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Andy Milner

EQ5 Backlash on dual axis motors

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Hi, I'm quite new to using my EQ5 and dual axis motors.

I've been putting up with what I now seem to have found out by reading online some "backlash"

The RA axis takes a lot of playing to get it tracking. I have to slew using the dual axis hand control until the motors actually start to bite and work. It's all very hit and miss.

The dec axis hardly moves at all.

I've read confusing posts on this for and other forums about taking the mount apart and re-greasing and adjusting wormgears here and there.

Can someone with some full knowledge of this problem possibly point me in the right direction to a step by step guide with photos so I can fix the severe backlash I have?

The mount is new and the motors only used 3-4 times. So I'm sure it just needs all fine tuning properly.

Thanks. Andy.

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Regarding the Dec axis what do you actually mean. Is it that it is very stiff and the clutch kicks in? If you mean it doesn't move much after you are aligned then this is correct. Your mount should only track in RA.

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The Dec I'm least concerned about since I'm taking subs and the RA is more important. But it does seem slower and works less often when trying to slew.

The RA motor loses tracking after say 40 seconds and I have to use the hand controller to re slew back a bit to get it to track again. Sometimes it's hard work spending a few minutes trying to get the motors to move. Everything's nice and balanced well, level and polar aligned as when i manage to get 20-30 second subs with the DSLR I have nice round stars. But it's such a headache getting to that point. Then I get a couple of subs then the tracking loses itself. I have to re slew back again to get the RA tracking again.

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If I'm reading this correctly, you're saying that the RA tracking is accurate, just not fast enough?

There is a lot of backlash in these motor units.  The gearboxes have (from memory) six sets of gears in, and it all adds up.  There's not much you can really do about it either, without going for something like AstroEQ and your own stepper motors and belt drive.

However, if the motors are tracking at the wrong speed that might perhaps suggest something like a power supply problem rather than anything to do with backlash.

What you could try doing is adjusting the balance on the RA axis to be a little bit heavy on the east side of the mount.  In theory that should keep the gears meshed and help maintain a steady drive rate.  That would at least discount the possibility that your problems are due to the OTA "rocking" across the backlash between the worm and worm wheel on the RA axis.  You can also tighten the mesh between the worm and worm wheel to remove some of the backlash there.  Someone else might be able to advise on that.  I've never owned an EQ5 and whilst I think it's pretty much the same as the EQ3-2 I'm not certain.

James

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Is it a EQ5 that you have added the motors to?

If it is, I think there maybe a adjusting screw on the motor mounts that allow you to remove the backlash. It is a bit fiddle to do as it is try and error.

Might be a idea to test the motors while not connected to the mount, just to make sure they are working properly and not delaying in changing direction

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Might be a idea to test the motors while not connected to the mount, just to make sure they are working properly and not delaying in changing direction

It may be worth a try, but without dismantling the motors to get at the gearbox it could be quite hard to see it changing direction.  It's hard enough to tell if it's moving at all.

James

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Thanks for advice. I will have a play round indoors and see where it gets me. I do already have AstroEQ so thanks for advising in getting that. I have not had chance properly to understand eqmod fully yet. I'm currently building a patio outside the summer house and intend in running astroEQ to enable goto very soon. Will AstroEQ and eqmod give better tracking accuracy?

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As long as you have a motor that runs at the right speed you should find that tracking accuracy is good if you get good polar alignment to start with.  Given good polar alignment all that is required is for the RA motor to drive the worm wheel at the right speed and you're sorted.  AstroEQ helps with GOTO and guiding (the latter of which helps account for imperfections in the tracking).

To get good polar alignment the best way is probably to use some form of drift alignment.  If you're using APT with your Canon 1100D for instance, there's a built-in system for assisting with that (called DARV I think).  It is a bit of a fag though not exactly hard, but you may end up deciding you need a permanent setup :)

James

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There is also the possibility of end float on the worm, if so the motor will take this up before moving the axis. Worth checking.  :smiley:

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Ooh, yes, good point, Peter.  I'd forgotten that.

