RST-135 polar align bug?

phips1702

Dear RST-135 users,

yesterday, I ran into a potential issue of the RST-135 mount, connected via USB to ASIAIR (most recent beta, I think 1.3/3.37). When trying to do the PA routine, the following happens: after the first step (plate solving), Asiair states that the mount will rotate 60°, which takes longer than usual to fulfill (in comparison with my CEM40, where it starts to rotate right away, here it takes at least 10 sec). Then the mount starts to rotate, but does not stop after 60°, but keeps rotating until the scope bumps into the mount and I have to shutdown the mount.

Any ideas what I am missing here?

Thanks and all the best,

Philipp

w7ay

Hi Philipp,

Before starting the Polar Alignment process, did you slew to a star to focus your optics? If so, I would recommend first going back to the home position (OTA pointed at west horizon, using ASIAIR Home button, or long press 0 button on the Hubo-i hand controller), then rebooting the ASIAIR and the RST-135 before slewing to the polar region to start performing PA.

Next thing to do is to start PA (that first plate solve) at a point that is away from the pole. This may seem counter intuitive, but the estimation of RA and DEC from a plate solve is more accurate further away from the pole than close to the pole. Right at the pole, the secant of one of the angles is zero, and that can cause large numerical errors when estimating the RA angle, unless ASIAIR uses a displaced angle to calculate the RA/DEC location (we don't have ZWO's code, so there is no way to tell if they treat plate solving near the pole differently).

With the RST-135, I start PA with the OTA pointed about 30 to 45 degrees East of the Meridian, so that after the 60 degree rotation, the OTA points about 15 to 30 degrees west of the meridian. This also makes it easier to reach the altitude bolt and altitude locks of the RST-135.

I also start with the DEC a degree or two away from the pole towards the Zenith (I am in the northern hemisphere) so that there is no ambiguity between positive DEC and negative DEC. Right close to the pole, it is hard to distinguish between -90º and +90º declination, and RA is almost impossible to calculate accurately.

With the ASIAIR, you do not need (or even want) to start at the pole to do polar alignment.

Now that Daylight Savings is over, be sure to set the correct GMT offset in the hand controller too. The RST-135 does not understand Daylight Savings Time (Korea does not observe daylight savings in summer :-), and you have to change the GMT offset manually. This *should not* affect PA, but it will affect Meridian and horizon offsets -- the mount could stop guiding for an hour before the star is still an hour before Meridian -- and stars near the horizon might report "below horizon" when they are actually not.

I have not been able to go outdoors for a month now. It is either too cold or too cloudy for my tastes (there is 3 inches of rain forecasted for today and tomorrow :-). But before that, I have not had any problem with PA with the RST-135 (all of the alignment problems comes from the abysmal alitude mechanism on the RST-135 itself).

See if the things above (home, RA and DEC starting away from the pole) helps in your case.

If all else fails, you can make do by telling ASIAIR that you are not connected to any mount. This allows you to do manual PA -- ASIAIR will ask you to use the hand controller to move the RA by about 60 degrees after the first plate solve (even 45 degrees is sufficient). Once the mount is polar aligned, you can then home the mount and tell ASIAIR that you have a RainbowAstro mount.

Good luck,

Chen

phips1702

Hi Chen,

thanks very much for your extensive answer - i will try what you described.

Upon testing, I realized that the data from the mount seems not to be transferred to ASIAIR, it just keeps displaying zero values. Do you have an idea, what I am doing wrong?

Cheers,

Philipp

w7ay

>> Upon testing, I realized that the data from the mount seems not to be transferred to ASIAIR,

>> it just keeps displaying zero values. Do you have an idea, what I am doing wrong?

No idea. Do a sanity check to make sure that the menu in the hand controller selects the RainbowAstro protocol instead of the LX-200 protocol, and make sure too that you are selecting USB instead of WiFi. And for good measure, sync the mount to its GPS (press and hold ENT on hand controller once GPS location and time is received).

If longitude field is undefined, I can understand why your mount does not move.

On three different iO devices (two iPad Pros and an iPod touch) and a Samsung Galaxy Tab A, once connected to "RainbowAstro RST/MC700GE-II" (Serial/115200 baud), everything in the Mount Info section gets populated properly. Except for the Time Zone -- ZWO told me that they could not pull Time Zone data from their RST-150h (same protocol with our RST-135), so Time Zone always read UTC+0.

With the mount in the home position, the DEC field in ASIAIR Telescope Settings should read 0, with the RA reading local sidereal time minus 6 hours. The RA will also increase with time, thus tracking the west horizon. With iOS, the Time field in Mount Info is only updated when you select the Telescope Settings window, but it is updated every one to 5 seconds on Android -- there are numerous irritating bugs like this in ASIAIR.

You should also see the tracking (green) LED on the mount flash when you turn the Tracking switch in the Telescope Settings window on (and stop flashing when you turn the tracking switch off).

The "Start" button of "Goto Home Position" should also start the mount hunting for the home position.

Finally, in the main ASIAIR window, you should be able to pull up the small "goto" sub window. And the direction buttons there should slew the mount.

If you have not be following my earlier posts on the RST-135, please be aware that when you change the Speed slider in the Goto sub-window, it will change "Speed 2" in the hand controller to match the speed of the slider. I.e., the ASIAIR hijacks "speed 2" in the mount to use for slewing (you can see the red Speed 2 LED on the hand controller flashing). As a result, when you leave ASIAIR, you will need to go to the hand controller to set Speed 2 back to your default before using the mount without ASIAIR.

With the ASIAIR, you can use the RST-135 most of the time without the hand controller connected. You do have to make sure that the clock in the RST-135 is synced to GPS (which is in the hand controller), though. I have found that I can run a couple of days without re-syncing the RST-135 clock to GPS. In earlier versions of ASIAIR, we could push time from the tablet over to the mount by using the Sync To Mount button in the ASIAIR Telescope Settings window. Unfortunately, that is no longer available in ASIAIR v1.3, so you need to use the hand controller's clock to GPS every so often.

Regards,

Chen

phips1702

Dear Chen,

thanks again for your great input - it was indeed the protocol settings, it was set to LX200 - upon setting to Rainbow RA and DEC settings are transferred to ASIAIR. Now that it seems to work, weather is crappy again - how else should it be :-D

Thanks again for the hints, I can´t wait to test the mount under live conditions.

Cheers,

Philipp

w7ay

>> I can´t wait to test the mount under live conditions.

Hi Philipp,

Glad it all worked out.

Clear skies,

Chen

PMTeam@ZWO

Hello Philipp,

We have tested the RST-135 through the driver with the Rainbow company. Above you said using the LX200, right? Just need to confirm,

phips1702

Hi,

with the Rainbow driver, it works, while the LX200 does not work properly.

Best regards,

Philipp