EQ6 AZ GT, pc control and PPEC

[sdufoer]

Hello all,

I use an EQ6 AZ GT with an eqdirect cable and EQMOD to do robotic observing of variable stars.  I use CCDcommander for this and Pinpoint for platesolving.

However, I found I have some trouble with this.

1) Automatic autoguiding is very difficult.  CCDcommander fails a lot for with finding a good guidestar and I now observe without autoguiding.  This is not a big deal, since my subframes are only 30s.  However, on some frames I have slightly eleongated stars in RA-axis.  This is because I have a PE of +-7 arcsec, and the mount can't keep up.
What frustrates me about this, is that the EQ6AZGT has permanent PEC, which uses encoders on the worm and an onboard table with correction-data.  However, EQMOD can't use this feature.

I'm wondering if another ascom driver, or another setup (pc-direct?) could use this feature?  I don't have the synscan controller, so I can't test it out.  Is it possible to tell the mount somehow to use the PPEC-guiding as standard guiding if I use pc-direct or the celestron ascom driver?

2) I found that I have errors with my goto's.  I have a series of alignment points, but when I do a slew to an object, and then a platesolve, it turns out that my software thinks that the telescope is pointed slightly on another location.

I give an example.

Object coordinates: RA 10h59m36s Dec +17°00'58" 

Allsky Platesolve result: RA 10h58m11s Dec +17° 05' 15.44" 

Mount (encoder):RA 11h02m19s Dec +16°25'09"

CCDcommander is not able to do Allsky platesolves (you can only do them automatically), so in the fits header of the CCD-image I get the encoder-result, and those are +-1° away from the real position of the telescope, which is too far away from the fov, so the normal platesolve fails.

What could be the cause of this?  With the synscan-controller I can sync the encoder, but I don't know if eqmod or pc-direct is able to directly talk with the encoders..

Any insight is very appreciated...

[Gembol]

I have been thinking the same. Hopefully anyone can help us...

[Gembol]

No one use PEC with EQMOD?

[chrisshillito]

Skywatcher's own PPEC is entirely proprietary and cannot be accessed by external applications - you can blame skywatcher for this.

ASCOM does not provide any interfaces for the management of PEC or indeed for the reading of encoder positions.

The EQMOD driver has its own PEC function that works well with the NEQ6/HEQ5/AZEQ6-GT.  EQMOD reads the encoder position from the mount and synchronises the PEC playback to it. To maintain synchronization you only need to park the mount mount at the end of your session. Whilst it is far to say the vast majority of folks don't bother with PEC but there are folks regularly using it.

As far as I know there are only two ASCOM drivers capable of driving the Skywatcher mounts - EQMOD and the Celestron driver - only EQMOD provides PEC.

With respect to encoders - EQMOD can resync them to known park positions. Whilst EQMOD doesn't not provide an equivalent of the "Auto Home" of the AZEQ6-GT you don't really need it - NEQ6 users seem to have managed without it just fine! If you need to you could always perform a handcontroller auto home as part of your set up routine before switching over to EQMOD and doing a resynch encoders to the home position.

When it comes to platesolving and syncs the encoder of positions of the mount are never changed/resynched but rather the driver measures the error between the actual position and the target position and applies a correction that is applied to reported RA/DEC coords and subsequent gotos

Chris.

[Gembol]

Very interesting and useful!

Thank you so much, chrisshillito!

[mikeobrien]

Thanks Chris,

I think the more you know about a setup the more able you are to get the most out of it and better understand what is happening when things go wrong. What is your opinion on using PEC in Ascom, is it best reserved for mounts with large periodic error, or coupled with autoguiding is it the way to go? I have an AZEQ6GT mount and before I started using Ascom I used its Permanent PEC function from the handset. I guess I need to do a comparison to get some valid data. Now if only the sky would clear!