AlexK

I see, yes, I saw such solutions as well, instead of the brass nut you can print one opening in half or just use a rack piece on the top. Still, quite a cumbersome mechanism, especially for tweaking in the dark, I think. The worm gear's beauty is that it's asymmetrical, which is creating an uneven wear forces which you can leverage to your advantage. If you print the cog a bit tighter than necessary (just reduce the fit tolerances in half), then the metal threaded rod will be able to shape it into the perfect fit in just a dozen of dry runs (don't run it to fast as plastic will melt from the friction energe release into the temperature buildup). Then add a lithium grease to slow the wear, and don't forget an easy cog replacement mechanism (e.g. bolts attaching the cog sector in place instead of wood screws). Finally, even metal gears have some slack, to amend that you can simply preload the west side of the platform (just shift your dob's legs a bit West) to create the always positive one side contact between rod thread and gear teeth.

Gotcha, so that's just a researching sketch so far. The cam piece is simply sliding along the rod (X-axis, red in your CAD, I guess) from right to left as on your picture but the point on the sector is moving down first, then up projected on the Z-axis. And its speed is accelerating first, then deccelerating as it's passing the lowest point, if you look at its motion projection to the X axis. Right? Now imagine that depending on Z (height from the rod zero level to the point where the cam is touching a pin on the sector) you are compensating for that speed change (which is dx per dt) by splitting the dx shift vector into smaller dx'/dt shift and some dz'/dt shift dynamically over that cam's surface. It's harder to imagine it on the full circle as it wouldn't work at too steep Zs, I would draw it for a 7 deg sector (7+7 = 14 degrees which is enough to drive the platform for an hour) .

Still, I would highly recommend using a real worm gear (printed cog, and metal rod worm), as you will be able to disconnect the worm any moment and reset the platform to any position manually in zero time. With the classic poncet, like you have pictured, you will have to "fast rewind" for quite a long time every N minutes (though not a biggie, but I could see myself swearing at it's sluggishness ).

Following. FIrst of, I would recommend rethinking your designs from scratch instead of repeating wood/steel EQP designs. For example, the shape of sectors you have copy-pasted is actually quite suboptimal. Folks making them from wood have to use straight angles and surfaces as that just simpler, while you can design a perfect elliptical shapes everywhere with super-optimal load bearing arching supports instead of trivial L-shape. The latter is even dangerous for a hollow 3DP part, as any "crease" with sharp angle (90 deg must be considered a sharp angle here) is a potential snap point weakening the construction. Consider the same for the South support too, don't make it like that Pisan-tower cylinder you pictured, use wide cones on each side, as all you actually need for the tracking is the contact surface only, the rest must be beefed up to accept strong screws and bolts into platforms not breaking the plastic at high tension. For the poncet drive, the classic version had a variant where on the rod you had a special cam "nugget" shaped in a special way to push the round (or also special counter-cam shaped) pin on the rocking platform so it's rotating with the constant speed with the motor moving the cam linearly along the threaded rod with the constant speed as well. Can't google-out it right away, but if you simply draw on the paper/in the CAD several phases of a point on the rod shifting and the point on the sector rotating just a bit ahead of it all the time (the dot on the rod should move at the X-axis speed equaling the speed the dot on the sector is moving along the same X axis at the very end of its movement range) you will see some spiral sector forming when you link corresponding dots. Just figure what math curve can approximate that (something like a cycloid: x= r(a-sin(t); y = r(1-cos(t))) just don't forget to make a correction for the rotation of the radius of the pin it is pushing. Though I recall that cam had some limitations, as it will be prone to strong bending forces at higher angles, it still might be worth investigating (see here: https://kisi.deu.edu.tr/saide.sarigul/Cam_Mech.pdf how to design cams in general, the curve we need to cam-follow is the cycloid).

