I’ve installed a Nexdome rotation kit on my 8’ Exploradome. The installation went really well, the stepper has no problems rotating the dome and the software plays nice with SGP. My problem is the sync of the dome slit to the scope, it’s consistently off by roughly 8 degrees on all targets. I’ve remeasured the parameters used in the Ascom hub and even tried adjusting each one to no avail. The home position magnet is set properly and it syncs to home.
How should I go about troubleshooting this problem? Is there one parameter I should be looking at? Any help would be appreciated.
Alex
I'm glad it's sorted out :)
I wrote the NexDome X2 plugin for TheSkyX Pro and in my settings dialog I allow the user to set the steps per rotation.
I wish the same thing was available on the ASCOM side for people using it on different dome than the NexDome.
The old 2.x firmware had the capability to calibrate on its own (and so does my own firmware on my own controller) to allow for use in any dome with any stepper motor.
Hopefully this will become available one day for this v3/v4 firmware (not really Babak's fault as he trusted the firmware developer and so far the feature delivery hasn't been what he expected... ).
just ignore these, they are sent by the controller.
so you kind of have to blindly type the command
This "XB—>WaitAT" means the firmware is still talking to the XBee to configure it.
it should stop after a while but you can still type thing in there (not easy to see what you are typing indeed).
Argn .. there is always something ;) .. and as I don't use Windows I had assumed (wrongly) that there was a way to change the number of steps per rotation in the ASCOM NexDome settings.
Ok, once you have figured out the value, you can update it using a serial terminal and sending the proper command.
I use CoolTerm usually but any serial terminal will do.
Connect at 115200 bauds, 8 bit, no parity, 1 stop bit ( aka 115200 8N1).
The send this command with a carriage return and line feed at the end :
@RWR,<new step value>
So if the new step value is let's say 54123 you would send @RWR,54123 (hitting enter should send the CRLF (\r\n), specially if you use CoolTerm as it's the default).
Rodolphe
There might be a way to figure out something close enough to get you going.
Go to the home position. then do a goto to the opposite side (so 180º appart).
Then measure by how much it is off.
Let's call this D.
We know that the default value is 55080 full steps per 360º.
So if you multiply D by 2 this gives you how much off you are in relation to a full rotation.
Then you can do (55080/360) * (360+(2*D)) , this is the actual number of steps per rotation you need to set on your controller.
The accuracy is tied to how accurately you can measure the offset.
That's the best I can come up with as there is no calibration command on the 3.x firmware (and 4.x).
Rodolphe
I don't know if the ASCOM stuff can do a calibration.... because i don't use ASCOM .. or Windows ..
I use TheSkyX and my X2 plugin has a calibration routine... not sure the ASCOM driver has a calibration routine.
The default number of steps per rotation should be fine though (I ran some high resolution test using my own controller and I got to within 8 micro steps of the default .. that's an error of 0.006 degrees..).
Calibration is really needed if you don't use a NexDome with your rotation kit. The default for the NexDome dome is correct.
The issue here is really an offset somewhere. Home position accuracy, some measurements ... and this get even more complicated as it involves multiple piece of software and hopefully they are not all trying to do the offsetting and geometry calculation on top of each other.
Edit : I just re-read the top .. you have an Exploradome ... so yes the default value of the number of steps per rotation is probably not correct and would explain part of the issue.
Unfortunately the 3.x firmware doesn't include a calibration command.
This is going to be a pain to figure out the number of steps per rotation with the 3.x firmware.
If you made all the measurement fro the point where the Ra and Dec axis cross it shouldn't make any difference as this is the origin for all calculation :
this sounds like the home position is not set to the right Azimuth so the origin for all measurement it off. Would your local magnetic deviation be about 8 degrees by any chance ... and you used a magnetic compas to set the home position ?
The Dome geometry is all done in the software, not in the controller. So it has to be set properly in ASCOM and/or SGP (or any other software involved in the sync between the telescope and the dome).
The dome only knows about where it's being told to go and doesn't know anything about where the telescope is pointing. This is all up to ASCOM/SGP.
So make sure the distance and dimensions are correct (including signs).
I don't use ASCOM (or Windows) so that about as much as I can do to help.