backlash on the NEQ6

[Daniel-K]

ive had backlash on mounts before but just how much is acceptable and what exactly does it do?

Dan

[perfrej]

I'd say none. You uget rid of it by tightening the worm gear axis bearings and adjusting the worm pressure against the what's-its-name wheel. Simple procedure. Check out Astro Babe's site for detailed instructions.

/p

[russellhq]

I would imaging it would affect goto and guiding. If you use plate solving, then goto shouldn't be a problem. And if you balance your mount and polar align correctly such that the gears are always loaded and you only drift in one direction, then guiding shouldn't be a problem either.

But as perfrej says, it's probably better to tune up the mount and get rid of as much as you can.

[Daniel-K]

thought so ive done it before on my old NEQ6 but it was a pain

[perfrej]

The adjustments you need take no more than fice minutes

/per

[perfrej]

Five... IPad...

[fwm891]

Do a belt mod - makes a great difference to guiding, slew noise etc...

[swag72]

Why don't you try it first and see whether the backlash is a problem to you? I say that as I have a little movement in my HEQ5 and it doesn't affect my goto neither my ability to do 30 minute guided subs.

[kirkster501]

My NEQ6 works brilliantly. It is a joy and highly accurate (long may it continue). Not done a thing to the drive since opening the box.

When you do have backlash in the drive of a scope - like my Dob 300 had - it is the most annoying, frustrating and infuriating PITA on earth!! The amount of acceptable backlash I would suggest is zero, or a very, very small amount - as Per states.

[jnc71106]

i've got backlash in my HEQ5 and like sara it has no effect on my guiding or goto so i have never bothered to fix it

[perfrej]

Backlash, by definition, is wrong and should be adjusted. My two cents' worth

/per

[StuartJPP]

I don't know too much about this subject, but surely backlash is a cumulative thing that will affect observing more than imaging...i.e. if you are going backwards and forwards to view different objects then the backlash can become a problem. If you are imaging for most of the night on the same object then it shouldn't be much of a problem.

Well that is my understanding since it also applies to CNC milling. Only when you change direction does the backlash come into effect.

[1parsec]

Usually backlash is only an issue for imaging.

Minimising backlash is always a good idea, but it shouldn't be some thing you spend hours worrying over.

I tend not to worry too much about Ra backlash as the drive is moving in the same direction during an exposure and if I slightly

unbalance so the east side is heavier the drive is always lifting the load and keeps the mesh on one side of the worm-wheel.

Dec backlash can create more issues with the direction changes during guiding but again dec drift is normally in one direction as well so the

unbalance trick works here too.

Dave.

[jackrussell0232]

Wow, there's a real range of advice here.

I'd have to say I agree with a few bits of a few of the threads.

1. 'Minimise backlash as far as possible'. Yes, of course you want to do this. And it's not too difficult to do on an EQ6. It's impossible to eliminate completely, or else your gears would be locked together and unable to turn due to excessive friction. But you don't want more than is essential to allow the gears to move over each other with a thin film of grease between them (not applicable to Mesu 200 obviously).

2. 'Backlash doesn't affect imaging'. Really? Do you like the soft focus effect in your astro photos? Do you image at 28mm focal length? Ok, so you can minimise the impact of backlash by always approaching targets in the same direction when doing a 'goto', and always keeping your scope slightly out of balance, so it always rests at one end of the the limit of backlash, but ask Olly, Per, Yves what they think about this. And that's not considering imaging in breezy conditions. Good luck with that backlash.

Some people will say they have backlash because they can feel an almost imperceptible movement when they manhandle their scope, some will say they have a little backlash because 10 seconds after pressing the east button and the motor running up, the scope starts to move east. This is all relative.

But I'd definitely recommend having a go at reducing it.

Just my two penneth,

Jack

[swag72]

'Backlash doesn't affect imaging'. Really? Do you like the soft focus effect in your astro photos? Do you image at 28mm focal length? Ok, so you can minimise the impact of backlash by always approaching targets in the same direction when doing a 'goto', and always keeping your scope slightly out of balance, so it always rests at one end of the the limit of backlash, but ask Olly, Per, Yves what they think about this. And that's not considering imaging in breezy conditions. Good luck with that backlash.

