MkIV drives.

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My own MkIV was equipped with 359 tooth 6" bronze wormwheels and geared electric motor drives without manual slow motions. Later MkIVs apparently had 7" RA wormwheels but they were never illustrated in the Fullerscopes catalogue for years after their announcement.


The Skytracker, variable frequency, MkIV drive box and control paddle were also included. The Declination drive has a reversible 240V motor. The RA drive has a non-reversible, 240V synchronous, drive motor. Which, when switched off with the control paddle, allows objects to drift across the field of view rather than offering a true reverse.

Once the RA drive is mechanically coupled to the polar axis (via the simple screwed rod clutch with attached knob) the telescope cannot be easily slewed by hand. Attempting to slew will make the worm jump noisily out of the teeth of the wormwheel. It is possible to find a middle position on the clutch which allows hand slewing with continuous electric drive but it requires some care in adjustment and careful balancing of the telescope.

(The hex head screw with locknut in the image above is to hold the new, stainless steel, polar axis shaft safely in the polar casting)

The RA drive motor with protective brass can removed.

The reversible Declination drive motor exposed.

The Declination motor drive, gearbox (without its brass protective can) and stainless steel worm driving the wormwheel:

Both motors are by Crouzet which supplied small geared motors for a whole range of timing devices. Washing machines often had a cam drum programmer with the contacts opened and closed mechanically by one or more of these little geared synchronous motors.

The motors and built-on gearboxes are enclosed in simple brass cans soldered together and a push fit onto the worm support base castings. Despite the push fit they seem to work well in protecting the motors.

NB: Later models seem to have a fine screw thread on the brass case so take great care if you are tempted to try and remove a drive motor can from a MkIV! Unscrewing would seem the safest option where any doubt exists. The motor case is made from very thin brass so use rubber gloves to get a really good grip rather than permanently disfiguring the motor can with any kind of gripping tool!

My own mounting has a stainless steel Declination worm but only a plain steel RA worm. The RA worm is very prone to rust and I would like to make (or have professionally made) a stainless steel replacement worm.

The worm brackets are held against the relevant mounting castings with a large bolt and flexible rubber washer. Small, socket head, grub screws offer adjustment of mesh between worm and wormwheel.

Here, an owner of a MkIV has sent me images of his mounting driven by stepper motors and a smart Meade "Autostar" control paddle. No doubt the overall gear ratio can be adjusted for in the device software to achieve the correct drive rate. A really smart and modern update. This MkIV looks almost as good as new.

GOTO is also available from a specialist British company called AWR Technology. There are images of their heavy duty intelligent drives fitted to a MkIV on their website. Scroll down to the middle of the page in the following link:

http://www.awrtech.co.uk/gallery.htm

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