EQ8 DEC backlash question..

[WanderingEye]

Hello all.

I wanted a bit of advice, I read and posted in the thread below, but it’s an old one, so thought I would start new, I have got a secondhand EQ8, and after reading all the issues with DEC backlash, I thought I would check it out..so I got a 500mm dovetail bar in the saddle, and moved the Mount head with the handset all round at approx 20 degree intervals, I also watched on the handset using the method described by @Zakalwe in the thread below, (this shows the mount position via the encoders) now in the full 360 degrees there was no movement on the scale on handset at all, or at least it did not register, but there was a tiny amount of movement at the end of the 500mm bar, just noticeable by feel...(all the way round)

Also I noticed that the tiny amount of backlash there is, was the least, when the clutch lever was opposite to the worm, so 180 degrees round, so I guess the pressure from the clutch on the gear has some effect on this issue, when the clutch lever was on the same side as the worm, the backlash was the most, but still tiny..

So is this something I should try and fix, or should I not worry...

Thanks 

original thread on this subject

 

Edited November 2, 2019 by WanderingEye

[michael8554]

Didn't quite follow your description, but I think you are saying that a full 360 rotation was accurately reflected in the handbox reading? 

Was that down to secs of degrees?

Also the amount of Dec backlash that can give guiding problems is too small to be felt by rocking - if you can feel it it's miles out. 

Michael 

 

 

[WanderingEye]

6 minutes ago, michael8554 said:

Didn't quite follow your description, but I think you are saying that a full 360 rotation was accurately reflected in the handbox reading? 

Was that down to secs of degrees?

Also the amount of Dec backlash that can give guiding problems is too small to be felt by rocking - if you can feel it it's miles out. 

Michael 

 

 

wow, I did not realise it was miles out....hmmm, maybe I bought a dud... 🙁

Yes it was down to seconds, and it does not alter when rocking the saddle with the dovetail bar..so there is not enough backlash to move even 1 second...so is that still miles out..??

Edited November 3, 2019 by WanderingEye

[michael8554]

I'm going to confess to my unsure knowledge here, but 1arcsec, a typical guiding accuracy, seems to be about 0.1 of a second of a degree. 

One for vlaiv I think...... 

Michael 

[Merlin66]

Michael,

1 arc sec is 1 second of arc. A degree of arc has 60 min of arc, or 60 x 60 =3600 sec of arc.

So you could say, 1 arc sec is 1/3600 of a degree = 0.000277 degree.

 

[ollypenrice]

The problem with some of the first ones was that the mesh was inconsistent around the wheel. The one I had was too tight in one part of the rotation and too slack in the other so there was no way to tune this out. If you have a consistent mesh - and it seems that you proabably do - then you should be able to adjust it to eliminate the perceptible play. I'd be optimistic in this case.

I've imaged successfully at moderate resolution on mounts with small but perceptible play in the worm and wheel. 

Olly

[michael8554]

5 hours ago, Merlin66 said:

arc sec is 1 second of arc. A degree of arc has 60 min of arc, or 60 x 60 =3600 sec of arc.

Thanks Merlin, 

So the 360 test was accurate to 1 arcsec, which should be easily guided out. 

Did the test involve some reversals? A series of slews in the same direction without any backlash reversals would probably be that accurate? 

"A tiny amount of movement all round" might be arcmins?

But this is all too academic.! 

If imaging results are good I'd be afraid my adjustments would throw it out. 

Michael 

[WanderingEye]

Well, I am not sure what the scale is on the EQ8 encoder, but what I do know is that the amount of backlash does NOT register on the encoder when I move, so it’s not enough to show there, but not sure how small the increments are in there.... 😀

Edit: just found this, the resolution of the encoder, so does that mean that the backlash is less than 1.2 arc-mins, as it does not register..??

17624 Counts/Rev., approx. 1.2 arc-minutes

Edited November 3, 2019 by WanderingEye

[gorann]

I have an EQ8, bought it new in 2016 and put it on a pier in my obsy. By wiggling the Dec axis I could feel a noticible backlash but was initially afraid to do anything about it. However, after a year or so I found enough courage to adjust it using the manual from Orion (attached here). After that I could at least not feel any backlash. Still, I was never really happy with the guiding curves, at least on some nights and I evetually ended up buying a Mesu 200. However, since I then also had nights with poor guiding I finally realized that there was nothing wrong with my mounts - it was the sky that was playing up. So to be fair to the EQ8 I built myself a second obsy this summer where it now resides lifting 40 kg of Meade 14"ACF. On good nights I get 0.4"/pixel (RMS) guiding with it (ZWO OAG with Lodestar X2), so EQ8 and I are good friends now.

