Re: [ATM] Unique New Equatorial Platform Design

[donald.good@comcast.net]

The claim that an invention is unique is a result of the sum total of the several claims of the invention.  That an invention includes parts already invented does not, in itself, invalidate the claim of uniqueness (and thus, patentability, at least in the US).  If such were the case, no invention could be patented if it contained a wheel (previously invented) or if it were made of steel (also previously invented).  Valid claims may be in the area of design (form, structure, sturdiness), manufacturability (economy, simplicity, materials, and even method), and use, among others.  Inventions would be nothing if they did not build on previous work.

An equatorial platform is by definition, a platform whose primary axis of rotation can be aligned with the axis of rotation of the earth.  This axis is a line, and in that sense, the line is far superior to the circle.  The Dobsonian is not an equatorial mounted scope unless it is at the north or south pole or on an equatorial platform.  The line in this case is defined by the centers of the ball bearings.  It may be convenient to imagine that these points are the opposing vertices of a cube (I prefer the diagonal on one face of a cube or rectangular solid), but that is not important.  Neither is it important that it cannot compensate for ground disturbances and atmospheric aberrations - no portable mount can.  And that there are other methods for compensating for atmospheric aberrations (e.g. active optics, digital stacking techniques using many short exposures) does not apply to how this mount compares to other portable equatorial platforms.

What is important in its claim to uniqueness is in the claims in part:

Can it be built simply, inexpensively, and with basic skills?  Appears to be Yes.

Can it be built strongly and sufficiently accurate?  Also appears to be Yes.  Even metal construction and welded frames require only minor increases in skills and expense.

Can it be accurately polar aligned?  Using 10-32 screws at what appears to be a separation of 3 feet vertical and 3.5 feet (42 inches) horizontal (rough estimate from the pictures) gives a direct separation of 4.6 feet (55 inches).  This figures to about 2.6 minutes of arc per full turn (20 sec per 1/8 turn) horizontally (at 42 inch horizontal radius).  The vertical adjustment operating thru a 40 deg angle at a radius of 55 inches is about 1.3 minutes of arc per full turn (10 sec per 1/8 turn).  (Someone check my numbers on this)  The drift and correction iterative method requires an accurately timed axis drive mechanism (see next).  A polar sight tool might have an intrinsic accuracy in this range.  So the alignment might be in the arcsecond if not sub-arcsecond range.

Can it be accurately driven at the correct rate?  This depends on how accurately the drive rate can be measured and calibrated.  Even with constant flow, the pictured water bag mechanism will not have constant rate due to changing pressure distribution and non-uniform shape change over the surface of the bag as it deflates.  As stated, a cylinder and piston would be more accurate (constant in rate) over a run.  But even there, how might rate change with changing load and pressure in the water due to tilt?  Repeatability with changing temperature is also a question due to water density and viscosity in the control valve.  A feedback method and mechanism to accurately and finely control flow rate automatically goes against the simplicity claim.  The accuracy is no longer inherent in the drive mechanism, but is instead, in the feedback mechanism.  The same mechanism can more easily and finely control an electric motor or stepper to the same degree of accuracy.  These questions also af
fect polar alignment if the drift and correction iterative method is used.

In conclusion, IMHO, the device is sufficiently unique to warrant the claim as an invention.  And in such case, it is generous of Dan to place it in the public domain.  I cannot fault him for wanting credit for it uniqueness.  We all appreciate credit where due.  

In particular, I have not seen a polar alignment mechanism on a portable equatorial mount, platform or standard, with such fine alignment control.  I would truly like to know if something of similar fineness exists?  And it is true that any rotation around and in contact with the surface of two spheres on the great circles (condition guaranteed by this geometry), is a rotation around the line between the centers.  This has higher accuracy than a solid axel thru bearings because it depends only on the accuracy or the two balls instead of all the balls in the ball bearings and the roundness and straightness of the axel.

Don

P.S. I once came across a web site on polar alignment accuracy that had graphs describing the alignment error tolerances as a function of exposure duration and object declination.  Does anyone know of it?
Thanks.
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