[SML] DMX/Programmable Winches/Hoists

[Jerry Durand]

There's multiple ways to use DMX-ish communications to provide safe 
movement, even a few that could be done with a standard lighting desk.  
But, I can not recommend plain DMX-512 for any use that endangers a 
person.  The ban is even written into the ANSI spec that has my name on 
it (in very find print on some addendum page).  The fine people who 
wrote this know of which they speak.

Now, given certain safety considerations like separate tethers and hard 
stops to limit travel, you COULD rig something up that would make the 
AHJ smile.  You could also use multiple DMX channels to add checksums, 
verification, whatever to make sure all goes well. You could also use 
Start Code 0xFF with a company signature like I gave before (that 
happened to be for our company) so that only your devices will listen to 
that DMX frame.  In that you could encode all sorts of stuff.

But, then you're in that DMX-ish realm and not just any lighting console 
could do it.

On 06/30/2016 10:32 PM, Michael Sauder via Stagecraft wrote:
> I've not had to look into these enough to ask for any documentation. I 
> do know the Kinetic Lights website says "... complies with all 
> international security regulations to move tethered elements above 
> people (BGV C1 now DGUV 17, UL, CE)."
>
> I only said that they've done enough to prove THEY (and presumably 
> their lawyers and insurance companies) think it is safe.
>
> As I gather, the two main issues with using DMX is that it's open 
> loop, and does not contain any error correction.
>
> Closing the loop is easy enough to do. Kinetic Lights does this by 
> return DMX channels.
>
> Error in the data stream is typically transient. If you think about 
> what we're controlling, momentary 1/40th second blips in the data is 
> not going to have a large impact -- a winch that has been receiving a 
> steady "0 feet @ DMX value 0" is not suddenly going to drop its load 
> 20 feet just because it receives a single errant "20 feet @ DMX value 
> 255." It's not a pyrotechnic, instantaneous response is not possible. 
> On top of that, it's easy to write the winch code such that the winch 
> will, for example, only move if the height parameter changes in a 
> continually increasing/decreasing manner with sudden changes ignored.
>
> Perhaps in the past DMX was not reliable enough for motion control, 
> but it may well be time to reconsider the knee jerk reactions against it.
>
> --
> Michael Sauder
> Show Control Programming and Design
> Email: michael.sauder at gmail.com <mailto:michael.sauder at gmail.com>
> Web: www.shownet.io <http://www.shownet.io/>
>
>

-- 
Jerry Durand, Durand Interstellar, Inc.  www.interstellar.com
tel: +1 408 356-3886, USA toll free: 1 866 356-3886
Skype:  jerrydurand