That's exactly the same tech, just SkEye taking it more seriously. For example, you don't have to wave the phone high above with the screen down after calibrating the SkEye by pointing at a bright star just once, so it will be more convenient to use when mounted on the telescope right by the EP (main or findre's). But you can try my method above with your SkyView app already (as I understand, you've got the iPhone, which is not supported by SkEye). On a side note, for those stuck with an iPhone, I could recommend getting a secondhand Android "phablet" for dedicated astronomy use (should be well under a $100 price tag of a cheap eyepiece nowadays). That way you are not only expanding your handheld computing capabilities, but also reducing the chance damaging your actual phone and losing the connection to the world. Which might be even life threatening in some rural dark sky "expedition".

The SkEye is the best app so far at utilizing smartphone's accelerometers/gyro sensors indeed. But it is still a "poor blind thing". So if the phone mishaps you may end up pointing into an opposite direction The CSSE tech is actually "seeing" where the telescope is pointed between stars (leveraging the "plate solving" algorithm). That's an ultimate advantage over everything else for amateur-grade telescopes pointing known to men to date except for their very own eyes On a side note, there are plenty of star charting apps leveraging the same sensors array as the SkEye to help matching the view in the sky with the chart on the screen, just bring the phone up above your head (with the feature ON). You can easily use that for the rough telescope pointing too without any cradle needed, here is how step by step: Zoom the chart to have some natural field of view chart displayed, e.g. 20 deg FOV screen width. Mark your desired target on the chart so it's easy to track on the screen. Place the phone screen against the rim of your UTA (don't worry, most screens are scratch resistant enough) so it is orthogonal to the optical axis (most UTA rims are, just make sure phone is not rocking on it) and so that you can see the center of the screen (some apps have the center marker or the EP FOV overlay feature, so just turn that ON for your widest eyepiece. Now just move the OTA (right by the rim where you are holding the phone, no need to look through the EP or a finder) until your target is centered on the chart. Done! Depending on your phone sensors accuracy (and less so on your optical axis orthogonality and collimation), you may end up right on the target with your widest EP. That's exactly how I've been finding the recent NEOWISE comet in the small clearing in the trees before the civil dusk was over (barely single star visible that low West) for example, as when I can see stars around my invisible target the QuInsight helps to point even better than the CSSE, and surely much faster, as it's leveraging my eyes and brain not some dumb microcomputer .

LOL! Just drive over the rim and into The Bush. I've found there are almost always pristine night skies up there during the AU summer last time visiting , and almost no city lights to bother you. An astronomy Paradise.

In this particular case, I would agree on a zoom feasibility with Steve. A 12" 1:5 light bucket is very forgiving on the EP optics quality/issues. Also, as the OP's instrument has the GoTo feature, the advantage of an ultra wide fixed field for manual tracking, finding objects, and starhopping is of a significantly lesser importance as well (when the GoTo actually works ). I see the point about experimenting with the "best magnification" as well, but aside from aesthetics of "clusters views framing" the best magnification for the desirable DSO observations, Keith has mentioned, is always close to the D/5-6mm, which for that collapsible 12" on Keith avatar now is 50x-60x, thus a 25 - 30mm EP would work best for DSOs with it.

I guess, you've missed the point of the worm drive. What you are describing looks like the classic Poncet platform drive, which indeed needs some flex connection like a driving finger or a disk/ball joint and nonlinear drive speed along the HA (hourly angle) range. What I've meant is building the real worm drive underneath: ...with the worm made from the trivial steel threaded rod (3D printer rods are not ideal for that actually as the cog will need thin tooth profile). And a 3DP sector of a huge cog between two passive sectors perfectly orthogonal to the polar axis, so the motor tracking speed is totally linear. I'll try to find the design I had in mind, but in a nutshell: the rod with the motor are installed on the long C-shape bracket engaged with the worm by a spring. You can rock the caret down with a pedal to disconnect the worm when need to reset the platform. Sure thing, with the modern electronics advancements a microcomputer-driven Poncet implementation is on par in complexity with the 3D printed worm cog, so it's up to you. But from my guts feeling the real worm drive should be much more reliable mechanically and have less of the guesswork (e.g. how you will sense the current Poncet position to define the driving speed? The original platform expects you resetting the platform to the end stop each time and then just tracing the time ellapsed). Sorry, Neil, it looks like we have eventually hijacked your thread. Though in exchange it has gained more visibility on the forum no doubt!

