I'm a bit further along with upgrading my observatory with electronics with a control system to rotate the dome, and raise and lower the shutter. I farmed out the PC board work to someone who has put relays, soft start controls, and other devices in the two NEMA enclosures. It'll probably take a month to get the boxes back. While waiting for that to happen, I've decided to take a shot a the lower shutter.
As I probably mentioned here some time ago, there is a lower and upper shutter. The lower shutter is about 33"x32", and has a glass window in it. My guess it the upper shutter is 12'x3'. The shutters are on two tracks, and roll along with wheels. Latches between the two can couple them together, so they both move up and down together. If not latched, the lower shutter sits on the apron (the circular structure on which the dome sits) of the dome while the upper one moves up/down.
The lower shutter was a mistake, when I first built the obs. It is quite unconventional. There may be 12 in the USA. As I quickly discovered, taking images through the window resulted in slightly distorted images. Not good. I had checked before buying the window shutter with five people who owned such a shutter. (It has something of a reasonable purpose for use in winter.) They all gave it thumbs up. I never asked what imaging through the glass produced good images. Nevertheless, the obs was still functional w/o the use of the window. The shutter weighs about 120-90 pounds.
A typical lower shutter is like a drawbridge. That is it pivots on the apron, and swings in or out with, in some cases, a hand winch, pulleys and wires. It only needs to be positioned 10-15 degrees above the horizon. Looking below that the sky is avoided because of the atmospheric thickness. What I want is to take the current lower shutter and make it look like a drawbridge. I plan to hire someone to do this. However, my enclosure-box guy thinks I can operate with a linear motor. He suggests using it on the apron and centered in the shutter. He's short on details and working on another project now until he can get back to mine. So my question is how is a linear motor going to help in this situation. Why in the middle??? I haven't a clue.