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GOTO accuracy issue

bomberbaz

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bomberbaz

bomberbaz

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Ok folks I hope someone can help me here. My flex goto has recently been less accurate than it should be. Can't put my finger exactly when it started but recently I re-aligned the scopes goto using the built in facility and also updated the firmware so we can rule that out, or can we.

The scope is placed on hard standing patio that is near level as you can get, I check every time with a level and usually end up placing a piece of plywood under one foot to get it even closer. I also collimate every time before I start alignment.

As I look through my eyepiece they are usually a degree to the left of the eyepiece, given its a newtonian that means its falling short of where it should be landing. If facing east through to west.

I know some might think just go to the left and you will find it but not always that simple, it should fall into a 1.5 degree fov. Plus sometimes if its a very faint fuzzy, well you know. (Please no scoffing you goto haters) :rolleyes:  Also I do have a starmap which I could use to find it easily enough but that's not the point really.

I though that if it is stopping short, then maybe if I let the 2nd aligning star run a little past the illuminated cross hairs this might compensate for this.

I can't find anything specific to this issue anywhere so wondered if anyone has any ideas.
Any thoughts ?  :confused:
Steve

Kropster, on 02 Nov 2015 - 8:14 PM, said:snapback.png

Can you do a three star alignment?

Is the time set accurately and are your position co-ordinates accurate?

Every little helps.

No 3 star alignment with this scope. Yes it is accurate time, use the iphone as always have, get within a second and yes cords are spot on. Good points and should have mentioned that in opening post.

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bomberbaz

bomberbaz

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Can you do a three star alignment?

Is the time set accurately and are your position co-ordinates accurate?

Every little helps.

No 3 star alignment with this scope. Yes it is accurate time, use the iphone as always have, get within a second and yes cords are spot on. Good points and should have mentioned that in opening post. ADDED NOW  :grin:

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Owmuchonomy

Owmuchonomy

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Hi Steve

I have this scope.  To be honest I usually find the GoTo to be spot on but on the odd occasion it has failed me its has been down to levelling.  It's a big tube to be spinning around on that lazy Susan while it does the 2 star alignment so I built an isosceles triangle out of 2"x 3" scrap timber to sit it on.  I find this easier to level and much more sturdy.  The other issues I have to contend with are 1). ota balance and 2). power supply.  

1.) I find that the balance point needs a bit of work depending on which eyepiece I'm using and I use a magnet to get this right.

2.) The supplied mains plug style power supply is on the limit so when I can I use my 4 amp obsy supply and this seems to be better

I did once battle for 15 minutes with the GoTo until I realised I was inputing 18:00 for 8pm.  Doh, I'll own up to that one!

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faulksy

faulksy

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when i used to set up my cpc 9.25 i used to align in a triangular arrangment ( brantuk , kim) told that. go to your alignment star starting in the east low down but just before you press align go vertical on the last stage, then head south get something at the zenith and again nudge up verticaly to the star then head west low down, this takes the backlash out of the gears and is more accurate or it was for me. doesnt matter with my nexus push to as its bob on all night. hope this helps

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bomberbaz

bomberbaz

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Have you tried moving the mount/scope manually after the first slew so the chosen star ends up centred then see how the second goto ends up......moving the base only as there are encoders on the motors.....

Yes tried that too tinker, worked to an extent but not completely or always.

I have actually just found there are new instructions on the SW website for updating the firmware that are slightly different to the ones on the manual.

Also when I last re-aligned the encoders I am not sure if I checked if I had an accurate alignment before I used this utility. I don't know if this would affect the accuracy adversely but it certainly wouldn't help it.

Anyway, I have just updated the firmware again as per the new instructions to see if that helps, and next time out I shall try to re-align the encoders again.

If this doesn't work, I shall do a factory reset on the handset and start over. I had forgotten about this facility.

I shall let you all know how I get on.

Steve

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Scooot

Scooot

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I would have absolutely no idea how I would find that out bto be honest although if it can slip then I suppose its a possibility.

Can't help you there, the encoders on mine are easily accessible and their shafts are just held tight in the housing with a grub screw. Don't know if you can get to yours but if you can just see if there's a similar screw and whether you can tighten it a bit. I'm not familiar with your scope so maybe they're all concealed in a housing or something but it was just a thought. :)

Just found this

http://www.eacocon.it/dobsoniani/FlexTubeGoTo.pdf

I think the grub screw holding the encoder shaft is in the little hole facing you at the top of the encoder in the 4th pic.

Maybe try everything else first and check this as a last resort.

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