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Help me idenetify this tracking error type!

Mount Imaging
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11 replies to this topic

#1 maxhy

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Posted 11 June 2021 - 12:44 AM

I have relatively large RA RMS guiding error (around 1.6") and I uploaded my PHD2 guiding log here:

https://openphdguidi...2_logs_aRGU.zip

 

I posted a conversation here: https://groups.googl...g/c/uGftD9w3Cvc and Bruce here helped me analysed guiding graph and extract frequency signature:

image004.jpg?part=0.2

He pointed out that long frequency error come from PE and low frequency one (13.5 cycle one ) is generated by spur gear error in HEQ5 pro.

Could anyone who is familiar with HEQ5 help me identify these errors?

 

 

Equipment:
183mm guide scope with 120mini (4.23arc-sec/px)
750mm main scope with 533mcpro (1.03arc-sec/px)

 

 

Thanks!

Yang



#2 OzAndrewJ

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Posted 11 June 2021 - 01:43 AM

Gday Yang

99.978% due to bad gear meshing between the motor and worm.

The EQ5 has a 9 tooth gear on the motor and a 47 tooth gear on the worm

and a 28 tooth idler gear between them.

As per attached plot, you can clearly see how absolutely consistent the ripple is

and based on the freq, it is happening 47x per rev of the worm.

It would be better for a proper magnitude analysis to grab several turns ot the worm unguided

but it is very clear your gears are not meshed properly.

For a HEQ5 it is relatively easy to expose the gears and adjust

In the piccy,

the green bolts hold the motor to the plate and are used to adjust the clearance between motor and idler.

the red bolts hold the plate to the mount and are used to adjust the clearance between idler and transfer gear on the worm.

I suspect in your mount, one of these joints will be very sloppy.

 

Andrew Johansen Melbourne Australia

RA Ripple.jpg HEQ5_Gears.jpg

 

 

 

 

 


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#3 rgsalinger

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Posted 11 June 2021 - 01:54 AM

Interesting picture!

Rgrds-Ross



#4 maxhy

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Posted 14 June 2021 - 03:45 AM

Gday Yang

99.978% due to bad gear meshing between the motor and worm.

The EQ5 has a 9 tooth gear on the motor and a 47 tooth gear on the worm

and a 28 tooth idler gear between them.

As per attached plot, you can clearly see how absolutely consistent the ripple is

and based on the freq, it is happening 47x per rev of the worm.

It would be better for a proper magnitude analysis to grab several turns ot the worm unguided

but it is very clear your gears are not meshed properly.

For a HEQ5 it is relatively easy to expose the gears and adjust

In the piccy,

the green bolts hold the motor to the plate and are used to adjust the clearance between motor and idler.

the red bolts hold the plate to the mount and are used to adjust the clearance between idler and transfer gear on the worm.

I suspect in your mount, one of these joints will be very sloppy.

 

Andrew Johansen Melbourne Australia

attachicon.gifRA Ripple.jpgattachicon.gifHEQ5_Gears.jpg

Hello Andrew,

 

Thanks for the explaination and frequency signature analysis, makes a lot of sense to me! 

 

I opened up my mounts' side lid and inspected those green and red bolts you mentioned, but they are all tight. You said "joints maybe sloppy", do you mean the distance between RA transfer gear and RA idler maybe too far to cause some backlash? I tried to turn the transfer gear by hand and there are some backlash I think. Do you know how to test them so that I can know how well they are meshed against each other?

 

 I took a picutre of my RA worms and here it is:

IMG-4803.jpg

 

And this is the picture of my RA and Dec gear (have a little comparision between them):

IMG-4804-1.jpg

 

 

Yang



#5 OzAndrewJ

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Posted 14 June 2021 - 04:35 AM

Gday Yang

I opened up my mounts' side lid and inspected those green and red bolts you mentioned, but they are all tight.

I would expect them to be tight.

Basically, to adjust the clearance between the gears themselves, you would ease off the relevant bolts

and then move the assy as required to tighten the meshing.

 

You said "joints maybe sloppy", do you mean the distance between RA transfer gear and RA idler maybe too far to cause some backlash?

Yep, either side of the idler might be a loose fit and hence give the result you saw.

That said, it may just be my eyesight or the lighting, but the teeth on the RA idler do not look like

a normal involute tooth form,ie they may be worn??? Dont know there.

Can you clean the grease of the edges and then get a very good face on close up of the RA idler

so we can see the tooth shape??

 

I tried to turn the transfer gear by hand and there are some backlash I think. Do you know how to test them so that I can know how well they are meshed against each other?

The normal test is turn the 47 toother on the worm back and forth and see how much slop there is

before the idler gear reverses and takes up the load on the motor gear..

 

Andrew Johansen Melbourne Australia



#6 daw316

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Posted 14 June 2021 - 05:51 AM

Agree.  The tooth shape is strange indeed.  How many hours on this mount?



#7 maxhy

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Posted 14 June 2021 - 09:18 AM

Hey Andrew,

 

The weird shape is caused by relection of grease under light.

I cleaned up the grease and took a close up shot of the RA gears. I think it looks normal? 

IMG-4808.jpg

 

Yang



#8 maxhy

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Posted 14 June 2021 - 09:21 AM

Agree.  The tooth shape is strange indeed.  How many hours on this mount?

I bought it a year ago. But I don't use it a lot it may have around 50 hours... But it is usally in the back of my car and get carried everywhere I go so I suspect the gears are affected by car bumps a lot..

 

Yang



#9 OzAndrewJ

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Posted 17 June 2021 - 11:04 PM

Gday Yang

 

The weird shape is caused by relection of grease under light.

Good, thats a cheap fix :-)

 

I cleaned up the grease and took a close up shot of the RA gears. I think it looks normal?

Certainly looks a lot nicer, soooo how loose is the fit of the idler????

ie how much slop is there in the meshing on either side????

 

Andrew Joahsnen Melbourne Australia



#10 maxhy

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Posted 18 June 2021 - 10:38 AM

Hello Andrew,

 

Certainly looks a lot nicer, soooo how loose is the fit of the idler????

ie how much slop is there in the meshing on either side????

Haven't got home till tonight, been away due to work.

I checked the fit, idler and 47 tooth worm aren't meshing against each other very tight. When I turn the worm by hand, I can definately feel some backlash.

 

I pushed the idler close to the 47 tooth worm a little bit and I'll have a unguided session when weather permits, maybe this Wednesday it seems :)

 

Yang



#11 Astrophotonics

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Posted 18 June 2021 - 07:32 PM

Rowan Belt Mod is your friend.



#12 maxhy

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Posted Yesterday, 03:47 AM

Rowan Belt Mod is your friend.

Hello Atrophotonics, 

 

I have heard of Rowan Belt Mod and watched several Youtube videos about it. Does it eliminate this kind of spur gear error completely?

 

Yang




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