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Flextube auto tracking losing Alt.


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Having trouble with my Auto Dob losing Alt during tracking. AZ tracking is fine. I did have to tighten the Alt nut shortly after purchase when it became slack and the gears started to slip. After this tracking was great and I was able to image with 5x Barlow easily but lately it has started losing alt and image only stays in view for barely 10 secs. I've tightened the Alt nut again a full turn but nothing has improved. Before I tighten the nut some more (worried about over doing it and straining motors) is there anything else that could be causing the problem?

Base is perfectly level and Goto handset is accurate. I even had a counter weight on the OTA when the problem first started (removed it thinking that may be problem).

Edited by Space Cowboy
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Well I tightened the alt nut some more and this time it was too much and the axis would not move so slackened back off and tried the tracking again. Had Sirius tracking nicely with 7mm and 3x barlow in the south west but when I moved to Saturn again it drifted in alt very badly. The same drifting happens when the auto track handset is used too. When I think back all the good tracking is in the south west sky and all the alt drifting happens in the south east sky. Anyone else noticed this?

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Is it a sudden nose dive (which mine does sometimes if tracking is switched off, due to there being no resistance from the gears) or a gradual tracking error

Not sure if it wil help but my alt problem was that when low down, under say 20 degrees the gears would spin but the tube wouldn't rise. I fixed that by tightening the clutch nut - this may be what you refer to as the alt bolt.

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Thanks for your reply Chris. Its a tracking drift not and sudden slippage., after tightening the clutch I've now ruled this out as being the cause. The lattitude is set correctly both with the goto handset and auto track handset. What puzzles me is how it tracks ok in the south west sky but loses altitude (drifts) in the south east. Its almost like there is no tracking in alt axis only AZ.

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Sounds almost like it can't track objects going up, but is fine on objects going down.

I'm afraid I can't offer any help....there are many more auto dob owners out there....come on, show yourselves !

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Hi Space cowboy,

you almost certainly know this already but...

i have to finish aligning on a target using the up and right direction controls, to get tracking to work. on my scope there a lot of play between the up and down drive so if i finished on the down, the gears have to use up the slack before tracking the object.

i take it the scope will drive manually up in slow speeds using both hand controls?

and you have used a good power supply?

not sure if you can do this while tracking, but the goto handset lets you see the encoder positions under "show position", you could look at this during tracking to see if it thinks things are moving. If this can`t be done in tracking, you can move the scope in this mode and change the slew rate, so could confirm that the scope moves at all rates of slewing.

(Did also think you could change your backlash and scope limits, but you`ve used the auto handset aswell)

not much science in it but a quick thing to do would be unplug the az motor cable from the alt unit, inspect connections at both ends and replace.

only thought being that power is being dropped over this drive through a high resistance joint etc and therefore lowering voltage over the alt drive.

like i say not much science but its quick.

bit new to all this so sorry if you`ve done things already.

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Thanks Trident for your ideas!

Yes I'm aware of the centering with one particular directional key quirk. I think you have to finish with up key in the east and down key in the west. The slewing is fine and I use a power tank but it might be worth trying a different power supply just in case though I doubt this will make any difference as the goto pointing accuracy works well. I will check the motor lead just in case.

I found another thread on here about tracking problems and it has been mentioned that resetting the alt with the auto handset each time the scope is used can help, rather than the manual saying this only needs doing once. So I will try that but again not sure that will affect things as the goto handset tracks no better.

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