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I have been using my GM8 for about six months now. Have had the clutches apart and cleaned lube off the surfaces,got the enhanced knobs... rebuilt the pointing model a few times. All good. And yes, it is balanced on both axis every time the configuration changes and as part of routine startup.
Have one problem, though -- responsiveness at any tracking setting in RA is good. And when moving in DEC, responds fine moving [arrow] down but not in the other direction. Seems quite unresponsive then a big jump.
I am suspecting it is a physical issue rather than something in the Gemini-2. But I am open to suggestions and advice from the more experienced. Any thoughts?
Thanks,
greg latiak avalon observatory
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Hi Greg,
It is important to take the cover off the (DEC here) worm and then rotate (rock) your scope back and forth around the DEC axis gently.? Look for worm side to side movement. ?
Sidecar side worm movement, even with the worm pressed tightly against the ring gear, allows too much hysteresis for quality tracking (in RA) and autoguiding (RA or DEC). ?
There are two ways of dealing with it: 1. A hanging weight to provide a constant torque on each axis.? This is easier to deal with in RA because the RA axis is always at the same angle (polar aligned).? But in DEC the angle is ever changing by time and target...still workable but...
2. Install a Belleville spring washer on the far worm bearing, to force the bearing on to the worm along its axis.? This works on both axes, and all orientations.? It is compact and invisible.? For work ?it requires polishing down the OD of the far worm bearing so it slides along its cylinder, and just putting a Belleville washer into the back behind the bearing. ?
After either treatment, ?you still need to adjust the worm-to-ring spacing, as for all worm drive mounts.? That is where the "1mm movement at the end of the counterweight shaft" recommendation.? That tiny amount of hysteresis is acceptable.? I have these washers R4 size for the bearing, (and for the AZ holddown bolts too.)
I have a PDF writeup on this in our Files section, or on the G11 improvements tab of my website at ?
Very best, Michael?
On Aug 27, 2017 04:54, " glatiak@... [Losmandy_users]" < Losmandy_users@...> wrote:
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I have been using my GM8 for about six months now. Have had the clutches apart and cleaned lube off the surfaces,got the enhanced knobs... rebuilt the pointing model a few times. All good. And yes, it is balanced on both axis every time the configuration changes and as part of routine startup.
Have one problem, though -- responsiveness at any tracking setting in RA is good. And when moving in DEC, responds fine moving [arrow] down but not in the other direction. Seems quite unresponsive then a big jump.
I am suspecting it is a physical issue rather than something in the Gemini-2. But I am open to suggestions and advice from the more experienced. Any thoughts?
Thanks,
greg latiak avalon observatory
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Greg,?
What happens when you continue moving in the unresponsive direction? Does it start to move smoothly after the big jump, or does it stall again and then make another big jump??
You should pull off the worm cover and carefully watch what happens when you move in the two directions. Also intentionally misbalance a little and see what the behavior is if north-heavy vs south-heavy vs balanced.? ??-Les
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On Aug 27, 2017, at 4:54 AM, glatiak@... [Losmandy_users] < Losmandy_users@...> wrote:
I have been using my GM8 for about six months now. Have had the clutches apart and cleaned lube off the surfaces,got the enhanced knobs... rebuilt the pointing model a few times. All good. And yes, it is balanced on both axis every time the configuration changes and as part of routine startup.
Have one problem, though -- responsiveness at any tracking setting in RA is good. And when moving in DEC, responds fine moving [arrow] down but not in the other direction. Seems quite unresponsive then a big jump.
I am suspecting it is a physical issue rather than something in the Gemini-2. But I am open to suggestions and advice from the more experienced. Any thoughts?
Thanks,
greg latiak avalon observatory
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This is backlash in the meshing of the DEC worm and spur gears.? It can be minimized by decreasing the spacing between the two (look for procedures in past posts of this group, which depends on your configuration, one-piece worm block or two blocks).? However you may be limited by the machining accuracy of your actual spur gear (how much it deviates from circular).? In my case, I tightened things up as much as possible (including eliminating side to side motion by pushing the right bearing block toward the motor) to the point where it binds/stalls at a high point on the spur gear.? After loosening the mesh up to avoid this, I am left with backlash that I have to live with.? I use the approach many others do and slightly polar mis-align and only guide one direction in DEC so the gear direction never has to change.? I wish I could improve the backlash though ...
Keith
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Sounds like it could just be DEC backlash. Have you tried measuring that with something like PHD2?
B
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PHD2 does complain about that when I am drifting... something about maximum pulse duration being too short, no matter how large a value I put in.
g
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have you tried using the guiding assistant? That should give you a lot of good input and recommendations
B
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Have you tried just pushing the button on the hand control and seeing what happens with the image (in an eyepiece or guider screen)? ? If it was me I’d put a reticule eyepiece into the scope and just use the basic system sans computer or guider – simplify the configuration to isolate problems and avoid interactions, and just my eye, hand, and brain. ? You probably just have too much backlash and need to do a mechanical adjustment of the worm lash. ? Mark C.
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Well, that is what I have been doing. But I use a video camera instead of an eyepiece because I have difficulty focusing with an eyepiece. But the principle is still the same. And since I got the GM-8, replacing a workable but not particularly serviceable and occasionally neurotic iOptron mount, I have had little use for PHD2, save as a drift alignment tool. With the iOptron, even after careful drifting, PHD2 was a necessity.