EQ8 Dec backlash adjust.pdf

Edited November 3, 2019 by gorann

[WanderingEye]

4 hours ago, ollypenrice said:

The problem with some of the first ones was that the mesh was inconsistent around the wheel. The one I had was too tight in one part of the rotation and too slack in the other so there was no way to tune this out. If you have a consistent mesh - and it seems that you proabably do - then you should be able to adjust it to eliminate the perceptible play. I'd be optimistic in this case.

I've imaged successfully at moderate resolution on mounts with small but perceptible play in the worm and wheel. 

Olly

So would you say less than 1.2 arc-mins of DEC backlash “small”...? I can just feel it at the end of a 500mm dovetail in the saddle.. 

Edited November 3, 2019 by WanderingEye

[ollypenrice]

2 hours ago, WanderingEye said:

So would you say less than 1.2 arc-mins of DEC backlash “small”...? I can just feel it at the end of a 500mm dovetail in the saddle.. 

Like Goran I'd just have a go at adjusting it.

Olly

[Stub Mandrel]

8 hours ago, WanderingEye said:

Well, I am not sure what the scale is on the EQ8 encoder, but what I do know is that the amount of backlash does NOT register on the encoder when I move, so it’s not enough to show there, but not sure how small the increments are in there.... 😀

Edit: just found this, the resolution of the encoder, so does that mean that the backlash is less than 1.2 arc-mins, as it does not register..??

17624 Counts/Rev., approx. 1.2 arc-minutes

Arc minutes are what you need for GOTO, arc seconds are 1/60  the size and what you need for guiding.

Backlash in DEC shoudl be as small as you can get it, but totally eliminating it isn't as important as it being consistent - if it is reasonably small and consistent PHD2 will be able to work it out empirically and compensate for it.

[WanderingEye]

31 minutes ago, Stub Mandrel said:

Arc minutes are what you need for GOTO, arc seconds are 1/60  the size and what you need for guiding.

Backlash in DEC shoudl be as small as you can get it, but totally eliminating it isn't as important as it being consistent - if it is reasonably small and consistent PHD2 will be able to work it out empirically and compensate for it.

Yes thanks for that, I guess I was just tying to figure out if what I had (somewhere under 1.2 arc-mins of movement) was already small enough for PHD to sort, or whether it should be smaller... 😀👍

[cotak]

On 03/11/2019 at 05:31, gorann said:

I have an EQ8, bought it new in 2016 and put it on a pier in my obsy. By wiggling the Dec axis I could feel a noticible backlash but was initially afraid to do anything about it. However, after a year or so I found enough courage to adjust it using the manual from Orion (attached here). After that I could at least not feel any backlash. Still, I was never really happy with the guiding curves, at least on some nights and I evetually ended up buying a Mesu 200. However, since I then also had nights with poor guiding I finally realized that there was nothing wrong with my mounts - it was the sky that was playing up. So to be fair to the EQ8 I built myself a second obsy this summer where it now resides lifting 40 kg of Meade 14"ACF. On good nights I get 0.4"/pixel (RMS) guiding with it (ZWO OAG with Lodestar X2), so EQ8 and I are good friends now.

EQ8 Dec backlash adjust.pdf 340.76 kB · 2 downloads

You don't have to make any adjustments between winter and summer? How large is your temp swing between the seasons?

I am curious if the new EQ8 might be something worth my while to look into.

[gorann]

7 hours ago, cotak said:

You don't have to make any adjustments between winter and summer? How large is your temp swing between the seasons?

I am curious if the new EQ8 might be something worth my while to look into.

where I live (60 °N) it is too bright for imaging between May and late August, so I generally do my imaging between +10°C and -10°C and I have not noticed a need for adjustment. I don't know anything about the new EQ8 but I would expect it to be as good as and most likely better than the old one. Why would they otherwise up-grade it? If they managed to get away with the backlash that affected many of the older ones, then it should be a really good mount, because backlash appears to have been the only significant problem with EQ8.

[cotak]

Thanks for the info gorann. Looks like the jury's still out.

[WanderingEye]

3 hours ago, gorann said:

where I live (60 °N) it is too bright for imaging between May and late August, so I generally do my imaging between +10°C and -10°C and I have not noticed a need for adjustment. I don't know anything about the new EQ8 but I would expect it to be as good as and most likely better than the old one. Why would they otherwise up-grade it? If they managed to get away with the backlash that affected many of the older ones, then it should be a really good mount, because backlash appears to have been the only significant problem with EQ8.

