mm module - means at least 90 mm of diameter of the whole thing (81 gear diameter + 3-4mm of outer shell on each side).

2. around 30mm of planetary system - 20mm gears + 2x5mm carriers (4mm thick + 1mm spacing), then 3x 6009 bearing which is 9mm thick - that together is already almost 60mm in height - add few times 3-4 mm of housing and support stuff ....

Now, I could design even higher reduction ratio in smaller diameter if I make output and input ring differ by 1 tooth - but that also require additional care when printing planetary gears as top and bottom gears will be offset and there will be overhang tooth from top gear to deal with in printing - which I wanted to avoid for this version.

Also - with less teeth in planets - I'll also need smaller bearings to support them in planetary system - at the moment planets are 33mm - which fits nicely on 608 bearings that are 22mm in diameter. If I want to go for say ~23-24 tooth per planet - that would require bearings with 15mm outer diameter - something I plan to source from Ali express at some point.

Wider support bearings would also contribute to rigidity. Bearings that I'm using are quite cheap and are not as so good - so there is a bit of "play" in them. This leads to things not staying on axis but rather bending a bit. Wider support bearings would reduce this bending for same amount of play in bearing.

The only thing I can think of immediately that could stop the cement grinder noise is switching to helical gears. These are good because they have multiple teeth engaged at once and "ease" into each mesh, unlike straight cut gears like used here and in the SW EQ mounts.

I believe the main disadvantage of helical gears comes from efficiency and limitations on maximum torque, but in most applications (car gearboxes for example) the benefits in terms of noise and smoothness outweigh the negatives.

Other factors certainly at play here but this gearbox makes very little noise for example with the helical shape

Might be worth an experiment with two gears side-by-side instead of redesigning the whole planetary gearbox at first.

2 minutes ago, kbrown said:

Suppose you should take into account lens distortion with this method. Software like Lightroom or Darktable can undistort the footage against known database of lenses. Failing that you should do that manually with a calibration grid.

A lot of camera lenses are distortion-free already thankfully. If anyone wanting to try this already has a DSLR and an 18-55mm kit lens, it is likely to be pretty distortion free wih no post processing.

Can't say the same for the typical 55-200 kit lens option however. (as I understand, most of these kit lenses are basically rebrands even if they have Nikon or Canon stickers on them)

3 hours ago, kbrown said:

In case you didn't already know, the stepper driver can make a massive difference on the noise the motor makes. I've been using the Trinamic TMC2209 since I learned about them (same as in my Prusa i3 Mk3). They are more expensive than basic drivers and also require more learning if you want to take advantage of the more advanced features of it but if smoothness is the goal, it's worth it.

This indeed. My stock Ender3 printer makes an awful racket. Sounds like some sort of robot orchestra when it's printing.

My boyfriend bought a second hand Ender3, with some mods including the mobo replaced with the Ender3 S1, which has upgraded stepper controllers.

It. Is. Silent. No noise besides that of things sliding over eachother and the fans.

As for the noise the gears make at higher RPM, this could be tolerance or backlash as gears should in theory sound relatively smooth when applying continuous force in one direction. But when switching direction even metal machined gears sound cataclysmic (unmodded skywatcher EQ mounts with the brass motor-to-worm train sounds like someone tried to put a car into reverse while going 70 down the motorway, as many of us have first-hand experience...)

Also Vlaiv, I'm very keen to see how you test the smoothness with a laser, I have envisioned using an optical mouse sensor myself as they can detect exceptionally small movements as well.

1 hour ago, Mr Spock said:

Yes.  It’s easier to see fainter stars with higher magnification as the background gets darker. 

Sometimes I struggle to get my head around this.

My best guestimate is that as stars are pinpoint, we capture 4x of their light with a 2x as big mirror, but because they also shrink with mirror size they appear brighter?

I.e. if we had a 1 meter scope and viewed way above the seeing limit, we'd reach the end of returns for brighter stars as the smudge gets larger with magnification?

