Problem with guiding HEQ5 Pro

[Freeman Solitude]

Hi everyone,

I think that I might need some diagnosis on my guiding with the HEQ5 Pro mount.

My other gears:

- 80mm small refractor, ASI 071MC camera; 

- 50mm f/3.8 guider scope, ASI 290MC guider camera.

Shouldn't be a lot of weight, and I tried my best to balance the mount, still I got graphs like this:

(I attached the whole log too, the pics here are only for a quick preview)

Guided ↑

Unguided ↑

This kind of jagged saw shape is very weird, since it shouldn't be happening on unguided graphs. Please provide me some insights if you could, many thanks!

Sincerely,

Freeman

[bw_msgboard]

Hi Freeman.  I think you’ve encountered a pretty common problem with these mounts and your mount will probably need mechanical repairs to improve your results.  To be sure we’re on the same page, an unguided session like this one is showing you the native tracking performance of the RA axis system, warts and all:

 

 

So the mount RA tracking wandered around within an overall envelope of 40 arc-sec in this 30 minute unguided session.  The more important problem can be seen in one of your guided sessions when we look at a frequency analysis:

 

 

This shows a 2+ arc-sec harmonic at the well-known but unwelcome frequency of 13.6 seconds.  Tracking errors that recur this quickly aren’t very amenable to control by guiding so I think this is really your limiting condition in RA.  If you look for advice with the manufacturer or on one of the forums with specific mount expertise, you can probably get some help on figuring out what to do.

 

You can probably mitigate this to a small extent by reducing your guide camera exposure time down to the 1-sec range and by using sub-frames if your guide camera supports them.  But in the end, I think you’ll need a mechanical correction.  If you do get a mechanical improvement, you must be sure to restore your guiding parameters to their default values because you’ve probably made a mess by trying to address this problem by fiddling with guiding.

 

Good luck,

Bruce

 

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[Steve]

Hi

Move the motor driven gear relative to the gear with which it meshes one tooth. Repeat until the frequency is minimised. Clean and re-grease that which moves whilst you're there.

The ~120s harmonic is handled effectively by using PPEC for RA.

HTH and clear skies,

Steve

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[Jynn Freeman]

Many to Steve and Bruce, I checked my gear box and found out a few problems:

1. I reduced the spacing between gears now (It was manually enlarged by myself to test if a larger spacing could help with my jagged graph, but no luck..)

2. My worm drive gear was Significantly higher than the idler gear. I’m not sure if that’s the cause of my problem, but I tuned it to be on the same flat surface with the idler now.

3. My idler gear can move horizontally, it’s not strictly tightened on its axel.

4. Both the idler and the motors might be a bit eccentric but I guess that should be smoothed by guiding. So I only tightened the contact between idler and its axels for now.

Not sure if there’s anything else I can do but I hope it works, will test it in the next clear night. Will report back soon.

Clear skies to you, star gazers!

Freeman

在 2020年9月27日，下午11:22，Steve <stev...@gmail.com> 写道：



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[Freeman Solitude]

Hi Steve,

I tried to fine tune my gears' spacing, but I missed the sweet spot of their relative positions... I was able to achive a perfect mesh but then I lost it really quickly when I tried to tighten things up and fix the screws.

Is there any trick, or any reference that I could make use of, like a high resolution photo of the gears with their positions and things like that?

English is my second language so I have some difficulties with understanding your guide here:

"Move the motor driven gear relative to the gear with which it meshes one tooth. Repeat until the frequency is minimised. "

Should I 

a. mesh one tooth of the motor driven gear, to the spacer gear,

or

b. mesh one tooth of the spacer gear to the motor gear?

Thank you for your help and patience!

Freeman

[Ken Self]

This post on SGL might help: https://stargazerslounge.com/topic/327933-orion-sirius-heq5-pro-ra-oscillation/?do=findComment&comment=3571660

As it mentions there are two sets of screws. One set holds the motor in the assembly and can be used to adjust the spacing between the motor gear and the transfer/spacer gear.

The other set holds the assembly in place and is used to adjust the spacing between the transfer/spacer gear and the gear that drives the worm.

[Freeman Solitude]

Hi Ken,

I've tried the method on stargazerslounge, the problem is it's very hard to find a proper position for those gears to mesh with each other perfectly. Since that I've been looking for some guides or instructions for checking the mesh if it's proper or not.
Sadly I haven't found any useful information on that yet :(

It looks like that the only way is to wait for a starry night and tune the meshing during guiding. Which seems to be... really hard.

Freeman

[steve]

Hi

I'm afraid that the only way -I know- to lose the 10s spike is by trial and error, and yeah, the only way to do that is to lose a night whilst you continually take out the motor and rotate the gears relative to each other.

Although important for backlash, it's not a case of adjusting the spacing of the gears, rather moving them relative to each other. You maybe lucky and find you need only one or two rotations. Get some adequate lighting and a table close by to place your keys and screwdrivers, good luck and go easy with your patience limits!

Cheers and clear skies,

Steve

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