The mount is a GEMINI-G40 which has been purchased without drives and polar finder. Its weight is about 30kg. This mount is able to withstand a weight of 40kg. This mount has a double (RA-DEC) 432 teeth gear. A special pillar has been designed (in black), the lowest as possible since this instrument is not foreseen for visual observations. Rollers have been installed underneath the base plate to allow the whole instrument to be moved easly.
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Overview
of the Hungarian G40 mount, the RA/DEC step-motors (SANIO DENKI-Step-Syn)
are visible, also the MCMT drive box unit is located underneath, a serial
cable goes to the PC.
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As
said in the previous section, the mount has been purchased without drives.
So MCMT drives needed to be installed.
Here
are the modification made especially for hoding properly the drives SANIO
DENKI Drives to the MCMT.
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| The initial attempt to install the drives was not sucessfull. It turned out that the plates were not able to cope with high speeds, and also the step motor did not fit well to the plates, the holding plate stiffness needed to be improved. | Drive and plate holder dismounted let me to check the mother screw. Here in yellow/brown is the 200mm 432 teeth DEC. cogwheel. | Stiffer plates made of aluminium, 8 mm thick, was designed and manufactured. The stiffness got improved a lot, also larger coupling devices were purchased and installed. Here is the RA drive. | Same applies for the DEC. drive. Now it's far better !! |
DEC
drive close view.
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The mount's two step motors (RA-DEC) are driven by a MCMT-VALMECA system (made/designed by Laurent Bernasconi,Cyril Cavadore, Serge Deconihout and Boris Gaillard). This is a very nice system having a lot of features, such as (in a nutshell):
- all the speeds can be set (various speeds, 1/128 to 1/2 micro-stepping available) remotely by software thru RS232.
- Current can be adjusted by remote software.
- embedded open loop encoders, meaning that separate encoders are no longer required, resolution is 25600 steps per drive revolution.
- Fully supported by our software PRISM.
Have a look
here for a full description about MCMT (in french)
Due
to 1/128 microstepping, there's no need to have any mechanic reducers, the
motors are directly attached to the cogwheel's main-screw. Also pointing is
feasible at speeds as high as 800x times the sidereal rate.
This system is a remarkable teamwork, and also a huge work. Currently this
system can achieve to slew the telescope thru a path of 90° in one minute
(experiments needs to be done to check whether the system is able to be faster).
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The
MCMT setup panel, which defines all the speeds for a given step motor.
Also encoder status can be watched.
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This is the current MCMT setup parameters (August 2001) :
The polar finder :
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The
polar finder is a EM-2S TakaHashi polar finder. a very nice part.
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