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LX90 GPS Slew Times

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#1 epenna

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Posted 06 October 2019 - 08:07 PM

I have a LX 90 GPS. I recently calibrated the motors and trained the drives, but it has not helped me with this problem: 

 

During Goto, once the scope decelerates from fast-slew, it takes roughly 70 second to find the object and beep. 

 

Is this normal? Is that just how long it takes, or is there something wrong?

 

Thanks, 

E
 



#2 sg6

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Posted 07 October 2019 - 11:27 AM

Seems a bit long, I assume you have timed it as you give a value.

Is 70 from the start of the fast slew or from when? Just to get an idea of the detail.

Whichever it seems long.

 

If from start of slew then check the Max Slew Rate, may be lowish to reduce noise. Just thinking it could be at say 5 or 6 and 8 could improve.

 

Unsure of the detail of the centering action. But the Meades I have met usually take around 15-20 seconds - 70mm to 14" Meades. The fine end bit being quite small say 5-8 seconds.

 

There is a crazy option: Slew rate is set low, scope predicts how long to slew for at full speed, slews for that time but as slew is set to slow is say half way there, then completes at the slow fine rate hence taking a long time.

As said crazy but ???



#3 Piet Le Roux

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Posted 07 October 2019 - 12:52 PM

I have a LX 90 GPS. I recently calibrated the motors and trained the drives, but it has not helped me with this problem: 

 

During Goto, once the scope decelerates from fast-slew, it takes roughly 70 second to find the object and beep. 

 

Is this normal? Is that just how long it takes, or is there something wrong?

 

Thanks, 

E

 

Check if you have "Quite Slew" selected : this would prevent it from slewing at max speed. 
 



#4 OzAndrewJ

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Posted 07 October 2019 - 02:23 PM

Gday SG6

 

Slew rate is set low, scope predicts how long to slew for at full speed, slews for that time but as slew is set to slow is say half way there, then completes at the slow fine rate hence taking a long time.

Nor quite true, it has no concept of time

It slews at full speed til a set distance from home, then starts to ramp down as it gets closer.

Once within a set radius of target, it stops, recalcs position and does a second slew to get even closer.

 

Andrew Johansen Melbourne Australia


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#5 sg6

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Posted 08 October 2019 - 03:53 AM

Gday SG6

Nor quite true, it has no concept of time

It slews at full speed til a set distance from home, then starts to ramp down as it gets closer.

Once within a set radius of target, it stops, recalcs position and does a second slew to get even closer.

 

Andrew Johansen Melbourne Australia

It was just a thought, met so much software in my time that it occurred as a possibility. Would not make sense but sense and software do not always go hand in hand.

 

The thought process was that it could  "Slew for 10 seconds, then slew at fine (slow)."

If 10 sec was still a long way off then the slow bit took longer.



#6 Piet Le Roux

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Posted 08 October 2019 - 03:56 AM

Gday SG6

Nor quite true, it has no concept of time

It slews at full speed til a set distance from home, then starts to ramp down as it gets closer.

Once within a set radius of target, it stops, recalcs position and does a second slew to get even closer.

 

Andrew Johansen Melbourne Australia

 

Unless "Quite Slew" is selected, then it would newer slew at full speed.



#7 OzAndrewJ

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Posted 08 October 2019 - 04:00 AM

Gday SG6

Its all a game, as at full speed, the slew speed is based on the supply voltage, it is not "controlled"

At the end of the day, the basic firmware simply uses hardcoded distance from target values  to set speed, it has no concept of "time"

 

Andrew Johansen Melbourne Australia



#8 epenna

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Posted 08 October 2019 - 11:43 PM

Thanks for the feedback... for clarification:

 

I have the LX90 plugged into an outlet, so the voltage is steady and high. 

 

I do not have it on quiet slew. I hit the goto button, and it gotos fast enough to make make noise for as along as it takes to get close to the object... then it slews too slowly to make noise for about 60-70 seconds before it beeps. 

