Please help Me

Hi. I recently purchased a Losmandy G11 for my 14" Meade. I have taken the mount out a few times, but have not precisely polar aligned it. Last night I polar aligned it and noticed a rather substantial error in the drive. I was using a barlow and 12mm illuminated eyepiece to polar align the mount. The star was drifting back and forth (see attachment) along the same path for as long as I observed it (about 30 min). It took about 30 sec to go up and down along the line. I know that all drive systems have errors, but this error seems rather large. The attached file accurately shows the distance the star moved across the cross hairs. Can anyone tell me what is going on.. Thanks Ryan B

Attached Image:

Ryan, if my calculations are correct and if you were using a 2x barlow, then you were guiding at 592x, which is PRETTY HIGH! That would make your fov of a typical plossl guiding ep at around 300 arc sec. So, you are correct that the observed periodic error was pretty large, maybe in the range of +/- 50 arc sec. That is definitely more than a G-11 should be. I would say to check all your fittings and tolerances and make sure everything is as close to being right as possible. Especially check the mesh between the worm and worm gear. It is adjustable and needs to be perfect for best operation. Basically double check everything, and get someone else that has some knowledge to help you. If you get the same bad results, time to make some phone calls.

Walt

With one of the several on line eyepiece calculators I came up with 652x with a .08 degree true field of view (assuming 50 degree apparent FOV). Now this is where my math gets fuzzy :S , I think that equals about 29 seconds of arc true field???

So if I'm right , that would put you somewhere around 15-20 seconds of arc PE which is about normal.


Robert W.

Walt is about right. From the drawing the
error is say 140 arcsec which is too large.
Something is wrong somewhere. Take the
cover off the RA worm and see if anything is
loose inside. The cover is usualy held on
by two small allen set screws on the cover.

There is a universal joint coupler inside. See if
either end is loose on the shafts. Theres a
couple little allen set screws to tighten if it is.

Also see if the worm mounting blocks are loose.
There is a black anodized aluminum block on each
side of the worm gear, and these are held by
allen head bolts that go through the plate below.
See if either or both are loose. These also control
the contact between the worm and wheel, so if they
are loose you will have to press the worn into
the wheel and make sure there is good contact.

The problen could also be in the gear box
attached to the motor. If it still persists,
try swapping the RA and Dec motors.

Mine tends to give the best tracking if the scope
is balance slightly against the drive (east side
heavy) so that the drive has to work more. This
helps keep the gear surfaces in contact.

Thanks for the help. All check all the fittings. If I can't fix it, it is going back to losmandy for some warrenty work. Thanks again. Ryan B