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RA Motor Guiding Issue


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Hi,

Last night I was planning to get some data on the Whirlpool Galaxy, and I decided to use the PHD 2 Drift Align tool to get everything set up the EQ5. Unfortunately, there seems to be a serious issue with PHD's communication with the RA motor. The Right Ascension motor tracks at the correct speed and without any odd noises while guiding is not happening, but when PHD sends a guide pulse to it, nothing happens, and the motor seems to stop or run erratically without any obedience to the program's commands. Essentially, it ends up with something like this; with the RA motor speed remaining at 0.00 or dropping from around 0.12 to 0.00. Although the image below shows about 20 seconds of the issue, I have run like it for around a minute to see if the motor picked up, and it didn't. Once or twice, I did manage to get the guiding working fine, with health oscillation speeds of around 0.20-0.30; but these occasions were very rare.

phd1.thumb.PNG.58421b4c18e7fe01f189c6dce4cb50a3.PNG

 

I've thought through the problem, and these are the things I know aren't causing issues:
 

1. PHD is communicating with the mount properly. I know this for 2 reasons. a) The green light on the motor handset blinks on every time PHD sends a guide pulse, showing it is reaching the handset.
b ) Manual guide works *half* of the time, once backlash has cleared, indicating connection.

2. The power source makes no difference. I tried the rechargeable D cells as well as a mains adapter, and the issue remained the same.

3. The handset buttons still communicate fine with the motors.

4. The guidecam (ZWO ASI) is working fine, images are coming through at ordinary speed from it.

5. The cables all appear to be working fine and are properly connected.

The best conclusion I can reach is that somewhere between the ST4 port and motor cable ports in the handset there must be a loose connection or damaged/dysfunctional part. Guide pulse signals are reaching the handset, yet the motors don't react unless the handset buttons are pressed. For some reason, the manual guide tool seems to be more successful in making the motors jump than the computer guiding; I don't understand how at all. I am not entirely sure if Dec is affected, but so far the main issue seems to be RA.

A side issue, which may be related to this, occurred a few days ago. I was trying to get an image of the sun perfectly centred in the FOV, and I was using the +16x motor adjustment speed on the handset. Occasionally, when I pressed the button for a smaller adjustment, the motor would lag and then continue to run for around 10 seconds, throwing the sun right out of the view in some cases.

This is a quick diagram I made, it should explain the setup.

5adb58e2c8430_SetupDiagram.thumb.PNG.25335447069da588bd681b1972ef7457.PNG

John

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Hi John,

Your setup looks fine. Looking at your diagram and reading your description I would suspect the ST4 cable or mount settings in the hand controller.

What is your mount tracking set as? Is it actually North/South hemisphere tracking and is it set for the right hemisphere?

what are your guide rates set as? At least 50% sideral?

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8 minutes ago, MarsG76 said:

To add to above, you're getting led flashes that PHD is communicating with the mout, but perhaps only the RA pin/component of the ST4 connected cable is faulty.

Or the ST4 cable is a straight-through pin-to-pin when it should be a changeover cable, or vice-versa...

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2 minutes ago, Oddsocks said:

Or the ST4 cable is a straight-through pin-to-pin when it should be a changeover cable, or vice-versa...

True, convectively it might seem like it's fine but electronically its delivering guide pulses to the wrong inputs.

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Hi,

I am tracking with Northern Hemisphere, that was one of the first things I checked when things started going wrong. Yes, the mount is set to 0.5 times sidereal, the other options are 16 and 2 times, neither of which are particularly suited to guiding from what ive found. I do have a spare "ST4" cable from an old Ethernet-phone cable adapter thing, I could try using that. However, as you say the fact that the pulses are reaching the light not the motor could be a fault in the "box" not the cable.

P.S. the ST4 cable I'm using right now is the one which came with the ASI guidecam, so its unlikely there is an issue there. I have been using this setup for almost a year, and as far as i can remember the problems started around the new year.

