tonyowens_uk

There are other perspectives here - e.g. that of the R&D engineering team who have to develop telescope mounts and their control electronics, and that of the business owners who have to pay for the R&D and the manufactured products and business overheads from sales of rather esoteric and very modestly priced equipment, judged against the standards of other kit mentioned in this thread, e.g. smartphones. Unpick this a little: 1. Most astro kit is developed and manufactured in China these days, by engineers with a hands-on outlook, supported by consultants in specific specialties. These suppliers are focused on cost leadership rather than performance leadership, and they target the volume end of the market rather than the high value/highly engineered end. There is no useful market in top-of-the-line mounts or telescopes - that is closer to handcrafting than organised mass manufacture. There is also little real innovation, which is understandable given the demographics of the user base. Consequently, you will not commonly find 'nice-to-have' but non-essential features that require significant engineering development to make reliable, such as sophisticated real-time mount error and refraction modelling, sophisticated GUI's, programmable PPEC, engineering test and diagnostic routines etc. These require meaty motion controller firmware stacks and fast hardware capable of multi-threaded refined trajectory calculation, motion input summing, high speed axis encoder decoding etc. This costs a lot of money and time to develop, for a target audience that will be generally unengaged by the complexities of getting it to work, and unwilling to pay a price sufficient to cover the R&D and ongoing support costs. Consider too the size of the global market for 50kg payload weight class GEM's and above. It is very small indeed. On the other hand, there are tens of thousands of quite basic, light-duty, cast aluminium, dodgy worm gear driven mounts sold annually with 8 bit microontroller user interface paddles and cheap Allegro-based microstepping GoTo motor drives. Think of the Christmas trade in the West, department store telescopes aimed at childrearing, and the cutthroat pricing that applies to that. This addresses an undiscriminating volume market. 2. After more than 3 decades in engineering one of the constant themes I see is lack of respect for engineering development by non-engineers. Bringing mount location, UTC, altitude, air temperature, mount axis position and other relevant use parameters onboard from either inbuilt or auxiliary devices like smartphones, to the required accuracy and with acceptable reliability, so that Goto can be completely automated and accurate is not simple and not cheap to do. And, to cap that, the market still values antidiluvian mount geometries like the GEM, decades after professional users have abandoned it for more rational and higher performance alternatives. 3. Look at unrelated specialist fields for what is done there. How about 'premium cars' - an increasingly meaningless term once one delves beneath the superficial. Telematics systems provided are invariably several years behind the state of the art, and invariably far less capable and ergonomic than the smartphone-based alternatives. Meaningful failure diagnostics and condition monitoring is never offered to end-users, never mind real-time powertrain optimisation and other functions. The fundamental reason for this seems to be that the business model of mainstream automotive OEM's is based in part on maintaining information barriers to end-users in order to generate revenues from repair costs outside the warranty period. (Tesla seem to be changing that. But Tesla is a market-maker and an evangelist...) The hot take here, is that is unreasonable to demand that astro equipment mount makers 'reach for the stars' technologically-speaking when we see little evidence that in other consumer fields, whether automotive, consumtronics, medical devices, domestic durable goods etc this is prioritised. The key ways to get suppliers to offer better more capable products is: 1. to assiduously develop a more discerning market, through special interest discussion forums such as this one, and 2. to encourage greater collaborative development of equipment between manufacturer and end-user. 802.11 Wifi modules with serial interfaces cost a few bucls and are easy to program. GPS modules and chips are very cheap. If these things really matter, either the end-user community need to engineer their own retrofits for popular mounts, or market premium pricing in favour of products with these attributes needs to be communicated convincingly to manufacturers.

Actually you are right. It’s doable in some dignity if the ferries are used. After we relocated from London to Ireland I used to travel weekly from Wicklow to London Bridge or to Cambridge. After six months of costly and stressful flying and car rentals I tried the ferry/drive alternative and never looked back. For people who don’t value rigidly scheduled work and sleep rhythms (astronomers?) the ferry option works particularly well.

