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Backlash repair - EQ3 Pro

astrophotography mount
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#1 SStanford

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Posted 16 January 2021 - 05:05 AM

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!



#2 sg6

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Posted 16 January 2021 - 05:54 AM

The adjustment is the worm that sits between the motor and the gear on the RA/Dec gear wheel.

Just a thought could just be the motors gears are not set right.

Not sure where the worm sits on the EQ3 - they are under 2 covers on my EQ5.

Do not know of a specific guide or instructions.

 

The covers need to come off and the motor may need to be removed - usually sits on a metal bracket.

 

The worm will have a small adjustment - cannot recall if at both ends - but the worm needs to be set to mesh "comfortably" with the gear on the RA/Dec axis drive. They can be set too tight and cause bigger problems. Hence the use of the word "comfortably".

 

The motors: I had this on an HEQ5 the motor was set up wrong. It wouldn't turn fully.

Fix was to loosen the motor and bracket. I then refitted the bracket and set the motor and its gear wheel against the gear on the end of the worm again "comfortably" and such that the motor gear sat about 0.5mm to 1mm below the level of the gear on the worm. Previous owner had set the 2 gears at equal height and that for some reason was the problem  Looked as if it should be right just didn't work.

 

Not sure about how tight the 2 gears interlinked, I simply took the bits off then rebuilt/reset.

 

Forget lubricant. That is the stuff applied to the 2 bearings well inside the mount, and to change means a strip down of the mount. Which means recording the bits that come off and how they need to go back on.

 

Be careful of "tightening" anything up. More goto mounts are broken through interfacing bits being tightened then anything else - well maybe firmware updates are worse.

 

I would half suspect your problem could be the motor gear and worm gear intermeshing is poor. It is also the easier to get at and adjust. That will if I recall just need a cross head screwdriver and a delicate hand. The worm will need an allen key and a very delicate hand.

 

Expect to spend a few hours, just to get it right, and don't attempt to rush it. On mine I had to adjust then run it. Decide what next and repeat if necessary. Basically if anything is tight (meets any resistance) - screwdriver or allan key - you have gone too far. Think I eneded up with "just nips, then back off 1/8 turn", maybe 1/4 turn.


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#3 SStanford

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Posted 16 January 2021 - 01:22 PM

Thanks sg6,

 

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?

 

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.

 

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




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