Originally Posted by sirjaymz
So do you have details on how you built the actuators and the overall masking system?
Trying to follow along with MrMister 's
build, but some of the Somfy motors are discontinued, so I will probably end up having to engineer something on my own anyway, but any insight on what you did, may shed some light on other usable methods.
I'm not sure I can recommend, in good conscience, what I did in comparison to MisterMR's very well engineered solution but I'll try to describe it here. My system only handles top and bottom masking vs his four way system. It's gone through a couple of iterations mainly because I originally had a 106" non-AT screen and recently upgraded to 135" AT screen.
I'm using 12" travel linear actuators like these
. The thing I'm doing that is probably a little unusual is that there is no upper masking panel. Rather than moving a panel down over the top of the screen I actually just move the entire screen down. If you look at the first 2 pictures in my post above showing the different masking positions you'll notice in "scope" position that the lower panel has moved up from the floor to cover the lower portion of the screen. The screen is actually attached to a frame that is hung on chains that go up and over sprockets and then down to attach to a carriage for the lower masking panel. By doing it this way I'm sure the top and bottom move exactly the same distance up and down since they're literally attached to each other with the chains. It also gives me an effective 24" of mask travel using an actuator that travels only 12".
The sprockets that the chains on each side are hung from are attached to a shaft/pipe that goes across so that one end can't move more than the other, which would create a trapezoidal screen shape. I have to say that getting the mechanism to move smoothly and evenly was the most finicky part of the process. The original version of the system had just one actuator right in the center of the screen. When I switched to an AT screen I could no longer center the actuator since the center speaker had to be there. I thought I might get away with moving the actuator slightly off center but that torqued the screen too much to one side so I decided to go with dual actuators mounted at the sides. You would think this would solve any problems with one side getting out of line with the other but surprisingly two "identical" actuators can move at slightly different speeds. I dealt with this by tweaking the voltage on the faster one to slow it down slightly.
This picture shows the screen frame. In the lower left you can see one of the arms that sticks out beyond the outside edge of the screen. Once the screen is mounted The lower masking panel is hung on these arms so that it travels up in front of the screen when needed. You can also see the two actuators mounted inside the right and left speakers.
by Russ L
, on Flickr
This is a closeup showing the chain and sprocket carrying the the screen frame above and lower mask carriage below (this was before the left side actuator was mounted).
by Russ L
, on Flickr
Hopefully this makes sense. I'm happy to describe more if needed.