Skywatcher GOTO dob missing its target

Kencollins

Hi all,

I took out the scope tonight for the first time in a few months. I set up as usual, aligned it with the two star method, time and location was correct ect.

When I told the scope to go to jupiter, it was missing it by 10' (minutes) horizontally.

I thought my alignment was out, so I tried to re-align with sirus and aldebaran. Told the scope to go to jupiter again, still 10' out.

I tried to re-align the encoder, made no difference at all.

It is a trus dob. Could one of the trusses being slightly bent cause this? The scope was in perfect collimation (saw the transit of Io on jupiter!).

I am stumped at this stage. It is a major pain in the ass as my finderscope has a diameter of 20', so everything is JUST out of view when I GOTO something!

Any ideas?

Nerro

no idea, but i had some issues with the GO TO when my power drops to a certain lvl.Then the mount has a mind of its own.i have read that its even worse when you are using rechargeble batterys.
I doubt that its one of the trusses as you are alligning the stars, i would say that maybe your scope wasnt lvl enough?

Kencollins

Hi, Thanks for the reply!

I was wrong in my first post, It is missing the target by 10 minutes, not 10 seconds!

I checked the voltage of the battery pack as an afterthought last night, it was reading 10.3V

They are cheap tesco batteries in it so maybe it is causing problems!

Plug

Could be a software issue caused by low battery voltage. Try good duracell batteries and then do an update. Don't update it with crap batteries.

Nerro

actualy i would highly suggest to invest in a good battery pack like one of these
http://www.ktectelescopes.ie/Astronomy-Accessories/Collimators-Powertanks-Other-Accessories/Skywatcher-17-Ah-Rechargeable-Power-Tank.html
Or you could DIY one...Tzetze has a good thread about how to make one.

Tzetze

It sounds like low voltage might be the problem alright.
How did it behave when doing the star alignment routine - were each of the stars out by 10' also?
I know you said that time/date was fine, but are you sure that daylight savings time was off? (1hr = 15')

Kencollins

I hope it is the voltage!

When aligning the scope you have to point it to the first star. When it tracks to the second star, it is about the 10' out. I am going to try aligning it again when the cloud clears.

I bought the expensive duracell batteries for it, the handset now reads 12.7V.

I think I will try and enter the backlash values when its clear too. Hopefully I can cancel out the 10' if it still exists after the new batteries!

It looks like a power tank is the best way to go...shelling out nearly 20 euro for a few nights batteries is madness!

Kencollins

Another question...

Can I sit the battery pack on the telescope mount or is it too heavy?

I was thinking of making my own, can get 12v 7.5 AH battery delivered for 16 euro!

ZeRoY

Kencollins wrote: »

Another question...

Can I sit the battery pack on the telescope mount or is it too heavy?

I was thinking of making my own, can get 12v 7.5 AH battery delivered for 16 euro!

You defo dont want to add un-necessary weight on the mount so no, keep the battery pack under the mount, between tripod legs or something.

7.5AH will probably power the mount for a good few hours, maybe up to 6-7h. If you make it yourself make sure to add a fuse box!

Edit: Powertank DIY by Tzetze

Kencollins

I am going to make it myself!

Have ordered a 10ah car starter from amazon for 35 euro. I intend to butcher it for all the parts and install them in a small toolbox!

I got to go out last night with the new duracell batteries and the performance was even WORSE.

Granted, I did leave the scope out between 8pm and 1:30am before I even got a chance to use it!

Would the low temps have meant the batteries were below the needed performance again? It was about minus 3.

I'm starting to get fed up now, it was working so well for months and now its gone rubbish all of a sudden!

Tzetze

Did you make sure that daylight savings time was set to off when setting up the time? (If that setting exists in your hand controller.) Being an hour out will equate to 15' at zenith but I imagine a completed goto alignment would compensate for time error.

Kencollins

Yeah DST is set to off, time zone 00. Have checked the time and date 10 times at least, so all is ok there.

I hope the low temperatures of the mount and battery pack were at fault last night.

In any case, I have stripped down the mount to see if there is anything happening at the motor and gears. The encoders all seem fine, and the motor runs straight away on pressing the buttons. I took out the motor and the grease on the gears looked very sparse.

I went and got some lithium grease in the motor factors and applied it to the small motor cog and the large mount gear with a kids paint brush. I might have over done it a bit, but hey, its only grease.

I also tightened the center retaining bolt a bit. It seemed a bit slack so I put a quarter turn on it. The mound certainly feels smoother anyway!

If the skies are any way clear tonight I will go outside again and have Ken -V- scope round 15. The people in the houses behind me (TURN OFF YOUR FU***NG BATHROOM LIGHT!!!!!) must think im a right weirdo for being in the garden at 2am!

Nerro

i have to ask again.was your mount platform lvl???if its not it really affects the go to accuracy aswell.

Kencollins

I have it on a paving slab set into the garden. A 1m spirit level shows that is is dead level. There is a tiny bit of shift on the slab when i stand on one of the corners, but I can't imagine a 20kg scope would cause too much drift!

I will put the scope on the footpath outside my door tonight (south facing) and see if i can align it with some of the stars....belteguese or sirus if it's clear early enough!

ZeRoY

Kencollins wrote: »

TURN OFF YOUR FU***NG BATHROOM LIGHT!!!!!

LOL welcome aboard. 1 next door and 2 behind me drive me NUTS at times!

Plug

You hardly forgot that its the month/day/year on the date entry?

Kencollins

I thought it might have been that, but the latest firmware added a MM/DD/YYYY to the menu so it helps!

Before the firmware update the only way I could be sure was try and enter a date beyond the 13th of the month!

Hopefully the firmware update, battery pack butcher creation, greased gears, level ground, and keeping the mount in the warm while the scope cools will help.

One problem though, low cloud and rain!

Kencollins

I went to try again last night, and it failed badly...

The scope was perfectly level, checked with 2 spirit levels. The time was corect to the second, and the gps was taken from my phone in DMS format.

I was using my new battery pack, and it was reading 12.8V constant for the whole time I was out.

I aligned with aldebaran and procyon. They are about 60 degrees apart, and alt 30-40.

The scope did put the second star JUST inside the 25mm eyepiece on alignment. However, when I told it to go to the Orion nebula, it missed on the AZ by about 2 degrees. Re-aligned with the reference stars, and again out by 2 degrees when I selected jupiter.

All of these stars are within the same 1/4 of the sky, so SURELY the scope should be at least putting the selected object in the eyepiece view?

The only other thing I remember doing was tightening the centre bolt a small bit when I got the scope. I thought it was a little loose as there was a small amount of wobble in the mount. I wonder if slackening off a little bit on this nut might make the alignment be better?

I'm pretty close to giving up on the GOTO at this stage

Kersh

Has it ever worked?

If it has, then tightening the centre nut wouldn't be the problem.

It seems to be much further off now than the original post.

Kencollins

Kersh wrote: »

Has it ever worked?

If it has, then tightening the centre nut wouldn't be the problem.

It seems to be much further off now than the original post.

It worked fine for the first few months. I didn't use it for 2 months, and now this! I loosened the nut and the mount does twist a bit more freely. If that doesn't work I think I am out of options!

Kersh

Let us know how you get on.