26
UNDERSTANDING THE R.A. AND DEC. CLUTCH KNOBS
WARNING! Be careful when moving the mount with the clutches. It is possible to catch cables or
fingers between the clutch knobs and the motor / gearboxes if you are not careful!
CAUTION! When moving the mount via the clutches, the servo is not involved, and therefore is
not keeping track of the axis’ positions. Bear in mind that internally run cables can be twisted and
damaged if you are not keeping track of, and accounting for movements made using the clutches.
If cables are run internally, you do not ever want to rotate an axis more than 360°. If you rotate the
mount, do not forget to de-rotate it before continuing your activities.
1. What do they do?
The three R.A. and three Dec. Clutch Knobs depicted in the Assembly Diagram have the function of connecting the
R.A. and Dec. Axes to their respective drive worm wheel gears. Their function is progressive, from slight tension (axes
free to move - as required during correct balancing of the tele-
scope) to a completely “locked up” state.
2.
How can you find out what they really do?
As shipped, all 1100 mounts have both sets of R.A. and Dec.
Clutch Knobs firmly hand tightened. This will give you a good
idea of the maximum tightness (clutch action) that can be
achieved by hand effort alone. At this point, you must bear in
mind that for optimum performance all three clutch knobs on
each axis (R.A. or Dec.) should be tightened evenly to the same
tension i.e. all three half tight, all three fully tight, etc.
In order to feel the effect of the clutch knobs, you may wish to
partially assemble your mount. Fit together the R.A. and Dec.
Assemblies plus mounting plate and counterweight shaft. Do
not put scope and counterweights on at this stage. With the
above assembly (with the clutch knobs firmly hand tightened -
“as shipped”), you can feel the amount of force needed to move
each axis by hand. Grab each end of the telescope mounting
plate and move it with a backward and forward movement of the
Dec. Axis. You will feel considerable resistance to this motion. Perform the same operation on the R.A. axis by mov-
ing the counterweight shaft backward and forward. With a well-balanced telescope, the above tightness of the clutch
knobs will be sufficient for all normal conditions of use.
Now, if you proceed to mount up and balance your telescope, you can “feel” what this resistance in R.A. and Dec.
(movement backwards and forwards) is like when you make these motions from the eyepiece end of your telescope as
you would during normal use when slewing (pushing) by hand to acquire an astronomical object within the field of view
of your finder or scope.
3. How tight can the clutch be and can you do any damage by pushing against them?
The clutches cannot be damaged by tightening; however, it is not necessary to tighten them as you would tighten the
lug nuts of your car’s wheel. You will see that each clutch knob has a 5/32 hex socket for tightening with a hex key.
With an extra 1/5 turn beyond hand tightening on each clutch knob, the axis (axes) will be considered completely
“locked up” and you should not attempt to push your scope by hand against this “locked up” resistance, or undue stress
will be placed on the worm wheel / worm and bearings.
Naturally, if you have a very heavy load, it is advisable to tighten the clutch knobs more than is necessary when a light-
er payload is mounted. When imaging you’ll want to ensure that the clutches are tighter so that there is no slippage.
4.
How do the Clutch Knobs of the 1100GTO differ from all 900 and 1200 mounts?
The 900 and 1200 mounts were designed with Delrin clutch plugs beneath the knobs. While these were quite effec
-
tive as a clutch material and did not damage the underlying worm wheel surface, over time the base of the clutch plugs
spread out after being tightened with greater force than necessary, preventing their full release.
The 1100GTO uses a different clutch system, and it also uses a different bearing system for the free rotation of the
axes. It will feel stiffer than the 900 or 1200 series mounts.
You should be aware that the clutch knobs on the 1100GTO have spring loaded tips that may still be applying pressure
to the clutches, even though the clutch knobs feel loose. Back the clutch knobs off by at least two or three full turns to
more fully disengage the clutches. There will always be some friction. The 1100GTO clutches can be fully tightened
without worry.
Clutch Knobs
R.A. (3)
Dec. (3)