PHD2 Guide Log Suggestions HEQ5 Pro

[matt_baker]

I can't tell whether the spikes I'm getting in RA are periodic or random (excluding any dithering events)

Dec seems to be fine for the most part, although that too has spikes (Overcorrecting perhaps?)

Would be greatly appreciated if anyone can take a look at this guiding log and provide any suggestions

PHD2_GuideLog_2023-09-05_002312.txt

[matt_baker]

Just taken a look at the frequency analysis and there's a 1.2" spike at 122s. Looking at some other posts, they appear to have a spike at 13.6s and a smaller one at 120-122s.

Although I don't have a spike at 13-14s, is this to do with belt tension perhaps?

There's 9 teeth on the pulley so it makes sense for it to be happening at 122s

Not sure what the much larger spikes are at the end however

[michael8554]

Hi Matt

Overall guiding was good "RA = 0.63 arcsec,  Dec =  0.41 arcsec".

But the Peaks were "RA = 3.38 arcsec,  Dec = -2.17arcsec". 

1) The Calibration threw up a warning  "Last Cal Issue = Difference,"

Guide rates were measured to be "Norm rates RA = 10.9"/s,  Dec = 9.6"/s;"

Probably due to not clearing Dec Backlash before the Cal, PHD2 had to apply 7 steps before Dec started to move.

And see how the RA and Dec pulses are bunched up into pairs and triplets, possibly due to Stiction:

 

2) There are 2 arcsec spikes in Dec that might be due to Backlash.

The log shows  "Backlash comp = disabled, pulse = 932 ms"  ??

3) A few of the frequent RA spikes coincide with Dec spikes.

But most are random.

There aren't any significant fast spikes in the freq analysis, just the 122s one.

So reasons may be due to wind, stiction, cable snags - post a image of the setup ?

Michael

 

 

 

[matt_baker]

15 hours ago, michael8554 said:

Hi Matt

Overall guiding was good "RA = 0.63 arcsec,  Dec =  0.41 arcsec".

But the Peaks were "RA = 3.38 arcsec,  Dec = -2.17arcsec". 

1) The Calibration threw up a warning  "Last Cal Issue = Difference,"

Guide rates were measured to be "Norm rates RA = 10.9"/s,  Dec = 9.6"/s;"

Probably due to not clearing Dec Backlash before the Cal, PHD2 had to apply 7 steps before Dec started to move.

And see how the RA and Dec pulses are bunched up into pairs and triplets, possibly due to Stiction:

 

2) There are 2 arcsec spikes in Dec that might be due to Backlash.

The log shows  "Backlash comp = disabled, pulse = 932 ms"  ??

3) A few of the frequent RA spikes coincide with Dec spikes.

But most are random.

There aren't any significant fast spikes in the freq analysis, just the 122s one.

So reasons may be due to wind, stiction, cable snags - post a image of the setup ?

Michael

 

 

 

The setup itself has very bad cable management, I've never got round to properly sorting that out.

My power box is located on the side of the mount as I have pretty much no where on the OTA for it to go, as the RPi takes the only space. The cables have to be somewhat long to make sure there's no snagging and ends up ripping off. I make sure when setting up that throughout the whole motion of the mount, there no cables are snagging.

My only solution that I can think of is removing the finder scope from the dovetail and strap both the RPi and power box in its place. My concerns with this are by moving the finder scope back, my dovetail for the telescope won't have any more space to move up as it's already at the limit with the camera being so far back. The other issue is that the main power cable is rather dense and large. This may cause a lot of cable drag as it moves around with the telescope.

I've attached some photos of the setup (don't mind the mess)

Also attached the guide log from the night after the one sent previously. Guiding had to be paused for some of it due to the powerbox falling off. The adhesive decided to give up, so I sellotaped it down as a temp measure. One of the huge dec spikes was the powerbox falling off again, so don't mind that.

PHD2_GuideLog_2023-09-05_220434.txt

[michael8554]

Hi Matt

1) Gather all the cables linking equipment on the scope and attach to the scope.

Attach the rest in a smooth loop to the top of a tripod leg.

2) Cals were much better, less backlash in them, accepted by PHD2.

Still showing bunched steps, which is stiction that might have a bearing on the guiding results.

3) Dec Backlash Compensation is still Disabled ?

Which reminds me, if the mount or any software other than PHD2 has any sort of Backlash Compensation, this should be disabled to avoid confusing PHD2.

4) None of your logs show a Guide Assistant run.

This should be a daily operation after a good Cal.

It will suggest settings for that night's conditions, and measure the PA error (no worse than 5arcmins is good enough).

And occasionally tick the "Measure Backlash" box to get a Backlash Comp setting.

5)  For test purposes run the GA for a worm period, so that the mount's PE curve can be inspected.

6) How is the scope balanced ?

East-heavy might help to minimise the overshoots caused by stiction in RA.

Michael

[alacant]

On 13/09/2023 at 15:09, matt_baker said:

spikes I'm getting in RA

Hi

Remove the polarscope and cover plate and loosen the cone bearing at the base of RA, rotating the circular nut anticlockwise around, say, 1/10 of a turn at a time, until the axis swings freely. There are three grub screws which bear against the thread to lock it (yeah, I know). In between loosenings, give the ra shaft a gentle tap upwards and swing again before retightening.

HTH

 

Edited September 16, 2023 by alacant

[alacant]

42 minutes ago, michael8554 said:

 [...] stiction that might have a bearing

Love it 😀

Edited September 15, 2023 by alacant

[matt_baker]

5 hours ago, michael8554 said:

Hi Matt

1) Gather all the cables linking equipment on the scope and attach to the scope.

Attach the rest in a smooth loop to the top of a tripod leg.

2) Cals were much better, less backlash in them, accepted by PHD2.

Still showing bunched steps, which is stiction that might have a bearing on the guiding results.

3) Dec Backlash Compensation is still Disabled ?

Which reminds me, if the mount or any software other than PHD2 has any sort of Backlash Compensation, this should be disabled to avoid confusing PHD2.

4) None of your logs show a Guide Assistant run.

This should be a daily operation after a good Cal.

It will suggest settings for that night's conditions, and measure the PA error (no worse than 5arcmins is good enough).

And occasionally tick the "Measure Backlash" box to get a Backlash Comp setting.

5)  For test purposes run the GA for a worm period, so that the mount's PE curve can be inspected.

6) How is the scope balanced ?

East-heavy might help to minimise the overshoots caused by stiction in RA.

Michael

Hi Michael, this was just the guide log from the day after back on the 5th Sept so none of the changes you suggested were applied. Although I did make sure to nudge the mount north that time to cancel any backlash.

I'll make sure to run a long guide assistant and balance it slightly east heavy and see if that helps. I typically balance so nothing moves. I'll measure the backlash too and see what that says

[matt_baker]

13 hours ago, alacant said:

Hi

Remove the polarscope and cover plate and loosen the cone bearing at the base of RA, rotating the circular nut anticlockwise around, say, 1/10 of a turn at a time, until the axis swings freely. There are three grub screws which bear against the thread to lock it (yeah, I know!!). In between loosenings, give the ra shaft a gentle tap upwards and swing again before retightening.

HTH

 

Just wondering what this does?

[TerryMcK]

It puts preload on the thrust bearing. Slackening the nut slightly will reduce the preload and let the mount turn easier. Although winding off the nut too much can result in too much clearance. Knocking or clonking being heard when the mount is turned.

Also as others have said concentrate on making your cable management better. The rig is very liable to cable snags the way you have it at the moment.