[SML] Chain Motor Help...

[Brian Munroe]

If you were putting 5 tons on a piece of equipment rated with a design factor (safety factor) of 10:1 for 1 ton, your new design factor would be 2:1.  Far below industry standards.  If you want a design factor of 7:1 and the manufacturer is using 10:1, you are good (putting aside for the moment other issues). If you wanted a design factor of 15:1 and the manufacturer is using 10:1, you have to de-rate the manufacturer's rating by 1/3rd. You should not "up-rate" the manufacturer's rating if they are using a higher design factor than you require. 

All that said, if you want to use chain motors to lift people, be sure that is an approved use by the manufacturer.  Also, using multiple motors (more than 2) puts in in to "indeterminate" load calculations for load on each point. Very difficult to calculate loads at that point without the use of load cells. 




Sent from a rather small device with big fingers

> On Mar 4, 2016, at 4:42 PM, Will Leonard via Stagecraft <stagecraft at theatrical.net> wrote:
> 
> Guys,
> 
> I have a show coming up where a designer where a designer would like us to use variable speed Chain Hoists to raise a lower a platform with 2 actors riding it. We are trying to negotiate the trick, but we are getting some push back when we said we needed a minimum of a 7:1 Safety Design Factor for this move. This means that the weight of the unit is such that we would need 11 1 Ton Hoists to raise & lower the unit, when we only have access to 4. The designer emailed us a link to CM's website that states that they use a 10:1 Safety Design Factor, so that should cover the move. 
> 
> I have always taken the rating of a motor (or hardware) & then applied my own safety factor to the already lower number. (i.e.: I'm not going to put 5 tons on a 1 ton motor just because it has a 10:1 safety factor.) So am I wrong in this? Are we just being whiney? Our designer is going to be here in a few hours to meet, so what do y'all think? Bill... Delbert... Bill... Dave... Steve... anyone?
> 
> Hope y'all have beer & BBQ if you're into that thing this weekend!
> 
> Thanks,
> - Will Leonard
> Associate Technical Director
> Alley Theatre
> O: 713-315-5449
> C: 713-252-9809
> 
> 
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