 



#9 Levant

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Posted 03 December 2019 - 04:28 PM

Hi Ranger 4, 

Please make sure that you have you tightened the both two axis screws because it will take excessive time to move the scope to desired point if those 2 screws are left loose.

Levent



#10 M57Guy

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Posted 10 December 2019 - 09:58 PM

70 seconds sounds like a lot of thumb twiddling to me, but my LX-90 is pre-GPS, and I've never measured slew times. 

I know my dad's LX-200 GPS takes what seems like forever to complete a slew, so maybe that's the nature of having GPS in control.

 

How is the accuracy after the slew?

 

As others have suggested, "quiet slew" mode sounds like obvious culprit but you've confirmed that's not the issue.

And, I'm guessing this isn't a "high precision" issue either?

 

How were the slew time before you calibrated motors and trained the drives?

 

My last though would be your power supply, but you said you're plugged into an outlet.

Is is powered by a long (say 100') extension cord?



#11 Piet Le Roux

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Posted 11 December 2019 - 01:46 AM

I did a mock two star alignment with my LX90ACF GPS and it picked Arcturus and Rigel Kent. After it had stopped at Rigel Kent I let it slew to Arcturus and timed it : about 35 seconds. I when let it slew back to Rigel Kent and it was about 35 seconds again. The GPS plays no part in the slew process, and it does not control anything it just enters your coordinates and time. The only things that I think could make a difference is your supply voltage and firmware version. saying that " I have the LX90 plugged into an outlet, so the voltage is steady and high." is not a good assumption : It should not be higher than 13.8V and should not drop bellow 12V under load, so it should be well regulated like a good lead-acid battery or voltage controlled lithium 12V power pack. The latest firmware that you could use on the LX90 is A4S4, I am using patched firmware A4s4. 

 

PS: If you have selected "cord Wrap"  it may in some instances "take the long way" to a object to prevent cord wrap. 

 

PPS: with "Quiet Slew" selected my Arcturus to Rigel Kent time was coincidentally 74 seconds !?   


Edited by Piet Le Roux, 11 December 2019 - 09:52 AM.


#12 epenna

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Posted 20 June 2021 - 02:00 PM

Hi all,

 

I wanted to bump this thread because I am using this scope again. Below is the OP, and some clarifications, as well as answers to questions in the thread:

 

I have a LX 90 GPS. I recently calibrated the motors and trained the drives, but it has not helped me with this problem: 

 

During Goto, once the scope decelerates from fast-slew, it takes roughly 70 second to find the object and beep. 

 

Is this normal? Is that just how long it takes, or is there something wrong?

 

Thanks, 

E
 

 

To Clarify: the scope races, fast and loud, to within a degree or two of the object... after that, it takes about 70 seconds to finally land on the object and beep. During that time, there seems to be a combination of slight movements (noticeable only in the eyepiece) and long pauses, an a final move, before it finally locks on. 

 

Quiet Slew is off

 

High Precision is off

 

Cord Wrap is off

 

50ft Extension cord to the transformer... have not tested the voltage, but it seems that voltage would be much less of an issue during the slower movements, right?

 

Firmware was last updated in Oct. 2019.

 

Accuracy is pretty good! Just takes a while. Maybe this is normal, but it seems odd. 

 

Any advice is appreciated. Thanks,

 

E



#13 Piet Le Roux

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Posted 21 June 2021 - 02:24 AM

Good day E,

You mention that you have a 50ft(15,25M) extension cord, is this on the DC or AC side? If it is on the AC side it is not a problem but on the 12V DC side you would have a big voltage drop when it is drawing current. The only way to be sure is to monitor the voltage while the mount is doing a goto. I have recently been informed by Andrew Johansen that with LX90 the voltage to the LED's are regulated so the motor calibration serves no purpose except to confirm that the drive works and for the controller to be compatible with other mounts. What firmware version does it display when the controller boot ?

PS what size LX90 have you got? 8" 10" or 12"


Edited by Piet Le Roux, 21 June 2021 - 08:26 AM.