I think, I have mentioned the EP which would work best for your second stage pointing task above: "Meade Series 4000 illuminated reticle 9mm" (they might have 12.5mm like that as well, not sure, but the 9mm might be adequate for your 8" SCT already). It has a movable reticle which you calibrate first in meridian and to have its center pattern coincide with the camera chip FOV in the much wider EP FOV. Then just placing your target (planet) into that FOV marker circle/square, with the mirror down, you will always have the target centered on the chip with the mirror up.

Hey, Keith. I had a chance to enjoy your beautiful Southern skies in 2012 driving through Queensland bushes and then from the scuba diving boat (yes I had my 4" Astroscan with me there too!) for 7 nights along the GBR in November (remember the Eclipse?). Good times... To have your question answered properly you should post your current instruments you plan to use these EPs with. And your interests in astronomy. Because that might dictate your choice. The common practice is to add that info to your forum signature (see mine?). In my opinion, a quality fixed EP would be a better bang for the buck in general. A quality zoom EP is fun to use on Moon and planets indeed (folks call it the landing illusion). But for deepsky I would rather get the widest AFOV EP you could afford (it makes views really breathtaking as if you are floating in space between stars). I have three 100 - 110 degrees eyepieces and would never even think going back to the keyhole-like EPs (all zooms I know about have quite narrow AFOVs). But surely you can try zoom EPs fun in some cheap variants instead. They are not stellar but many folks found the $70 Meade zoom not so bad that you immediately want to get Televue $400 one instead. Perhaps, you have an idea to just save on the EP set to have fun while you are waiting for your AP rig/experience building up? As the visual gazing is not your thing at all? Then a zoom might be feasible, because it might be helpful for imaging targets pointing and framing later as a single piece of equipment. Just figure if the cheap 8-24mm would work for that task, or you must go for 3-6 instead. I'm personally got the illuminated reticle 9mm Meade Series 4000 fixed EP, as that what AP folks are using for guiding and framing planning work. OTOH, if you've got some spare dough (folks considering AP hobby usually do ), just go for best of the best TV Ethos 101 deg EPs (and their zoom) as I did. And see for yourself. They worth their price in the weight of gold (well, silver at least ) so you will have zero problems reselling them later to fellow colleagues in the hobby.

In addition, as far as I have mentioned a smartphone, I must mention the Celestron Starsense Explorer (CSSE) modern marvel. But so far it means you have to buy their telescope first . Then move its phone cradle to your telescope. If you never heard about it, in a nutshell, it allows to point a telescope to any invisible target in the sky using your smartphone (its photo camera and accelerometers sensors), and the guide for moving you scope by hands on the screen of the phone. Very similar to the Push-To flow, just 100% guaranteed landing on your target.

With a short frac in bright Bortles, I believe you just need to invest into the widest field (preferably over 100 deg AFOV) EP and practice the star hopping with good handheld digital star chart. When you can have the properly configured star chart view frankly side by side with the eyepiece view and a finger flick sync, it quickly becomes a second nature. So you will recall RDF and RACI times like a nightmare I do. All the way to looking with one eye through the EP and with another on the screen.

Exactly. CMO and MMA are even better for quick measurements. I'm using Meade 4000 with the X-Y movable reticle: And have a couple of micrometer eyepieces for microscopes (with one marked handle). By the way, in most cases, all you need to illuminate a non-lit reticle is getting some scattered light into your aperture (e.g. tape a piece of paper to the OTA rim and shine at it with the flashlight, the finger works too ). In a light polluted sky it's not necessary at all as soon as you are well dark adapted.

The same trick is working for the accurate alignment through the telescope as the eye detects concentricity (this time with the edge of the FOV) better then centrality. So, don't hesitate to defocus it until the star donut is barely visible but almost reaching the field stop (a cheap narrow FOV EP, which is often just dusting in the EP box, will finally find the purpose! Been doing that with my ETX-125 all the time). The illuminated reticle EP is fun to play with though. And, if you are into the science even a little bit, is a must have for celestial measurements (drifting method).

