My RA is acting strangely

[Free Mind]

Hello, I have a Sky-Watcher EQ6 r Pro mount. Everything has been nice for quite some time until the Right ascension started to behave strangely. It doesn't matter how well-balanced the mount is, polar alignment, etc. The RA has a periodical error that doesn't allow me to expose over two minutes. The guiding jumps every minute and a half with a mistake of over 1arc second making my stars egg shape. I thought at first that I was dealing with wind, but it was never the case. I don't have any bending or loose guiding scope. I reached the point where I believed that it was my RA motor that was damaged. Can you look at my log and let me know what you think? Thank you. https://openphdguiding.org/logs/dl/PHD2_logs_34jf.zip

[Bruce Waddington]

It's hard to diagnose specific hardware problems using just a guide log but it looks like there could definitely be a mechanical problem in the RA drive.  Here's a look at the repetitive errors you're talking about:

The pattern here is that the sidereal tracking is impeded by something every couple of minutes but then tracking picks up again.  Because the initial pause triggered corrective guide commands, you then get this pattern of over-shoot.  If we look at the frequency components of the behavior, they look like this:

Moving from right to left, the peaks occur at periods of about 130, 65, 45, and 33 seconds.  I don't think this necessarily means anything is truly damaged, it might be a loose spur gear or a belt that isn't staying on track - I can't say because I don't know the details of the RA drive system in your mount.  You might be able to get more focused advice on a forum that has more EQ-related hardware experts - the 'Mount' forum on CloudyNights, for example.  If you post the graphs along with the log, you might be able to keep the discussion more focused.

Good luck,

Bruce