Balance Issue

[griz11]

I was seeing some really bad guiding the other night. So I started looking for the reason and found out when the scope gets close to vertical the balance goes bad. If 0 is straight up it happens at about 10deg. Not only does the dec balance go away but it messes up the balance on the RA axis as well. Mount starts to oscillate when its guiding. I had something similar on my old SCT that I solved with a little weight shaft that attached near the objective. I just can't see how to solve this balance problem. It would require weights that changed position as the tube changed position. So how do you handle this? The PHD2 guiding plot is all over the place. Used to be a nice tight group. And when the scope is lower it still does but when the scope is almost vertical all bets are off. Is this something that happens with refractors. Do you just have to stay away from those angles when imaging?

Griz

[knobby]

I really am no expert but are you imaging with a diagonal in place, that would change balance massively between horizontal and vertical ?

[D4N]

It could be a few things that are causing your mount trouble.

Check your cables, if one is going tight this will easily throw off your tracking.

Double check your dew shield isn't sliding back on itself.

Check for flexture or if OAG if that is moving at all.

Is there play in the mount that manifests when the scope points up?

My frac has been ok tracking at the zenith.

Sent from my iPad using Tapatalk

[griz11]

It seemed heavy on one side so I put the dual saddle back on and was able to get it balanced perfectly. But that put me slightly over on the other axis so another weight is on the way. Having the guide scope out on the outrigger did the trick. The main scope is a little over a quarter of an inch from being in the spot it was before the dual saddle was put on. So I'm thinking a little lead tape on one side of the scope might work to correct the overbalance. Or maybe rotating the focuser 90 deg. Anyways as soon as the clouds go away again I'll try it out. I should have the other weight by then. Found an issue with my wedge now that its fully loaded. I am over the weight capacity on that piece a bit. Doesn't present a problem except when I'm trying to drift align. Once you loosen up the az plate a bit so you can adjust it the two plates aren't anchored and will sometimes slip. Need to put a pin in the center to anchor that. Its just the distance between the sides of the slots and the screw but that is enough to cause some bizarre stuff to happen. It gets really close to being aligned then one more adjustment was throwing it way off again.  I just happened to be twisting around on it and saw it slip ever so slightly. Going to go look for a hoseclamp that is big enough to go around the two plates. They are pretty stiff and I'm thinking it might hold the two plates in alignment so I can get the drift align done then I'm good. Things you get into when you try and build a frankenrig

Griz

[ollypenrice]

The explanation may be this; you have some Dec backlash. When you are pointing below the zenith you have some out-of-balance making the rig camera end heavy or objective end heavy. Either will load the worm drive onto one side of mesh and hold it there. It won't tend to float back and forth across the free play (backlash) in the gears but sit on one side of mesh. However, near the zenith the heavy end and the light end are arranged with one directly above the other and so they cancel each other out and allow the scope to oscillate across the free play in the gears. To kill the backlash you now need a little weight off to one side.

Olly

[Thalestris24]

Hi

What Olly said. I'm a newt owner and I find it important to balance the scope in the vertical before adding any offsets for imaging.

https://www.youtube.com/watch?v=uK2bXfVNoQU

Louise

[griz11]

Yes there is some play in the dec axis. I have not touched either worm yet I wanted to make sure I knew a little more about the mount before I started adjusting on that stuff. I put the side by side saddle back on and now its balanced just right. It needs a tiny bit of offset to make it all work. But I think I'm going to have to change the mount. The wedge is just not handling the weight. I had this weird problem the other night trying to drift align and I've traced it to the two plates on the bottom of the wedge. They have just enough play in the 3 slots to allow it to rotate that it can slip sideways. Thats why I was getting close to having it aligned then making what I thought would be the final adjustment threw it way off. I have a couple of ideas on how to fix this. I put a stainless hose clamp around the edge of the two plates to keep them lined up. Tightened up it will keep them from slipping I think. If not I located a G-11 head without motors that I can get fairly cheap. If I do that this rig will be for DSLR and experimentation only and the other one will get the WO. I'll move the servos and Scitech to the G-11 use the steppers I have and grab another arduino to make a goto system out of the existing rig. I'm always worried when I'm experimenting with electronics I'm going to blow up something right before a nice clear spell with no moon   Another option I'm looking at if the Losmandy alt az adjustment block will bolt onto my RA axis I can just get one of those and solve the problem.

I read up on adjusting the worms today. There is a set of flats you can use a feeler gauge to set them. So that shouldn't be too difficult. The WO is heavy on one side. The side with the two knobs for the focuser. You can change the behavior by rotating the focuser. Its not offset much maybe 1/4 of an inch. But that and having the guidescope on the outrigger does the trick. Losmandy makes a bucket for a Meade tripod that will fit on my pier. So it won't be a problem to mate the G-11 up with it should I decide to go that way or the mount I have now with the added base from the GM-8. Then again the clamp might fix it. If it works I can take the wedge up to the local machine shop and have a pin put in that base for it to rotate around with no slop. That was a hard problem to figure out. But it all made sense once I tugged and pulled on the mount and actually saw the two plates get out of alignment. Its not much but enough to throw off a drift align in a big way. So I'm happy and a little smarter than when I woke up this morning so its all good.

Griz

[griz11]

Turns out the WO rings have a tapped hole on the side so you can add a little weight to get the balance perfect. Some washers and a nut and bolt should do it. Which is good because I didn't want to use the dual saddle really. Just more weight and possible misalignment. Mounted on top of the WO the guidescope is pretty close to perfectly in line. Going to go ahead and buy the G-11. Its going to be a bit heavier to move but can always haul it to the yard in the basket of my scooter. I'm hauling 22lbs now and its 35 so I should be able to make it work. The Meade field tripod is around 20 so not much difference and fewer trips. A pretty good deal on the G-11 so I don't want to pass it up. It will handle anything I can afford to put on it so I'll be set.

[griz11]

The washers fixed the imbalance. Now its good everywhere. But I'd like to find something that didn't look so diy if I could. The threaded holes are M5 anyone know of some small weights with that for a center bore? Looks like its between 1/2 and 3/4 of a lb. Don't have anything to weigh them accurately. I misread the weight on the WO on their page. I thought it was 11kg not 11lb. So that kind of changes the whole picture with the GM-8 vs G-11. I was thinking I should get the G-11 since I was right at the weight limit of the GM-8/Starlapse. But I'm well within it now so I think I'm going to try and find a solution for the polar align. I was thinking the other night why not try it with just the guidescope lock everything down and put the WO onboard. A little unconventional but it should work. Any droop would be measurable with using the same drift align program. Then I could just set it to accommodate. I'm worried if I go with the G-11 its going to be too heavy and end up gathering dust. 35lbs plus 22lbs of counterweight. Just wish we'd get a night of partly cloudy at least so I could test the band. The Astrotrac wedge has a center peg of sorts. But there is a little slop in it. Wouldn't be a problem under less load though so its not the wedge's fault I'm having this problem. I have till the end of the month to decide so hopefully I'll get a night before then to test. Actually I think the band and knowing about the problem and taking precautions will get me through it. I'd like to keep what I have its nice and lite and easy for me to use.

Griz