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Perhaps someone has a source of industrial quality USB cables they can pass along? Specifically I'm looking for USB 3 Type A to Type B plug cabling designed for industrial environments. This is the opposite of consumer and office-grade cabling. So I need either silicone or polyurethane (not PVC) sheaths, either flat or circular section, gold plated contacts, 3-5m length, choice of straight or right-angled plugs. This is for permanent outdoor use hooking up imaging equipment in Wicklow's cold wet windy climate. Many thanks Tony Owens
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International Astronomy Show 2022
tonyowens_uk replied to FLO's topic in Sponsor Announcements and Offers
Graeme if you are still interested contact me off list to discuss or speak with Grant or Rob at FLO about the EQ8 modernisation service. It’s not a kit BTW. The service is collect and return as the modifications require a tool room or R&D lab to perform properly. Tony Owens -
AstroOptik Philip Keller
tonyowens_uk replied to tonyowens_uk's topic in Discussions - Scopes / Whole setups
Thanks Dave, thats a good thought. Tony -
Does anyone know whether Philip Keller the optical design engineer and supplier of professional Wynne correctors is still in business? If anyone has contact information for Hr Keller or his business I'd appreciate a referral, thanks. Tony Owens
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No. Dignify the discussion by reading my essay. All that to try make a case for: more thoughtfulness about terms like quality in highly engineered systems the avoidance of loose language and the lazy equation of cost with quality and to discourage the casual dissing of the work products of other people (e.g. Onstep) without evidence! Best Tony Owens
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Hi newbie! I dont think its meaningful to speak of the quality of a motor or any other technical component in the abstract. A 200 step/rev hybrid stepper motor cant be compared to a brushed DC servomotor without looking at the context. If that is running an axis of a telescope mount, we are looking at torque vs speed characteristics, electrical efficiency, noise emission, 'cogging' behaviour, spindle positioning elasticity (drive stiffness), robustness, wear life, ease of packaging, ease of commissioning and reliability. And in this application no meaningful comparison is possible without also including the motor drive electronics, cabling, connectors and firmware. On one side we have Maxon/Scitech and industrial sealed connectors and screened cabling. On the other, we might have a Chinese generic 400 step/rev NEMA17 hybrid stepper driven by a Trinamics TMC2209 driver and commanded by Onstep running on a modern ESP32 embedded controller, with unshielded and unsealed motor wiring. Or it might be a similar controller board operating a Clearpath SDSK stepper-servo with 6400 tic embedded encoder via Onstep's step/direction interface, and wired with silicone-sheathed shielded cable and metal IP65-rated M12 multipole connectors. In terms of measured following error during tracking (motion quality), the difference between these three solutions may well be negligible. Autoguiding compensates perfectly for the lack of a high-resolution axis encoder on all of these solutions. The torque capacity superiority of the stepper solutions is irrelevant as input torque capacity of Mesu's friction drive will limit how much motor torque can be delivered. The speed advantages of the servo are irrelevant as the steppers can 'pull' higher overall transmission gearing if necessary. As the friction transmission is (as I understand) backdriveable, the efficiency of the stepper-based drivetrain may be more efficient if the mount spends significant periods held stationary. Or not, as the case may be. There will be no difference in noise emission when tracking between these mounts except for the servo's faint 20 kHz commutation whine. None of these systems will exhibit cogging behavior visible in images (provided the servo is properly tuned with a small 'deadband' of about +/- 2 encoder counts and provided the Trinamics driver running the simple stepper has plenty of drive current available). One big difference between the simple stepper system and the other two (servo and servo-stepper) might be drive (motor rotor) positioning stiffness. Whether far superior rotor stiffness of the latter solutions provides any benefit will depend on the amount of friction in the Mesu's transmission. As this is far lower than worm drive mounts, for example, it may well be that there is no perceptible difference. But in a worm drive mount, especially of the antibacklash type where drag friction is significant, a difference is likely to be apparent in rms guiding error. Another difference