Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Backlash repair - EQ3 Pro


Recommended Posts

Hi All,

With ongoing issues related to slewing in the EQ3 pro it's quite clear that there is some significant backlash.

I understand there is a way to repair this myself; does anyone have details of guide for the EQ3 pro to reduce the backlash?

I also understand that the lubricant is important to reduce backlash. Can anyone make any recommendations here too?

Thanks again!

Link to comment
Share on other sites

I've added a few picture here to hel me explain myself.  I'm completely new to backlash correction so let me know if I've overlooked something here!

I've taken the covers off the RA and Dec motors to look for any noticeable misaligment in the gears but nothing immediately stands out.

Dec motor gears engage in less than 1 second at rate speed 1 when alternating direction. Only concern here is that with the slo-mo controls attached, theres a good quarter turn on the slo-mo handle before the gears engage. Should this be tightened or is it a non-issue? If so; how do I tighten this to the gear?

image.thumb.jpeg.ec3feae5e60f44cf9f41d51c364f6db1.jpeg

image.thumb.jpeg.302ff4d0b470627c80badde1142eac11.jpeg

 

RA motor stragely doesnt work when pressing west (left) on the handcontrol at rate 1, only responds at rate 2 or higher.  Any reason for this that anyobody knows? it takes the gears about 1.5 seconds to engage at rate 1 when pressing east  (right) on the handcontrol from the opposite direction.  Unline the Dec slo-mo; the RA slo-mo control is tight and engaged to the gears tightly.

image.thumb.jpeg.b1c846e860b569c2f74aec1d66fa6597.jpeg

image.thumb.jpeg.3a5f68a518699751c468bb1c17ef0e60.jpeg

Would be hugely grateful if someone could offer some insight here :)

Link to comment
Share on other sites

RE: RA left x1 not working~ turn the motor off & the Earth will spin & the correct 1x  rate to move the object across the FOV. 😉

I can't offer any great insight into reducing backlash other than from my non pro eq5 it's a case of adjusting any slop in the gears to a 'best fit'

Then going over the whole procedure again.

Note: too tight a mesh of the gears is much worse than a little too loose as you may strain/damage something. Spur gears need a slight amount of play (cigarette paper between them maybe?)

  • Thanks 1
Link to comment
Share on other sites

10 hours ago, SStanford said:

Dec motor gears engage in less than 1 second at rate speed 1 when alternating direction. Only concern here is that with the slo-mo controls attached, theres a good quarter turn on the slo-mo handle before the gears engage. Should this be tightened or is it a non-issue? If so; how do I tighten this to the gear?

One second is a lot when guiding. You would normally take exposures of 2 to 3 seconds then guide with corrections in the order of 100ms at 1x sidereal (that would be 1.5 arcseconds). So with 1 second backlash you are moving the motor 15 arcseconds before the mount moves and if it is inconsistent you could end up moving the scope a large amount if you add that to your guiding pulses to try to compensate. On top of that you delay the enxt exposure by 1 second which is a significant amount for the normal 2 second expsoure. During that time any  drift is moving the guide star 30% further than usual.

The gear you are looking at is not the only contact point. There is also the worm to ring gear interface which is under the housing.  There should be screws on the housing to adjust that gear mesh.

Backlash is less of an issue in RA. The RA axis is always moving West at a constant 1x sidereal. To guide east is just stops till the stars catch up and to guide west it needs to move at 2x sidereal. The gears should not unmesh except when slewing East at more than sidereal rate.

 

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

@SiriusB; thanks for this.  It seems I didn't need to mess with the Dec worm gear at all.  I've just tightened the two black grub screws as shown below and it has removed all the movement (except the tiniest tick) in the dec axis.  quick response in alternating directs with the hand control too.

DSC_0432.thumb.JPG.a8b4e2a29f6b03ac6eff48fed1ed870f.JPG

@kens; thanks again! the fact that the is no slewing at rate 1 to the west in RA explains why I wasn't having much success with DARV PA!

With the Dec gears sorted, its clear that there is quite a bit of wobble in the RA worm gear.  when turning the slo-mo handle back and forth the wobble seems to be on the gears axis. I can see there are two black grub screws underneath the axel in the housing; these have been tightened fully.  And ideas how I can reduce this wobble? would unscrewing these and pushing the axel further into the housing and tightening sort it out?

Additionally; I notice my RA is very tight when removing the clutches so whilst working on the above I thought I'd try and loosen this up. 

I've followed the excellent guide by @wimvb here but unfortunately my allen key isn't long enough to reach the three grub screws in the disk via the RA lock bolt.  Before I start messing around with this which tool am I using to unscrew the disk as shown below? I'm conscious that I will likely need to re-grease the RA axis, can anyone make a recommendation for the best to keep this smooth?

DSC_0431.thumb.JPG.8530e34b0837765bb65485520b6a7da2.JPG

Link to comment
Share on other sites

As an update: Found an allen key long enough to reach the three grub screws to adjust the metal disk to loosen the RA axis. Once loosened, the disk cant turn more than a fraction and is very firmly stuck on the thread. I assume this can can be unscrewed further with a tool capable of fitting the two holes on the disk as shown above. As it is I'm only able to turn the disk using an allen key in one hole.

Once the grub screws are loose the RA moves much more smoothly and loosely but once tightened again it goes back to how tight it was previously. I decided to balance my current OTA whilst loose then, once marking the dovetail and counterweight bar accordingly, I retightened the grub screws and reassembled the RA setting circle, polarscope and RA locking bolt. Out of curiosity; what is the purpose of the RA locking bolt? the mount will always be tracking in RA so why would anyone want this axis locked?

As for the RA worm gear I loosened the two grub screws underneath the housing and attempted to bring the gear closer to the housing, eliminating the slight wobble. It seems to be as close as it can be but still wobbles as it did previously so I'll have to accept the backlash issue moving to the West (left on keypad). I don't think this should be too much of an issue however so long as I my targets (from parked) are selected clockwise, if that makes sense?

Certainly learned a lot this weekend regarding the mechanical makeup of this mount!

Link to comment
Share on other sites

23 hours ago, SStanford said:

I've followed the excellent guide by @wimvb here but unfortunately my allen key isn't long enough to reach the three grub screws in the disk via the RA lock bolt.  Before I start messing around with this which tool am I using to unscrew the disk as shown below? I'm conscious that I will likely need to re-grease the RA axis, can anyone make a recommendation for the best to keep this smooth?

Needle nose pliers may work, or just two allen keys. I used a piece of wood with 2 nails driven through. As for grease to use. Most people use Lithium grease, but it will depend on your climate. Make sure it still works in cold weather. A good quality bycicle grease may do a proper job. It is important to clean everything from debris. Skywatcher low end mounts can have a lot of metal debris inside. You don’t want this between gears or in the clutch mechanism. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.