James

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I have the dual axis motors and there is a degree of backlash in both RA and DEC, though the backlash in RA is fairly minimal. If the polar alignment is good then I find it tracks very accurately for prolonged periods. I do some astrophotography with a DSLR at prime focus (though via a coma corrector) and I find that 60 second subs are generally very wgood and 120s subs are also usually fine  (the occasional sub does have eggy stars but it isn't bad considering). I find that at high mag you need to be more  aware of the backlash if you start off by slew against the tracking direction, it takes about 5 seconds or so for the backlash to work itself out, but otherwise at 200x it will track accurately with the object in the centre of the field of view of the eyepiece for several minutes (I'd say half an hour before you have to tweak again). Even with my old Nikon D70s mounted I find that even having a far from ideal balance (the camera is quite heavy and iit isn't always on the opposite side of the OTA from the counterweights when I'm aligned on an object)  then the tracking is still ok. If you're having to constanty tweak the position then this suggests that something isn't right. I find that the backlash in DEC is a bit of a pain as you need to push the slew button for a couple of seconds for the backlash to catch up but as this isn't as critical as RA then I don't mind so much.

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I am a bit supprised that a new mount has these problems i can only think that there is some play in the motor gearing or incorrect meshing.

My personal views regarding stripdown etc is dont, adjusting the worm gears is fine but replacing the grease is something i would never do i may be the only one but i think that the original stuff is better than anything else you can buy.

Alan

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Andy, this might be totally irrelevant,

But you can't use the hand contoller with AstroEQ / EQMOD.

QM posts some interesting guiding details with Asto Tortilla over in the AstroEQ for EQMOD thread. DIY Astronomy section.

I don't yet do AP but realize that the gear to gear setup for EQ5 is never going to be ideal, however I am looking into belt drives.

Rich

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I have the dual axis motors and there is a degree of backlash in both RA and DEC, though the backlash in RA is fairly minimal. If the polar alignment is good then I find it tracks very accurately for prolonged periods. I do some astrophotography with a DSLR at prime focus (though via a coma corrector) and I find that 60 second subs are generally very wgood and 120s subs are also usually fine (the occasional sub does have eggy stars but it isn't bad considering). I find that at high mag you need to be more aware of the backlash if you start off by slew against the tracking direction, it takes about 5 seconds or so for the backlash to work itself out, but otherwise at 200x it will track accurately with the object in the centre of the field of view of the eyepiece for several minutes (I'd say half an hour before you have to tweak again). Even with my old Nikon D70s mounted I find that even having a far from ideal balance (the camera is quite heavy and iit isn't always on the opposite side of the OTA from the counterweights when I'm aligned on an object) then the tracking is still ok. If you're having to constanty tweak the position then this suggests that something isn't right. I find that the backlash in DEC is a bit of a pain as you need to push the slew button for a couple of seconds for the backlash to catch up but as this isn't as critical as RA then I don't mind so much.

That's very interesting. When you say you need to slew back against the tracking direction for 5 or so seconds. I do this every couple of minutes. I'm quite happy doing this once at the start and would be very happy if this would last 30 minutes like yours before I need to repeat to take the backlash out.

What I will do is wait till I get out again and re-try everything.

How I currently balance is east heavy and PA with the polarscope using a PA app on my phone to give me the exact time location where Polaris is. This seems to keep me perfectly aligned. I think I'm polar aligned well. However this seems a plausable reason why I go off track. I know I'm polar aligned using the polar scope and Polaris is bang in the middle of its bubble locator. The Big Dipper is orientated well and the "time" location of Polaris seems accurate. BUT maybe it is out slightly and this is causing me to re slew. I guess really I should be happy with 30 seconds. And look forward to using AstroEQ and goto from the laptop. :)

I was hoping to attach my DSLR piggy back for longer exposures.

All of your tips are great, I will have a look at everything again. What I'm concerned about is if this will happen when I start using eqmod and cartes du ciel for goto. So will find out.

By the way Rich, it's okay I'm not going to use the hand control with eqmod as AstroEQ is all I need. Thanks for concern I guess I sounded confused so it's best you check. :)

Thanks peeps.

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The thing that made all the difference to me was running it from a mains power transformer, I found the batteries drained fairly quickly leading to the motors running slow.

http://www.astronomyboy.com/cg5/ shows details for adjusting out backlash.

I found with my EQ5 it was all too easy to go too far and end up with the mechanism "tight", you also face the possibility of bending something.  I guess if its tight the motor may be working against too much resistance making it run slow. 

Cheers

Ross

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I should just clarify that when I said "slewing against the tracking direction" I meant that it was only at the point of adjusting to get the object in the centre of the FOV. The motor will then tick along in the opposite direction at tracking speed and it will first take out the backlask in the cogs before the telescope starts to track. It's only really noticebale at high power. I quite often give the RA a brief nudge with the slewing button in the tracking direction to take the slack out but once settled then it tracks happily for long periods. I use rechargeable batteries and they seem to be fine for at least two hours of tracking - and probably signifcantly longer.

