EQ3 Pro short period error

[mikey2000]

Hi all,

 

I'm looking for EQ3 masterminds to maybe offer some advice with my Skywatcher EQ3 Pro Synscan.    I'm sort of new to guiding with PHD2 and I finally got around to running an EQMOD autopec.  I didn't get to try it as it clouded over (and has remained cloudy ever since.... Grr)

 

The helpful chaps at the PHD2 Google Group took a look and discovered something.  Apart from the large slow periodic error, when you zoom in a bit you see a regular short period oscillation.  Here is a bit of the unguided RA movement (from a PHD2 long Guide Assistant run) (scope balanced to be definitely east-heavy)

(image attached!) (I can't make it appear mid-post

Do you see the sawtooth?  It has a regular period of about 19-20seconds, with a 5arcsecond amplitude.  The PHD2 people say it is too much/too often to guide out effectively.

 

Any ideas on how to minimise this sawtooth?  Should I be hopeful my EQMOD autopec curve will help?  Is there something I can do to the mount?

 

I was thinking maybe slacken the RA worm just a little bit.  With the slow mo control removed, it is rather hard to turn the RA worm.  I don't know if that's normal and maybe to be expected as the motor is still attached to the other side.

 

one other factoid - with the clutches loosend, the mount is easy to move in each axis but it is never floppy.  On my old EQ2 mount, balancing was easy as it would drop one side or the other at the slightest imbalance.  Not so with my EQ3Pro - there is always a slight resistance but it feels smooth enough.

 

Any advice much appreciated!

 

[Cornelius Varley]

I think you missed something out of your post.

[mikey2000]

Hmm.  I sometimes struggle to get pics attached to posts.  I've added it now

[Stub Mandrel]

3 hours ago, mikey2000 said:

With the slow mo control removed, it is rather hard to turn the RA worm.  I don't know if that's normal and maybe to be expected as the motor is still attached to the other side.

Sounds like you may need to ease the engagement of the worm and wheel a tad to me.

[kens]

The short period suggests that it is the tooth engagement period between the motor gear and the spur gear. You cannot eliminate it with PEC as it has a different period to the worm.

[mikey2000]

Kens,  I feel sad now :-(. 

 

Are you referring to the gear that sits on the end of the worm spindle?  Is it worth having a fiddle to make sure the motor gear is sitting against it nicely?

Any other suggestions on how to tune my mount's RA?

 

[wimvb]

My guess is also that this may be the ra motor gear teeth engaging. You can adjust the motor by loosening and adjusting the allen bolts that attach it to the bracket/mount. It's quite easy to tinker with.

The ra and dec axes should move smoothly with the slo mo controls if the mount is not powered. With the mount powered, it's nearly impossible to move the axes with slo mo controls, as you have to overcome the motor torque that is geared.

[kens]

2 hours ago, mikey2000 said:

Kens,  I feel sad now :-(. 

 

Are you referring to the gear that sits on the end of the worm spindle?  Is it worth having a fiddle to make sure the motor gear is sitting against it nicely?

Any other suggestions on how to tune my mount's RA?

 

Its the gear on the end of the motor spindle. As Wim says its pretty easy to fiddle with. I believe the EQ3 has a similar setup to the Super Polaris in which case it is very easy to do as you can see the tooth engagement as you adjust the motor position.

[wimvb]

The eq3 has a simple plastic cover that you take off to reveal the motor gear. It's held in place with two small screws.

[mikey2000]

I made some big improvements without any mechanical adjustments....

 

1) EQmod AutoPec seems to work reasonably well.  I used the pecprep utility to smooth the curve out a bit.  The big long period is greatly reduced.  I assume PHD2 has less work to do now.

2) I Changed the eqmod pulseguide setting to 0.7 (from 0.5) to give PHD more 'oomph'.  It now does a reasonable job of keeping up with the shorter, smaller periodic swings.

 

As a result, the graph is comfortably contained inside +/-2" for seemingly indefinite periods with just an occasional excursion of 4" momentarily (doesn't show up in a 4min sub)

 

So, DEC is now +/-1" most of the time (a cinch to polar align with the PHD2 drift tool) and RA +/-2" with plenty of hits inside the 1" circle (I love the PHD2 'target' visualisation!)

 

At full zoom, I get a little bit of rugby-balling from time to time but I'm really zooming in here.  My camera is 6000x4000, equating to 1" per pixel on my scope.  If I downsize to 3000x2000, almost all minor errors are hidden.

 

Guess what though - it's cloudy for the next few days, punctuated by an ever fuller moon. :-)

[Stub Mandrel]

This is very helpful report Mikey.

I hope to get a guide camera and an Ha filter in the next month to use with my EQ3. A coated f3.6 50mm achromatic doublet lens (182.6mm focal length) arrive this morning, and it will be going into a homebrew guidescope, it should be just about an ideal focal length for the 130P-DS and very light.

Neil

[mikey2000]

I think you will have more success than me then!  I've loaded my EQ3 with a 150PDS!  My main camera is no heavier than my 32mm eyepiece though (what a chunk of glass!)  My guidescope is that QHY miniguidescope - it is feather weight but only 130mm.  So I'm guiding a 750mm FL scope with a 130mm FL guidescope.  I believe that is best described as 'ambitious' :-)  I still get occasional DEC glitches but I think that's because my guidescope occasionally jumps a bit  - I don't think it's well enough secured.

 

I keep meaning to de-load the mount by trying a DSLR lens instead of a telescope, so reducing the payload by 50% and see how that goes.   Maybe one day!  I have a 70-400/5.6 which might be quite useful at 400mm for those larger nebulae (they don't all fit in the FOV of my 150PDS.)

[Stub Mandrel]

54 minutes ago, mikey2000 said:

I've loaded my EQ3 with a 150PDS! 

Kid's stuff

I've used s 150PL on mine, 1200mm fl! You do lose a high percentage of subs though, at least when pointed nearly straight up.

Now someone with a 200P-DS will come along....