Affordable automation for very lightweight scenery?

[DRU]

I just opened my new Rosebrand catalog, and I saw that they now sell Wahlberg Motion Design automation devices. They have a scenery rotator (http://wahlberg.dk/shop/motion/rotator/) that you might be able to hook up to a custom-made roll drop, or they have winches (http://wahlberg.dk/product-category/motion/winch/) that are designed to lift lightweight objects. The only concern I have is that they are DMX controlled, which breaks the unwritten rule of not using an open-loop control system, especially DMX, for automation.

 

[soundman]

This got me thinking, and this is purely hypothetical- what if you used a winch that pulled on a length of wire rope that was anchored to the grid on one end, but looped down through a pair of blocks attached to the scenery? Problems I can see would be leveling the scenery, a lighter piece would definitely wobble as it moved up and down, but control of the height could be managed by the amount of cable the winch pays out. I don't have any projects that need something like this, but was just wondering if this would be viable or catastrophic.

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Ive done it on a large projection screen. But instead of deading off to the grid the line ended up going to another winch. We did this so if the main winch faulted the backup could take up or let out enough line to complete the move in either direction.

Rigged as drawen it will be very tippy. Each of our winches had two lines so we were able to rig it so it wouldnt titer totor. Or a shared balance point.

 

[Malabaristo]

.The only concern I have is that they are DMX controlled, which breaks the unwritten rule of not using an open-loop control system, especially DMX, for automation.

Actually it's a written rule and part of the DMX standard--except the language is that DMX is not appropriate for safety-critical applications. The justification in this case is that the load is small enough and/or soft enough to be inherently safe. In other words, it's completely acceptable to use DMX for automation as long as the automated device is incapable of causing serious injury (regardless of the DMX input).

 

[BillConnerFASTC]

That 50 kg winch seems capable of causing serious injury.

 

[soundman]

I would feel better if there was some sort of Estop system. Some of the smaller winches would need to be re zeroed after a power cycle so simply killing input power would not work for those.

 

[sk8rsdad]

I would feel better if there was some sort of Estop system. Some of the smaller winches would need to be re zeroed after a power cycle so simply killing input power would not work for those.

Well, according to the manual some models can be (are?) equipped with an Emergency Stop. However, the manual has some inconsistencies about how it should be wired and might benefit from some proofreading.

 

[Malabaristo]

That 50 kg winch seems capable of causing serious injury.

What if the limits are set so that the range of movement for that 50kg object passes through a space that nothing else ever enters? (...too high to touch people, no moving scenery or anything else that might interfere, etc...) A mechanical hoist failure could still potentially cause the load to fall, but gravity doesn't obey an E-stop anyway. It would take some thoughtful risk evaluation, but there are some circumstances where it could be a reasonable choice. Obviously if the safety plan is, "It's fine as long as these two things don't move at once..." then a spotter with a deadman switch would be the better choice.

To a certain extent I'm playing devil's advocate here: I agree that the 25kg and 50kg hoists have a lot more potential for being used unsafely than the smaller versions.

 

[BillConnerFASTC]

First, I am only considering overhead lifting. If its not overheads, I'll agree other rules apply.

So, are there situations where something like this could be applied safely, where spotters and limit switches prevent movement and absolutely assure no failure? Probably. But limits and redundant limits please, as the control doesn't know where it is and it it blew by top limit, might not be long before termination on the line hit an obstruction or the drum, and down it came. I think I could find other failure modes that without the benefit of a closed loop control system might be a hazard.

I'm also worry that the average RoseBrand customer may not be quite so experienced and discerning, and not quite fulfill the requirements for a "qualified person" in making these judgments and design decisions. Does a person who is not qualified even recognize and know enough to know they aren't quaified?