John

Edited by JohnSadlerAstro
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Hi,

Thinking about it, as Venus will be up this evening, I could try an extremely rough polar alignment and then try to get guiding on the planet as it becomes visible shortly after sunset. (We have rain starting around 8 o clock) Although PHD wont be able to guide properly, it should show up whether changing the ST4 cable makes the motor respond to the program? Do you reckon this will work?

John

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Hi John

No mention of Calibrating PHD2 ?

If you can successfully Calibrate, then PHD2 and your cable are working fine.

Using an old Calibration allows you to get into Drift Align, but PHD2 doesn't know that your cable may be faulty, but doing a new Calibration will.

Your PHD2 grab shows that big RA pulses are being sent, right up to the Max RA level, and PHD2 is complaining 'cos nothing is happening RA wise.

Same with PHD2 Manual Guide. If you set to 5000ms then you should see big jumps in RA, after backlash is cleared.

You could check for an intermittant ST4 cable by Calibrating at the Drift Align Azimuth position, if successful try West and East moves with Manual Guide, and again if successful make a big slew and try Manual Guide again to see if the connection has gone.

Michael

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  • 3 months later...

Hi,

Sorry to bring back an old thread, but the same issue is happening again.

I tried to resolve it by using a different ST4, and it seemed to be ok for a bit. I guessed the mount needed a clean and tune-up, which I did a month ago. So far, tracking has been really good quality, with nice "snappy" motor moves at 16x and 2x. However, guiding is a complete disaster. The RA mostly goes to oscillation of 0.00, although I can hear "movements" and the green light on the handset flashes, yet nothing seems to be happening. I tried drift align, and it was just complete nonsense, I don't know if the Dec was even moving most of the time, I'm really getting frustrated by the problem now. I haven't got any proper Deep Sky Imaging in for probably 6 months now.

I just spent £££ on getting a nice visual setup, thinking I could use it while the other one was running. Probably a mistake, as I will now need to throw more money at the mount. ? And even if I do, what happens if it doenst resolve the problem and the same thing comes back again? :confused: 

My setup is still in this form, with 4x1.2v rechargeable D cells. THe slightly lower voltage doesn't seem to make any difference. I have tried using a power adapter instead, and no change. I also tried manual guide and it seems to work fine. Although its all so confusing im not 100% sure.

901354596_SetupDiagram.thumb.PNG.c7e0309e6174b09c10e9d78ef2a7fa11.PNG

These are the guiding logs from last night:

PHD2_DebugLog_2018-08-16_215714.txt

PHD2_DebugLog_2018-08-16_222808.txt

PHD2_DebugLog_2018-08-16_225255.txt

PHD2_GuideLog_2018-08-16_215714.txt

PHD2_GuideLog_2018-08-16_222808.txt

PHD2_GuideLog_2018-08-16_225255.txt

I don't want this to sound like a sob story, but you know those times when you just look at something and cant face it. ?

Does anyone know what might be causing the issue? I almost need someone to look at the mount irl and see if they can work it out.

John

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Hi,

Thanks for the suggestions, that's really interesting--I never realized balance was so critical. Thinking about it, I didnt have the DSLR and CC attached at the time, so the scope was probably mirror end biased. I don't know if this could have been causing it?

John

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4 hours ago, Owmuchonomy said:

Smells like a poor calibration and wrong duration setting.  How was your calibration?  Did you achieve at least 15 steps?  Balance is very important too but I suspect the software settings.

Hi,

This is the calibration:

image.png.f5be7afaed0bb5ecf393a1a60192604d.png

So to adjust the duration, that's the field at the bottom of the screen along with aggressiveness, etc? I'll uninstall PHD so I can wipe all of the current settings etc and get a clean sheet to put everything into.

Would it help to change up one step in the motor speed, to 2x and reduce the durations to say 250? That would in theory clear out the backlash faster?

John

Edited by JohnSadlerAstro
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