I believe you have the Red Dot Finder (RDF) in mind? A device helping you to point the telescope? Telrad is the best investment you can do for that. As the rest of similar products has a lot of flaws and deficiencies at about the same price range. While an illuminated eyepiece is not helpful at the pointing task at all. The C90 OTA is indeed not big, but I believe Telrad would fit it out of the box using included sticky tape on its mount cradle. It's big on purpose to amend cheap optics issues other RDF devices have. Just select the location opposite to the declination axis of your SW mount head to avoid any interference with its motion. You can point with Telrad directly in a trivial RDF manner from any eye distance from it or employ advanced techniques, such as the TPM. Another option to consider is moving the optical finder from the OTA to the counterweight arm of your GEM. Or just move it closer to the eye as the stock one I see on images is a straight through, so it shouldn't really be too bad on any GEM if mounted properly. If you are using a prism, consider upgrading to the RACI optical finder (also with the prism).

I guess it was not set up properly yet on the first video? As I see the scope rocking like crazy from touches

N/P! On a side note, an EQ platform will interfere with core Dobsonian principles no doubt, as a dob is not intended to work on a significant slope (that's why a trivial EQ wedge you have sketched above would not work well with it if at all, you need an EQ platform). So, many folks has figured that for the visual tracking it is better to have two of the pads on the N-S line and on the West side of the platform (the third is tangent to that line on the East) as eventually they will get more load as the EQP tracks over the meridian. Also, it's beneficial to point at your targets having the platform more or less leveled (insignificant slope, and Alt/Az operation is more natural when working with digital star charts), and track from there for 20 min (half of a typical platform tracking range), which is enough for most objects/projects, even for the sketching as you practice more. Considering the latter, I'm poking an idea of repeating this barn door design instead: Much more 3D printable! Can naturally utilize 3D printer parts you've been talking about. And It's also a more feasible tracker for Northern-ish latitudes (>45) like those in UK.

wobblewing, that's right, you've missed the point. Neil has been complaining earlier that his dob is too sticky, so he's got an idea to put that bearing (LS) on top of the platform to replace the baseboard of the original dob mount. It has nothing to do with the platform's cone mechanics, but people often just eliminating that baseboard moving PTFE pads from it to the top board of the platform and making a hole for the center pin. Just to reduce the bulk and weight. OK, as Neil seems to be OK having the lazy susan (LS) on this thread: Dobson mount was never intended to mimic or replace a real fork mount because the trivial particle-board or even solid wood construction will never match the real compact fork mount due to the increased flex and softness of the wood degrading such a fork mount's performance over time with just normal use. In fact, when you are operating the Dobsonian you don't actually rotate it on its axes, you are repositioning the OTA over 7 teflon pads which are providing perfect stability of the OTA in any possible position and at the same time minimising the effort required to reposition it any moment by a simple push, which is also precisely conditioned to eliminate any sudden jump (that stickiness Neil is suffering from) of the OTA from a static state to moving and back. The size of the pads, their shape and locations, as well as materials of mating surfaces are important and matching the weight of the OTA and OTA + rocker. E.g. for the latter folks are using even vinyl records disks! As even the texture of teflon-mating surface matters. Adding a ball bearing anywhere (like that LS) will require addition of a brake. The brake is usually a dumb friction slab on the side, which will shift the view on engage/disengage. The LS will produce vibrations, will get clogged and have sticky spots, and on a platform will for sure spin on its own as with time people will not engage the brake fully for convenience. On some recent dob models from China, their engineers tried to use needle and roller bearings in tandem with PTFE, but the result is so miserable that owners tearing off that abomination and installing classic pads when their multi-months hunt for the specific starbound-like textured laminate succeeds. So, my advice: don't do that. Ever. Instead, look for the actual root cause of your dobson system's issues. They are usually trivial and easy to fix for no considerable cost.

Sure, I'll explain. I.o.w.: there is nothing relevant to a Mars mission what might require anyone giving any credit for it to the Roskosmos evil corporation To the USSR? May be for the general inspiration.

