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Thread: Skywatcher tracking problems (solved)

  1. #1
    VincentMcKenzie's Avatar
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    Default Skywatcher tracking problems (solved)



    Just posting this here in case someone else falls victim to the same problem.

    I have a SkyWater Skyliner 200P Flextube Auto, and for some time now the tracking has been awful on it. In fact, after leaving the mount for 12 hours to see if it had rotated, I realised it wasn't moving at all while supposedly meant to be tracking.

    Well it turns out that if you set a negative latitude it doesn't track, and you can easily do this accidentally.

    The mount must always be switched on while horizontal (0 degrees altitude). If, for any reason (say knocking the power lead) it is switched on at any other angle, then the mount will assume that angle is 0 degrees.

    If you press buttons 2 + 3 at the same time (note that they're right next to buttons 1 + 2 that you have to press in the dark and cold to activate tracking), then you will set the latitude to whatever the difference is between where it thinks 0 degrees and the current angle.

    As an example, if you knock the power lead while your scope is pointing at 60 degrees, then later on accidentally press 2+3 while it's pointing at 45 degrees, then the mount will now think you're at latitude -15 degrees and no longer track.

    Also, as a note here, if you knock your power lead while the scope isn't pointing exactly North, the mount will reset where it thinks North is to the current position. This messes up the altitude tracking.

    The way I work around this is as follows. At the start of every viewing session do this:

    1. Point the scope at Polaris (i.e. North).
    2. Move the scope down by hand or controller until it's level (i.e. 0 degrees), either by using the scale on the mount or a spirit level. It helps of course if the base is on level ground.
    3. Turn the mount off for a second and back on. This sets the 0 degrees point for both Altitude and Azimuth. You should do at least these steps at the start of every session.
    4. Finally, to set your Latitude, move the scope up using the controller until it's pointing at Polaris again.
    5. Press buttons 2+3 (Set Lat) together to set your Latitude. It does remember this forever, but it's easy to accidentally change it (see above).
    6. You now have both the North, 0 degrees altitude, and your Latitude set and the scope should track perfectly for visual stuff, and well enough to do 60 second exposures without seeing star trailing on the central object.
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  3. #2
    mgirdwood's Avatar
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    Default

    hi Vincent,

    i had the same trouble when i first used mine a couple of weeks ago, took me a few goes to work out what the problem was. Re tracking itself. have you worked out which of the track speeds is best for which objects are which lattitude ? i dont seem to be able to get that right.

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    VincentMcKenzie's Avatar
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    Default

    The tracking speeds only apply when you're manually moving the scope with the handset. It just moves faster or slower depending on which speed you've selected.

    As it knows your latitude, and where North is, it should track at sidereal rate all the time with tracking on, and not move at all with tracking off. So, with tracking on, you should be able to point it at any star or DSO and it'll track it for an hour or more before it moves off the view of the eyepiece. Planets, comets, and the Moon are slightly different as they don't stay in the same place in the sky, but should be pretty good too.
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    Default

    i tend to set mine every time i use the scope.
    at least if i'm going to use the tracking for any
    period of time.
    as you said,it's so easy to mess it upo without realising it
    sometimes.
    clear skies,

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    Default

    hi vincent,

    then i must be doing something wrong as i can not keep an object in the view for more than a couple f minutes.
    hence the question relating to what i understood were 3 different tracking rates....

    back to the drawing board.

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    Default

    Sounds like it

    However there is also a lot of slack in the gears of these mounts, so it might be related to that. You have to take up the slack manually otherwise even if the tracking is working fine the object might move of the field of view before the slack has been taken up by the tracking movement.

    If the scope is pointing East half of the sky, then your scope should move to the right and up slowly as it tracks. If your scope is pointing to the West then your scope should move to the right and down as it tracks. You can test this by simply setting your scope up indoors, telling it to track (pressing buttons 1+2 at the same time), and leaving it for 6 hours. It should have rotated about 90 degrees clockwise in that time. If it hasn't moved at all either you have the latitude set wrong (see my first post) or it's broken.

    One thing to note is that I don't believe the scope accurately tracks if you move it by hand, because after taking the mount to bits you can see that it keeps track of where it is pointing by how far the motor has moved it. When you move it by hand the clutch slips and the motor is not turned and so it looses track. Other people may disagree on this, but from what I can see there's no way for it to know where it's pointed if you don't use the controller for everything.

    Try this... Set the scope up as I described in the first post. It should now be capable of tracking.

    If the object is in the East half of the sky then to take up the slack in the gearing you have move your scope using the controller up and right until the slack is taken up.

    If the object is in the West half of the sky, then you must have pressed the down and right buttons last until the scope actually moves.

    The important thing here is that you MUST have moved the scope using the up and right (East) or down + right (West) buttons to take up the slack in the gearing, otherwise it can take a few minutes before the tracking can take up the slack in the gearing.

