Automatic computerized telescope dome rotator at the NFO
Category: New Forest Observatory
Posted by: Tom How
Yet another visit to the New Forest Observatory today. That is my third trip out to the New Forest this week to setup the automatic telescope dome rotator. Telescopes, metalwork, computers and electronics: My favourite type of project. This has been an extremely satisfying way to spend a few summery days off. Who would lay on a beach when there are toys to be played with?!
Greg's setup uses an array of 4 telescopes atop a Paramount ME German Equatorial Telescope mount in a 2.2 metre Pulsar Optical telescope dome. The slit aperture is about 630mm. This means that the dome slit aperture needs to be aligned with the scopes to within a few inches to avoid problems. Constant visits (nearly every 10 minutes) to the dome would be needed to keep manually moving the dome slit aperture into the correct position. Clearly some kind of automated dome rotation system was going to be required to reduce user error and allow a modicum of sleep.
Actually the real reason is to give Greg one less thing to moan about in his ongoing crusade against the German Equatorial Mount.
Most commercial dome rotation systems have a couple of major failings: Either they aren't integrated, or they cost far too much! The standard dome rotator supplied by Pulsar optical falls down on both fronts. For the best part of a grand you get a motorised dome rotator that isn't integrated to the telescope. For unattended imaging this is useless. Other computerised systems do exist, but not for less than £2000. This type of project is the sort of thing I thrive on so I was desperate to try a bit of astronomy DIY. Once Greg saw a bit of demo simulation software I created, he was willing to cough up for the parts to make it a practical reality. A fool and his money?
The trigonometry needed to calculate the required dome slit azimuth from the telescope pointing data is long and involved - but computers are good at calculations. I knocked up a bit of software that fetches the pointing data from TheSky via ASCOM to calculate the required dome slit azimuth. The software interfaces with a couple of large stepper motors to actually move the dome.
Finally I got some Tom How metal work onto the NFO mini-wasp system in the shape of two stepper motor brackets. I think my rude metalwork compliments the precision finish of the Paramount quite nicely. I'll leave it to Greg to apply the red paint.
Once we'd got the metalwork sorted the software side worked after the usual tweaking. With any drive dome system you can always expect some slippage in the transmission and motor stalls - therefore we've used a solid state compass mounted in the top of the dome to provide positional feedback.
Below is a short video of the system in action. Greg is sitting on the floor with the video camera. At the beginning of the clip you can see the telescopes on the left pointing out of the dome slit aperture. The telescope mount is then moved to a slightly different part of the sky. After a few seconds you can see the dome slowly rotate to the correct place. You can here the thud-thud-thud action of the motors.
Of course, now Greg wants more powerful stepper motors. His excuse is to help it run past any sticky parts on the circumference. In reality I think he just wants to see the dome slewing around as fast as the Paramount itself.
All in all, a fine way to spend a few warm summery days. Here is the video of Tom How's patent dome rotator! Through the door of the observatory you can see the NFO South Dome.
Greg's setup uses an array of 4 telescopes atop a Paramount ME German Equatorial Telescope mount in a 2.2 metre Pulsar Optical telescope dome. The slit aperture is about 630mm. This means that the dome slit aperture needs to be aligned with the scopes to within a few inches to avoid problems. Constant visits (nearly every 10 minutes) to the dome would be needed to keep manually moving the dome slit aperture into the correct position. Clearly some kind of automated dome rotation system was going to be required to reduce user error and allow a modicum of sleep.
Actually the real reason is to give Greg one less thing to moan about in his ongoing crusade against the German Equatorial Mount.
Most commercial dome rotation systems have a couple of major failings: Either they aren't integrated, or they cost far too much! The standard dome rotator supplied by Pulsar optical falls down on both fronts. For the best part of a grand you get a motorised dome rotator that isn't integrated to the telescope. For unattended imaging this is useless. Other computerised systems do exist, but not for less than £2000. This type of project is the sort of thing I thrive on so I was desperate to try a bit of astronomy DIY. Once Greg saw a bit of demo simulation software I created, he was willing to cough up for the parts to make it a practical reality. A fool and his money?
The trigonometry needed to calculate the required dome slit azimuth from the telescope pointing data is long and involved - but computers are good at calculations. I knocked up a bit of software that fetches the pointing data from TheSky via ASCOM to calculate the required dome slit azimuth. The software interfaces with a couple of large stepper motors to actually move the dome.
Finally I got some Tom How metal work onto the NFO mini-wasp system in the shape of two stepper motor brackets. I think my rude metalwork compliments the precision finish of the Paramount quite nicely. I'll leave it to Greg to apply the red paint.
Once we'd got the metalwork sorted the software side worked after the usual tweaking. With any drive dome system you can always expect some slippage in the transmission and motor stalls - therefore we've used a solid state compass mounted in the top of the dome to provide positional feedback.
Below is a short video of the system in action. Greg is sitting on the floor with the video camera. At the beginning of the clip you can see the telescopes on the left pointing out of the dome slit aperture. The telescope mount is then moved to a slightly different part of the sky. After a few seconds you can see the dome slowly rotate to the correct place. You can here the thud-thud-thud action of the motors.
Of course, now Greg wants more powerful stepper motors. His excuse is to help it run past any sticky parts on the circumference. In reality I think he just wants to see the dome slewing around as fast as the Paramount itself.
All in all, a fine way to spend a few warm summery days. Here is the video of Tom How's patent dome rotator! Through the door of the observatory you can see the NFO South Dome.
