Tracking woes

[Pitch Black Skies]

I've noticed a consistent spike in my RA tracking.

It happens about every minute.

What mechanical part of the mount is this most likely to relate to? What component if any does a complete rotation at tracking rate in 1 minute?

I'm guessing the worm drive or maybe one of its bearing but I would like to know what you think.

[alacant]

Hi

RA overshoots after correction pulses. Although it won't fix any mechanical imperfections, lowering RA agression will at least offset the overshoot.

If it persists, break open RA and inspect/clean gears, replace bearings and readjust.

Cheers.

[newbie alert]

I'd doubt it's your worm as that doesn't do a full rotation in a minute, then I thought of the gears and doubt that would do a full rotation in a min..  what mount is it? Poss from the Ra motor itself

[Pitch Black Skies]

@alacant Cheers, I'll definitely lower the aggressiveness to stop overshooting.

I have a complete set of bearings ordered and some grease so hope this will help improve it.

Both axis's were very stiff on this mount from brand new. It's not easy to find perfect balance when it's like this.

[Pitch Black Skies]

@newbie alert It's a HEQ5, Rowan modding hasn't helped.

I reckon it's something that is rotating as it's quite consistent.

[Pitch Black Skies]

Maybe this will shed some more light on it?

It's not as consistent in this snapshot but there's clearly a spike in the RA 60-90secs or so.

Edited April 30, 2022 by Pitch Black Skies

[vlaiv]

4 hours ago, Pitch Black Skies said:

What component if any does a complete rotation at tracking rate in 1 minute?

Are you sure it is 1 minute exactly?

There is no significant period of 1 minute long in Heq5.

These are significant periods for HEQ5. Usually 3rd and higher harmonics have minimal contribution

[vlaiv]

2 minutes ago, Pitch Black Skies said:

It's not as consistent in this snapshot but there's clearly a spike in the RA 60-90secs or so.

If it is not exact period - it is unlikely related to mechanical periods.

What is your shooting location like? Do you have something like row of houses in the distance that your mount "traverses" as it tracks?

Could it be local seeing effects? Which direction? East/West or South?

[Pitch Black Skies]

@vlaiv I'll have to do a bit more investigating. That's a really useful page you've found there.

This one is from March 25th. It's M51 in East location. No houses.

This looks more sporadic.

Edited April 30, 2022 by Pitch Black Skies

[alacant]

1 hour ago, Pitch Black Skies said:

Both axis's were very stiff

Ah, ok. That's the cone bearing at the base of each axis which simply needs loosening. No need to dismantle to get the axes spinning and always worth trying new belts.

48 minutes ago, vlaiv said:

significant periods for HEQ5

The OP's mount is belt driven.

Edited April 30, 2022 by alacant

[newbie alert]

1 hour ago, Pitch Black Skies said:

@newbie alert It's a HEQ5, Rowan modding hasn't helped.

I reckon it's something that is rotating as it's quite consistent.

Look at the pulley on the motor.. make sure its not oscillatiing

If the axis is stiff make sure the locking nut isn't over tightened, as that can cause issues

[vlaiv]

43 minutes ago, alacant said:

The OP's mount is belt driven.

That really does not matter.

With belt mod - motor shaft still has pulley on it that has 9 teeth - each of those teeth moves one place at ~13.6s - if belt meshing is issue on motor gear - you will see issue every 13.6 seconds (I had that due to poor belt tension).

One whole revolution of motor shaft is every ~122.4 seconds - so if motor gear is out of shape - you will see that period.

Worm gear still has 47 teeth and turns every ~639.2 so if that one is out of shape (or worm itself) - you will see that period.

Harmonics of those periods can still be present.

Only thing that is removed is transfer gear - which is replaced by belt.

[rnobleeddy]

Doesn't PHD2 have a way of analyzing if there's significant periodicity to the noise? 

Humans are very good at spotting patterns that doesn't exist in noise - so it's worth confirming if it is periodic or not. If you can attach the log, it's a pretty easy thing to in R or Python.