I think this can also mean imagers see fewer stars with a 50mm frac than a 130mm? I have seen some photos that show really tight narrowband images where the stars almost seem to have disappeared but they still seem quite strong in NB in my 130mm frac and in my 200mm newt

On 03/03/2023 at 14:33, Glued said:

I'm such a scaredy cat I get unnerved sitting in my own garden sometimes. I can't imagine I'd cope well if I ventured further away from my house than that!  

On 03/03/2023 at 16:03, ScouseSpaceCadet said:

You're safer far out in the countryside than an urban garden. I've jumped out my skin a couple of times in the garden with ears pricked and eyes on stalks. Although it was probably just next door's rats or a cat rustling!

Loads of people solo wild camp etc without issue. The farther away you are from civilisation the better. Especially in the UK with no bears or wolves to size you up. 

I sometimes run outside to swear at my equipment mid-session (things like the mount bugging out and needing the old off/on treatment, or me forgetting to plug something in etc) totally fear-free.

Other times my mind is trying to tell me I'll need to fight for my life at any moment.

I have jumped a fair few times, once when I heard walking, only for it to be a hedgehog! Another time when I heard a soft but loud snap and THUD. That turned out to be the apples falling from the tree haha.

3 hours ago, Marc1980 said:

Good evening.

It's been a while since I've used my scope properly and I'm keen to get it serviced (if that's even a thing). I live in Cornwall. Does anybody have any suggestions of where I could take it?

Thanks so much

Marc

If a mirror-based scope, the only service you can really get is a re-coating, where you send the mirrors away and they remove the old coating and apply a new one to the glass. Mirror alignment is easily handled at home, and would be lost in transport between you and anyone who could do it for you anyway.

For a refractor, the most common need for a tune-up is fungus or re-coatings. Fungus often grows between lenses that get water between them. Happens a LOT in normal photography. Sometimes it can be cleaned off, sometimes it's a bit too stubborn. Refractors can sometimes need adjustment of the lenses, if they are de-centered. This is a bit specialist, especially when you get to triplets. But for the most part refractors stay the line if well built so unless dropped should be fine in that regard.

16 minutes ago, tomato said:

Kodak Ectachrome 400 ASA was good for 15 mins exposure under a dark sky, but that was back in 1988, I don’t even know if it’s still available.

Struggling to find the 400 iso version, but 100 is available https://analoguewonderland.co.uk/products/kodak-ektachrome-film-35mm-colour-iso-100

I wonder how many of the types of film mentioned in this book are still in production!

Many that went off the market have come back due to film getting a resurgence in recent years, but some (Fujifilm Across 100 for example) came back with a slightly different recipe.

By my understanding, few films available today are suitable for astro, as they either suffer from insensitivity to Ha or they have intense reciprocity failure (6 minute sub on rollei infrared 400 got me 4/5ths of nothing haha)

I am trying illford 3200 now, and might try the fujifilm across 100 II next, but my poor star adventurer isn't guided so I am a bit worried I'll be getting star trails if I go much longer on exposure. Unless I find a way to put it on my HEQ5, but then I'd rather image with my main scope on a given clear night if possible!

I hope the book proves a good read!

1 hour ago, Adreneline said:

Just to add one thing - this is a single 120s frame taken with an unmodified Canon 6D (full frame) using the 6" RC at 1370 mm with no calibration frames - all I have done is apply a screen stretch and then a screen capture.

 

... and yet people claim you cannot use a full-frame sensor with a 6" RC - well I have done and it looks pretty good to me in terms of frame illumination / lack of vignetting.

I also used the RC with a mirrorless Canon M6 MkII (APS-C) sensor :

 

... this is a single uncalibrated frame - 120s - a simple screen stretch in PI as with the 6D - 1370 mm.

HTH

Adrian

 

That definitely busts the myth I heard then!

Maybe the myth applies when these scopes are used with the 0.67x reducer/flattener...

This thread is making me want one of these now ha.

One factor to consider is that (as I understand) all of the affordable 6" and 8" RC scopes are rebrands of the GSO RC line. This means they all have a small flaw in the primary baffle (you can print or buy a print to pop over the baffle tube to fix it, but unless you do, flat calibration isn't as good.)

