Re: iexos-100 wobble and bad star alignment

Wes Mcdonald


1.  The iexos100 does have backlash adjustments.  There is a video somewhere, probably can find a link on the ES web site or perhaps someone can provide it.

2.  A few key points about how the mount works.

a.  The motors only know where they are because every movement made by the mount is kept track of in the firmware.  This means if you ever move the telescope with the clutches released, the mount firmware no longer knows where the mount is.
b.  Get your mount physically polar aligned.  This is a process that does not involve the telescope or motors if you are using the polar scope or tunnel.  Now you must return your telescope, by loosening the clutches and manually placing the scope, into the polar home position.  This position is one that has your scope approximately pointing at Polaris, preferably with a 45' offset from the center of the eyepiece.  Now is the time to power the mount.  At powerup the PMC8 assumes the telescope is pointing at polar home.
c.  The 2-3 star alignment can proceed and should be closer on the stars than you experienced.  However there is no sequential improvement to the alignment star positions...each star will have about the same error until the process is complete and Explorestars does the calculation for the virtual alignment.  At that point subsequent goto performance will be better
d.  Goto performance can be wrecked by mislevel in the east-west direction, I call this tilt.  Tip (north-south) is removed by the polar alignment.  In principle mislevel is accounted for in the 2-3 star alignment, buy in general I suggest you try to get the mount level before doing the alignment.
e.  If you have DEC home error, that is you have the scope twisted a bit off if the RA axis when you begin the 2-3 star alignment, this error is not removed by the 2-3 star alignment.  
f.  If the telescope is mounted on the saddle with a bit of tip, called cone error, this will affect your gotos.  This tip is not removed by the 2-3 star alignment.
g.  If you are using Explorestars with a 2-3 star alignment, you must understand the mount is being driven while in P (point) mode to maintain pointing despite polar alignment error.  For visual this is great.  But for photography it might not be great, as P mode does corrections 5 times per second.  For photography one needs to place the unit into T (track) mode.  In T mode the RA motor runs at sidereal rate exactly, while the DEC axis does not move.  If there is polar alignment error the object will drift on the field of view.  
h.  One way around some of this is to use short focal length telescopes.  
i.  Also be sure to use the SYNC button once you center your scope on a desired object.  Explorestars takes this to be the correct position and uses this knowledge to point the scope subsequently.  The result is that most. if not all, of the PA error etxc is removed FOR A POSITION NEAR WHERE THE SYNC WAS DONE.   So gotos to nearby objects should be good.

These points will help I think.


On Thu, Dec 10, 2020 at 10:04 AM Yorksman <harry@...> wrote:
Yes, I have successfully manually slewed after having a 'good enough' polar alignment. I had exactly the same problem as you did so I selected Pleiades in ExploreStars, the slew was way off but then respositioned by hand and then pressed the 'T' buttons. This was a 30 sec exposure, seems to track well enough. First ever shot at the stars. I expect if I wanted longer exposures, I had better get a better polar alignment. I think the polar alignment just aligns the mount and lets the electronics know where it is. The telescope is quite separate until you move it and sync it with something. "Way off" is something one hears often for the first slew or two, but tracking works well enough. Have a go.

Wes, Southport NC
EXos2-GT PMC-8, iExos 100
ES ED 127, 10" LX200GPS+wedge, Astro-Tech 8" Newt, ETX-90, 60mm no-name guide scope ~ 260mm FL
Polemaster, Orion ST-80 and SAG, ZWO 290MM, D5300 astro modified
Nina, Bootcamped Mac Mini control computer, RDP to iMAC
110 amp hour lead acid deep discharge battery for field power
Electrical Engineer, Retired

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