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8SE alignment driving me crazy

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#51 philippe44

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Posted 12 September 2013 - 09:32 AM

It looks as if Phillipe is further North, I don't think he ever said where he was.

Phillipe, can you give your approximate location please. To the nearest degree will do and won't compromise your security.

There was talk about changing motors and/or encoders. Where did these come from and are you sure they are the right ones?
Chris


Thanks Chris - I'll do the tests later today when I get back home. With regard to location, no problem : I'm in Vancouver, BC, Canada. The motor / encoder discussion was at the beginning : this scope, although new, had a failing Azm encoder (no response 16, just moving slowly w/o stopping when pressing any Azm button - started with jerky Azm rotation, then died). I checked that it was just the IR rx/tx that sits on top of the motor, but had to replace the whole motor assembly. I bought the part from Celestron directly

Philippe

#52 philippe44

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Posted 12 September 2013 - 10:01 AM

Chris
Philippe
Can you confirm the amount and direction of the error? In essence, is it always short or long on the target and is it in proportion to the angle traveled to get to the target. By that I mean, some error when the target is X degrees in error for some angular change and 2X in error for twice the angular change. Using the idea from Chris, do you see 90° of change in the AL angular readout when going from horizontal to vertical. Your mount may have the wrong gearbox in the AL assembly. This test alone will determine if the gear ratio is correct.

http://www.celestron...tar-6-8-se.html


Will do Chris test, but I think it seems to overshoot in general. The part I replaced was the Azm motor using the SKU NEXF6-01 bought from Celestron. And Azm behaves very well. I did not touch the Alt motor nor the assembly

#53 Arctic_Eddie

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Posted 12 September 2013 - 10:35 AM

This is a really long shot but could the two motor cables be plugged into the wrong controller board? Can you confirm that the left/right slew buttons cause the mount to move only in AZ.

#54 philippe44

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Posted 12 September 2013 - 11:04 AM

This is a really long shot but could the two motor cables be plugged into the wrong controller board? Can you confirm that the left/right slew buttons cause the mount to move only in AZ.


Yes, I can confirm that the wiring is correct

#55 Arctic_Eddie

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Posted 12 September 2013 - 11:14 AM

Your 90° test later today will be very helpful. If you level the OTA before turning on power then the AL reading will be 0.00. Elevating to vertical should make the reading very close to 90.00°.

#56 philippe44

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Posted 12 September 2013 - 11:51 AM

Hi Philippe,

I've been trying to recap a little on what has been said and also to form a picture of your particular night sky and timings but first, a couple of issues from the foregoing posts which perhaps you can confirm/clarify ?

1) Balance. At one stage you state that your 8SE's OTA is fairly well balanced; maybe a little backend heavy. The statement suggests that you are looking for good balance which, in fact, should not be the case.

The 'scope's OTA should have a significant imbalance (but by no means severe), in order to put a load on the gears. Thus the OTA should be placed either to provide fore-end heaviness, (when fully loaded with all usual accessories), or rear end. Experimentation, (and I know you've already done this), should then be resumed to determine whether a Positive or Negative Alt. GoTo approach is better suited to this imbalance.

I DO APPRECIATE YOU'VE ALREADY BEEN "THERE" ! :bow:

It looks as if you are currently using a Negative Altitude GoTo Approach setting. Can you confirm this just for the record ?

2) For an object to move out of the field of view of a 24mm EP in 15-30 minutes, mediocre to poor tracking is indicated. This may be attributable to poor anti-backlash settings and/or the phenomena I described in that article I wrote for CN in 2007; (see above).

Can I therefore ask you describe in some detail, how you set the anti-backlash for your 8SE ?

Now to that model of your particular sky.

I have tried to model this using Stellarium's planetarium on the current evening sky as seen from Los Angeles, (owing to the fact that I don't know where you live specifically in Ca. but on the basis that the Los Angeles sky will differ very little if at all from yours).

Thus, and correct me please if I'm totally in error, I estimate the following:

1) Viewing Window: Approximately (dusk to dawn) 8:00pm to 6:00am PDT.

2) At ca. 8:00pm Duhbe lies at ca. Alt. 19-20 degs. just west of north and reaches its lowest Alt. point (ca.6 degs. at ca. 12:30 am.(due north).

