Help needed with G11 mount.

[Stefan12]

Hi all,

Could someone please tell me why my Losmandy G11 is making grinding sounds while I'm slewing?
I've only had this mount for a couple of months and ever since I got it, it has made these grinding sounds. I thought nothing of it, but the fact that I have not been able to get consistent guiding in declination makes me suspicious that something is wrong.
I've tried everything to sort out the DEC jumps in PHD, but nothing seems to work, which leaves me thinking something is wrong with the Motors.
Below is a link to a quick youtube video I made which shows the problem.
I've also attached a PHD graph showing the jumps in DEC I'm getting.

I'm using a Orion 50mm mini guider with QHY5 camera.

https://www.youtube.com/watch?v=G80ykEhF8lo&list=UUo5mKBobdAWk5SdGMxaJ9SA


Stefan

[multiweb]

Sounds like the meshing might be too tight or one of the grab screw is sticking out. Have you opened the block and looked at it? Nothing major to worry about.

[adman]

The "frequency" of the grinding/buzzing sound is somewhere between the motor speed and worm speed, so It sounds like you might have a problem with the gearbox. The motor is obviously working, but it looks like either the motor is not meshing properly with the gearbox, or maybe some teeth have stripped inside the gearbox...

Did you buy it new or 2nd hand. Are you comfortable taking the motor/gearbox off to have a look?

[Stefan12]

I bought the mount new from opt-corp in the US.
Since making the video I've swapped the motors around. While the RA sounds better, the DEC still sounds horrible.
I'm not comfortable fiddling with any part of it to be honest, in case I make things worse.

[Stefan12]

Marc, no I haven't opened the block as the allen keys supplied with the mount do not fit the tiny screws on the worm cover. As far as I know I need a 1/16th allen wrench.

[multiweb]

You're going to have to get in there. There's really nothing you can break. It's a very simple design. First thing you can try is to relax the meshing a little see if it's still doing that horrible noise. Next you'll have to check the coupling between the gearbox and the worm. Last check if the gearbox is not damaged as previously posted. Gearboxes are about $25 each so no big deal. If the mount is new they might even ship a new one for you. Have you contacted opt-corp about this?

PS: the covers are only wedged. Just loosening the small crews will suffice to remove them. Then you'll have a clear look at the worm and the Oldham coupler.

[wasyoungonce]

If it sounds bad in DEC only...separate the DEC motor from the gearbox (2 hex head screws, takes 2 mins) and run the motor in DEC to listen to it.

Now run the motor at slew speed in DEC ....if it's "grinding" then it's in the motor.

If not it's in the gearbox/worm drive assy.

[Stefan12]

Thank you for all the suggestions guys.
No I haven't got in contact with Opt-corp yet.

I'll let you know how I get on :)

[Stefan12]

I've gotten the worm cover off now and unscrewed the motors from the gearbox. Both Motors are running fine with no grinds.
The G11 is still all new to me, so how do I adjust the meshing? Are there any instructions online? What should I be looking for if its the Oldham coupler?
It sounds like the grinding is coming from the gearbox, but it could be the coupler. It's hard to tell.

[el_draco]

If you have a stuffed gearbox, let me know. I have a couple of spares and you can have one for the cost of postage.

Rom

[multiweb]

The oldham coupler won't be an issue. You have to make sure the two end blocks are parallel or the bearings will be pinched and might pop every revolution of the worm. You can use the cover as a wedge to align them. So loosen both hex bolts so you can rotate the blocks, then hold the cover against the front face of the blocks so they're aligned, then squeeze them slightly so the worm is snug between them, finally mesh the worm in and tighten slightly the hex screws without rotating the blocks. Takes a little practice to get it right. Or get the one block worm from losmandy.

[JohnG]

This may help you, old but still current with the standard blocks.....

[wasyoungonce]

Stefan

meant to say...there is some good info on Gemini gearboxes here (http://gemini-2.com/Gearbox_mod.php).

And this gent (http://www.wilmslowastro.com/tips/g11gemini.htm) has some info regarding gearboxes and worm mesh that is pretty good.

edit:
If you think the issue is the Gearbox...swap them from DEC to RA and re-test. This is the easiest way to narrow the issue!