Juwei 17 tracking accuracy.

[Володимир Козак]

Hello everyone! The other night I was testing my new setup and guiding results wasn't as good as I expected them to be.
So here are the parts of my setup that are important to this question:
1. Juwei 17 Harmonic drive mount on sturdy tripod;
2. ZWO ASI 120MM mini guide camera;
3. SvBony SV165 30mm F/4 guide scope;
This pair of guide camera-guide scope gives me resolution of 6.45 ''/pixel, which is more than enough for my imaging resolution.

Before purchasing this mount I saw reviews that its periodic error is quite high, but after analyzing my guidance logs it seems to me that my copy of the mount is even worse than the average. I would like to hear the opinion of people who have more experience with PCB2: are these acceptable guidance results for these mounts? Or maybe I should return the mount for a refund?

Here is link to calibration and guide logs: https://openphdguiding.org/logs/dl/PHD2_logs_j2fE.zip

[Bruce Waddington]

I think the Guiding Assistant run you made pretty clearly shows a very large periodic error in the mount (RA in red):

Unguided tracking:

Periodic components of tracking error:

This shows a peak-peak tracking error of 73 arc-sec with a period of about 470 seconds.  This strikes me as being unusually large even for a strain-wave mount, but it's something you should take to the manufacturer.  Do they consider this sort of performance to be within specifications?

In the meantime, you don't have the luxury of using 2-second guide camera exposures with this mount.  It will need to be guided much more aggressively.  I suggest trying to use 0.5 second exposures while increasing the "predictive" factor in PPEC to  90.  With the much shorter exposure times, it will also be important to set an appropriate Min-Move value, something best done by re-running the GA using the shortened exposure times.

Good luck,

Bruce

[Володимир Козак]

Hello, Bruce! Thank you for your reply. 
To be honest I think I am going to return this mount to the store, but I just wonder how I can improve my guiding with such huge error except setting 0.5 sec exposures and 90% predictive value. Should I set periodic error as 470 sec, and turn off auto mode?

понеділок, 21 липня 2025 р. о 05:37:46 UTC+3 bw_m...@earthlink.net пише:

[Володимир Козак]

Hello, Bruce! Thank you for your reply. 

To be honest I think I am going to return this mount to the store, but I just wonder how I can improve my guiding with such huge error except setting 0.5 sec exposures and 90% predictive value. Should I set periodic error as 470 sec, and turn off auto mode?  

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[Brian Valente]

FYI the recommended fast exposure/cadence for guiding Bruce recommended is typical for strainwave mounts. In general, they benefit from aggressive guiding. We have seen a few Juwei 17 mounts with similar high error come through the forums. I don't recall what was the result, I believe one customer sent the analysis from this forum to Juwei and asked for their feedback.

Brian

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CADi98SCuZyNcmPsPA%2B_DoesTox-V5yNZ%3DL3S_Q8uUQ_arQuTew%40mail.gmail.com.

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Bruce Waddington]

The longer 25-minute guide session you ran shows that the oscillation period is more like 440 seconds, so you can try that.  Some of these strain-wave mounts have large tracking errors that aren't truly periodic in the same way a worm-driven mount is.  So I don't know how well this will work although I think the shorter exposure times will definitely improve things assuming you can still get a useful number of guide stars to work with.

Bruce

[Володимир Козак]

I wonder if using PPEC algorithm for guiding is the best choice for this type of mounts if their tracking errors aren't truly periodic?

понеділок, 21 липня 2025 р. о 18:34:43 UTC+3 bw_m...@earthlink.net пише:

[Володимир Козак]

I wonder if PPEC is even right algorithm to use if my mount's tracking error isn't truly reriodic? Maybe I have to use different algorithm ?

понеділок, 21 липня 2025 р. о 18:34:43 UTC+3 bw_m...@earthlink.net пише:

The longer 25-minute guide session you ran shows that the oscillation period is more like 440 seconds, so you can try that.  Some of these strain-wave mounts have large tracking errors that aren't truly periodic in the same way a worm-driven mount is.  So I don't know how well this will work although I think the shorter exposure times will definitely improve things assuming you can still get a useful number of guide stars to work with.

[Bruce Waddington]

We can't really know, it all depends on how the mount behaves over longer time frames and in different sky pointing positions.  I think it's really something the manufacturer should be addressing assuming you don't want to just return the mount and move on.  But keep in mind, nearly all the strainwave mounts seem to suffer from large tracking error to a greater or less extent.

Bruce

[Володимир Козак]

After hours of searching various forums for information about the intermittent error of these mounts, I have a better understanding of how these mounts work. And I want to give this mount one last chance using the new guiding settings.

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/fa195b3b-920b-411f-a9f5-dc9de244f7cdn%40googlegroups.com.

[Володимир Козак]

I would like to know if he received any response from the manufacturer.

понеділок, 21 липня 2025 р. о 18:16:33 UTC+3 bval...@gmail.com пише:

[Brian Valente]

I suggest you search the group's past messages for Juwei, you will probably find a number of references to customers and their results

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/38b76519-37b1-491a-ac87-dce0486b1013n%40googlegroups.com.