While I don't doubt that it wold be favourable to eliminate all backlash, the small amount that I have does not affect my 30 minute subs (I even did some hour long ones for fun and they were spot on) and it doesn't seem to give me a soft focus either. Certainly no one has mentioned this to me and I'm sure that they would have done had my focus been off. So while I do agree that it's better to have none ...... I'm sure ...... I have found no ill effect by having some. This is only based on my personal experience with my HEQ5, maybe other people's mounts will behave differently.

We've got enough to worry about in AP, so if I can remove one bit of worry (ie, it has no ill effect) then that's alright by me! Gives me time to worry about everything else that can and does go wrong!!

[jackrussell0232]

Sara, it's not that I disagree with what you're saying. You get some excellent images out of your rig.

It is quite true that you could have 5+ degrees of RA and dec backlash in your system, but if the gears are always engaged and driving in the same direction, the backlash would never be seen. Imaging at 450mm focal length (baby Q) is more forgiving of mount errors too. (that's why I've started).

It's just that in my experience, if I'm taking a number of long subs over several hours, without allowing a flip, my dec guiding will change direction (sometimes it does this anyway, within a sub). I'm pretty sure that's why I found my autoguiding seemed to have an easier time after I tuned out most of my dec backlash.

And I certainly agree that if you think something is wrong with your mount, but you're getting great images, you should leave well alone!

Jack

[jambouk]

And the impact backlash has also needs to be put into context of the speed of the optics on the mount; at f/15 a bit of backlash is much more of a nuisance than at f/4 i suspect.

I've just (well yesterday) nearly eliminated the backlash from my azeq6; just waiting for a clear night to see if it will improve my goto accuracy.

James

[JamesF]

I've just (well yesterday) nearly eliminated the backlash from my azeq6; just waiting for a clear night to see if it will improve my goto accuracy.

How are you measuring the amount of backlash that is present?

James

[jambouk]

James, I don't know that it is was technically 'backlash'.... When both clutches were locked, there was a load of play in both axes, and I'm convinced as each axes crossed its equator (meridian for RA and an imaginary line between the east and west horizon for the declination) that the 'slack' allowed the scope to flop in the direction of travel by the amount it was slack.... I think, but have no proof, that since I've tightened this slack up (none in the dec axis now and only a smidge in the RA) that my GOTO is better.

I never formally measured it, and not even sure how I would have done / should have done.

James

[ollypenrice]

Heh heh, Per and Yves and I know each other well and Per knows the case for friction drive as a zero backlash solution. It is one of only two such options, though buying a well engineered 10 Micron approximates to a third! Per and Yves and I also know that Per and Jonas Grinde go unguided with 10 Microns and respectable focal lengths. Personally I think that a friction drive 10 Micron would be even better, especially long term, but who knows?

Nobody wants backlash but most are likely to have some and finding the right 'out of balance' factor is likely to be the best bet on budget mounts.* You can eliminate it on an EQ6 by fine tuning? I don't believe it! What about the spur gear primary drive? I'd say, get it as good as you can mechanically and then find the right 'out of balance' factor. East heavy, obviousy, but the dec imbalance may need a bit of experimentation.

Olly

*Dammit, why did I say budget mounts? I'm running two Takahashi mounts here as well, hardly budget, and they need the right imablance. When they have it it they do the business.

[JamesF]

James, I don't know that it is was technically 'backlash'.... When both clutches were locked, there was a load of play in both axes, and I'm convinced as each axes crossed its equator (meridian for RA and an imaginary line between the east and west horizon for the declination) that the 'slack' allowed the scope to flop in the direction of travel by the amount it was slack.... I think, but have no proof, that since I've tightened this slack up (none in the dec axis now and only a smidge in the RA) that my GOTO is better.

I never formally measured it, and not even sure how I would have done / should have done.

James

If it's that much that you can feel it then I reckon it must be pretty bad.  I think you can still have a fair bit that isn't easily measurable directly by sight or touch though.  I've struggled to find a good method to measure it myself in any meaningful way.  I have some ideas I want to experiment with though.

James

[JamesF]

You can eliminate it on an EQ6 by fine tuning? I don't believe it! What about the spur gear primary drive? I'd say, get it as good as you can mechanically and then find the right 'out of balance' factor. East heavy, obviousy, but the dec imbalance may need a bit of experimentation.

I agree.  There has to be some play between the gears otherwise as has already been said friction will cause excessive load on the motor, or if you have a powerful enough motor you'll get huge amounts of wear on the gears.  Accepting that you just get it as good as reasonably possible and then relying on weight imbalance and guiding to do the rest seems the most practical approach.

James