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tonyowens_uk

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About tonyowens_uk

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    Nebula

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  • Gender
    Male
  • Interests
    Hillwalking, cycling, engineering, travel, wine, politics, telescope-making, model-making, invention, history
  • Location
    Wicklow, Ireland
  1. You're a brave chap Gordon. I'm most impressed at your project planning - critical people like neighbours and planners squared off in advance! I think your farmer neighbour's kids ad their friends will need to be shown the sights when the scopes and cameras are installed and the warm room running. That was a dodgy-looking tractor and I can imagine stress levels were high during those lifts! Bravo! Tony Owens
  2. Have you a lathe Gina? If so you could consider printing the mating flange surfaces with loads of skin thickness and then face the flanges and machine a 2mm deep x 3.2mm wide O-ring groove into one, for a BS1806 2.62mm cord dia O-ring in whatever ID you need. Bit too lush maybe? Tony
  3. Is that transparent dome polycarbonate or PMMA or glass Gina? And are you binning the images?
  4. (Courage x Brains x Hard Work) x (recursions)^0.5= Quality of Result! In this case, looking at that 90 sec image the QoR speaks for itself. Stunning Gina.
  5. 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.
  6. 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.
  7. 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
  8. 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
  9. Sounds like you have nailed a big part of your issue!
  10. 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
  11. Nice! I'm still new to 3D FDM printing and would not have thought of that!
  12. 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
  13. 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
  14. 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
  15. 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.
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