Gear / motor for lowering screen

[stubious]

I've got a ~3m wide heavy fabric screen mounted on a 2" mild steel pipe that sits on pillow block bearings about 2.5m above ground. I've got a sprocket attached to one end via a taper lock bush. I was planning to motorize (or build a hand crank) to make it easier to raise/lower the screen down the road and just hand lower/raise it as needed until then. However, I've since discovered that the fabric is heavy enough that once it gets ~1m or so of fabric unrolled, then the weight of it just causes the entire thing to unravel. I'd guess the fabric weighs in somewhere between 0.5 and 1 kg per sq m.

So, I need to accelerate my plan to automate this and/or find a way to stop the tube rotating where I want it to. I suppose I could go with a weight hung from the bottom of the chain once I get to my desired height (pretty hacky, not sure how heavy I'd need) or open to other ideas / suggestions / pointers.

Given I need the solution to prevent further rotation, not sure what the best approach is and if I need to go down a worm gear route. I'm open to motorizing it, but a bit overwhelmed by the huge volume of options out there - feels like I need to narrow the options before I go too deep on it.

Picture below of the setup - the gear is close the ceiling and a few cm away from the wall on the left and about 350mm away from the wall behind it. There is about 2.4m from the sprocket to the floor.

Let me know if any other info would be helpful to provide advice!

 

[Burnerman]

I think you are on the right track - a worm can drive a pinion but the pinion can’t drive a worm.....sort of an automatic locking, if you get my drift.
Any mains driven motor will need a gearbox to slow it down, so how about a car wiper motor (12v)?
I think the rotation speed would be about right but obviously a 12v battery would be needed.
You have a chain sprocket on the top, and a hand crank (bike style) could make the mechanism easier to turn from lower down.
Of course, a simple pin pushed through the sprocket could stop the rotation!
John

 

[Deleted member 174758]

Stepper motor with a built in brake? Commonly used in all sorts of automated kit, from inkjet printers to CNC routers