Another is cost. At the end of the day you're pitting these scopes against others in their price range.  The only type of scope I can think of that is cost competitive with the 6 & 8 inch RCs is a newtonian. But as you say despite being cheaper for more aperture, they are heavier and take up more storage space! Other compact options like those from celestron could work but do cost a lot more.

Then there's the collimation, which seemingly can be quite complicated on an RC as the focuser needs to point at the center of the secondary, but the secondary then needs to be tilted to bounce the laser back to the source in the focuser. This can apparently create a little dance that can take some doing. I forget the final step for getting the primary lined up but I recall it being easier than getting the secondary and focuser to behave!

Another factor is that RC scopes get better with size, their illumination and corrected diamater get larger with a bigger primary, and they can even go down to f6 above a certain size instead of the common f8 or even f9 for small ones. I think (?) the RC6 struggles to provide a well illuminated and corrected view for APS-C

Sadly I don't have direct experience, but as I understand this is some of the more prudent info when considering one.

22 hours ago, DaveS said:

I've been tearing my hair out trying to work out why I wasn't getting an image from my QHY 268 after putting it back on the 'scope.

Then I thought to check the reducer (Which is sunk into the focuser)

 

🤦

I had something similar happen when I switched from a newt to a refractor.

The GPU coma corrector and the flattener both have the same 55mm backfocus, so I figured I could just take one corrector off, new one on! Job done, time to image.

I had astigmatism lines off axis on my images that looked like they stretched for lightyears!

After a few weeks of imaging without the corrector, not sure WHAT was going on, I realised... The GPU has an m48 thread, the new corrector has an m42... So the 6.5mm of length in my m48->m42 adapter was no longer present!

5 quid on ebay later for an m42 extension tube, all is well haha.

To be totally clear: You have a dew shield of some sort extending from the scope?
I could see light from the moon, street lamps, house windows or even far off-axis stars/planets refracting or scattering on the front corrector plate if it's not shielded.

Other than that, I don't know what to suggest as I've no experience with this scope, but I wish you a quick resolution!

4 hours ago, Peter Drew said:

Still beats me that wormwheels and worms are eccentric in this age of high tech machining.  I don't recall significant issues with gear sets I used to make on very everyday equipment.  I was very careful with each step of the process though.     🙂

I should imagine it depends a lot on the method used to manufacture. One would expect a lathe to produce very good, concentric and round parts. But if it's cutting too fast, too much pressure on the part, and the part is not supported at both ends, you may end up with the part being produced with an undesirable shape. I think gears are also not easy to dimensionally inspect. Mind I don't have any experience with that aspect of machining myself...

In theory, a larger gear being driven by the worm would be less affected by backlash between the gear and worm, as 1mm of movement at 200mm diameter is half that of 1mm of movement at 100mm diameter driven gear. Could be that, given less-than-perfect materials, the real solution is to make the whole thing bigger? Alas brass is rather expensive, but other materials must be suitable too, like hardened mild steel, if properly lubricated and protected...

I keep thinking about if some way might exist to re-circularise the worm, some kind of lapping process perhaps? Lapping paste instead of lubricant on the worm and driven gear, get the backlash just shy of binding and take her for a whole shaft rotation or two. Then adjust again. Maybe after a few goes around it will be much closer to a snug fit?

I might not be brave enough to try it on my own kit, mind you haha.

I got the pegasus power box advance, It's been great at keeping my kit going. My only wish was that it'd have more USB ports instead of the 4 wide 12V sockets. One more USB would let me plug the mount into it, meaning only one cable going from laptop to telescope.

I didn't get to test if it powered my HEQ5 properly as I abandoned last night's session. But given as when the accessories are all powered up, dew heaters at 90% each, main cam using TEC cooling to 0c, and mount on standby only used about 1.5A of the 3A my power supply could provide... I think it would have worked? Maybe slewing would send it over the edge though...

10 hours ago, JeremyS said:

What’s Mr Reid’s thoughts on the matter?

