Modification of a Meade RCX400 12" f/8

Hi all,

I finally had some time to work on the conversion of the Meade 12" RCX400.
All the original Meade electronics were removed !
Just an example of the poor Meade quality in this picture: they cut away part of the electronics board to fit in the focuser motor ...

Hooking up the RA and DEC motors and encoders to the SiTech drive was pretty straight forward.
I made the connections with a DIN DB9 connector because the cables had to go through the frame of the fork.
Here's a picture of the test-setup.

The RCX scope on the work-bench:
The most difficult part is the focussing system.
The original system has three servomotors (with cheap feedback "encoders", see top picture) that move the frontplate.
These motors will are resplaced by three stepper gearmotors (supplier Anaheim Automation) and driven by a stepper board (supplier Phidgets).

Here are some details about the components:
- the stepper motors are Anaheim Automation TGM35-075-18-12V-011A-85R-LW6
- the Phidgets driver board is type 1062 - PhidgetStepper Unipolar 4-Motor

The software for the focuser is written in C#.
Based on some examples that came with the driver board, this is pretty straightforward job.
The drive board also remembers the position of the motors, even when it is switched off.
So now the focuser is a real "absolute focuser" which can really go to a fixed position.

To put in the stepper motors, there is one little problem : you need to disassemble the frontplate and the internal lightshield.
There is risk of damaging the main mirror in this, especially when removing the lightlight shield, so if you try it: take your time !

Here 's a picture of the interior of the RCX with the frontplate and the lightshield removed.

The black rods connect the motors to the front linear guides.
There are connected by means of flexible couplings, which fall apart as soon as you remove the focus-motors.
You need to reach into the tube to reassemble these couplings.

The scope is now back in the observatory reading for testing.
The first results were very good:
- focusing and collimation with the new motors worked great
- goto's with the SiTech drive were also accurate.

Next item on the To-Do-List:
- intialiaze and test the PEC function of the SiTech drive (the Meade drive system has a very bad PE ...)
- write the Ascom driver for the focuser/collimator
- connect the dew-heater of the RCX to the weather station of the observatory (dew-heater gets switched on as soon as there is risk of dew... )


Sterre Observatory
Ghent University