I have been playing with the backlash adjustment per the instructions on the Losmandy site. What I noticed is that when I press either DEC button, there is a profound lag before the worm starts turning. If I press the button a second time it starts moving immediately -- it seems more like the button scan is being ignored than a mechanical backlash issue.
I am thinking that the next time I can experiment I should probably try the web page and see if there is any indication that the DEC motor is being driven.
I am also curious if clutch tension has any impact on backlash.
greg
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Follow-on Note:
I have no idea what I am looking at with the servo status screens. When I move in RA, the status screen is showing me fluctuating values with servo lag of -5 and duty 7.
When the DEC servo runs, it shows a lag of 15 and a duty of -21.
When nothing happened (my issue) it showed a dec servo lag of -1 and a duty of 2.
Looking at the hand controller balance screen when I am moving the mount the displays for DEC and RA are similar.
I noticed the TVC setting is '5' by default (de fault is always de user,.,,;-), would this have any influence on moving with the HC?
g
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If you are guiding via PHD or external program, I recommend you set TVC to 0 and let the guiding program handle DEC backlash ? On the rest of the servo status stuff, I primarily use it for diagnostics, if things are going haywire or not moving at all, you can check here and confirm ? It’s also helpful to check for correct balancing ? ? Thanks ? Brian ? ? Brian Valente Brianvalentephotography.com ?
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From: Losmandy_users@... [mailto:Losmandy_users@...]
Sent: Tuesday, August 29, 2017 1:38 PM
To: Losmandy_users@...
Subject: [Losmandy_users] Re: DEC latency in one direction? ? Follow-on Note: I have no idea what I am looking at with the servo status screens. When I move in RA, the status screen is showing me fluctuating values with servo lag of -5 and duty 7. When the DEC servo runs, it shows a lag of 15 and a duty of -21. When nothing happened (my issue) it showed a dec servo lag of -1 and a duty of 2. Looking at the hand controller balance screen when I am moving the mount the displays for DEC and RA are similar. I noticed the TVC setting is '5' by default (de fault is always de user,.,,;-), would this have any influence on moving with the HC?
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Thanks, Brian.
For the kind of observing I generally do, the basic tracking of the mount is sufficient. If I get any drift I assume it suggests I need to spend another evening drifting... Right now, I just use PHD2 as a drift assistant.
greg
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oh in that case, i'd say you can safely ignore those screens :)
B
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Greg, ? Ok, thanks for the clarification. ? Then, once you convince yourself that the DEC balance is pretty even (as suggested by another responder), I suggest you inspect the couplings motor and shaft of the worm gear. If those slip you might see this kind of behavior. ? I never use TVC, by the way, but yes, it should effect what happens when the handset buttons are pressed. Try setting it to zero. ? Tightening the clutch should have little effect on the gear mesh, unless somebody has put a wave/spring washer in the wrong place! Or it is way too loose. ? Mark C.
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Thanks, Mark,
I got bored watching the worm spin back and forth. I am still not sure what I am looking for, but the difference in the indicated servo values makes me wonder. Its not really like its winding up some backlash... looks more like something further upstream. Here is why... when the servos kick in there is a reasonable flutter of values up and down as the thing turns. But if I hit a key and it doesn't respond, there is no indication that there is anything more than a blip that goes to the motor. I think I am going to post this over to the Gemini group and if that doesnt work out maybe its time to call Losmandy. After all, I have only had this head for eight months and bought it new.
greg
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Greg, ? If you bought it new 8 months ago the first thing you should do is call Losmandy. They can walk you through it much better than going back and forth in Yahoogroup, as useful as these things are. ? Best Wishes, ? Mark C.
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Greg,?
Something easy to try:
Compare the DEC response using the virtual handbox provided in Gemini.net to the physical handbox.
You must be sure the "slew setting" of both are set to the same motion speed (guiding, centering, or slewing).? I think allows you to set up the handbox speed too...
I am thinking....: If the handbox has a sticky up arrow button then it is a handbox problem.? If both Gemini.net and handbox behave the same, it is a worm mesh problem. ?
Best, Michael?
On Aug 30, 2017 19:03, "'Mark Christensen' mjcw500@... [Losmandy_users]" < Losmandy_users@...> wrote:
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Greg, ? If you bought it new 8 months ago the first thing you should do is call Losmandy. They can walk you through it much better than going back and forth in Yahoogroup, as useful as these things are. ? Best Wishes, ? Mark C.
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Thanks, Michael.
That was my first thought... but the behavior is uniform regardless of the source of command input. And I did investigate the worm mesh. It is very binary in that on command it either moves or it doesnt. And when it doesnt there is no indication that the motors are straining against something. In fact, there is no indication that the motor is being powered at all. So I have turned to looking at it as a software/electronics issue rather than mechanical or traditional 'user error on device'. The RA axis exhibits none of this.
g
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Good reply.
You can also switch the cable output between DEC and RA too, and determine if the problem is in the DEC motor etc. ?vs the Gemini unit. ?
Then you can get down to the possibility that the worm coupling may be loose (check those setscrews!)
Best, Michael?
On Sep 1, 2017 06:00, " glatiak@... [Losmandy_users]" < Losmandy_users@...> wrote:
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Thanks, Michael.
That was my first thought... but the behavior is uniform regardless of the source of command input. And I did investigate the worm mesh. It is very binary in that on command it either moves or it doesnt. And when it doesnt there is no indication that the motors are straining against something. In fact, there is no indication that the motor is being powered at all. So I have turned to looking at it as a software/electronics issue rather than mechanical or traditional 'user error on device'. The RA axis exhibits none of this.
g
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Michael Herman