Roll/Pitch Optical Head

The need to point and track two different stars requires four independent axes, two for each star. So my instrument needed to have 4-axis capability. The optical path that looked directly out needed to have altitude and azimuth controlled, and the optical path that looked at the second star needed to have pitch and roll control. So I needed to add a pitch/roll capability to the mechanics and the optics.

Here is my initial hand sketch of the pitch axis. The item 'filter gear' was later deleted. Note that the pitch rotation axis lies in the mirror reflecting surface. The encoder was directly coupled to the pitch mirror to avoid any backlash.

Here is the bare optical bench for the pitch axis. Visible are the sub apertures and the mounting plate for the pitch hardware.

The pitch axis and the pitch turn mirror were added. The turn mirror was mounted on a tilt mechanism so that the pitch optical path could be tightly controlled. In this photo, the left sub aperture viewed the sky directly, and the right sub aperture viewed the sky through the two mirrors.

The large white gears were not used as gears at all, they were just providing a surface to which the pitch mirror could be epoxied.

The roll axis would be a shell that fits over the optical tube so that the upper half of the telescope could be rotated without changing the pointing direction of the main optics. It was cut from a large PVC pipe.

The rotation axis was defined by the central pivot, which was a 1/4"-28 bolt that threaded into a cup that was epoxied to the corrector plate and covered the secondary mirror access screws. The corrector plate appeared to be flat glass. The shell was trapped by four friction drives that both rotated the shell and provided mechanical location.

Here is an image of the entire pitch assembly (including a rotating filter wheel below it) supported on the single central pivot bolt. This bolt was lubricated, and the entire assembly was rotated 8 full turns to engage fully the bolt into the support cup. After that, it only moves one full rotation to map out the 360 degrees of roll. The filter wheel has blockers and a solar filter, but no colored filters.

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