However, when the telescope is to be driven mechanically, and especially when it is to be used for photography, an equatorial mounting, having one axis parallel with the Earth's axis and the other at right angles to it, is a necessity; for here the alt-azimuth is, or thus far has been, out of the running, since it will not make the necessary double corrections automatically.

This is one reason why all our great telescopes are equatorially mounted.

This situation struck A. B. Hendricks, Jr., 115 Wendell Ave., Pittsfield, Mass., one of the earlier followers of the amateur telescope making hobby, as remediable Why not use a mechanical linkage that would combine the altitude and azimuth motions automatically into a single, smooth equivalent of the equatorial motion?

After some study he drew up the simple sketch shown in Figure 1 (taken from an old notebook and therefore not in ideally reproducible form). In the upper part of this sketch is a telescope tube mounted on a vertical axis which rotates in azimuth. This vertical axis is driven through a linkage from another axis set diagonally (parallel with that of the Earth) and therefore an equatorial axis. Hendricks, when he sketched this proposal in 1936, called it a "transformer, equatorial to alt-azimuth." The diagonal element is driven at a uniform rate. The object sought is essentially to drive the altitude and azimuth at the desired non-uniform rates. In 1936 this sketch (Figure 1) was offered, through R. W. Porter, for the 200" mounting, but it proved that this type of mounting had already been considered by those who were designing the telescope, but not employed because of the difficulties involved in overcoming the rotation of the image on plate, inherent in it.

A year later Hendricks evolved the proposal shown in Figure 2 (another notebook sketch). This again shows a miniature 11 equatorial placed below the alt-azimuth. In Hendricks' language, "the arched declination axis carries, pivoted within it, a spindle rigidly connected in a radial direction to the driving drum, which in turn is pivoted horizontally in the lower end of the azimuth axis on ball bearings. The horizontal component of the motion of the declination axis is transmitted directly to the driving drum, and through the axis of ..this drum (altitude axis) to the hollow vertical spindle (azimuth axis). The vertical component is also transmitted directly to the driving drum and thence through the steel driving bands to the telescope trunnions, through a cross-shaft within the pedestals, and two additional sets of drums and 11 bands. Some parts are shown in half section."

In l936, Hendricks had discussed the problem with H. F. Morse, Saseo Hill, Southport, Connecticut, and Morse set off to accomplish the equatorial-to-alt-azimuth transformation in an entirely different manner (Figures 3, 4). He made the telescope mounting shown, and has exhibited this telescope several times at the conventions of amateurs held at Stellafane, near Springfield, Vermont, where it is always surrounded by a knot of by-standers.

To many, on first seeing it, the working principle is a puzzle. The principal unique feature of the Morse mounting is the curved, scimitar-like member seen in the photographs. This is the link, in the Morse version of the concept, which automatically brings about the desired transformation of uniform motion into non-uniform motion.

But let's begin at the beginning. The following is a composite of Morse's description and your scribe's efforts-errors, if any, being chargeable to the latter.

At the very bottom (Figure 3), almost hidden in the grass and the shadow, is a bird's-foot base, holding in its center a short, stubby, vertical shaft.

Supported on this shaft by Norma-Hoffman ball bearings is a large rectangular frame of fabricated metal, which can be rotated about this vertical axis.

Near its top part this frame supports the horizontal axis bearings. The hollow end of one of the horizontal axis trunnions shows clearly in the photograph.

Supported on the upper end of the stubby vertical shaft of the base mentioned above, in addition to the rectangular metal frame 311 just described, is a trough-shaped platform (see also Figure 4) which is tightly clamped to the shaft. At one end of this platform rises a diagonal bracket. This bracket contains the bearing for another stubby shaft, the polar axis shaft.

On this stubby polar axis shaft is mounted the long, curved member-the alt-azimuth circle. This curved

member, which is supported only at one end, can be rotated about the polar axis just described; that is, in Figure 3, swinging toward and away from the eye (like a sickle turning in the hand when the wrist is rotated but not otherwise moved). Its radius of curvature in any such rotational position remains in the common point through which the three axes-optical, horizontal, and polar-pass.

Slidably mounted on the curved inner surface of the alt-azimuth circle is a small carriage (Figure 5). Between the two sets of wheels of this carriage is a disk with a central hole (actually, this disk is a small ball-bearing). This disk is mounted in such a way that its bore always points toward the point through which the telescope's axes pass. The telescope tube, mounted on the horizontal axis, carries, at a central point in its bottom, a short pin, and wherever the tube is pointed this pin remains inserted in the central hole of the bearing.

