NexDome Rotation Control System

[Startrek]

Being of the older gentry and not going down the path of a fully automated unattended observatory, I decided to design and build my own Dome rotation control system for my NexDome
Of course Sidereal Trading encourage you to use the Voyager software to control your NexDome and run your imaging session but I didn’t want to go down that path as it would be discarding my existing programs and learning a new one ( I’m old school )
I also have a second laptop inside the house in my study connected to the Dome laptop via a Cat5e cable running Windows 10 Pro Remote Desktop which is used for monitoring the imaging session
My Dome rotation control system is just a simple electromechanical design made up of timers and relays which is set to track the celestial objects Azimuth movement across the night sky. All I do is select an object for the evenings imaging, jump on Stellarium and record its azimuth movement per hour in degrees as it tracks across the sky either towards the south or north
I have a master time to keep real time 24/7 and can be programmed for up to 6 on / off set times per hour for up to 8hours
Then a time delay relay is used to rotate the dome either clockwise or anticlockwise with durations between 0.5 sec and 10 sec which equates to azimuthal movement in degrees
The timer can be changed mid session to compensate for variations in azimuth
Last night I tested the system on NGC 4945 Tweezers Galaxy and it worked really well , I only had to go out to the Dome and change the timer once through a 4 hour session
The existing NexDome rotation control unit rocker switch can still be used manually to rotate the Dome to the imaging start position, then my automatic Dome control system can take over
Attached are some photos and a control schematic drawing
It’s not perfect but it works good enough to let the Dome rotate on its own for a few hours without intervention

[AdamJL]

Really good work there, Martin :)

[Startrek]

Adam,
Thanks, appreciate your reply
I was out imaging again last night, although a bit windy which doesn’t worry the rig in the Dome, conditions were pretty good and only had to tweak the rotation manually once in 4 hours , so my little system is working better than I expected
I don’t if anyone else has designed and uses a similar system ( although not conventional) does work
Looks like some goods nights ahead for at least the next week
Cheers
Martin

[Startrek]

Just an update .....

After using my custom designed Dome rotation control system over the past 2 weeks or so , the only limitation or weakness in the design using azimuth movement is when your imaging up towards the zenith approaching the meridian ( +70 degrees)
I found that azimuth movement to keep the scope centred in the dome opening could no longer work and a 180 degree manual rotation of the dome was required to keep the scope centred in the opening and tracking clear with some very small manual adjustments of rotation until the object past the meridian and started to ascend again

Other than that it’s working really well. Imaging M83 the other week only required intervention after 3 hours , just a minor manual tweak

Last week I was imaging the Prawn nebula for nearly 4 hours and only required one small manual tweak

It’s not fully automated ( I never wanted that anyway) but it sure beats checking the Domes position every 15 to 20 minutes if it was totally manual

If anyone’s interested, thanks for reading .....

Comments welcome

[Pepper]

Neat setup mate.
May I ask how drive is applied to the dome?

[Startrek]

I bought a Dome Rotation Motor ( accessory) with my NexDome
It mounted to one of the uprights and has a gear wheel which drives the Dome around via a rubber strip with gear teeth double sided taped around the Dome. The NexDome solid state controller box has a manual rocker switch on the outside for clockwise and counterclockwise rotation. It also has a USB port for connection to your computer so you can use Voyager software to control your Dome. I just extended the rocker switch wires ( 3 off ) common , clockwise and anti clockwise down to my custom control box. I have an isolator so I can only use the manual switch and not my control system together.
Photo of NexDome rotation box top left of photo
Cheers
Martin

[Pepper]

Thanks for that.
I want to motorise my dome one day. I do find I don’t really have to move it manually much anyway as I made my slit wide all the way past zenith. Be nice to have a motor though.

[Startrek]

My slit is only 600mm wide and my OTA is 230mm diameter
I might be upgrading late in the year or early next year to a 10” newt which is 280mm wide
The narrower the slit the more darker it is inside and reduces dew and shields against gusty winds too. With a NexDome it is a pain to manually move it all the time due to the relatively narrow slit. My little semi auto control system to rotate it makes AP so much more enjoyable