[SML] Motor controls in scenery

[Mark]

> On Apr 8, 2015, at 4:52 AM, Bill Conner wrote:
> 
> 
> Message: 15
> Date: Tue, 7 Apr 2015 20:47:26 -0500
> From: Bill Conner <billconnerastc at gmail.com>
> To: Bill Sapsis <bill at sapsis-rigging.com>,    Stagecraft Mailing List
>    <stagecraft at theatrical.net>
> 
> This would not be called a hoist by most people.  No encoder or any
> thing but a simple momentary up-down toggle and two limit switches.
> 
> My question remains are two limits at each end of travel common for
> scenery for a short run production?  What is he standard of care as
> defined by law, as: Would the average set designer/tech director who
> works on short run productions like high school and community theatre
> do this.
> 
> -- 
> Bill Conner Fellow of the ASTC


The way I see it, Bill, it's either right or wrong.

The ANSI standard that Bill S quoted would be the absolute minimum precaution one would take.

The reason for another set of limits is not only if the machine misses one set, it will then hit the other. The second set of limits should cut a the power or deactivate a secondary control circuit not related to the the primary.

On some machines there is a third circuit that cuts power if two parts make contact (crash)

Aside from the the fact that, mechanically, the machine should be built with the proper design factor on all components (weak link of chain). The drive should be adjusted so that if it senses unusual force needed, it will stop calling for power.

When I work for the rock n roll factory, we usually follow the most stringent standards that may apply, worldwide. The Europeans, particularly the Germans, have Machinery Directives that specify everything from control circuitry to redundant brakes.

If we don't follow common sense and the standards that we have written, some AHJ -will- write some for us, that may not be as common sense and practical.

And the real reason is, we don't want to see anybody get hurt...

Mark OBrien
ETCP Certified Rigger/Entertainment Electrician
360-630-9007

Sent from my iPad, spelling iffy...
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