Beautiful part of the world if a bit hard to get to Magnus! My compliments too on your land and seascape photos from your personal website that you linked to BTW. Jaw-dropping light and scenery. Tony Owens

Good result on the leaktesting and snagging of the leaks I/D'ed by that Gina! Its not altogether reassuring that the silicone didn't stick well to the PETG, but provided the joints are lightly compressed all may be well when they see rain and condensate. Given the work it took to address environmental sealing, you have earned the karma for leak-related problems to recede! Re location of the electronics: you are right. The proper place for electronics, given a choice, is in controls enclosures. Which implies properly sealed field wiring to sensors and devices is needed. The machine-build world has lots of high cost elegant solutions to this which I'm sure you are well familiar with. One idea you could consider is a 5m USB 3 cable run up the pylon to the ZWO camera (you might want the extra bandwidth in a later ASC incarnation) and seal this using a tight-fitting sleeved rubber grommet lubricated with Hellerine (or olive oil!) and stretched over the connector at one end of the cable. Maybe this one: https://ie.rs-online.com/web/p/rubber-grommets/1366294/ which is polychloroprene rubber and is stretchy with good recovery. A cable tie around the sleeve to seal off the cable entry. Print the ASC enclosure base to take the (expanded) grommet diameter once this can be measured. No need to cut anything. How much force to stretch this I dont know. Warming it would help. There is an electronic technician's loom-making tool for stretching grommets and heat shrink sleeves but I dont know if it would be strong enough... Tony

Sounds like you have nailed a big part of your issue!

The angular bearings are fine Huw. Loads of preloading capacity - they will be nice and stiff and still run with low breakaway friction. They are unsealed I believe so lube with fluorocarbon thickened grease e.g. DuPont Krytox then keep them clean and forget about them. Those are are man-sized roller bearings Huw. I assume you are happy to deal with the overconstraint issue that will arise if you run the driven Dec trunnion shaft in those and keep the other idler trunnion shaft just 'propped' in a ballbearing pillow block! (either the fork or the OTA will flex a bit as the OTA is moved through its range of motion, which can be undesirable if significant). You could either align the constrained trunnion accurately with the 'prop' one, or use a flex-plate interposed between the drive trunnion and the OTA to decouple the tip/tilt nonlinearities. Or you could just do it and take your chances! I assume your existing trunnions are imperial shaft sizes. Otherwise you would find that 40mm ID taper bearings are cheaper and stiffer than those HM-801346-X2310 units. You can avoid the problem of sourcing precision grade taper bearings (usually P5 or P6) to deal with the 20 micron run-out tolerance on their inner races if you can make the trunnion shaft hollow and optically align it with the opposing 'prop' trunnion! As for the basic notion that the driven trunnion shaft should be run in a bearing design that constrains it like a machine tool spindle - basically you are correct! And taper roller bearings in popular sizes (as used for auto wheel bearings) are the cheapest, stiffest solution. Unfortiunately not the lightest and most compact. Tony

Nice! I'm still new to 3D FDM printing and would not have thought of that!

