Smbd What is the reason for this low speed ?
The following is what I deduced, by looking at the commands that the ASIAIR sends to a mount.
The ASIAIR needs to rotate about 60º to plate solve at two locations. In spherical geometry (not in Euclidean geometry), the two locations are vertices of a triangle where the third vertex is automagically the pole, if the two points have the same declination angle.
Remember the joke about a hunter shooting a bear, walks 1 mile south, then 1 mile east, and another 1 mile north and found the same bear that he shot -- and you are asked what is the color (!) of the bear? (White, of course, since it must have been a polar bear that he shot.) That is precisly how polar alignment works in ASIAIR.
To ensure that the two points are at absolutely the same declination angle, ASIAIR does not dare use a GOTO (also to avoid any Meridian flip). Instead it uses an hour angle slew, while not touching the declination motor at all.
So, the next question is how does the ASIAIR slew by 60 degrees without being able to use a GOTO?
From what I could tell, what the ASIAIR does is to slew at a known slow speed for a fixed amount of time (probably half to a second, although I have never timed it), resulting in a small safe angle. From this first small slew, the ASIAIR then uses the ratio between this slew speed and the maximum slew speed to determine how long it takes to complete the 60º (thereabouts, my RainbowAstro mount usually ends up with 61º or 62º -- 60º is just deemed to be large enough so that the error when solving for the third point of the spherical triangle is sufficiently small.
The two speeds that ASIAIR chooses for this Rube Goldberg exercise are two of the factory default speeds of a mount (the faster speed is the max slewing speed of the mount).
ASIAIR regularly fails to do this 60º rotation if the two speeds are no longer set to the factory defaults. For example, if the user had changed the slower speed to one that is lower than the factory default, the mount would run away when it tries to complete the 60º (yes, like crashing into the pier), and if the user happened to have changed the slower of the two speeds to a higher than the default speed, then the mount would hardly move.
Anyway, that is why ASIAIR uses two speeds to complete the 60º. And the fundamental reason is that it needs two points on a sphere where the hour angles are different, but the declination angle are precisely the same. It cannot depend on a GOTO to achieve the constant declination.
Spherical geometry is a lost art (no longer taught in school unless in the USA, you had gone to Annapolis or Colorado Springs). And GPS really was a nail in the coffin for spherical trigonometry, but you can find a Boeing white paper where there is a diagram of that magical triangle with an apex at the North Pole (scroll down a third of the way).
https://www.boeing-727.com/Data/fly%20odds/distance.html
For longitude, just substitute hour angle or right ascension, and for latitude, just substitute declination angle, and voila, you get what you need to solve polar alignment. "Colatitude" in the white paper then just means points with same declination.
Chen