3) It then proceeds to climb in the sky reaching its highest visible point, (26 degs). at dawn around 6:00am.

If this is a reasonably accurate model with which you can agree, may I ask at what time were you making your observations when you mentioned that, when slewing to Dubhe, your OTA finished its slew, some 15-20 degs. below Dubhe. It sounds as if it was either virtually pointing to the horizon or below it considering the 15-20 degs "off" that you originally mentioned.

Also, from what you have described and if my viewing window is correct, you seem to have targetted objects which lie west of the north/south meridian line. Have you yet tried objects to the east of the line and if so, with what effect ?

Please don't take it that I'm calling into doubt anything you have stated, Philippe, I'm just trying to obtain a more complete picture of what is going on, hopefully for all of us involved here who are trying to help solve this enigma.

Best regards,
Tel


Hi Tel - I'm in Vancouver, BC, Canada, so I'm close to what you see but Dubhe still is much higher (I think 25° @ 10 pm). So yes, the error in pointing Dubhe make the pointing close to the horizon, but not to a point that is below. I made these tests between 8:30-10 pm. I've not tried a lot the eastern
meridian because it is very blocked from my site, but I'll try to find a solution tonight.

About balance, in the picture I've added, you might see a black sticker which is the balance point of my OTA. The OTA is on the mount on purpose not exactly at that balance point, but a bit further left and in fact I'm now doing the tests with Pos-Pos approach and the scope being front heavy a bit (I changed that to try something different). My understanding of the process, and maybe I got that wrong, is that the approach should finish "against" the load of the OTA so that OTA "weights" on the gears for better lock. So my gotos finish right and up (as well as my alignments).

For the backlash setting, once I've done a fake alignement, I'm pointing to anything small I can clearly view, I set speed to 4 and then set a Alt backlash Pos and Neg at 10. Then moving the Alt, changing Pos and Neg values to the max value I can have before the start or stop shows jerkyness : stop is "dead stop" and start, even if delayed, is smooth. Is this correct ?

I'm not taking any "offense" of your suggestion and I appreciate a lot the help of everybody here, especially yours. This would not be the first time I do silly mistakes and will certainly not be the last time, hence I'm asking for collective wisdom. I'm experienced in electronics & embedded sw (basically this is my job) but I'm still a very green beginner in astronomy. In any domain, there is always something to learn from the others !


Thanks a lot

Philippe

#57 philippe44

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Posted 12 September 2013 - 09:54 PM

And the reading is ... 72° instead of 90° ! Thanks so much Chris for the suggestion. BTW, I check that a full Azm revolution is 360°. So at least I'm not totally crazy, there is something wrong with the Alt control :jump:

[edit #1] What's interesting is that it looks much more like a calibration problem rather than missed pulses : going from horizontal to vertical shows 72° all the time and going back to horizontal brings it back to 0° - at least this is consistent with the behavior I was describing earlier when repeating a goto to the same star again and again.

[edit #2] Looking at the coding wheel, it was far away from th IR unit, so I adjusted it a bit, did not change anything. I also did a MC motor update (Alt), did not change anything. I really think that this is my second bad encoder on the same scope - maybe a faulty batch. But I'm hesitating between changing the motor, the board on the mount (calibration parameters stored there - I mean there has to be a parameter that says X pulses = Y ° of Alt and this cannot be in the HC) or could it be a problem with the gears themselves (but nothing looks strange there) ... :confused:

#58 Tel

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Posted 13 September 2013 - 05:41 AM

Hi Philippe,

It looks very much as if Chris has identified the positional anomaly. :bow::bow:

It now remains to determine its actual source.

Given though that the angular distance between the horizontal and the vertical produces a constant 72 degrees and not the expected 90 degrees thus "undershooting" the true value, how can one explain that, while Dubhe is "undershot" in making a GoTo to it, the other stars/objects you have mentioned,(e.g.Vega, Altair, M13) are overshot" ?

In making a GoTo to, (for example), Vega: knowing that on completion of the slew the OTA will "miss", might it be worth recording what the HC has to say in terms of its "Get Axis Position" and also its recorded "Get RA/Dec" for cross reference purposes.

Is it also worth making a GoTo to say, Vega, via the "GoTo RA/Dec." function rather than via "Named Star" ?

