EQ6 backlash

[david maitland]

Sure this one will of been asked a thousand times, is there a way to reduce backlash to a minimum and what is a reasonable amount. Cheers 

[Tommohawk]

 

1 hour ago, david maitland said:

Sure this one will of been asked a thousand times, is there a way to reduce backlash to a minimum and what is a reasonable amount. Cheers 

Probably more than a thousand! Here's my take on backlash but others have different views! I dont have an EQ6, mine's an HEQ5 but I think the same applies.

Mechanically you can reduce backlash by adjusting the mount - the worm can be moved closer to the main gear but of course not too tight so that it seizes. Because the gears are never perfectly centred and also wear more in some places, you may find its loose in some areas and tight in others. 

I find the easiest way is to remove the intermediate gear to disconnect the motor so you can turn the worm through the entire 360 degrees manually and check for tight spots. You can also get a belt drive conversion which may help to reduce backlash in the intermediate gears.

In my opinion, and I think I may be in a minority, backlash isn't the main problem - or even a problem at all!

You can completely avoid backlash by being deliberately slightly imbalanced. The real issue is that the mount will only drive smoothly against the weight, not with the weight behind it. You can try this for yourself - if you remove the intermediate gear, set the mount so theres a slight imbalance and try manually driving the worm in either direction. One way, ie against the weight, it will be quite smooth; the other way will be more jerky.

In RA all you need to do is make it "East Heavy" so the mount always drives against the greater weight of the scope or counterweight depending which side you're imaging. In theory you could have a mile of backlash and it wouldnt matter. Honest.

DEC is a bit more of an issue, because it may need corrections in both directions. Again you can avoid backlash by a slight imbalance, but corrections may need to be in both directions so you can't be driving against the weight in both directions. In fact if you dont have perfect polar alignment its possible to ensure that youre always driving against the weight - but you have to figure out which way to do this, and i've never managed this!

I will now be shot down in flames - you can make your own mind up!

 

[david maitland]

Many thanks tommahawk, brilliant reply it also makes sense, cheers 

[Tommohawk]

12 hours ago, david maitland said:

Many thanks tommahawk, brilliant reply it also makes sense, cheers 

No problem, glad it was helpful - couple of quick after-thoughts though which are perhaps obvious.

Firstly if there's miles of backlash it may affect the pointing accuracy. Also when I suggested that deliberately mis-setting polar alignment might be helpful, this only works if autoguiding. If not autoguiding, PA is crucial. Also of course if PA is not accurate, pointing will be affected.