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I struggle to see that it should be an issue at the moment when it's not really that cold, but rechargeables particularly don't have that good a reputation for performing well as temperatures drop.

James

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James,

I did worry about this when I first got the rechargeables but they seem to be fine - my observing/ imaging sessions aren't as long as some others I expect. The camera batteries, on the other hand, do get drained and I change these after an hour so they don't go flat. I should really get power supplies for both as I can run a cable from the house. I expect that I've asked yout this before, and sorry if I have, but what power supply would you recommend for the dual axis drive?

Dave

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That's a few rechargeables at 1.2 volt per battery and the voltage really wants to be 13-14 volts...the Maplin/FLO PSU is a nice one i use 2 to spread the load over 3 dew shields and driving the mount.....

http://www.firstlightoptics.com/power/maplins-xm21x-7a-138v-regulated-mains-power-supply.html

Edited by Tinker1947

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I believe the EQ5 dual axis motors are only 6V, and you really don't want to supply more than that because the handset is a bit touchy.

I used a 6V wall-wart type power supply when I used the same on my EQ3-2, mostly because I had it lying about.  Generally I'd recommend a 6V regulated supply capable of providing at least 1A.

James

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I believe the EQ5 dual axis motors are only 6V, and you really don't want to supply more than that because the handset is a bit touchy.

I used a 6V wall-wart type power supply when I used the same on my EQ3-2, mostly because I had it lying about.  Generally I'd recommend a 6V regulated supply capable of providing at least 1A.

James

Opphhs 6 Volts, for get the Maplin/FLO....:)

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My understanding of the op's problem is that of backlash, and the gears aren't meshed correctly.

Relatively new here but I have used the EQ5 PRO for two years- different motors but similar problems of backlash.

The motors on the Pro are held on with just one screw. (Yes, just one). With the EQ5 payload of only 9Kgs, I have two 5Kg counterweights, the explorer 200p weighing a fair bit, a camera, cables hanging off, ...  I'm frankly not surprised that I'm having to sort out the meshing as often as I do. (Even with spot on balancing)

Despite the fact that the reviews all suggested that this combination is not ideal for astrophotography, I have managed 4mins unguided and 10mins guided on the third and last outing last year with phd (forgot to refocus after forgetting to put the lp filter on!), but I have had to come to terms with the fact that I will have to work at it. In a strange way, for me, the meticulous setting up and tinkering is kind of fun!

If your dual axis has the same fixings, by the way, and you decide to make adjustments, watch you don't pop the threads. Been there!

My understanding of the op's problem is that of backlash, and the gears aren't meshed correctly.

Hope this helps in some small way.

Rob

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On 3/13/2014 at 19:57, Fogagen said:

My understanding of the op's problem is that of backlash, and the gears aren't meshed correctly.

Relatively new here but I have used the EQ5 PRO for two years- different motors but similar problems of backlash.

The motors on the Pro are held on with just one screw. (Yes, just one). With the EQ5 payload of only 9Kgs, I have two 5Kg counterweights, the explorer 200p weighing a fair bit, a camera, cables hanging off, ...  I'm frankly not surprised that I'm having to sort out the meshing as often as I do. (Even with spot on balancing)

Despite the fact that the reviews all suggested that this combination is not ideal for astrophotography, I have managed 4mins unguided and 10mins guided on the third and last outing last year with phd (forgot to refocus after forgetting to put the lp filter on!), but I have had to come to terms with the fact that I will have to work at it. In a strange way, for me, the meticulous setting up and tinkering is kind of fun!

If your dual axis has the same fixings, by the way, and you decide to make adjustments, watch you don't pop the threads. Been there!

My understanding of the op's problem is that of backlash, and the gears aren't meshed correctly.

Hope this helps in some small way.

Rob

Hi Rob

I have a similar set up to you and I am just getting into guiding so far without success. Could you tell me what settings you use for PHD this could give me a better indication of how bad my backlash is. Many thanks Ken 

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47 minutes ago, KRYPTON said:

Hi Rob

I have a similar set up to you and I am just getting into guiding so far without success. Could you tell me what settings you use for PHD this could give me a better indication of how bad my backlash is. Many thanks Ken 

It might be better to start a new thread on this subject. Rob (Fogagen) hasn't logged on to the forum for over a year so you might not get a reply from him.

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