Huw I looked over your previous thread on your R&D work on worm gearing so I think I've got a picture of your drive designs. Having refined some of the rough edges that were previous there I'd make a few suggestions for taking things further: 1. As you've discovered there are a great many variables involved in getting instrument gearing to run well. So focus on one problem at a time. Work on one drive at a time. Remove as many variables as you can from that drive before making changes so you can clearly see which are important and which are not. So in that vein get rid of heavy grease lube and use a semi-grease like engine assembly lube on the worm mesh. 2. You need to be able to measure the effects of your changes. As you know for imaging use (backlash less than 500 millisecs/7.5 arc-seconds) the tangential tooth clearance on worm gearing is only a few microns. That is not reliably measurable using most DTI's let alone lever arms, 'feel' etc. So either use the sky and PHD2 for measurements or buy/borrow a laser displacement sensor and do the work on the bench. If you can get a 1/4" bending beam torque wrench or a Tohnichi gauge in the correct torque range that will help you set bearing preload on the worm shaft in a scientific way. 3. The gold standard in instrument adjustments is use of flexures. Try not to use bearings where possible. The conical tipped preloaded setscrews may work for a while (subject to differential thermal expansion and wear) but flexures are the way to go. I can help with standard designs for doing different adjustments and as you have a mill and are not aesthetically obsessive you should be able to make anything needed! 4. Remove the payload and balance the mount as well as possible before performing mesh setting. 5. Your RA and in particular Dec drives will have fairly narrow torque limits within which they exhibit good tracking and backlash control behaviour. If there is no 'design' as such in your drives and you dont have these limits, I'd suggest you choose conservative values like 5 Nm for RA and 2 Nm for Dec and balance and operate your mount to within those limits. It should be possible to jury-rig means of assessing your out of balance in each axis. 6. Remove as much friction from the main bearings as possible. If you are using a pair of simple ball bearing pillow blocks on each axis ensure they are properly aligned and preloaded enough to remove clearance. but not enough to raise starting torque to more than 1 Nm or so. 7. Your wormshaft bearings ideally should be angular contact bearings and must be square to each other and axially preloaded. Again use starting torque as the criterion for correct preload. But here a much lower figure in the range 0.-02 - 0.1 Nm should be used, depending on the type of bearings and the detailed design of your mount. 8. Dont use Rep-rap commercial-grade timing pulleys and belts if you can avoid it. Use quality kit. Try Transmission Developments in Poole or Misumi for quality kit. For your mount Gates GT3 type in 9 or 15mm width would be about right. Only one pulley should be flanged not both. The belt needs to be tensioned significantly to work properly but don't overload or obsess about this. 9. All instrument gearing for imaging needs to be lapped then burnished. Never use aggressive grinding media for this, especially with a soft metal wormwheel unless you want to turn it into a permanent grinding wheel! The abrasive gets embedded into the soft surface and can be impossible to remove. Aluminium gears should be hardcoat anodised to BS 2536:1995 to 20 um thickness. Burnishing should be done with oil or light grease, minimal torque load, low speed and lots of direction reversals. 10. As you've discovered the mesh preload used should be as low as possible especially in thin wormwheels to minimise nonlinearity from wheel deflection out of its own plane. Astro imaging is desperately sensitive to the slightest imperfections and flexure and friction enforce very conservative torque limits. 11. Keep drive adjustments independent of each other. Your mesh clearance adjuster for example imposes a parasitic lateral displacement of worm to wheel when it makes a radial clearance adjustment. This changes the mesh line. If the worm radial runout is significant there will be a visible nonlinearity from that effect for example 12. You use a gearbox on your servomotor. Look hard at that for quality standard. Most such things don't come up to the mark for transmission linearity and backlash. Backlash can be measured directly down to a degree or so using hand tools and a protractor on the bench. Anything more can be measured by using the Guiding Assistant feature in PHD2, with at least 40 minutes of 1 second guide camera exposures. Doing an FFT on this data will provide a very revealing analysis about the mechanics in your drive, including the gearbox. Have a think about these points if you want to improve your tracking capabilities. I can give you a hand with some of this if you want to contact me off-list. Tony Owens

I look forward to your repeat leak tests with interest Gina. I have notions about using 3D printed enclosure components myself on one of my own projects, with integral flanges and sealing cord grooves, that cannot be moulded conventionally. I will be guided by what you discover! BTW - did you find the clear RTV sealant peeled easily off the PETG printed parts, or not? I am thinking about adhesion and possible issues in that area. Obviously the RTV evolves acetic acid and water during cure, but neither have any effect on PET so with some cure time should have no effect. On the other hand the so-called PETG filament is likely to be a proprietary blend with a few unspecified substances in the blend to improve lubricity, provide colour or whatever. There might be an issue there... Best of luck when the cure is complete and you retest! Tony

Typical switch and hysteresis values as I recall Gina. I remember getting into trouble when I adjusted the screws - the behaviour was not predictable as I recall as there was cross-coupling between the adjustments. I sure I forgot to mark them before fiddling! Tony

Exactly. Its a bit of work to wire all that and more to adjust the setpoint and hysteresis for each of the two switches, but the result would be more informative. My thought about having a volume at the control room end was to have enough dry air to feed the leak. But we have little idea of the magnitude of the leak that needs feeding. On the positive side, this method of dehumidification actually requires there to be a leak in the camera volume. Otherwise there would be no nett inflow of dried air, and no therapeutic effect, and some form of twin-tubed air exchange mechanism or controlled-leak would be required, with more complexity.

I envy you the fast cheap delivery. We dont see a lot of that in Ireland. Two sets of contacts = DPDT? I think one screw controls contact closure pressure and the other controls opening pressure. It would be interesting to know what sort of leakrate you will be looking at. Re use of water manometers. The vapour pressure of water is what it is, given a closed system pressure and temperature. A gradient can exist along the capillary, though it will equilibrate quickly enough. Use a dessicant in the camera, and the water column in the manometer will shorten. But as reading these is differential (LHS column height - RHS column height), that would not affect accuracy. But it will kill the dessicant needlessly. To maintain non-condensing conditions exist the camera volume during cooling periods probably best not to use a water manometer anywhere (except for initial switch calibration perhaps). One thought would be to pump air using a bicycle pump into a reservoir 2L PET water bottle with screwcap) a quarter-filled with dessicant, and to connected this to the camera via a 4mm soft PU pneumatic tube. The pressure switch would be teed off this line, near the bottle. And when the switch resets (or the PET bottle gets a bit flaccid) just give it a bit more air. With some determined initial purging, that might actually work, depending on the leak rate! Tony Owens

Just a thought Gina if you are leaning towards overpressure monitoring. Don't overlook washing machine pressure switches. Cheap, reliable, switching pressure generally in the range 3" - 7.5" H2O. Many are adjustable. Most are a bit large but certainly not all. All the diaphragm and microswt stuff taken care of. Best to go get one from a local appliance repair business. Tony Owens

I hadn't seen that motor Gina - with the offset output shaft. It will fit perfectly as-is and no more transmission needed!