    So armed with that knowledge, go ahead and point your scope at something... Jupiter say, using a big (low magnification) eyepiece.

    At this point, as you watch the object in the eyepiece, you should see Jupiter slowly (over the next minute or so) drift to one edge of the field of view as the Earth rotates. Turn tracking on by pressing buttons 1+2 together. The red light on the handset should now start flashing indicating that it's tracking. It doesn't matter what speed it's set to. Let Jupiter drift until it's almost at the edge of the eyepiece. Now press button 2 (medium speed - I use this) or 3 (fast speed), and press right and up (if looking East) or down (if looking West) until Jupiter is back in the centre of your eyepiece. It may take a few seconds before your scope starts moving (that's the slack being taken up). Do not press left - if you do you'll just add the slack back to the gearing. If you really need to move left then it's better to just wait for the Earth to rotate, unless you've moved the object off the field of view.

    Now just leave it alone... Jupiter should stay in the centre of the field of view. If it's moved off the field of view within a couple of minutes then your scope isn't tracking.

    To answer your question about the tracking rates... The handset offers you 6 speeds. Three are used with tracking on, and three with tracking off. Use speed 3 with tracking off to move your scope to different objects. Use speed 2 or 3 with tracking on to centre an object once you've got it in your eyepiece. Use speed 1 with tracking on to make tiny adjustments - this speed happens to be the same speed as the Earth rotates, so it takes about 30 seconds to a minute to move an object from one side of the EP to the other at this speed. In short, the speed settings only adjust how fast you want to move the scope when aiming it, not how fast it tracks.
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    thanks for the return, i guess the "akward" operation then will be to get used to the correct slack removal hand controlling.

    i keep looking for some clear skies and i will see how i get on.

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    Thanks for this post Buddy, I'm still learning how to use mine. Very helpfull
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    Quote Originally Posted by VincentMcKenzie View Post
    Sounds like it

    However there is also a lot of slack in the gears of these mounts, so it might be related to that.
    I can vouch for the slack in the gears Vincent.
    When I took delivery of my 200p Auto and began to experiment with the motors, I very quickly became aware that my scope couldn't even balance at 0 degrees. Using the motor very slowly to lower the inclination of the tube, it would get down to about 5 degrees and then flop down past horizontal until it came to rest!
    I took the cover off the gear assembly and without knowing what I was doing just tightened up the central bolt (just a little mind!).
    All seemed well after that, but reading through this thread, I'm beginining to wonder if they are slackening off again since my auto tracking isn't right lately.
    I will try the advice given on this thread first, to see if that will help my tracking. To my mind though, I have far to much "backlash" on my mount, and I might just tighten the bolt a little again. I'm reluctant of course, because I'm aware I might be putting too much strain on the electric motor.
    Any thoughts guys?

    Alec.
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    There is a lot of confusion between slack in the gearing and slack in the clutch. If the clutch is too slack, then it will slip when the motor tries to move the telescope, or if you add a camera or big eyepiece it'll drop down to the ground, or a gust of wind could rotate your telescope. When you manually push the scope with your hand it might move a tiny amount (a couple of degrees or so) and then you feel resistance. If you push harder you will move force the motor to move. If you push harder still the clutch will slip and the scope will move without the motor whining. The clutch is there to protect the motors and gearing from damage by being forced to move to fast or pushed too hard. It allows the mechanism to slip before it breaks.

    All tightening the clutch does is make it require more effort to push the scope before the clutch slips. This is fine if it's too loose. If you tighten it up too much it won't slip when you push the telescope, and you risk damaging the gearing and motor if you force it all to move too fast (i.e. when moving the scope by hand).

    The above is completely different from slack in the gearing. This is also called backlash. You can test for this by selecting the fastest speed and holding the left button until the scope visibly moves (or longer). Now look through the eyepiece. Set the speed to the slowest speed (or better still medium or fast with tracking on). Hold the right button... If the scope starts to pan right immediately then you have no slack in the gearing. However on my scope you can probably hold that button down for several seconds before the telescope actually moves. That's because the motor has to take up the slack in the gearing before the telescope will move.

    This slack is a HUGE problem for tracking, because (at least on my scope) the slack is about 5 degrees worth of movement. So if I move the scope left until it's pointing at an object, then turn on tracking, the object will move off the field of view before the tracking has taken up the slack. In fact, if I don't move the scope to the right to land on the object it'll take TWENTY MINUTES for the tracking movement to take up the 5 degrees of slack in the gearing.

    Alas, tightening the clutch does not tighten the gearing. The only way to remove slack in gearing is to replace the gears with ones which are machined with a much greater precision of teeth. However, there are workarounds (such as moving right to land on the object, so the slack is already taken up).
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