Gemini German Equatorial Telescope Mount by sanmelody

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									               Gemini G-41 German Equatorial Telescope Mount
                                         User’s manual

                              Main features and parameters

 Capacity: approximately 35 kg, depending on tube length.
 Weight: 22 kg
 Favourable Tube Assembly/Counterweight ratio
 Power: see your controller's manual!
 Precision dual axis drive system with microstepped bipolar stepper motors
 Wide range of polar elevation adjustment (0 - 35, 35 - 60, 60 - 90 degree latitude)
 Adjustable, stick-free slip clutch
 Removable counterweight shaft (30.5mm counterweight bore required)
 700x slewing rate (recommended maximum)

A precision drive system comprising ground steel worms, large 217 mm brass gears and a
microstepped stepper motor is standard. Tracking accuracy is within 5 arcseconds (without
P.E.C.) during several turns of the gear.

                  Backlash in both axes is smaller than 1 second at siderial rate.

        250 sec integration with ST5-C camera, 800mm F.L. (2.5"/pixel) unguided G-41

                              G-41 German Equatorial mount

                                            Safe use

Make sure that the power source used is stable! Noisy power will cause
malfunctions and may eventually demage the Driver.

Always connect the motors and Driver Unit first, then the power! Doing otherwise
will result in demage to electronics.

When turning the telescope, watch the cable of the motors! They should never be

Keep the mount away from dust, sand and other kinds of dirt! Protect it from rain!

The mount should NEVER rest on the motors when stored or transported! Use your
transport box!

During transport the slip clutches should NOT be locked! The worm may suffer
demage otherwise.

Drive does not start.
Incorrect polarity, insufficient current,  unstable/noisy power, broken power cable, 
electronic transient,  fuse blown .

Motors vibrate and do not turn the telescope.
Large unbalanced mass. Rebalance the telescope!  Foreign particles (sand, etc.) at the gear.
Clean the gears! Use Molibden enriched grease for lubrication!  Motor cables broken. Repair or

Motors run but do not turn the telescope.
Clutches became loose. Tighten setscrews!

The motor fails in some positions.
Readjust worm against the gear! See instructions on page 9!

                             G-41 German Equatorial mount


1. Polar align. (if required),
2. Connect the motors and the Driver Unit,
3. Put the counterweight on (slip clutches released),
4. Mount the telescope,
5. Release the slip clutches and carefully balance the telescope. (Remember that finders,
   guidescopes, large focussers may introduce significant unbalanced weight, especially with
6. Check polar alignment,.
7. Connect to the Power Supply!
                                    The mount is ready for use.

                                 Pulsar Controller Setup

Please set the parameters in the Mount Parameters menu as follows
TrackCurr       800mA (works down to 600mA)
GoToCur         1000mA (max 1400mA)
Stop Curr       300mA (or same as tracking current for autoguiding)
RA Mot rotation       left
The other parameters should be left at the default values!

These current settings are valid for 12V and give low noise and consumption (0,5A @ tracking,
0,9A@ GoTo) If you need more torque, change the settings!

                                   FS2 Controller Setup

Please set the parameters in the Mot1 and Mot2 menu as follows!
Curr1           0.7 A                             F*4              0%
Curr2           1.4 A (maximum)                   Offset           0.01
Freq1           20 Hz                             Accel            5 or best value
Freq2           0 Hz                              Clear            usually 0
Offset          0.02 A                            Freq3            40Hz
S/Rev           200                               L/R              Left
Gear            432                               EncR             none
Wave            micro                             EncD             none

Please set Misc/Teeth at 432!
Rate 5, which will be used for the GoTo function also, depends on the load and the power supply.
Try 700 and decrease if the drive fails! The maximum slewing speed depends also on supply
voltage. Acceleration (Accel) should be slow for heavy loads. For autoguiding select rate 1 which
should be set below 1 (siderial) to exclude any backlash!

                                 G-41 German Equatorial mount

                                           Polar elevation

   is adjusted after slightly releasing (maximum 1/4 turn) the two hand knobs(one on either side)
   locking the polar shaft. The elevation of the polar shaft can be adjusted by the rigt/left handed
   screw mechanism. This is done easiest with the telescope and counterweight removed.


Release ¼
turn only!


      Adjust slightly above the pole and fine adjust after loading tube and counterweight! Do not
    remove the hand knobs! It may be difficult to replace them. Lock the hand knobs firmly. Do not
                                    use tools other than your hands!

                                    G-41 German Equatorial mount

There are three elevation ranges of the mount.

Standard: 35 – 60 degrees latitude (shipped unless specified otherwise).
Low: 0 – 35 degrees latitude.
High: 60 – 90 degrees latitude.

The image below shows the different elevation adjuster sets for the different ranges.

To use the mount in the Low range, the RA head must be reversed in the base as shown below.

The elevation scale will not work in this position unless the mount was ordered for low elevation originally.

                             G-41 German Equatorial mount

                                  Slip Clutch Operation
                                     (R.A. and DEC.)



        Do NOT use excessive force on the locking handle! Lock it gently!

         An unbalanced telescope may cause errors, or failure, of tracking.

Please remember that the slip clutch is also a protection feature that prevents excessive force
from acting on the worm and gear! When the clutch is too tight and the telescope cannot slip
when accidentally bumped, the worm and gear will sufffer demage.

          The slip clutch may be adjusted by lifting and turning the handle.

                                 G-41 German Equatorial mount

                                 Collimating your Polar finder

  G-41 may be equipped with an optional high precision, bright field Polar finder. This 12x30
  finder uses a standard 10mm Plössl eyepiece and hence offers smaller than usual field and eye
  relief but provides better precision than most other models. The large objective permits seeing
  faint stars that make the alignment very accurate. The first time the mount is used the Polar finder
  should be collimated with the Hour Axis using the six screws in its adapter.