emerges when looking at ease of commissioning. The Scitech servo system needs careful tuning to obtain stability without micro-oscillation at tracking speed or sluggish response to positioning moves, which makes building the systems more involved. None of these systems (so far as i'm aware?) employ speed reduction gearheads so all should be equally reliable. The only one that is environmentally-sealed to normal industrial standards for outdoor use (advisable for remote-controlled observatories for example) would be the servo-stepper one I mentioned with waterproof connectors. So there you have it. There is a very big difference between the cost of these three systems, the Scitech one being most costly by far. This is easily explained by: the manufacturing economics of the relevant component suppliers the avoidance of the need to recoup very substantial R&D costs on the Onstep system which is a GPL development that is designed to run on COTS hardware the fact that there are multiple parties involved in the supply chain for Scitech which leads to greater margin-taking For many end-users, performance differences between these systems will not be apparent, meaning that there is no perceptible diffrence in 'quality'. For a minority of users who need the greater simplicity of repairs and maintenance of the stepper system e.g. remote controlled imagers, that might be a better choice for them. For another minority who are interested in remote satellite tracking and orbital parameter calculations and need high dynamics, a servo-stepper system might be their choice. And perhaps a few (like me) admire the form and finish and heritage of historical highly-engineered assets - for us, the existing Maxon/Scitech solution is also appealing. Tony Owens
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Quality of a motor or a motion controller has little to do with its cost. Stepper motor and servo motor drive systems have their own strengths and weaknesses, and in some applications the motor technologies can be blended (servo-stepper). What matters is the motion quality delivered, and the reliability and maintenance requirements. There is no reason I can think of why a microstepped Mesu friction mount should not track as well as the Maxon skewed-rotor/Scitech model, particularly if closed-loop steppers (servo-stepper technology with embedded encoder) are chosen. You seem to suggest that the Onstep control software is inferior to Scitech's. Do you have evidence for this?
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The owner of the Skywatcher brand, and Celestron Corp and various other entities, and of the patent portfolio underpinning Skywatcher gear and manufacturing processes is Nantong Schmidt. David Chen is still executive chairman. I toured the manufacturing and engineering facilities in Dec 2018 and they looked healthy and financially successful to me. Tony Owens
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Hi Mike. I agree with you about combining PPEC with properly-refined autoguiding - I've never seen a clear benefit myself in the case of EQ8's. What works for me extemely well (using the original motor board/motors used in the original EQ8 and antibacklasg gears) is very frequent small corrections, with a predictive guiding algo from PHD2. With the much improved motor board that appeared with the mount refresh, the picture is likely to be different because of the more refined microstepping behaviour, and I havent investigated that yet. Re references to the 'under the hood' EQ8-specific investigations and improvements built into GSS, I suggest you search for contributions from Andrew Johansen in particular. cheers Tony Owens
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Hi Mike, Three examples of differences in favour of GSS v. EQMOD are: 1. If you use the integral PPEC on the EQ8 or EQ8R, I believe that incoming autoguider move commands that coincide with a PPEC 'bin' transition are ignored, which negatively affects guiding accuracy. This happens with EQMOD controlling EQ8, due to a design flaw in the EQ8's firmware design. My understanding is that this also happens with the newer EQ8 firmware versions (cross-compiled for the STM32 that runs the EQ8 motion controller). In GSS there is a workaround. 2. Very short autoguide corrections sent to either EQ8 or EQ8R are executed very rapidly in GSS using GoTo moves. EQMOD has nothing comparable. 3. EQMOD is not in active development. GSS has at least three intermittently active developers and a growing user base You can read about the first two of these issues on the GSS forum I hotlinked in my earlier post, if interested. Best Tony Owens