I'm going to email him I think, but I wanted to try and get some more info first.

I just spun the camera around to see if it's on the front end or back end of the scope.

Here's the two files, when I look at matching stars in each corner, I see much the same error. So it seems to me that the corrector is probably fine. Either the scope's optics are just not all that, or Mr Reid's work has been undone in transit perhaps? Maybe there is an issue in my camera train causing this, though I'd know not what.

In have noticed the focuser barrel seems to wobble a tad, Not sure if that could cause all this or not...

LUM 180 degrees.fits LUM NO ROTATION.fits

These being the stars I paid most attention to: one image with the camera unrotated, other with the camera and corrector turned 180 degrees. Star shapes look the same to me, near enough. But in a full image the shape changes in each corner, with the corner opposite these stars being much tidier.

Unfortunately all is not well. Some issues remain with the scope, maybe it has even worsened as there is now a notable amount of colour at the corners!

I got the chance to give it a test last night. Of course having not had the opportunity to til now, I sent her to look at M42! Aside from my constant amazement whenever I image this target at how little exposure is necessary for a clean image (in this case, 6 minutes!), I am rather disappointed to learn that this endeavour of sending the scope off for service has largely been in vain. I wouldn't say useless as I need to investigate further, and Mr Reid did affix my focuser which I did not attach properly the first time, as well as clean some "mist" from the fluor element.

But coma is still present, and maybe pinching (looking at Hatsya, that halo's points seem a bit odd, I don't notice it anywhere else and to be honest, that effect doesn't bother me much). And worst of all chromatic aberration at the corners! I am not sure if this could mean the lenses are misfigured, or if I now have an issue where the corrector at the other end is just not up to task. I have always meant to replace it with a higher quality one but maybe this is the time? I don't know. But if we assume Mr Reid's work stayed in place in transit, the problem must lie elsewhere!

Keen to hear anyone's thoughts on this 😬

10 hours ago, andrew s said:

For my interests this would do nicely 

 

Spectrograph on one side, photometry on the other.

Dream on.

Regards Andrew 

Why stop there?
https://www.astrosysteme.com/en-us/products/az2500-f6-f2/

Anyone got 7 million euros to spare?

The retail pages say it is threaded for 2" filters, which use M48 thread. You can see the thread on the camera side is smaller than the barrel on the focuser side, so the camera side thread is almost certainly M42x0.75mm (T2)

You can see in this thread a version with M48 connection on the camera side, and see how much bigger the thread on the camera side looks compared to the same 2" focuser barrel.

Hope this helps

58 minutes ago, Carbon Brush said:

I would be good to separate focus droop on loading from a focusser that doesn't point down the tube centre.

Set up the collimation and then change scope orientation. Two separate tests.
Horizon to zenith. Tube horizontal but rotate in the rings.

In either case you are looking for movement.
Horizon to zenith change tends to indicate something sagging under the weight.
Rotation in the rings tends to indicate some side to side play in the focusser.

I have yet to try collimating a CC. But on a standard newt, or a Mak newt I find a simple laser useful.
Just look at where the reflected spot lands and either move the scope as described, or apply gently finger pressure to parts.

HTH, David.

I think lasers can't collimate cassegrain telescopes fully, as your beam goes from focuser to secondary, then when the secondary is properly collimated the beam comes back to your laser source. I.e. you get no reflection onto the primary.

I think there are multi-beam tools that let you collimate cassegrain telescopes with a focuser-mounted tool, like this one: https://www.teleskop-express.de/shop/product_info.php/info/p11188_TS-Optics-2--LED-Collimator-for-RC-Telescopes-and-all-other-Types-of-Telescopes.html

But like you I have little experience collimating a cassegrain scope, so I can only offer up the little knowledge I have...

This might be some help, even though a CC and an RC are a bit different:

Looks good! Did you use the Astronomik UV-L3 cut trick with your FMA180 or are you shooting it "full spectrum"?

Trying to work out if this little thing is going to satisfy me or if I will want to save up for something like the ACL200 or Borg 55FL