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The old dob mount served for 18 years, but having no
clock drive got really old. This is the new and improved mount. See
Dale Keller's 10" f5.6 Newtonian
for information about the telescope itself.
This is a split ring mount, similar to the Polomar
telescope's mount. That was actually an accident. After playing around with several
split-ring designs, I decided on this one. After building the mount, I knew it
looked familiar. Then I saw a picture of the Polomar scope and realized where I'd
seen that design.
Features are:
1.Fold-down mount - everything folds down into a flat, easily transportable, 65 pound
package (just the mount).
2.Right Ascension and Declination drives, controlled by a hand controller.
3.Extreme stability, because the split ring cage is supported by three widely separated
points.
4.Quick setup without tools. It takes about 5 minutes from lifting it out of the truck to
being ready for use.
The split ring is made from 2 sheets of 3/4" plywood glued together and shaped with a
router. The ring rides on a pair of skateboard wheels. These are freewheeling, since the
clock drive is mounted on the lower end of the cage. The cage is made from thinwall 1"
square steel tubing. The telescope is held in a dobson-type cradle, and can rotate to
comfortably direct the eyepiece. The side bearings on the cradle are dobson-type wooden
disks, and they rest on teflon pads. A teflon pad is held against the top of the disk by an
aluminum bar. This is required for when the telescope is pointing at the East or West
horizons to keep the top bearing from tipping out of it's cradle. The cage/split ring
assembly weighs about 40 pounds.
The declination arm is driven by a stepper motor and can
move about 10 degrees North or South. The brake tension on the declination arm is
adjusted by rotating a screw which tightens a split wooden clamp on the declination
brake disk. The declination arm assembly can be quickly removed with a
knob and knurled nut.
The lower cage shaft is 1.5" diameter and sets in a thrust ball bearing. It is held
in place by gravity. The clock drive clutch/ring gear
assembly rides on this shaft. The worm gear is mounted on a
pivoting arm, allowing it to be moved away from the ring
gear for quick disassembly. The backlash is controlled by a
screw which presses lightly against the worm gear arm. The
ring gear/worm is a Byers 9" unit driven by a
microstepped, geared down stepper motor. The
clutch is homemade, turned from aluminum scrap on a
lathe.
The base is made from common 1x4s screwed and glued together. It
folds flat in about 5 minutes, and all the screws used
to set it up have knurled heads. The leveling feet are adjustable by hand and have
locknuts to lock them in place. They have about 3" of travel. The base
weighs about 25 pounds.
The electronics box contains two PIC
microcontrollers, one to control the declination stepper motor, and one for the clock
drive. A handheld control box allows slewing in all
directions at two different speeds. A small gel cell 12 volt battery drives it all.
The battery will (someday) also supply current to the telescope tube to feed the
telrad, dewzappers, and illuminated reticle eyepieces.
Someday I may add digital setting circles, but I still like star hopping, using a
variety of star charts.
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