Nice and minimalist! With a pinch clamp to fix the quadrant to the focus ring and a bit of axial length to that clamp to react the radial component of pinion contact pressure, through the quadrant, and into the focus ring. Alternatively, provide a lower bearing land for the lower skirt of the quadrant to ride on. Pinion/quadrant mesh clearance adjustment via slightly oversized camera fixing screws. Use of Nye Lubricants PTFE damping lubricant to kill any stick-slip in the gearing and pinion bearing. I assume you are connecting the motor to the pinion shaft via a timing belt given the offset position of the shaft? Tony Owens

I don't think so Gina. Remember that low outgassing grades of silicone adhesive and potting (not RTV types admittedly) are extensively used in aerospace for mounting large refractive optics. Silicones are fine at low as well as high temperatures. If the adhesion of the sealant is not in question, I'd look carefully at permeability of the printed parts. Layer adhesion (a function of internal voiding) of PETG is purported very good - less so some other filaments, and its vapour barrier properties are well-known from food packaging uses in PET foil form. 1. Would it be practical for you to reverse-pressurise and waterbath/bubble test the enclosure you require to be hermetic (without the camera inside obviously)? I'm thinking about how to simply prove the seal integrity and identifying cracks/porosity if any 2. Crude and a cop-out perhaps - but would a 3mm plastic tube run into the enclosure and used either to positively pressurise it to a couple of inches of water head, OR a flow/return pair of such tubes solve the problem permanently? The air pump could be a small high head DC fan and the dessicant for the recirculating system could live in the vessel along with the fan somewhere indoors near the pylon... 3. If disassembly is not a requirement, there are alternatives to RTV silicone sealant and encapsulant which may work better for you. RS Components for a quick review, and Easycomposites UK for a more focused assessment of some of them. Keep going! Tony

I wouldn't agree with that. A few folk on here may know me as the chap that developed retrofit antibacklash gearing for the EQ8 - in response to my own experience with severe Dec backlash. which was similar to yours. I studied the mount in detail, visited the factory where they are made and consulted with the design engineers about it. They are not engineered like 10Micron mounts, but then again they cost only a quarter as much, and they are solid and serviceable for long FL imaging once the backlash problem is tamed. 2015-on EQ8's are much better than the original ones in respect of Dec backlash, even if not as good or as reliable as genuine anti-backlash mounts. What's more, they have big accurately hobbed worm wheels and ground worms which generate low PE and are easy to autoguide with substantial payloads. There is a good ecosystem of community-designed extensions to the rather basic Synscan motion control system, e.g. EQMOD, Green Swamp, Wifi dongles and an engineering diagnostic tools. For those who can see beyond the 'rough and tough' cost-optimised persona of this product, and are willing to make allowances for its funny little ways (e.g they come in a huge flight case, but have no reverse polarity power protection or motor short circuit protection), EQ8's are a solid workhorse at a bargain price. There are several people on this forum who rely on one for much of their imaging work. Incidentally, no mounts of this weight class are mass-produced. The global market for such items is very small. All are built in small batches. Tony Owens

A mate of mine from Melbourne has helped one of his pals who has an AZGTi to get connected to EQMOD. As you mention the Custom option needs to be used. You are correct about both gear ratio and motor encoder resolution. In addition, as there is no PPEC function on this mount the mount controller returns zero for the microsteps per RA/Az worm rev, causing a divide by zero error. Apparently it is possible to manually override this in EQMOD. Our own AZGTi is still laid up and awaiting a spare part so I cant confirm what to do exactly. Give it a lash and let us know you get on! Tony Owens