[Pitch Black Skies]

@vlaiv @newbie alert

I think it might have something to do with my belt tension. I have it super tight. I wonder if it is causing the pulley to oscillate? I'll test it tomorrow.

When I don't have the belt super tight, I can manually twist one of the gears slightly without the opposite gear turning. It's the equivalent of backlash I presume.

[Pitch Black Skies]

The DEC backlash seemed considerable, however the guiding numbers in DEC were great. This is when the belt had a bit of slack. I've tightened it since but haven't tested it.

The spike seems to only be in the RA axis though.

 

 

[Pitch Black Skies]

The worm drive seems to be way too tight on both axis's. The gear is really stiff. I'm surprised I'm not getting binding. I've adjusted it now. It's moving freely with zero play. I've put the belt back on and it seems more responsive when a little tighter.

[newbie alert]

There's a locking ring on the worm spindle within the worm housing the one with the small bearings in.. that maybe locked down to much.. you want it to move fairly easy without lateral play on the spindle.. tightened down too much just locks the bearings up.. 

[Pitch Black Skies]

@newbie alert Cheers, the worm was just pressed a little too tight against the drive. I fixed it in the last post with the 2 grub screws.

The other night I was checking for backlash and I adjusted until there was binding and then backed off just enough until the binding stopped. I suppose it just goes to show, you can't really do it by ear. For the best results,  it's better to strip down I think. I'll just have to wait about a week or two now for a clear night to test it all 😌.

Gonna take a look at the axis's locking nuts too, it's possible they can be loosened slightly to help with balance.

Edit, locking nuts were too tight. There is a huge improvement now in both axis's. It's much easier to find a perfect balance.

Edited May 1, 2022 by Pitch Black Skies

[Pitch Black Skies]

11 hours ago, alacant said:

Ah, ok. That's the cone bearing at the base of each axis which simply needs loosening

Yep, that has made a huge difference. Looks like I didn't need to buy the set of bearings after all.

Edited May 1, 2022 by Pitch Black Skies

[alacant]

14 minutes ago, Pitch Black Skies said:

I didn't need to buy the set of bearings after all.

Hi

No, it's a wise move. We've never seen a 'clean' sw mount out of the box. The mount will benefit from cleaning and re-greasing and it will allow you to eliminate free movement/bearings in any future fault diagnosis.

Cheers

10 hours ago, vlaiv said:

That really does not matter.

Mmm. I wonder;)

Edited May 1, 2022 by alacant

[Pitch Black Skies]

Guys, this gear that I'm turning. I can get it either rotating very easily with a slight fraction of play, or rotating a bit stiffly with zero play. I'm not sure which is correct.

[alacant]

1 hour ago, Pitch Black Skies said:

rotating very easily with a slight fraction of play, or rotating a bit stiffly

It should have the same resistance throughout.

Firstly, make sure RA is at balance.

Assuming the worm shaft bearings are ok, remove the belt, loosen the mesh between the worm and its gear and try again. Repeat until the movement is even though 360°.

Err on the slack side: RA is always meshed.

Cheers

Edited May 1, 2022 by alacant

[Pitch Black Skies]

@alacant Cheers, all done. Will report back when I get a clear spell.

[newbie alert]

5 hours ago, alacant said:

It should have the same resistance throughout.

Firstly, make sure RA is at balance.

Assuming the worm shaft bearings are ok, remove the belt, loosen the mesh between the worm and its gear and try again. Repeat until the movement is even though 360°.

Err on the slack side: RA is always meshed.

Cheers

Sorry I don't follow, I haven't got a heq5 but I don't understand what you're trying to mesh and then you say Ra is always meshed?

 

[Pitch Black Skies]

16 minutes ago, newbie alert said:

Sorry I don't follow, I haven't got a heq5 but I don't understand what you're trying to mesh and then you say Ra is always meshed?

He's just saying to loosen the mesh between the worm gear and the RA gear ⬇️

and then mesh them back together gradually with the grub screws.

When he said RA is always meshed he was referring to getting the best results rather than having a fraction of play between the mesh.