I don't know if such additional information will help but......

As to the problem lying solely within the gears, one aspect might point to this if you recall the poor tracking of your 'scope which in turn, suggests excessive backlash despite the fact that you seem to have corrected for this successfully.

I can't imagine though, that backlash would account for the 72 deg. / 90 deg. anomaly. The difference is far too great. It's almost as if the clutch is indeed slipping but this aspect has already been covered.

One other thought: Try removing the OTA and recording the angle obtained between the horizontal and the vertical. Does it still record 72 degrees instead of 90 ?

I just think that while the above doesn't immediately solve the problem, it may serve to broaden the picture ..... :idea:

Best regards,
Tel


Note: As I'm sure you know, you can obtain the Alt./Az. position for any given time and the RA/Dec. co-ordinates for any object from Stellarium or any other planetarium.

#59 cn register 5

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Posted 13 September 2013 - 06:34 AM

It's nice to be right occasionally :)

Did you get this mount second hand? Could someone have been adjusting or replacing things in the alt motor or drive? Maybe there's two motors for these that fit but have different gearing. Perhaps a different encoder wheel with the wrong number of lines on it.

There isn't any way to change the gearing in the firmware but maybe the motor control firmware for a different version of mount would help. I see SE4, SE6, and iSeries MC firmware.

I suggest contacting Celestron. They should be more aware of what is going on here than we are. If there are serial numbers on the motors these will be of interest to them.

Chris

PS I see it was new. Definitely a problem for your dealer. I wouldn't have messed around with the azm motor either.
C


#60 Arctic_Eddie

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Posted 13 September 2013 - 06:39 AM

Overshoot is expected as the mount actually goes 90° when it thinks it was only 72°.

You could swap encoders to see if they're different. Maybe the problem is that the AL motor has the wrong encoder. That may be the way they correct for different final gear sizes while using the same gearbox.

#61 philippe44

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Posted 13 September 2013 - 08:21 AM

Hi Philippe,

Given though that the angular distance between the horizontal and the vertical produces a constant 72 degrees and not the expected 90 degrees thus "undershooting" the true value, how can one explain that, while Dubhe is "undershot" in making a GoTo to it, the other stars/objects you have mentioned,(e.g.Vega, Altair, M13) are overshot"

As to the problem lying solely within the gears, one aspect might point to this if you recall the poor tracking of your 'scope which in turn, suggests excessive backlash despite the fact that you seem to have corrected for this successfully.

One other thought: Try removing the OTA and recording the angle obtained between the horizontal and the vertical. Does it still record 72 degrees instead of 90 ?


I did try with and without the OTA and go the same 72° result. About the overshoot and undershoot, sorry I might not have explained that correctly :I meant going to Dubhe it goes under and going to M13 it goes above. But for me this is consistent with the mount traveling more than the encoder reports, as the alignment stars are below M13 and above Dubhe - no ?

[edit] I did swap the encoders this morning and got the same result : 90° of Alt reads as 72°, while the full circle on Azm reads to 360°, so not en encoder problem. It really really feels to me like a a wrong firmware setting (parameter) of the pulse/angle ratio for the Alt motor

#62 Arctic_Eddie

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Posted 13 September 2013 - 12:33 PM

The possibilities are dwindling. Looks like firmware and wrong gearbox are all that's left. Never heard of a gearbox problem so that leaves firmware. Maybe it's got the MC code for a GEM mount with a different gear ratio.

#63 philippe44

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Posted 13 September 2013 - 01:04 PM

The possibilities are dwindling. Looks like firmware and wrong gearbox are all that's left. Never heard of a gearbox problem so that leaves firmware. Maybe it's got the MC code for a GEM mount with a different gear ratio.


Fully agreed - I did re-update the MC firmware still w/o success. The problem is that it might not have updated such NV paramaters like gear ratio (that I know from my experience of embedded SW developer, FW udapte usually does not update NV paramaters, unless absolutely needed)

#64 Arctic_Eddie

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Posted 13 September 2013 - 01:50 PM

What versions did you use? I remember a note someplace that the MC and HC had to be done in a particular order. It might be worth trying an earlier version that's known to be good.