Roscosmos? Don't make me cry through laughing. Russians had no single screw changed in their general space hardware since 90es. They afraid new screws bought in China may not fit old threads As the education, science, and high-end engineering and industry of the inherited USSR legacy, which you are referring to from the memory I guess, have been raged, scavenged, and profanized by hundreds of high-ranked former-KGB-backed theeves (many now retired in UK mansions and castles) for almost 26 years in a row. All that legacy tech has been sold to China for a single man fortune money a piece. China would rival Musk on Mars not Rusia. Russian space tech is over 30 years old, their scientific data is nearly non-existent due to the lack of funding of anything not bringing immediate wealth to the ruling "party" club ("space taxi" is all they've been investing into lately, and Mask took that over in just 10 years). It's a atypical, but still banana kleptocracy now. All the best Russian minds are working in the US and EU/UK now, including for Musk, and not looking back for prob another 20 years waiting for the mafia state to eat itself out, thanks to sanctions.

wobblewing, perhaps, you should rather start a new thread on your project instead of hijacking Neil's (standard forum rules). Just post a link to it here and in your's to this one for the useful cross-reference. I'll comment on your design progress there then (there are a couple of options on the driving scheme which you might want to consider). Re the lazy suzan. In short: DON'T! The Dobsonian mount is not a simplified fork mount, it just looks like it for a not mechanic. You will ruin half of Dobsonian principles replacing 3 friction pads fine-tuned system with any ball bearing, creating a finger-spinner toy from your telescope mount. Again, I don't want to hijack Neil's thread, so if you are curious to know the details, start the new thread on that bad idea and link here, I'll explain what's the issue.

The key to success with visual NB filters (and without them too, actually, but less productive) in a high light pollution location is the eyes darkness adaptation. You need to learn how to gain that adaptation to the maximum and how to maintain and regain it through all phases of astronomy activities from pointing your telescope to the target - to observing it long enough to pick details (which is similar to a CCD camera, the longer you "soak in" the more that light will reveal, eyes need longer "exposures" though depending on the observer's experience distinguishing sub-peta-photon differences ). With a 10" aperture you might expect to see quite a lot of interesting DSO stuff already, just stick to a higher magnification to keep the background sky glow at bay. NB filters help making the latter easier at lower magnifications too, but limiting your DSOs to gas nebulae (diffuse and planetary). Though stay assured, at 10" there are plenty accessible already with experience (cumulative number of tries). Myself, I believe that the the real joy starts from 12" only and frankly from scratch ) To maintain your darkness adaptation longer when observing you might want to modify your telescope in certain ways as well to eliminate as much scattered light from your surroundings as you can (e.g. flocking, dew shield, eye guards, head cover with air venting, etc).

To drastically reduce the risk of any law enforcement responding to pilots complaint in your neighborhood use the GLP only momentary when pointing. The probability you hit a plane by an accident are on par with the meteorite landing in your backyard. The image with the GLP in the pole finder port above shows the sleeve over the GLP button which is pushing it permanently. Instead, I would recommend airsoft gunsights GLP types with the remote trigger you can stick anywhere on the OTA/mount. E.g.: (https://www.amazon.com/Twod-Picatinny-Adapter-Remote-Pressure/dp/B01NCHTID5) That particular one also has some axis adjustments under the caps (quite limited though). I have one with some modifications on my shotgun for some years, quite decent piece of gear. By the way, the aluminum weaver mount on it is removable (some folks don't know that), and comes with the tail cap button (which is interchangeable with that remote release cap). I'm personally against GLPs for telescope pointing in favor of collimating sights (Telrad, QuInsight), as GLP beam is ruining the darkness adaptation (unless you go with the red beam, but the latter is hard to use in a light polluted sky). However, for the PA task it should be OK as you are using it only once per night during the setup. I do have GLP, RLP, and even BLP in my astro-bag primarily for outreach tasks though. And sure thing in some cases that might be the only viable way to point, e.g. my Astroscan when used on the laps or in hands on the neck strap.

No prob. But perhaps it would be easier to simply install the pointer on the OTA or even on the mount in parallel with the optical axis? I'm using just 2 ropes on my Astroscan: a) - pointer; d) e) f) ropes.