#14 epenna

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Posted 24 June 2021 - 05:45 PM

Hey Piet,

 

The extension cord is AC.

 

It is an 8".

 

Current update is 4.3EG.

 

What do you think?

 

Thanks, 

E



#15 michael8554

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Posted 25 June 2021 - 03:58 AM

Never heard of this before.

 

Is it in Dec, or RA, or both ?

 

Try a GOTO that only moves in Dec, or in RA.

 

Same result ?



#16 epenna

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Posted 25 June 2021 - 07:04 PM

Hey Michael,

 

I will test it and get back to you. 

 

I am using mount in alt/az. btw. 

 

How long does your scope take to find the target after the initial fast slew?

E



#17 michael8554

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Posted 26 June 2021 - 06:07 AM

Okay, a slew in Alt.

 

Maybe pick two targets due south above each other for the Alt test.

 

After the fast slew has ended, mime takes takes 5 to 7 seconds to the beep.



#18 Mitchell M.

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Posted 26 June 2021 - 08:59 AM

After the fast slew has ended, mime takes takes 5 to 7 seconds to the beep.

Sounds about right with my Meade 8" lx90gps, 5 to 7 seconds, pretty consistent.



#19 epenna

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Posted 30 June 2021 - 10:26 AM

Mitchell & Michael,

 

Wow! Five to seven seconds sounds like heaven. I'm under a bit of light pollution, so I tend to target hop. 

 

I got to figure out what's going on with this scope. 

E



#20 epenna

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Posted 10 July 2021 - 06:26 PM

Okay... here is some more weirdness... have yet to get the scope out under the stars, but did some indoor testing:

 

When I unplugged the LNT module (which is aftermarket, not the original, and take a little shimming to sit right)

 

And I get 15-30 second beep times for objects below 45 degrees of elevation. Above that, 70 seconds. 

 

I have a sense that the time increases the higher the elevation, but did not yet undertake a thorough testing of the notion. 

 

I replug the LNT, and it's 70 seconds regardless of elevation. 

 

E



#21 epenna

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Posted 12 July 2021 - 12:42 PM

After observing last night, I can say the issue is definitely in the ALT system. 

 

All the extra time taken is the scope moving in ALT and pausing. Sometime it would pass the target, pause, and then back up to the target. 

 

I did have a moment last night where -- having been a star hopper for most of my observing -- it struck me what amazing telescope the LX90 is, and that perhaps I am getting too hung up on saving thirty seconds per goto. 


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#22 michael8554

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Posted 13 July 2021 - 08:54 AM

Shouldn't make that much difference, but have you Trained Drives ?



#23 epenna

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Posted 13 July 2021 - 01:07 PM

I trained the drives about a year ago... after the last update to the handset. I was planning to do it again next time I can get the scope out of my backyard (No targets distant enough for training from my backyard.) Motors and sensors are calibrated.

 

But it seems to me that the problem is on the software side, not the drive side, since the scope will actually goto past the target and then return to it. The accuracy is very good... just some sort of lag between the encoders and the dsc software? 



#24 OzAndrewJ

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Posted 13 July 2021 - 04:36 PM

Gday epenna

Your symptoms could be software

Can you go into the edit screen ( or use my PEC editor )

and read back what the drive train values are.

( Also read back the lash "percentages" )

The mount uses this value on reversing to allow for gear lash.

If it is massively wrong, it can result in under or overshoots on reversing.

If it is very large, and the lash percentage is low,

then it takes one second per 7.5 arcsecs of lash to take it up ( at sidereal )

 

Andrew Johansen Melbourne Australia



#25 epenna

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Posted 17 July 2021 - 11:24 AM

Hey Andrew,

 

Thanks for the suggestion. Here's what I found, if I understood your post correctly:

 

AZ/RA  ratio:     -02.75075

ALT/DEC ratio: +02.75075

 

AZ/RA %:     10

ALT/DEC %: 10

 

What do you think?

 

E




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