I think the principles of their design are spot-on. 1. No counterweights: These are an Edwardian engineering anachronism that have no other function than to allow badly-designed worm gearing to deliver acceptably smooth operation and wear life. Sadly the GEM with counterweights has become something of a meme. Industrial robots have managed to combine good accuracy and repeatability for many years without resorting to them, as have professional scope mounts. 2. Compact and lightweight. The value of this to end-users is more substantial is commonly realised by equipment manufacturers. The success of giant-killing small tracking AltAz mounts from iOptron and Skywatcher is evidence of that. With the shift away from long exposure CCD technology to CMOS stacked subframes, and the growing awareness that high resolution (>24 bit) axis encoders and direct drive provide no compelling advantages over an autoguided open-loop mount outside a permanent observatory, I expect to see fewer cost-optimised 'toy' tracking AltAz mounts in the future and more 'authentic' mounts based on industrial automation technology, like this one. 3. Billet-machined construction. This offers no functional advantages whatsoever compared with a mount made from machined castings (and sometimes serious stiffness disadvantages), but in the minds of many buyers it connotes superior performance 4. Freedom from routine mechanical maintenance. This is increasingly important as imaging equipment proliferates, and it characterises harmonic-type reducers as are used here. The pricing is going to be an issue I suspect. The controls environment (ASCOM, smartphone interfaces, homing, cable-wrap, backlash detection and compensation, sky modelling) is generally a greater challenge than the mechanical engineering. It will be interesting to see how well evolved this is. All credit to the developers for bringing this to market! Tony Owens

Gina Based on what we read your approach to developing this camera to be as simple as possible (but no simpler) and how you've allocated your time to testing is exemplary. Its a bit of a pain to have to put the remote focusing back in but youve already developed this module if I understand your previous sky camera efforts so hopefully it will be 'just' a packaging problem. And while that is being designed and built I'm sure I'm not the only one curious about the hermeticity and environmental resistance of heavy duty 3D printed structures like those you've used. Being able to monitor the dessicant condition visually from afar is a nice touch. how that changes in the face of daily thermal hilo's and rain and vibration will be interesting. Thanks for the filament material reference. I'm only getting started myself. Tony

Gina what was that translucent filament you made the exterior casing and dome retainer ring from? Also have you had any problems with outgassing (acetic acid and moisture) from the RTV sealer on these types of projects involving optical windows? Thanks Tony Owens

FWIW Gina I have an iPhone app I very occasionally use called VibSensor which enables vibration and tip/tilt logging using the inbuilt accelerometers. It operates across a decent frequency range and does power spectrum analysis, automatic resonant frequency ID'ing etc. Sensitivity (with recent iPhone) is quite good and span with most smartphones will be 0-2G. By comparison of power spectrum before/after treatments such as the torsional damper, this might help you get to the bottom of any resonance issues with your Z motor mounting and coupling, as well as help you quantify bending stiffness of your printbed and the print carriage on its linear ways. If you decide to try this, I'd recommend fixing the accelerometers (smartphone) to the structure you are interested in using 3 bits of Blu-tac. Those larger frame size steppers can be installation-sensitive. Other treatments I've used myself to try and tame resonant behaviour and loss of steps include clamping a heavy steel annulus around the motor body (round motors obviously) and mounting the motor flange using purpose-made hard elastomer motor mounts like these: https://www.ebay.co.uk/itm/Nema-23-Stepper-Motor-Damper-Pad-Anti-Vibration-CNC-3D-Printer-Mill-/151856260838 Tony Owens PS: Credit where credit is due: The tip about coupling the accelerometers to the structure was from Es Reid in a different engineering context but it works well for this too!

That figure sounds fine to me Rob. Its easy to add a front baffle later to kill off-axis lighting during critical lunar imaging or similar. Tony

OK I see. Well there is no real rule for tube extension length beyond the focuser that I'm aware of apart from the matter of adequately baffling the background visible at the eyepiece around the secondary mirror. There are two extremes. 1. Dematerialised to just a potato chip-shaped flocked disk opposite the focuser like in many ultralight truss Dobs 2. At the other extreme (Intes Micro Mak-Newt's) it can be a set of close-pitched knife-edged baffle rings stationed along the tube directly opposite the focuser hole, and the provision of an external internally-baffled tube extension (dewcap/baffle tube) of around a 1.5 times the scope aperture. Your choice will reflect convenience, weight, hassle and the quality of baffling you need which depends on what you want to do with the scope! MN86 from Intes Micro. Note huge dewcap/baffle ...with internal knife edge baffles ...and yet more baffles behind the secondary. The scope is pointed a few degrees away from the Sun (light entering from the LHS) but the off-axis light is fairly well suppressed even thought this is a Newt This is the tube and optical layout for an unmodified MN86 Mak-Newt (no dewcap/baffle in the model). It is almost identical to an 8" F5.9 regular Newt in baffling and layout. Food for thought perhaps? Tony Owens