   The 3 allen screws hold the finder centered in the adapter, the 3 thumbscrews are
                                    for adjustment.

                                G-41 German Equatorial mount

                         Collimating the Polar Finder with the Hour Axis

         field of wiev
                                                                           wanders on
                                                                           this circle


0.     Sight Polaris through the Hour Axis without the Polar Finder! Insert the Polar Finder!
1. Center Polaris and focus the eyepiece! Use the elevation and azimut controls only! (see fig.
   above, left) Fix the eyepiece with the Allen screw and DO NOT move it later on!
2. Rotate the Hour Axis cca.360 degrees! Stop where Polaris goes farthest from the center!
3. Move Polaris halfway towards the center as shown (above, right)! Use only the Polar Finder
   collimation setscrews now!
4. Repeat from 1 until Polaris stays in the center when the Hour axis is rotated!

5   Rotate and adjust (in Az and Elev.) the Hour Axis until Polaris is in the large circle and the
    two fainter stars around are in the smaller circles.

Note: you can go through steps 0-4 in daytime using a terrestrial object a few hundred meters
away. Do NOT remove or rotate the polar finder’s eyepiece after the alignment was done! You
will lose collimation.

                  For each new setup of the mount, repeat step 5 only.

                                 G-41 German Equatorial mount

                                        Worm adjustment
  (This is not part of normal maintenance. It will be necessary after serious abuse to the mount.
  Please make sure that you understand what you do before doing anything. You can damage the
  G-41 has a spring loaded worm in order to maintain a very small backlash. If you experience
  backlash or the worm is seized, it needs adjustment. Please study the drawing below to
  understand the principle!

play adjusters                          Spring load adjuster (tighten
                                        max.2 turns)

  The axial adjusters are seen after the worm cover plate is removed. The axial adjusters must allow
  a minimum axial play so that the worm can be pressed against the gear by the spring. See
  wormadj.avi for a short animation!
  Note: it is necessary to release the counterlock nut before adjusting the screws!

  If the axial play is excessive, backlash will appear in all sky positions. Tighten the axial
  adjusters a fraction of a turn and check for backlash! When the backlash is gone, check that the
  spring can still press the worm against the gear! With a small screwdriver, force the worm away
  from the gear (at the edge) and release it. There should be no backlash now. If there is, release the
  axial adjusters a little!

  If there is no axial play (the worm is seized), there will be backlash in some sky positions only
  and probably failure of slewing at other positions. Release the axial adjusters a little, and check
  for backlash as described above!

  Fasten the counterlock nuts after adjustment, taking care not to turn the screw at the same time!
  Note: there is a minimum spring load even if the adjustment screw is removed. The spring cannot
  be removed from the screw side.

                           G-41 German Equatorial mount

Tools needed for the worm adjustment: posidriv screwdriver, 5,5mm open end wrench, 2,5mm
hex, 1,5mm hex key,
                                 Adjusting the axial play

                                G-41 German Equatorial mount

                         Note on the pointing accuracy of the mount

The pointing accuracy with a given setup is ensured by paying attention to the following:

1. Polar alignment The final alignment must be made with the telescope on the mount.
Otherwise mechanical effects will jeopardise accuracy. Polar finders without a collimation feature
will note give good results.

2. Optical tube optical axis (not mechanical) perpendicular to Declination axis
It is not always enough to use two identical tube rings. With reflecting and catadioptic telescopes
you should always make sure that rotating the tube does not affect where it points in the sky (or
ground). After optical collimation the check must be repeated. This check is recommended also
for refractors.

If you find that rotating the tube makes a difference, rotate and fix the tube where its optical axis
is perpendicular to the Declination axis! Star diagonals are not recommended for this test. See
the figure below!

                                                                                  center of field
                                                                                wanders around here

         one of two positions
         where you should fix
         the tube


                               An equvalent method is the following:
1 Align your polar finder as described above!
2 Center Polaris in the fileld!
3 Align the telescope parallel with the Hour axis!
4 When you swing the tube in DEC, Polaris should cross in the middle of the field! If not, adjust
the tube on the platform!

                               G-41 German Equatorial mount

                               Gemini GHS tripod - how to use

The tripod is in folded position for transport. Release all handles (2 black, 1 red) and 3 black
handknobs! The collar on the column and the legs are free now.



   Adjust the height first, then you can compensate ground slope by adjusting leg
                                   angle one by one!

                                  G-41 German Equatorial mount

   The red handle has double function: locks the collar on the column and a leg also. Do not release
   the red handle when the mount is on!

Release for adjustment /
Lock for use

   The limiters stabilize the tripod. Release 1/2 turn for adjustment and lock for use!

             Release for adjustment /
             Lock for use

                        G-41 German Equatorial mount

The mount is fixed by the central handknob and two screws at the sides. The Qlock
 option features a spring loaded internal M10 screw with 1:2 gear reduction (not
                   shown here) to replace the central handknob.

M8 screw with
plastic washer                                                     Central

                                  PEC encoder

                      PEC encoder connection at RA motor

                        G-41 German Equatorial mount

                       Getting to know your Polar Finder

 To take advantage of the GoTo function of a transportable mount, Gemni have
 developed a high precision Polar Finder. To enjoy this precision you must first
 work a little: collimate the Polar Finder with the Hour Axis. You can be assured
that models not providing means for collimation will never reach the precision of
                                     this product.

     Eyepiece                                                 M42x1 adapter



Allen screws are not comfortable to use in the dark but are safe against unwanted
adjustments. You can completely lose collimation by a single accidental turn of a

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