EQ6 RA guiding issues

[DiscoDuck]

I've been having trouble with RA guiding for my last few sessions. Massive spikes in RA as per the attached PHD2 log - up to about 4". Dec on the other hand is ok.

I thought it might be balance, but ensuring it was imbalanced correctly made little difference. Also tried balancing perfectly and going very imbalanced.

Some guiding was much worse than what you see there, with the spikes happening every couple of guide frames.

Guide star was a bit faint, but if that was an issue, surely it'd have effected dec too. But tried a brighter guide star and similar issues.

Is the RA meshing too tight and it's sticking? What else could cause this?

Comments and ideas/advice much appreciated.

Thanks,

Paul

[ChrisV]

I'm no expert but I've seen periodic spiking when I've used the backlash compensation.

[alpal]

Hi Paul,
would my experience help you?

here:

https://www.flickr.com/photos/24719437@N03/6001169049

[Russj]

G'day Paul, I have a NEQ6 which had graph similar to yours but was perhaps a little more spiky, although I could still image at 10 mins subs with round stars,...... go figure :confused2:. I eventually got my rms down to .6 (on a good night) by the following.

1. I hypertuned the mount, (didnt replace any bearing).
2. fitted a Rowan belt kit
3. Run PEC in EQmod
4. Run Predictive pec in PHD2

My mount works well now, rms will still move over 1 on a poor seeing night which is to be expected.

I used to look at some of the almost perfect graphs on other forums and wondered how they do it on cheaper unmodified mounts in light polluted cities, something did not ring true to me, the reason I mention this is because I went down this road, spent a lot of unecessary time trying to get a near perfect graph, which I stil am unable to achieve, my graph still spikes a bit but I've got tight round stars, thats all that counts in the final washup.

These links may help, https://groups.google.com/forum/?fromgroups=#!forum/open-phd-guiding
http://www.astro-baby.com/EQ6%20rebuild%20guide/EQ6%20Strip%20Down%20Home.htm

If I can help with any of the above let know

Hope this helps Russ

[Imme]

Couldn't agree more with that last paragraph......there are probably 300,000 or more mounts out there in the world, the best 50 guide graphs get posted as 'this is how good my guiding is' and then we all try to compare ours to that.

As long as you stars are round then the guiding is perfect in my opinion!

[Atmos]

Something else that might be worthwhile is stripping your mount down and giving it a regrease. For a time I had some guiding issues (random 2” spikes) that started appearing. After a regrease they went away. You just have to remember how tiny a particle needs to be for it to show up in the tracking ;)

[DiscoDuck]

Thanks Chris. I think (may be wrong :)) that backlash compensation only affects dec guiding. In any case, I've been using that for quite a while without issue and this problem only surfaced in the last couple of weeks.



Thanks. I agree the bar is rubbish! Don't know why they couldn't do a better job. In my case, I don't think it was the cause of this particular problem as it was in a stable position and not moving. But definitely worth my looking at. Thanks again.



Thanks Russ. Much appreciated. I've already got a belt kit in there and had a re-grease at the same time. That was about 2 years ago, so it may be in need of a refresh/retune. I'll chase that up.

I've played with PEC before in EQMod. Never tried PHDs one. Can that work together with the EQMod one or do they interfere?

Re stars, yes, they were not as bad as the guide RMS would suggest, but the frustration is I've had much better up until now, i.e. RMS usually no worse than 0.5" RMS.

Thanks again for the advice. I'll look into the re-grease/re-tune etc. And again very much appreciated.



Well, round and small is even better :)



Thanks Colin. Sounds like it's time to pull out the lithium grease! :P

[Russj]

I've played with PEC before in EQMod. Never tried PHDs one. Can that work together with the EQMod one or do they interfere?

The software developers at PHD guiding forum stated that eqmod PEC takes care of the PE at the mount, leaving other errors for PHD PPEC to correct.
So yes you can use bothe at the same time.

[DiscoDuck]

Great. Thank you.

[alpal]

Hi Paul,
I spent over 20 years working with closed loop control systems.
Wobbly parts just don't work.
Did you take the counter weights off & just move the bar up & down?
How much play was there?
I think the latest belt driven EQ6 has solved that problem.

May I also add that Roger Davis from Bintel had a look inside my EQ6 once &
he adjusted the DEC axis for the correct amount of play.
The EQ6 can come out of the factory with all sorts of problems
& many have to be checked out by experts such as Roger.
It only takes one bit of grit somewhere or a mal-adjustment &
the guide graph will go crazy.

There are experts around who can hyper-tune these mounts
with special bearings etc -
but I wouldn't bother unless the counterweight bar is upgraded first.

cheers
Allan

[DiscoDuck]

Just a quick update for others who may encounter such a problem: I backed off the RA meshing a bit (as per AstroBaby's site) and the spikes seem to have gone. I think it was RA sticking, as before the adjustment I could hear a slight change in tone as it rotated when slowly slewing.

Of course, I have more backlash than a Trump tweet now! :) But biasing the balance to the east seems to help with that.

Thanks all for the advice.

Other things like counterweight bar I may leave as I'm waiting on a new mount arriving anyway in the next couple of months :D

Thanks again.

Paul