Synscan blues

[earth titan]

I consider myself pretty persistent and resourceful, as well as reasonably switched on IT wise, but synscan has me beaten.

Level mount, polar aligned (i know this is correct). Scope pointed correctly at north (home). Switch scope on and punch in the details on the controller.

1 star alignmentworks (although it is miles out). 2 star the same. 3 star fails all the time. Must be missing something.

Double checked time and date settings (us format for date) and coordinates.

Getting fed up now.

Bet its something really simple.

EQMOD much the same....... Must be my settings.

[Merlin66]

When the scope slews to the first alignment star, and it's out of centre...how are you re-centring it in the FOV?

[NigelCampbell]

Check the coordinates you enter. Make sure that they are correct. Also make sure the date is in the US format month, day, year. Enter NO for Daylight Savings.

[MikeP]

If none of the previous suggestions solves your problem, I always offer this advice when this problem comes up with EQMOD ....

1. Power up, connect to your planetarium program, slew to any of the listed stars. Don't bother centring it or even looking to see if it is in the FOV.
   
2. Park. Wait for the mount to park itself, disconnect and power off the mount.
   
3. Loosen the clutches and move the mount to the home position (I'm guessing it won't have parked itself there). Re-tighten the clutches.
   
4. Now power up and proceed as normal with the alignment procedure.
   

If you are using EQMOD by connecting your computer via the handset, once you have connected, do not use the handset for anything i.e. keep your fingers off its buttons. Do all slews, adjustments and synchronises using the EQMOD interface / planetarium.

Mike

[AstroMum]

I tried the 3-star alignment four times before succeeding. My "solution"? Doing it quicker!

I was spending nearly half an hour each time trying to get the blasted stars aligned. When I whizzed through it in about ten minutes, I was greeted with an "alignment successful" message at last!

I managed to do it faster that last time because I'd picked easier stars to spot. If you're finding it takes too much time to align to a certain star, go back and pick another instead.

[gooseholla]

Yeah I had problems with taking too long to find certain stars. In the end I did it in a couple of minutes and it worked. It gets every object just off centre now - but that is more my fault than its.

[earth titan]

I do recall a suggestion, of auto slewing to first star then unlocking clutches to manually align, relock clutches then accept. Not sure if this would work, but seems to me the use of the slew buttons on the controller would achieve the same.

[Merlin66]

That's the way to do the first star....

By unclutching the encoders don't move but the scope does - to give you a first "calibrated' position.....

[earth titan]

Will try that. Ta.

[Jiggy 67]

That's the way to do the first star....

By unclutching the encoders don't move but the scope does - to give you a first "calibrated' position.....

Hi Merlin, I've seen this mentioned a few times but I don't understand the mechanics, can you explain how this works??...I'm gonna try it next time I have a problem but would prefer to understand it

[earth titan]

I would like to know as well !

[Merlin66]

The motors are fitted with encoders which monitor the movements ie measures the number of "steps" used to move the scope from one position to another.

When the mount slews from the park position to the first alignment star it's using the internal calculations to determine the direction and number of steps...

When you loosen the clutches and re-position the scope onto the star, there are no signals being sent to the controller to add more/ less steps, so it still thinks it's internal model (position v's steps) is correct and then continues to use the same "model" to slew to the second and subsequent stars.

If you use the buttons to re-position the first star, you're really telling the mount that the "model" is incorrect and it tries to "modify" the #number of steps/ movement based on this feedback.

HTH

[Reggie]

Merlin, Is the unclutching in one just one axis? I'm presuming the RA axis? Otherwise if you have to unclutch and manually align, it tends to suggest that you're not correctly polar aligned in the dec axis? So, this is where things break down slightly for me, if it's out on that first slew, then surely the model is wrong because you're not correctly aligned? Either that or I'm not quite understanding where this intial error comes from?

[Merlin66]

The initial position of the "park" in the model says it will be pointing at the pole on the meridian.

When you align on the first star the error isn't with this star but the initial position.

The scope only says to it's self...hmm he wants me to move to X,Y - that's 1000 steps in X and 587 steps in Y - OK lets go.

That's it. The mount doesn't know anything about your PA concerns, or cone error or any other error...

If the initial position is 110% correct, and there's no mechanical issues, you should end up on the first alignment star.

By de-clutching and re-setting, you're basically correcting for the 'error" between the initial position and the real position of the star.

[chrisshillito]

Good explanation Ken.

One thing I would add is that the 'encoders' in the Synta mounts are simply counters maintained by the motor controller firmware. The are not physical encoders and this is why you can manually move the mount the RA/DEC axis without the 'firmware encoders' changing. Only moves made under firmware control will change the encoder value. The encoder counts are held in volatile memory which means that every time the mount is power cycled the counts are lost. The firmware therfore assumes that on power up the RA/DEC will be at the home position with the telescope pointing at the pole.

Polar alignment is one source of error but the more significant factor is usually due to an inaccurate home position and the further your initial slew is away from the pole the greater the effects of this error.

By manually correcting on the inital slew you are effectively refining the home position based upon the assumption the this is the main cause of the pointing error.

Chris.

[Reggie]

Thanks guys, that was very much appreciated, as there are a number of errors that could be considered, I wondered which one exactly we were correcting for, you've certainly cleared that up.

[earth titan]

Makes sense. But don't the manual slew buttons move the scope in the same manner, without changing the absolute position which is entered when you press enter? Dunno if this is clear?

[Jiggy 67]

Thanks guys, makes sense to me, your simply correcting for any errors in the initial home position which adds up cos I have had much better results since I started following Astro Sheds advice on getting the perfect home position, I will be unclutching in future if I'm out

---

I am here: http://maps.google.com/maps?ll=53.365581,-2.732031

Sent from my iPhone using Tapatalk

[chrisshillito]

Makes sense. But don't the manual slew buttons move the scope in the same manner, without changing the absolute position which is entered when you press enter? Dunno if this is clear?

If you're moving the scope by pressing 'buttons' you are moving it under the control of the motor control firmware in which case the position 'encoders' will change.

When you add an alignment point the position encoders themselves are not changed/corrected, all you are doing is telling the control software how to map the current position to a RA/DEC coordinate.

Chris.

[earth titan]

Got it. Thanks all. Will try this, next time the clouds clear.

[chrisshillito]

Another point I should have mentioned is that once you've manually shifted the mount onto the first target star you can of course use then EQMOD to fine centre it prior to accepting the alignment point.

The whole decluch and manual align process is only really aimed at helping you get a more accurate home position so that on subseqent nights your initial alignment goto will be more acurate. Home position error itself shouldn't compromise the pointing model once the first point has been added but it is of course preferable for the initial alignment goto to put the target star in the FOV of the finder.

Chris.