I have been doing a load of testing on mine over the last few days, and have some interesting findings...

They have improved the clutches on the new EQ8, which was a large cause of backlash in the older ones, mine included, when the clutch is engaged it causes there to be no backlash in the opposite direction to the clutch, in fact it’s quite right there, while there is a  bit of backlash in the other 3/4 of the drive, if you then loosen the clutch, the tightness goes...the clutch was a bad design, and pushes the DEC shaft in a lateral way, only a small amount  but enough to make people believe that there spur gear was not perfectly round...this is false assumption, at least on mine... try it and see, run your drive all the way round on full speed, while connected to a power supply that shows the AMPS being drawn, when it gets the the part opposite the clutch, you will see the draw go up as it tightens, stop there and release the clutch, and move round 180 degrees, then run again and you will see the tight spot has moved with the clutch position....

I have tested this extensively over the last few days, and i have removed all the backlash, well as much as I can feel, and I can run all round 360 degrees with perfect results no backlash, and drawing the normal 1.4 amps all the way around, but as soon as I apply the clutch it binds in a certain position, and the amps draw goes up to 1.9-2.0, and an audible Wine can be heard as it starts to bind, again release the clutch, and perfect all the way round...

 

[gorann]

5 hours ago, WanderingEye said:

I have been doing a load of testing on mine over the last few days, and have some interesting findings...

They have improved the clutches on the new EQ8, which was a large cause of backlash in the older ones, mine included, when the clutch is engaged it causes there to be no backlash in the opposite direction to the clutch, in fact it’s quite right there, while there is a  bit of backlash in the other 3/4 of the drive, if you then loosen the clutch, the tightness goes...the clutch was a bad design, and pushes the DEC shaft in a lateral way, only a small amount  but enough to make people believe that there spur gear was not perfectly round...this is false assumption, at least on mine... try it and see, run your drive all the way round on full speed, while connected to a power supply that shows the AMPS being drawn, when it gets the the part opposite the clutch, you will see the draw go up as it tightens, stop there and release the clutch, and move round 180 degrees, then run again and you will see the tight spot has moved with the clutch position....

I have tested this extensively over the last few days, and i have removed all the backlash, well as much as I can feel, and I can run all round 360 degrees with perfect results no backlash, and drawing the normal 1.4 amps all the way around, but as soon as I apply the clutch it binds in a certain position, and the amps draw goes up to 1.9-2.0, and an audible Wine can be heard as it starts to bind, again release the clutch, and perfect all the way round...

 

That is very interesting. So the clutches made people think that the spur gear was not perfectly round🙄. Wonder if Olly @ollypenricemay have a comment on this - I have read about his problem with assumed oval spur gears on an early EQ8:

 

Edited November 5, 2019 by gorann

[ollypenrice]

2 minutes ago, gorann said:

That is very interesting. So the clutches made people think that the spur gear was not perfectly round🙄. Wonder if Olly @ollypenricemay have a comment on this - I have read about his problem with assumed oval spur gears on an early EQ8....

No, if I locked the clutch at one position of the wheel on the worm I might have either backlash or too tight a mesh. If I released the clutch, moved the Dec housing and re-locked the clutch nothing would change. But if I drove the wheel 180 degrees with the motor I'd get the opposite of what I had before, so backlash would turn to binding or vice versa. Moving the Dec housing manually by unlocking the clutch had no effect on whether I had backlash or binding.

I think you may be using the wrong term when you say 'spur gears.' For the problem to arise over a scale of 180 degrees in Dec the problem has to lie with the worm and wheel. Spur gears are like this: https://www.indiamart.com/proddetail/spur-gear-15890246548.html

Olly

[gorann]

1 hour ago, ollypenrice said:

No, if I locked the clutch at one position of the wheel on the worm I might have either backlash or too tight a mesh. If I released the clutch, moved the Dec housing and re-locked the clutch nothing would change. But if I drove the wheel 180 degrees with the motor I'd get the opposite of what I had before, so backlash would turn to binding or vice versa. Moving the Dec housing manually by unlocking the clutch had no effect on whether I had backlash or binding.