#65 philippe44

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Posted 13 September 2013 - 02:20 PM

5.14

#66 Arctic_Eddie

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Posted 13 September 2013 - 02:38 PM

Confirm that the HC version is 4.18. It plays well with MC5.14. Be sure you're using the MC and HC updater and not the newer one for the HC Plus hand sets.

#67 Arctic_Eddie

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Posted 13 September 2013 - 03:32 PM

Found this info today. With all the CPR values available, they could easily use a different one to account for gearbox changes.

http://www.cloudynig...6063248/Main...

http://www.usdigital...CFatj7AodW38AkQ

#68 philippe44

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Posted 13 September 2013 - 07:48 PM

Confirm that the HC version is 4.18. It plays well with MC5.14. Be sure you're using the MC and HC updater and not the newer one for the HC Plus hand sets.


Thanks for the links !
I have a HC+, so the FW is 5.21.2336

#69 Arctic_Eddie

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Posted 14 September 2013 - 05:29 AM

Are you using the updater for that version of controller? The new one is Celestron Firmware Manager (CFM) v.1.0.2100. I would expect, as you did, that the gear ratios would be taken care of in the motor control source code as:

#define PPDG ??? // Pulses per degree

http://www.celestron...a=viewdownlo...,7

Also, MCLewis is a good source of info on this subject.

#70 cn register 5

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Posted 14 September 2013 - 05:51 AM

Which MC firmware type?

I can see:
Advanced Series 5.14 (latest 5.20)
CGE 5.14 (latest 5.20)
CPC 5.14
SE4 5.14 (latest 5.20)
SE6 5.14
SLT 5.14 (latest 5.18)

This is using MCUpdate v2.2.5 and clicking on the "download from the web" button.

The wrong firmware type could explain this if the gearing between models is different. I'm not sure how much protection there is, if any, from installing the wrong firmware.

I think that the MC firmware update program needs to be used and I think that the NS+ HC will work with it.

AFAIK the same boards are used in a variety of mounts, with the difference being the driver firmware and that some don't have connectors for limit switches and the PEC sensor.

But really this is way beyond what you as a user should be tackling. What is your dealer doing about it?

Chris

#71 Arctic_Eddie

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Posted 14 September 2013 - 06:00 AM

I thought the HC+ controller required the CFM updater and only with specific FW versions. With this gear ratio problem, I almost think his mount is using a GEM FW where a different gear set is expected.

#72 philippe44

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Posted 14 September 2013 - 07:32 AM

Yes, I'm using CFM, not HCupdate. I've tried to install a wrong firmware (just to see) and it refused so there is a safety mechanism. MCupdate identifies it as a 6SE, which is normal. My dealer says go to celestron. This is very strange story indeed because when I bought this telescope from them (would not boot and was saying 'wrong firmware'). I had to bring back the initial mount that was not working at all. They exchanged it with this one, so I suspect something happened on their side ... everything was new (normally)
I absolutely did not mess with the FW or these units before - this is the exact story

#73 cn register 5

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Posted 14 September 2013 - 09:27 AM

Don't you have consumer protection laws in Canada? Can the dealer really sell you a faulty mount and abandon you? This mount came with a two year guarantee didn't it?

Celestron will quite reasonably want the mount back so they can find out what has happened. It's difficult to see how it could be the firmware but it could be a motor that was intended for a different mount.

The other person who might be able to help is Andre Paquette http://www.astrogeeks.com/ . He used to be the Celestron developer and lives in Canada. He may be able to help about what's happening here or may be able to update something.

Chris

#74 mclewis1

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Posted 14 September 2013 - 10:22 AM

Philippe,

To help me understand ...

You first bought a 6SE that did not work.
The dealer replaced the mount for that first 6SE.
Is this second mount the one that said "wrong firmware" or is that error message from the first mount?

Your dealer should certainly be taking care of you ... you have a failure out of the box and not a warranty repair for a scope that's been in use for a while.

#75 Arctic_Eddie

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Posted 14 September 2013 - 12:01 PM

Can you look at the encoder specs at USDigital.com to see if the one you have is correct? The other link in my same post said the PPR is 256. It's starting look like your dealer may have repaired the second mount with the wrong parts. Also, you may have gotten the first mount back with the wrong parts. I don't think anyone on this forum has ever seen this kind of problem but you sure have our attention as to the cause and fix.






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