[SML] DMX/Programmable Winches/Hoists

[Bruce Cooper]

On Wednesday, June 29, 2016 5:21:29 PM CDT, Jerry Durand via Stagecraft 
wrote:
>
> On 06/29/2016 03:18 PM, SAMUEL JONES via Stagecraft wrote:
>> Real question, no arguement. Why would that be? With the number of
>> programmable hoist systems, I would think that DMX would just be
>> another way.
>
> DMX has no error checking (yes, I know you can work around that and
> implement error checking, but then it's not pure DMX).  So, an error
> that would do no more than make a light flicker for a fraction of a
> second could kill someone.


  Add to that: 

-No realtime feedback mechanism for encoder or other data [yes, RDM is a 
possibility, but not really intended for such and would almost certainly be 
overloaded in short order by encoder data alone.], 

- no heartbeat or Axis Presence monitoring. - Purpose-built Automation 
control software will either stop the cue, the axis, or the data output if 
an axis is not present/not returning heartbeat. Lighting consoles will 
(almost always) merrily continue sending data whether the axis is present 
at the beginning of a cue, leading to the possibility of  unintended 
movement when (for example) a connector is re-made by someone 
troubleshooting in the middle of a cue.

- consoles that aren't built from the ground for winch control - It's easy 
enough (working too quickly, usually) even with purpose-built automation 
software/consoles to make injurious or deadly mistakes when programming. 
(This is the reason for the program-test-add actors workflow) Adding in DMX 
translation by the programmer adds another possible point of failure]

- no E-Stop capability - It is possible to add this as an outboard system, 
but again the console doesn't know about it and will probably keep sending 
data so if the E-Stop is lifted the winch could begin moving.


DMX is a one-way system, where the console fires off DMX values and just 
expects that the system will end up in the right state.  With lights, this 
poses no life-safety hazard.  With winches, even a 10 pound weight moving 
into head/meatspace at even reasonable speeds [< 2ft/sec] can do some 
serious damage.

 IF there is any life safety risk at all, I personally wouldn't ever use 
DMX controlled winches, no matter how light the load on the end.  Getting 
caught in moving winch line shouldn't be forgotten as a possibility.

  My $.02 as a guy who used to run a fair number of winches in 
ever-changing configurations and got to do the risk assessments.

:Bruce Cooper
--
Itinerant Stagehand, (currently non-practicing) Navigator 
Programmer/Operator, Ever curious fixer of things.