Roger
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Posts posted by Roger
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My mount is on order - so my advice at present is generic! My present set-up is various 'scopes and 'scope-pairs on a home-designed plate, in turn on a Vixen Atlux.
If everything within your OTA is normal, this might be where the OTA attaches to the plate - or even plate-to-mount.
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This could be almost anything! If the scope dinged the dome, it could have just jarred something slightly loose in the set-up. Recheck all bolts, tube rings, etc. for tightness. With the mount switched on (and in control) I'd gently get a hold of the tube and try moving it/restraining it slightly in all directions to see if there was any play, and if there is to identify that and eliminate it.
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actually attach it to the OTA close to the camera so as not to place unnecessary moment loading on the focusser
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pragmatic suggestion: Get a weight and attach it to the lighter camera....
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Excellent.
The knowledge base on these mounts is building up in here thanks to great team spirit.
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I cannot believe that this weight swap has made any difference to the underlying problem. Generally less flexure and fewer low frequency problems will be experienced if the heavier weight is nearer to the fulcrum (as you had it before the swap). The underlying problem sounds more like the one Lukas describes in "losing USB..." , eventually resulting in a return-to-base repair, with which he is now very pleased.
I hope I am not the prophet of doom, but I fully expect this problem to return to haunt you.
Post hoc ergo propter hoc.
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Luke
I sent you a PM.
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And I am more than a mite relieved too (will soon be a proud owner...)
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Thanks for that. Our understanding of balance is identical - and the fact that the countershaft does not rotate throws another idea out of the window!
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Note: Edited post above to eliminate ambiguity of axis descriptions, not changing any detail or context. Roger.
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I see in a lot of places on here the phrase "balancing in different positions". Surely a telescope system is either in balance or out of balance? I am assuming by this phrase what is actually meant is to make sure that not only the counterweight correctly balances everything else, but that, when uncoupled, the plate, scopes, camera etc. has no left/right load at any position, i.e., not only is the OTA assembly balanced along the optical axis, but also perpendicular to it.
Is this correct or is there some eccentric arrangement with this mount I have failed to grasp?
I am sure I hasten to add that this will come clear when I get the mount.
Assuming my assumption is correct, one possibly very useful addition to the software may well be something that, by slewing the scope around on its counterweight shaft axis with known Alt, with its counterweights at the lowest point and manually entered datum for OTA pointing to the horizon or pole star, coefficients of which direction the balancing error is might come in handy so that one can first get the OTA balanced correctly perpendicular to the optical axis, and then along it (this I believe would be quite straightforward software to write and very useful for those with complex OTA arrangements).
A quick question for mount owners or ASA: When the mount is slewing, does the counterweight shaft rotate with rotation of the OTA on that axis? And a supplementary: If it does rotate when slewing, does it also rotate when the mount is unpowered and the OTA manually rotated about its countershaft axis? If affirmative to both, there may well be a very much easier way to do this balancing. I will talk to ASA offline - it may well be patentable.
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As a systems engineer, a wheeled base will almost certainly mean you need to back I (of PID) way down. I stress I do not (yet) have one of these mounts, but that is what I'd first try.
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If the troubles originally started following a lightning zap there could be latent damage on any pcb sadly.
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Insulation breakdown (insulation in the widest sense, oxide layers in semiconductors), ie static damage, could readily give rise to a runaway situation such as this. Thanks for sharing.
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I also agree regarding dedicated serial ports. The present setup here is a PC with a 4-port serial card (PCI) installed (one for the focuser, one for the mount, one for the autoguider and one spare!).
Glad you've identified a burned out part. However, is that cause or effect? I hate to be the prophet of doom, but if you have an issue where the micro or other control circuitry is misbehaving for any length of time, this may be a symptom of the failure mode induced by a brownout rather than the cause of lost comms (its drive may have gone half level or similar allowing high current and high voltage at the same time across a switching element that ordinarily experiences one or the other).
I stress yet again I've not seen any circuits but I would find it incongruous that the logic / low level electronic supply lines would be sub-regulated from a high current motor drive rail (they would be regulated from a separate feed from the prime mover independently decoupled before any voltage reduction).
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I would agree about RS232. The problem is most PCs these days don't have a native serial port - and the USB converters decouple you from the real RTS/CTS and other control lines!
Let's hope it is a 1-off and there is no generic problem.
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How many is this communication drop-out affecting? I believe I have identified at least two on here.
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I like the look of that 40A power supply!
However, if as you say the mount keeps going, then the glitch internally is I guess not likely to be solved by a beefier supply - unless of course it actually stops and immediately recovers - which is not the same thing. If you have one (or a couple of lead acid batteries) to hand, it is worth a try for sure.
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Folks - I have likely made about 5 by adding 2 and 2. Apart from the safe experiments I have suggested of additional decoupling close to the mount power pins and replacing permanent power supplies for a short time with lead acid batteries, please do not go off on tangents without checking what you're doing with ASA. I may be totally wrong with my thoughts. I am just an engineer considering a purchase and have never seen one in action apart from for a brief 5 minutes last month.
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Or if you haver access to an oscilloscope see if you can detect any appreciable drop-out on slewing - may be easier.
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Well, I use a Siemens PSU with 24V and 20A output, short leads (it's sitting at the base of the mount). FUnny enough, the motors keep often running even without connection to the PC
In the FAQ it says that peak draw is 20A on slewing - so this could be the issue. Please humour me and put a couple of car batteries in series there for a while (either alone or in parallel with your Siemens block) and see if the problem goes away.
EDIT - Best to use the batteries standalone for this test - not sure if that Siemens lump likes being put in parallel with batteries.
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ok. Well, I'd be interested to know from ASA if this is by design (it possibly is a safety feature - too much power being requested so lock out - in which case it may be a parameter they would be prepared to adjust), or an unintentional lock-up, perhaps resulting from the brownout, which I contend should be soluble.
I wonder if for expedience, turning down all the mount PID gains by, say, 20%, would help? I must stress this is with no mount experience just clutching at straws.
Oh - last thought: Is the power supply man enough or is it possible that is browning out? How long are the leads to it? Might be worth putting 10,000µF across the main rail connections up at the mount end of the power cable.
<small edit for clarification of capacitor position>
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I have not studied anything - I am simply a prospective customer having admired the design and principles of the mount at Astrofest last month. I've never even seen the inside of the mount, let alone the PCB layout!
If one is really fortunate this might be soluble by a rerouting of wiring so that the power to the high current stuff does not interfere with the area of the PCB with USB controller on it. One would need to examine the topography and circuits to know if this would help (or would be possible).
It is also possible that the high rate of change of current in the motors is the problem - and that the interference is magnetic. A ferrite bead or two on the high power wires might help there just to take the edge off the d2I/dt2.
One thing is for sure, it is always worth isolating as far as possible in such designs the control circuits from the power circuits. Good layout techniques are as important (if not more so) than the circuit design itself.
One question - maybe naïve: When you lose USB comms, does it ruin the current image, or is that ok, but you just lose comms for the next one? Put another way, can you unplug the USB connection for a short while and connect it back up again mid-exposure without causing problems? If that's the case, it may be possible to design a comparatively cheap external board that goes between the PC and the mount that "sniffs" the USB traffic, and simply flicks a relay on and off when comms goes wrong, forcing the USB to retrain from first principles. Of course if you're using the auxiliary USB hub that would be out of the question as camera capture would be interfered with (although to prove the point a camera connection could be taken back to the computer without going through the mount).
pier-tech DDM85 and keeping polar alignment?
in ASA DDM85, 100, 200, 500
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I agree with your prognosis - but I stress it's only theory!