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Speed Limiting hinge? Answered

Ok, I'm building a motorized projector screen, almost exactly like this: http://www.youtube.com/watch?v=GgIqx-iKNcw , except on a much larger scale. The actual screen will be made out of blackout cloth (what the back of curtains are made out of), and the screens construction will be similar to this: https://www.instructables.com/id/Cheap-DIY-100quot-Projector-Screen/ .

The screen's size will be somewhere around 20x20 (feet), because it will be used in a fairly large auditorium. The screen will hinge up and reside (when not in use) above the stage. The top of the screen will have some hinges attached, so the screen can "fold up" into the ceiling. Toward the bottom, on the back of the screen, there will be a steel cable attached to the frame. This steel cable will be fed into an electric winch, which will be mounted on the ceiling. So, when the electric winch is activated, the screen will either hinge out, or it will hinge up into the ceiling. I know its hard to understand, I've done all the explaining I can. Ask questions if you have to.

Anyway, the problem is this: What if this steel cable broke/got frayed and snapped/got chewed up by a darn rat, etc? The projector screen would come hurtling forward, knocking out anyone in its way.

So, I need something that limits the speed that the screen can be lowered. I need some kind of hinge that limits how fast the screen can be lowered, so if the cable does snap among other things, the projector screen will make a graceful descent and people will have enough time to get the hell off the stage.

Now, Do I think the steel cable is going to snap? Hell no. In fact, the steel cable I'm planning on using will handle over 1000 lbs. The total weight of the projector screen? Maybe 70 Pounds, at the most. These speed limiting hinges are just for that "extra" step of safety.

So, does anyone have any suggestions?


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Best Answer 11 years ago

Use two cables.  One to raise and lower the screen and one hooked to a counter weight that is slightly less than the force needed to lift the screen.  That way if either breaks then you still have the other to control the lowering of the screen.

Second option is to use gas cylinders like on a hatchback to control the speed going down.


11 years ago

Why not have the screen roll up like other projector screens? That will keep it clean, and out of the way. Then it can be motorized, or just pull down like the rest, against a spring.
A twenty foot screen will not fall fast, it's own sail area will slow it down. You could have safety lines at each corner on friction hubs, this could serve as backup for the motor to pull the screen back up.
Car tail gates weigh about seventy pounds. The shocks that help them are real cool, and  you may not even need a motor to raise the screen.
Trying to control the screen from the hinge will require a much stronger frame than would be necessary otherwise. Control it from the easy end.
A large screen in an auditorium could catch anything on top of it, and drop it just when you want to show it off, very embarrassing. It would be a sure target for pranksters.