I think you may be using the wrong term when you say 'spur gears.' For the problem to arise over a scale of 180 degrees in Dec the problem has to lie with the worm and wheel. Spur gears are like this: https://www.indiamart.com/proddetail/spur-gear-15890246548.html

Olly

Yes, I also wondered about "spur gear".  In any case, let us hope this is now problems of the past and that newer EQ8ts and especially the Mark II EQ8 is the affordable good heavy duty mount we once longed for

Edited November 5, 2019 by gorann

[WanderingEye]

17 minutes ago, gorann said:

Yes, I also wondered about "spur gear".  In any case, let us hope this is now problems of the past and that newer EQ8ts and especially the Mark II EQ8 is the affordable good heavy duty mount we once longed for

Yes, I meant the worm and wheel..... sorry... 😀

[WanderingEye]

1 hour ago, ollypenrice said:

No, if I locked the clutch at one position of the wheel on the worm I might have either backlash or too tight a mesh. If I released the clutch, moved the Dec housing and re-locked the clutch nothing would change. But if I drove the wheel 180 degrees with the motor I'd get the opposite of what I had before, so backlash would turn to binding or vice versa. Moving the Dec housing manually by unlocking the clutch had no effect on whether I had backlash or binding.

I think you may be using the wrong term when you say 'spur gears.' For the problem to arise over a scale of 180 degrees in Dec the problem has to lie with the worm and wheel. Spur gears are like this: https://www.indiamart.com/proddetail/spur-gear-15890246548.html

Olly

You are correct my terminology was wrong, but the science is correct....it’s worm and wheel and worm and spur gear... 👍

[ollypenrice]

10 hours ago, gorann said:

Yes, I also wondered about "spur gear".  In any case, let us hope this is now problems of the past and that newer EQ8ts and especially the Mark II EQ8 is the affordable good heavy duty mount we once longed for

Certainly, and I want to be clear that I'm only discussing my old mount now because I was asked to do so.  If SW have sorted it out, as it seems they have because Sara is another exacting but happy user, then that's great. I think what so irritated me with my early EQ8 is that SW stated categorically that the Dec mesh was adjusted by hand because there was there was no spring loaded compensation. That means that they must have been perfectly well aware that the mount was binding on one side and rattling with backlash on the other, yet they sent it out anyway. As a result I spent two whole days unboxing, assembling, dismantling and reboxing the mount. 

If my 14 inch Meade LX200 mount expires, as they sometimes do, I'll almost certainly buy an EQ8 for it. I'm not hostile towards the present EQ8 by any means.

Olly

Edited November 6, 2019 by ollypenrice
Typo

[WanderingEye]

1 hour ago, ollypenrice said:

Certainly, and I want to be clear that I'm only discussing my old mount now because I was asked to do so.  If SW have sorted it out, as it seems they have because Sara is another exacting but happy user, then that's great. I think what so irritated me with my early EQ8 is that SW stated categorically that the Dec mesh was adjusted by hand because there was there was no spring loaded compensation. That means that they must have been perfectly well aware that the mount was binding on one side and rattling with backlash on the other, yet they sent it out anyway. As a result I spent two whole days unboxing, assembling, dismantling and reboxing the mount. 

If my 14 inch Meade LX200 mount expires, as they sometimes do, I'll almost certainly buy an EQ8 for it. I'm not hostile towards the present EQ8 by any means.

Olly

Yes it does sound like your issue was more than just a poor clutch...but this clutch issue is in the present EQ8 mounts, but not the newer EQ8-R pro, as they have the new upgraded clutches, which AFAIK stop this issue...also it’s much worse on the DEC side rather than the R.A.. 😀

[gorann]

Not sure if anyone reads this thread any more, but I just wanted to report that my EQ8 (bought in November 2015) still behaves very nicely, and it has allowed me to get very close to some quite distant galaxies. By coincidence I just saw this video advertizing the more recent EQ8-R, and at the end of the video the seller proudly announces that it is capable if guiding at 0.6"/pixel, and that was with OAG on a 1000mm FL telescope. As long as seeing cooperates I regularly get 0.4"/pixel with my old EQ8 (recent curve attached) even if it is carrying 40 kg of SCT and 40 kg of counterweights. It came with a lot of DEC backlash (I could both see it and feel it when wiggling the saddle), but after I adjusted that according to the manufacturers instructions, I can at least not feel it.

Conclusion: if you are lucky enough to have an EQ8 of the old model that performs well there is no reason to upgrade to the EQ8-R. They also had to get rid of the "Freedom-Find" encoders in the new mount to fit in the new cable management. I expect that it may mean less pointing accuracy and maybe leads to the possibility to crash into the pier since the mount no longer knows where it is (but I may have missunderstood this).