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Polar alignment aid for Tak EM200 (dumb) mounts

Having recently taken my EM200 out of a 5 year period in mothballs, I realised how dumb the mount is, in that there is no automatic alignment procedures 'built in'. Many newer scopes have alignment systems that work fine, but not the Tak, and I'm guessing there are still many like this out there.

Thinking about a solution, initially, the mount would need to be physically  put in the local home position of 90 degrees for dec, and local vertical position for RA ( ie with weights down).

I note when the Tak is initially powered on, it seems to set itself to a random encoder position when SS is initially connected, regardless of the physical position of the mount.

If Sky Safari could  select a pointing target of the local Home position, 0 degrees RA and  90 degrees dec, and with the mount physically positioned in to as close to the Home position as possible, then to an 'Align" on that position, that would mean the mount is now synced to the local Home position.

If then an alignment star, eg Polaris, ( or really any star, but preferably nearby) and the mount is commanded to GO TO say Polaris, the mount should then move to where it thinks Polaris is.

Then, using the physical knobs on the mount, adjust E-W and UP and DOWN until the scope points to Polaris, a reasonably  close polar alignment should be achieved. (I think?)

 

It relies on being able to set the local Home Position as a valid GO TO target for SS, and for SS to Sync that Hour angle and Dec to the Mount's physical position. 

This should work for both hemispheres, and also when the usual polar alignment stars are not visible due to trees or other obscuring features.

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6 comments

  • 0
    Avatar
    Bill Tschumy

    Brian,

    Thanks for taking the time to make a suggestion.

    I have a Tak NJP mount and I guess I don't see the problem.  You have to polar align the mount no matter what to start with.  Then you turn on the mount and point the scope to a star.  Select the same star in SkySafari and tap Align.  That's it.

    I don't think aligning on the counterweight down position will be accurate enough.  It is just too hard to judge that accurately enough. 

    BTW: when you first power on the Temma computer, it always defaults to RA = 0; Dec = 0 as the assumed position.  It is not a random encoder position.

  • 0
    Avatar
    Brian Clements

    Hi Bill, Thanks for the response.

    When in the field, a rough polar alignment can be achieved via a compass and inclinometer, but I'm looking for a better resolved Polar alignment without the requirement for drift aligning or trying to work out the polar scope.

    When I power on my Tak, and do not make any other adjustments, and then connect SkySafari , the position shown/reported on SkySafari appears to be random. Hence my request to set a 'home position' in SS.

    However, I have since noted, that despite the initial apparently random position reported by SS, if I set say Polaris as a GO TO, the mount seems to move toward Polaris as though it was from the home position, and not from the seemingly random one initially reported by SS.

    Perhaps on connecting to the mount, SS could be amended to report /display the 'Home Position' that the Tak is said to be at? 

    But moving on from that, then would it be feasible to tune the polar alignment relatively closely by adjusting the physical controls to position the mount to centre an alignment star?

    Does SS make movement control adjustments in  a relative manner? ie does it send control commands to move so many degrees RA and Dec from the last reported position? (Also adding RA step increments - as reported by encoder, or as calculated by SS?)

    I'm thinking (guessing) that must be the case because the Temma is dumb, and doesn't know where it is really and relies on being told how far to move each time my the control software. The only position Temma can remember is the 'Home Position'. - or can Temma create a map itself when powered on?

    Because the Tak Temma2 is relatively slow to traverse large angles, how does SS take accrued RA adjustments into account while slewing?

  • 1
    Avatar
    Bill Tschumy

    Maybe your EM 200 is different but on all Temma mounts I've worked with the mount always powers on thinking it is pointed at RA = 0; Dec = 0.  I've never seen anything like random.  Of course that RA/Dec could be at any altitude and azimuth depending on your time & location so it could appear to be "random".

    The Temma is not really dumb.  It knows the RA/Dec is is pointed at (after being told that) and knows how to move the mount to a new RA/Dec.  All we tell it is to go to a specific RA/Dec and it handles the rest.

    Unless you get a reasonably accurate polar alignment, the Temma mount will not perform well. Because you only align on a single star, there is no multi-star alignment model that it uses.

    On iOS there is a great app called "Polar Scope Align Pro" that makes it really easy to use the polar scale to get an accurate alignment.  You don't have to worry about local sidereal time or position angles.  It just tells you exactly where to position Polaris in the polar scope reticle and after doing so you are accurately aligned.

     

  • 0
    Avatar
    Brian Clements

    For me.

    I set the physical position of the Temma2 mount to RA=0 and Dec=0. At power up I believe the Temma thinks it is at that precise position. I do not make any hand controller movement adjustments.

    When I connect SS, it shows the Temma to be at some random location. It does not show it to be at RA=0 Dec=0.

    If I select a target star and initiate a GO TO the mount moves as though it was originally located at the random position and drives to the target from that point. As though the Temma was already ALIGNed at the random position shown.

    If I physically release the clutches, and manually position the mount to point at the star accurately, and do another ALIGN on that star, everything works fine.

     

    It is as though on FIRST connection, the Temma does not report  its initial position as RA=0 and Dec=0. Rather ,it ALIGNs itself to be at the position shown on the SS screen. If I am running a session with SS, and the iPad goes to sleep and does a re-connect, it seems to recover fine. It is only at the First connection that the issue shows up.

     

    Maybe we should be in the Temma folder rather than the new feature folder?

     

    Cheers, Brian

  • 0
    Avatar
    Robert Nielsen

    Brian,

    I know the manuals (and lore) say that the Temma system initializes at power on to RA=0 and Dec=0, but in my experience ... it intiializes to a random location.  I have both a EM-200 Temma2 and EM-500 Temma2 ... and they work the same way.   Always random ... I have not been able to figure out the pattern.

    When you say "it ALIGNs itself to be at the position shown on the SS screen" ... I don't think that is quite right.  What I think happens is that the Temma system initializes with some random RA and Dec coordinates.   Then SS connects to the mount and asks what position it thinks it is pointing.  The mount returns the random coordinates, and then SS shows that location on the screen.  I don't think SS tells the Temma mount a position when it connects.  It does that when you execute an ALIGN operation in SkySafari ... after which things seem to work (as you said).

    So the easiest explanation (and what I have seen in my experience) is that the Temma system is not initializing to 0.0,0.0.  It is initializing to a random set of coordinates.

    By the way, which *version* of Temma do you have?  Temma?  Temma2 (which is what I have)?  Temma2M?  Temma2Z?'

    Robert

  • 0
    Avatar
    Bill Tschumy

    Brian,

    Robert is correct.  We never send any commands to the mount to set its position on startup.  We are just reading the location from the mount and displaying it.  

    This is the first I've heard that some Temma mounts come up initialized to a random location.  That seems strange.  I have never seen that with my NJP mount although it is somewhat old.  I wonder if the newer Temma mounts have some non-volatile RAM that holds the last position of the mount.  The you start up it may just be reporting the position it last was at when shut down.

    I'm not totally sure why this even matters.  Polar align your scope, point it at a known star and (after selecting the same star in SkySafari) tap Align.

     

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