In Figure 3 the tube is so positioned that its optical axis coincides with the polar axis and in this one special position alone the curved member can be swung without moving the tube. However, when the carriage is moved along the curved member (Figure 4), and the curved member is then moved (by rotating the short polar axis at its end), the optical axis is caused to rotate around the-fixed polar axis and the telescope is automatically constrained to follow the star toward which it is directed.

Another way to explain this unique drive would be the following: Follow a star for a time by means of an ordinary alt-azimuth mounted telescope. Then the trace of a given point at the rear of the mirror would take the form of a curve like the curved member of the Morse telescope.

When handling the tube of this telescope one has the feeling that an invisible spook also has hold of it, since it resists attempts to move it in any direction other than one which would follow a star. For example, if one tries to move it only in azimuth, it insists on moving at the same time in altitude. The "spook" is the curved guiding member.

What advantages does Morse claim for this mounting?

"The object," he states, "was to avoid certain inherent shortcomings in large equatorial mountings.

"Estimates indicate a much lower cost. Materials could be better used-with lessened total weight.

"Because there would be no transfer of weight from one bearing to another, there would be no distortion of parts.

"Because of ease and flexibility of the adjustments, less precision work would be required on various details.

"Astronomers would work in an always level position and in a constant temperature room at either end of the horizontal axis, where light could be directed with three reflections.

"Beaus the tube moves about the horizontal axis in one plane alone, the tube could be made very rigid and at the same time relatively light. The whole instrument could be floated m an annular tank of mercury, thus leaving only enough weight on the annular track (precision ground) to insure accurate rotation around the vertical axis."

AMATEURS who aspire to build 200" telescopes usually start more modestly, say with a 100" telescope, and

work up by 100" stages. Erl A. Dart, 2466 S. Bannock Street, Denver, says he had never before built a complete telescope, so he simply started right out on the 200" telescope shown in Figure 6. The job consumed 60 hours of time, $4 worth of brass and two watch crystals (for the mirrors): it's a model, 3/32" = 1 foot.

IF YOU don't want to buy, or in present times can't buy, a synchronous motor for a telescope drive, there is a way to make one yourself, and C. J. Myers, 417 N. Virgil Ave., Los Angeles, Calif., explains it thus:

"It may be that most amateurs are not aware that almost any AC motor can be converted into a synchronous one. A washing machine motor, fan motor or, for that matter, any squirrel cage motor will do.

"All that is necessary is to determine the number of poles and cut an equal number of flat spots on the rotor. For example: a 4-pole motor would have a rotor divided into 8 equal spaces. Cut every second or alternate area down about 3/16". The easiest way to do this is to set the rotor off center in a 4-jaw chuck-although a milling machine will do a better job, as the rotor should be balanced afterward. The motor will now have about one-third its original H.P. at synchronous speed.

"The number of poles equals the frequency X 2 X 60 divided by the nearest synchronous speed up (based upon the number of cycles).

"Most small motors are 4-pole. If the rotating element is cut, it should be balanced. The usual method is to have two parallel knife-edges (any sharp straight metal) on which the motor is rested on its bearings. Small holes are drilled in the heavy side until it will come to rest in any position.

"The governor fly balls on all generators at Boulder Dam are driven with this type of motor. The speed drift is about the lowest in any power house built today."

Asked to supply a little background data on motors, Myers writes: "This motor speed business seems to confuse a lot of people. All motors having salient poles (with teeth) run synchronous. All motors with round rotors (without teeth-smooth) will have a definite slip below synchronism in proportion to load. This is where my formula comes in. Usually the name plate on this class of motor indicates the speed at full load. For example: the synchronous speed for a 4-pole motor, on 60 cycles, is 1800 rpm, but the average motor runs 1760 rpm. The same motor on 50 cycles synchronous is 1500 and the motor runs 1440. The formula for a synchronous motor is frequency X 2 X 6O divided by number of poles. In other words, any motor that is converted will speed up about 5 percent. Any good winding shop could change the number of poles within limits depending on the size of the motor."

Suppliers and Organizations

The Society for Amateur Scientists
5600 Post Road, #114-341
East Greenwich, RI 02818
Phone: 1-401-823-7800

Internet: http://www.sas.org/

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