EQ8 Backlash

[Grimmeister]

Hi Everyone,

I am seeking some advice from other EQ8 mount owners but I do not want this post taken out of context as it is an investigation in progress and has not reached any point of inaction or response from or problem from the distributor. I am just seeking some comparisons from other EQ8 owners Let me explain the full situation:

I have purchased a new EQ8 mount recently and have now had an opportunity to trial this out in the field, in all other aspects I am very happy with the mount with the one exception of the declination axis. To me the declination axis has far too much backlash in it. (I am aware that a worm drive gearing system does need some backlash, this just feels way too much).

I only found this by the fact that the drive takes up to 2 seconds to engage when viewing a star via a camera when drift aligning. In normal set up and testing inside I did not see or notice this at all????

Now I will state up front that I have contacted Tasco and they are working through the usual steps with me like upgrading Motor controller and hand controller firmware etc. I suspect however the issue is with the worm wheel gear.

My thought process so far: If I drive the declination axis through a full 360’ stopping say every 45’ to have a feel, the backlash at the best point in the rotation is basically zero very firm and ridged, however if I keep driving this axis and check each 45’ period it gradually gets worse till I reach 180’ out from the best mesh point.

When I say it gets worse I can actually hear the gears when I alternately “wobble” the saddle plate from side to side. At the best point in the drive I cannot feel or hear any backlash?????

It looks very much to me like the worm gear is slightly off centre resulting in the worm drive alignment not being able to get any closer than the “closest point” as mentioned above, this means the worst point (when the work wheel is furthest away) I will get the issue as seen.

Has anyone else felt the backlash in their EQ8 was a problem or faced a similar situation? I fear this will need to be sent back to Tasco for a warranty repair if they can determine there is an issue.

Thanks for your time to read and any comments most welcome.

Cheers

Anthony

[AstroJunk]

I have noticed some backlash in the Dec when moving the scope around by hand, but it has translated into nothing of concern when using the scope.

I have planned to pop the covers off and have a look at the worm one day, but that day has yet to come - Looks like you are going to be the first to peek :)

[librarian]

Hi picked up my EQ8 and i see an issue with backlash, or at least i assume its a backlash issue!

I can certainly feel backlash if i lock up the axis and rock the scope, but it does not feel too excessive!
Where i do see it is when calibrating for guiding...it takes a while for the calibration process to remove the backlash and then (as it should) it calibrates North, however when it comes to calibrating South..i see very little movement over 12 + steps and i see a large jump to centre the star on completion of calibration.
it makes me wonder if PHD has calibrated correctly.

At first i thought that the issue was with PHD 2 since i used this when 1st trying it, however i see it also in the original PHD

It appears to guide o.k. after a settling in time, but initially it is slow to correct drift in Declination which i put down to backlash!!

Ray

[raymo]

I think you are right when you say that you will have to send it to Tasco.
Years ago I had the same problem, but in R.A. not Dec, with a new
Vixen Super Polaris, which was quite pricey in it's day. The supplier
replaced the mount. I hope you get a satisfactory outcome.
raymo

[Grimmeister]

Hi Ray,

Thanks for your post, this is exactly what I am seeing and definitely affects my guiding. I think you will find the guiding engine in PHD and PHD2 will be either identical or very very similar so I doubt this had any affect.

I wrote a bit more about the issue here: http://www.astrophotography.id.au/eq8-first-run-in-a-dark-sky/ and I would be interested if you too have a "normal" point and a sloppy point in declination??? It takes a while to check but that was the only way I could get a handle on the issue.

Cheers

Anthony

[Grimmeister]

Hi Jonathan,

I found a web site here: http://www.dangl.at/ausruest/eq8/eq8_e4.htm that has the EQ8 in all it's nakedness. I am not game to pop the covers for fear of voiding warranty etc. so will await Tasco's guidance on the matter.

Again I would be interested to see if you have a normal area during the rotation and a loose area as my mount???

I am sure you live about 15 minutes away so maybe I could pop in one day and compare the two mounts??? PM me if you think this would be okay??

Cheers

Anthony

[librarian]

Hi Anthony. i have carried out an initial check on the dec backlash of my EQ8.
I found that backlash is minimal throughout 360 degs.
however; at 180 degs from the park position, i do detect some tightness or perhaps better put; less backlash than i would be comfortable with!
it might be the case that when the manufacturer states that the saddle should be in the scope up position (the arrow) this determines the best position for the worm and worm wheel for the range of likely slew!

I have checked my backlash with a scope attached, this means that there is moment of movement.. if i remove the scope then i would be hard pressed to find any backlash at all.
This does not explain the issue of PHD and the delays i see calibrating South!!
need to carry out more checks and I'll post when i have done that.

in the meantime any other specific checks that you would like me to carry out please ask.

Ray

[AstroJunk]

On further deliberation - could you have a poorly seated dec bearing? It might be noticeable in a movement of the counterbalance shaft as you spin the axis. They did delay production due to a bearing issue I was told...