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Nigella if you have not already looked at GSS as an alternative to EQMOD for controlling your new EQ8R, it would be worthwhile. There is a discussion list for GSS here: https://gss.groups.io/g/main GSS is in active development (it was originally developed to work around some of the EQ8's limitations, which it does rather well) with meaningful new functionality still appearing. You will no doubt have a large list of issues to work through with your 12" imaging Newt on your new EQ8R to get it operating reliably at the expected performance level, but when you get that under control, best have a look at GSS. Tony
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Most pro-sumer mounts use stepper motors driven in microstepping mode. In the case of the older Skywatcher models, e.g. EQ8, there is a definite motor torque benefit to using the highest drive voltage possible. For safety, a regulated power supply set to 15Vdc maximum with at least 5A capacity and preferably 10A is my recommendation. Use sensibly short cabling from the supply to the mount, with 16AWG stranded wire, or more. That will hold cable loss to 0.3V or so. The reason for maximising torque is that in tracking mode when microstepping is active, significant friction arises in properly set up worm gear drives. This causes a 'following error' to arise - a lag beween the commanded stepper motor shaft position and the actual position, to the detriment of tracking accuracy. Fortunately the effect is small, but it is there. Boosting torque reduces following error. Tony Owens
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I need to qualify my comment Ken. The comparison would be against quality antibacklash worm gears, not fixed-centre gears. Remember that many traditional mounts have neither ground worm gears, nor precision-grade worm bearings, nor antibacklash provisions. And in some cases not even proper environmental sealing of the oily bits. There is a huge quality spread across the hundreds of models of worm geared mounts available. Tony
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From what I've seen, Skywatcher (Nantong Schmidt Instrument Company) have enormous manufacturing operations of their own, for optics, tubes, machined parts, worm wheels, finishes, assembly, test and many other things. Obviously they dont make their own PCB's, castings, small lenses and so forth. No OEM does. Such things come from specialist suppliers. But they do have an excellent design engineering team, who are very much involved in the latest developments, and plenty of resources. So far as harmonic gears are concerned, as used in the compact mounts referred to on this thread, these all come from specialist companies who serve the automation/robotics/semiconductor processing equipment markets. The technology has been around for decades, but it is difficult to master, as it involves materials, heat treatment, motion control, creep-grinding and structural analysis expertise of a high level all under one roof. At the hobby level,harmonic gears are 3D printable, but for ultraprecision uses such as imaging telescope mounts, neither Nantong Schmidt nor anyone else is going to be producing their own! It is worth mentioning, that for all their advantages (compactness, low backlash, low friction losses), harmonic drives have many disadvantages too (indifferent linearity (large periodic error), lack of torsional stiffness, cost). When autoguided by fast guide optics and star centroiding software with with good response, they should track fairly well. But they will not match the accuracy and low PE of a good set of machined and ground worm gears, never mind friction drives.
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Noob Question concerning dec. backlash in EQ8-R Pro
tonyowens_uk replied to AstroAndy's topic in Discussions - Mounts
Hi Mike. Loved your account of the 12" Cass/RC build on your site BTW! The EQ8 is awkward as its neither fish nor fowl. The underlying mechanical precision and structural stiffness is superior enough to encourage seeing-limited imaging, but the omission of anti-backlash worm gear meshing and extensive use of thermally-reactive aluminium components (shafts, structure, worm wheels) frustrates being able to set a stable mesh clearance as ambient temperature changes. On top of that, many have run-out issues of the Dec worm wheel relative to the Dec worm, caused by tolerance stack effects. Consequently, it isnt possible to establish stable meshing friction around the Dec axis, never mind stable backlash. If run-out doesnt get you, temperature changes will! The best that can be done without surgery is to clamp the Dec clutch as lightly as possible, and set the worm meshing clearance at the 'tightest' position angle around the axis, judged empirically. The surgical fix is to replace the standard Dec gearing with an antibacklash one, which is very effective, and replace the standard clutch with a modified design. But this isnt particularly cheap.