Installing a ServoCAT on the 18'' Obsession

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On May 15, 2020, the ServoCAT arrived.  The installation did take some time, but thanks to the very good instruction documents and movies, everything went without problems.

Installing the powered ground board

The first step, and in my opinion also the step that took the most time, was to install the powered ground board.  Because the 18'' Obsession telescope has a triangular ground board, a new, round ground board was made. I bought birch plywood of quality B/BB, with a thickness of 18mm.  Most wood shops can provide the birch plywood, but probably you will need to ask explicitly for it.  Around ground board with a diameter of 58cm was made.

The new ground board.
The new ground board.

The old ground-board can be removed by loosening the screw in the rocker box.  Don't forget to remove the washer.

The screw to remove from the rocker box.


Also remove the washer in the center!

The old, triangular ground board is no longer needed.

In one of the feet of the new ground-board, a hole should be drilled to put the power connector.

The hole for the power connector.

Next step was to add the contact plate perfectly in the center of the ground-board. 

Contact plate added at the center of the ground board.

At the bottom of the ground board, the small brush plate insertion and the center hole pivot.

The center hole pivot (top) and the brush plate insertion (bottom).

The power connector can now also be installed in one of the feet of the powered ground-board.

The power connector in one of the feet of the ground-board.

Now, the swivel post can be installed, together with the spring. 

The installed swivel post.

The bronze bearing can be installed in the rocker box.  Make sure that the bronze bearing sit deep enough in the central hole by using a hammer. The powered ground board distribution kit can also be installed.  At this moment, power is already available inside the rocker box.  

The rocker with the powered ground board installed.

Installing the azimuth motor

For the azimuth motor, a hole has to be drilled in the rocker box to install the clamp. 

The clamp in engaged position.

An other hole has to be drilled at the bottom of the rocker box.  Make sure to drill in the correct position, because I first had a hole at an incorrect location... The motor can be installed now, as well as the digital encoder for the azimuth.

The installed encoder and azimuth motor.

The springs to the motor can now be installed and the clamp can be attached to the motor.  When the clamp is engaged, the motor touches the ground board and it is impossible to move the telescope manually.  When the clamp is disengaged, the telescope can be moved freely again.

The installed azimuth motor.

Installing the altitude motor

To install the altitude motor, the teflon pads must be switched with new teflon pads, with a groove.  These new teflon pads can be seen in the picture above.  A screw has to be attached at the end of the altitude bearing.  Watch out because the material of the altitude bearing is very strong!  A cable is attached to this screw and runs through the grooves of the teflon pads to the motor.  The cable is turned twice around the roller of the motor and then goes to the clamp that should be installed on the truss tube block.

The installed altitude motor.

The altitude encoder needs to be installed on the same side of the motor.

The altitude encoder.

Cleaning up

Basically, the installation is now done, but some extra cleaning up is required.  An extra hole was made at the back of the telescope, where all cables can go.  These are the cables for the motors (2), for the motor encoders (2), for the power (one for the ServoCAT and one for the Argo Navis) and the digital encoders for the Argo Navis (1).  This removes all the cable clutter.

All cables for the Argo Navis and the ServoCAT.

Another hole was made at the side of the telescope to guide the cables for the altitude motor, the altitude motor encoder and the Argo Navis altitude encoder into the rocker box. 

The cables for the altitude motor and encoders.

For the first tests the ServoCAT was attached to the telescope using a small rope.

The installed ServoCAT and Argo Navis.

My father in law made me a mounting bracket, so everything looks very clean now.



First tests

I was happy to see the telescope move for the first time.  At first, the speed was still set to 'Guide', so the telescope was moving very slowly.  After setting the speed to 'Slew', the telescope really started moving. It was of course around full moon, so I only did a few tests at night.  And these first tests were very promising.  I centred on M13, and using a 5mm Nagler eyepiece, M 13 was still perfectly in the field of view after 30 minutes.  The goto function was not yet perfect, but the Argo Navis was only roughly aligned.

Testing the ServoCAT during the day.




Location: 3370 Roosbeek, België

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